This is the effort of two retired guys, John Fisher K5JHF and I, (and other AQRP members) to make some useful kits available for you at reasonable prices to encourage kit building and homebrewing. As you can quickly determine, these kits are all based around readily available, low cost Microcontrollers with flash (program) memory and most use a certain LCD display that was very, very, inexpensive. The criteria for us, as "low buck" designers, was that firmware development tools have to be free, hardware interface tools have to be inexpensive, and PC board design tools have to be free.

As we run out of parts we'll just order more if there is interest in the kit. Some kits may be retired as the number of kits grow or demand falls off. Should be fun and educational and that's what this is all about. I'll make improvements to the web site as time allows and hope to make it convenient to use. Both John and I are ready to answer any questions and help out.

I just got back from the post office and the rates went up Jan 27th, 2013, especially for DX, so I had to adjust the postage charged.

I realize there are some Hams out there who think they will have difficulty with the small surface mount parts placement and soldering and "think" they can't do it. I highly encourage you to try. If you "ping" a small part across the room and it's lost forever, contact me and I'll send you another at no cost. Some may have vision problems, steadiness problems, etc, again I encourage you to try.



To order kits please contact me directly at K5BCQ followed by an @ sign followed by ARRL.net with no spaces. Or via mail (OK in QRZ).

There have been some problems with the email forwarding through the ARRL Website so let me try this as an alternative; hopefully to also cut down on the robospam. You can also contact me through windy10605 followed by an @ sign followed by Juno.com with no spaces. Let me also do the same for the other email IDs.



The Hi/Lo Temperature Kit #1

Back for yet another 30 Kit Run

An assembled Hi/Lo Temperature Kit #1.

Closeup of the small microcontroller board with the temperature sensor (8 pin SOIC). The microcontroller is on the back of the board.

This is one of the easier to build kits. It simultaneously shows the Low, Actual, and High Temperature readings in degrees F or degrees C (so it's educational too). You reset it by momentarily turning the power OFF and back ON. There are two versions of the code which you need to specify when ordering ....."T" (Toggle) which will automatically toggle between degrees F and degrees C every 5 seconds ("T" is the default if you do not specify "T" or "F") and "F" (Fixed) which will read degrees F without the jumper "J1" installed and degrees C with the jumper "J1" instsalled. The battery consists of 2-AA Alkaline cells and should last about one year. Use Alkaline cells because of the 1.5V rating. Rechargeable NiCad cells at 1.2V are really too low for proper LCD contrast. The temperature sensor is a MicroChip MCP9801 which is spec'ed at +/-1 degree C from -10C to +85C and +/-3 degrees C from -55C to +125C.

So what comes in today's Hi/Lo Temperature kit ? .....Bill of Material:

The price for of this Kit is $10 plus $3 postage in the USA and $9.50 postage for DX.


The Si570 Controller and Frequency Generator Kit #2

An assembled Si570 Controller. The LCD shows Memory location "36" and 14.060Mhz with the cursor in the 1Khz position.

You can see the Si570 chip soldered on the back.

New V4.x board with 4 mounting holes and a more convenient way to interface the I2C Bus to an externally mounted Si570.

This is the packaging used by Bill Sepulveda, K5LN, using a vinyl overlay printed with a color printer. He described the technique in a Dec, 2002 QST article and it will also cover up small holes and other "oops" marks on the panel.

This standalone unit (no attached PC required) has a frequency range of 3.5Mhz to 1417.5Mhz (yes, 1.4Ghz) depending on the Si570 part used. I have tested it up to 1200Mhz which is as high as my scope will go. Really an amazing, low jitter, and very low spur levels chip. You can go to the SiLabs website and look at the specifications. All setup and control is via the rotary encoder knob and it's push button. Power is battery (3V) or external power (5V-12V). It's compatible with all Si570 CMOS and LVDS versions, single ended or differential output, and any default frequency. This makes an ideal signal source for SoftRocks and many other projects. The Si570 Controller and Frequency Generator Kit includes a 12 digit LCD frequency display, a programmed MC9S08QG8 microcontroller, and a rotary encoder for tuning. It can ordered with a CMOS Si570 chip which is spec’d at 3.5Mhz to 160Mhz. Using other LVDS Si570 parts, the frequency range can be extended up to 1.417Ghz.

NOTE: I have received a few emails from people who accidentally applied reverse voltage to the 12VDC input and took out some parts. To prevent this from causing damage, in the future, I am adding a silicon diode to the kit .....to be mounted in series with the 56 ohm resistor (R1). If you think you might accidentally reverse power sometime on an existing unit, and who doesn't, I would suggest adding a diode to your Si570 Controller.

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ERATTA for V4.x Boards

Looks like SiLabs has changed the programming spec and disabled some math multipliers to facilitate their implementation of "Speed Grade". "A" Grade (1.4GHz) parts are not affected. I don't know how "B" parts are affected by the present Si570 Controller code. We use the "C" grade CMOS (160MHz) and LVDS (280MHz) parts. Using the existing Si570 Controller code does not appear to affect CMOS "C" level part operation, but the LVDS "C" level part is now limited to 260MHz with the existing Si570 Controller code (4 programming dots).

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Jack Smith, K8ZOA, of Clifton Laboratories has provided an excellent evaluation of the CMOS Si570 capabilities and the Si570 Controller kit at Clifton Laboratories

Sid Boyce, G3VBV, provided additional insite on how he used his Si570 Controller at G3VBV info

Features:

The display is a 12x1 serial LCD (3-3/4" x 7/8") and the programmed microcontroller is a Freescale MC9S08QG8. All the parts are supplied (except the batteries) and an instruction sheet is provided.

There are many output options available ranging from normal termination resistors to isolation transformers to LVDS/ LVTTL level converters. Some of thse devices have their own frequency limitations such as the MiniCircuits RF transformers are spec'ed to 800Mhz and the FIN1002 is spec'ed to 400Mhz. It's totally dependent on your application. The Si570 Controller board has footprint options for many alternatives. Also some of you bought Si570 parts from Tom Hoflich, KM5H, and may want to use those parts. Some of you have sample parts or parts from other sources. For that reason, the kit is offered with or without the Si570 part. The Si570 parts I supply are CMOS "C" speed which means they are spec'ed 3.5Mhz to 160Mhz by SiLabs (although they have been observed much faster than that).

So what comes in today's Si570 Controller kit ? ......Bill of Material:

The price for of this Kit without Si570 is $25 plus $4 postage in the USA and $12.75 postage for DX.

The price for of this Kit with CMOS Si570 (160MHz) is $40 plus $4 postage in the USA and $12.75 postage for DX.

The price for of this Kit with LVDS Si570 (260MHz...see Eratta above) is $45 plus $4 postage in the USA and $12.75 postage for DX.

Options:

There are 2 optional parts available. None of thse are required for an operational kit, only if you want complete DC isolation or LVDS conversion from differential to single ended LVTTL.

Mini Circuits TC1-1TG2+ (easier to solder than the previous TC1-1T+) RF Transformer is $2 plus $2 postage in the USA and $2 postage for DX. No postage if ordered with a kit. You only need this part if you want complete DC isolation.

FIN-1002 LVDS to LVTTL Converter $1 plus $1 postage in the USA and $2 postage for DX. No postage if ordered with a kit. You only need this part if you are using a LVDS Si570 and you want to have an LVTTL single ended output vs the differential LVDS output.


The Morse Code Buddy Kit #4

A MCB with keyboard, headphones, and a set of homebrew Iambic paddles made from two sections of hacksaw blade. Those blades are hard to drill but have the right spring feel.

Closeup of the MCB. The large pads (on both sides of the keyboard connector) are for attaching two spring contacts which, when grounded to the keyboard connector shield become a small iambic paddle. Neat, huh ?

More detail on soldering relay contacts as a cheap iambic paddle ....sorta.

This is the MCB-II. The Beeper and Microcontroller locations are switched, making it much easier to change out the microcontroller for different functions.

ERATTA: It has been brought to my attention that some of the MCB-II boards don't have thermals on the R2 ground pad and therefore that point is not grounded. The fix is relatively simple. scratch some of the adjacent ground soldermask off and bridge the bare copper to the ungrounded resistor pad with solder. The second problem is that C3 is labeled but the pads are missing. The fix is to solder C3 on the bottom, between pins 3 and 4 of the microcontroller socket.

The Morse Code Buddy (MCB) allows you to receive and send practice code at speeds of 3-wpm to 40-wpm with a keyboard or iambic paddles, or just shirt pocket use for receiving practice code via the beeper or headphones. For those in the know .....and real CW operators, this is a Type B iambic keyer. There are three versions of the microcontroller, which is pluggable. The "C" version sends random 1x1, 1x2, 1x3, 2x1, 2x2, 2x3 calls (USA and DX) with 20 varying tones on a per call basis (sorry, no random noise in the background). It will send all alphabetic combinations. The "P" version sends random groups of all Morse Code letters, numbers, and characters. The "B" version will allow Beacon mode where one character string you define is repeated at an interval you define. Handy for calling CQ on a basically dead band or use during transmitter hunts. Hit any keyboard key on any of the versions and it reverts to iambic keyer mode.

It's also a 512 byte memory keyer, with adjustable tone, keyboard or iambic paddle input, Tx keying via a 2N7000, and it's powered by 3-AA Alkaline batteries (>100hrs). Do not use rechargeable NiCads. It's not required from a power standpoint and the 3.6V voltage is too low. The two large pads to the side of the keyboard connector can be used for isolated mounting or fabricate a set of paddles from the pads to the grounded shield of the keyboard connector (old relay contacts ?) and you have yourself a set of homebrew mini-paddles. Cool, huh ? ....check out the picture above.

The power options are many since the power requirement is 4-5VDC. You can use the battery box provided with 3-AA Alkaline batteries for portability, you can tap 5V off your rig if that is available, you can use an external 5V power supply, or you can tap 5V off a computer USB port you may have on the desk (all you need is a cable with the USB connector). If you use a cable for power it's a good idea to provide a strain relief using a plastic tie-wrap through one of the two holes at the keyboard connector end of the board.

This is a relatively easy kit to build. Some of the parts are an interference (tight) fit so they stay in place when you flip the board over for soldering.

Features:

So what comes in today's MCB kit ? .....Bill of Material:

The price for of this Kit is $15 plus $4 postage in the USA and $9.50 postage for DX.

Each kit is supplied with a "C","B", or "P" microcontroller (you specify). If you want more than one, please add $5 for each additional microcontroller to the above numbers.


The Stamp Amp Kit #8

Small Audio Amplifier board with 26/46 dB Gain. This shows the old one and the new kit board now offered.

This was a quick Audio Amp using a single power supply DIP OpAmp. You never know when you need one ....or two. Powered by 5-6V DC.

So what comes in today's Stamp Amp Kit ? ......Bill of Material:

The price for the Stamp Amp kit #8 is $10 plus $3 postage in the USA and $9.50 postage for DX.


The Digital QRP mWattmeter II Kit #9

K5BCQ's mWattmeter II packaging scheme using a "Royal Crown" LMB #CR-531 box. The tactile pushbuttons (Up, Down, Mode) which come with the kit (you can use both Up and Down pushbuttons or only one of them) are mounted on the bottom of the ADC/Microcontroller board in this enclosure scheme and protrude far enough to be used from the front of the enclosure if you bevel the hole edges a little. The bezel and On/Off toggle switch are not included in the kit. I call this "flounder packaging" ....due to this enclosure's aspect ratio and the LCD on top ;o)

Inside of the LMB #CR-531 box. The AAA bias battery can be mounted on either side to suit your enclosure. Here it is on the bottom of the Directional Coupler board. The Berg connectors were added on my unit because it was removed often during development.

Top view. Mount T1 on the top of the coupler board and T2 on the bottom of the coupler board using a small piece of double sided tape as a spacer off the board. This locates the board between the two transformers for isolation. It also puts a spacer between the toroid coils and the ground plane to reduce capacitive coupling. The single turn of wire is a short piece of RG-188A/U coax (just like RG-174A/U but it's Teflon so much more "solder iron friendly") and ground (ONLY) one end of the shield to a nearby ground via on the board. This provides a Faraday shield between the primary and secondary of the transformers to reduce capacitive coupling between the windings.

I cut slits in the coax jacket to make it more flexible. Any derbis comes from a "helpful" cat (Inspector #2) who insisted on checking all the solder joints and as you can see, it's very stressful and tiring work.

This shows the bottom of the coupler board. I cut slits in the coax jacket to make it more flexible.

This a mWattmeter kit built by Ken, VA3ABN, ......looks nice.

Thanks to John Fisher, K5JHF, and Milt Cram, W8NUE, for the microcode and Ben Bibb, NO5K, for taking one heck of a lot of data in his lab. Power measurements have been surprisingly accurate from 160m to 6m at better than 3% in the QRP <5W range which was the focus of this design. I was talked into raising the power to 20W at a later time. Thirty-three curve fitting polynomials are used, three per band, 11 bands. All thirty-three are second order. Eleven band selections, between 6m and 160m, are used to further improve accuracy by not having to "average" any data readings.

This particular project has provided me with considerable education. In order to maintain good accuracy (<3%) at the low end (the design point) I've found out that the data is only as good as the test equipment used to obtain the curves. The math is straight forward, the hardware is not. First, it's much easier to make an accurate mWattmeter using my design point than it is to make an accurate INLINE mWattmeter, or even more so, an accurate INLINE mWattmeter which shows VSWR. Directional Couplers with toroids are not known for stablity/ accuracy and a separate enclosure with better RF bypassing of the analog voltage would help some, but ferrite material is inherently affected by temperature (power) and RF coupling between the two transformers. Second, there are Amp output impedances to consider, LPF characteristics, Attenuator characteristics, etc, etc. There is a considerable difference between "ham quality" and "commercial quality" instrumentation. This is my best run with available instrumentation.......most of it lab quality, callibrated, and excellent, some of it, like the LPF, "ham quality". At a later date, if someone can provide me with better ADC voltage to power data, it's relatively easy to update the microcode via the BDM socket on the board and/or the kit is now supplied with a 16 pin DIP socket for the microcontroller.

IMPORTANT: The mWattmeter V2.0 microcode will only produce correct readings with the Directional Coupler wired as described and shown above. The earlier V1.0 microcode compensated for unwanted coupling between the toroids and is no longer required. The mWattmeter II is designed for 50 ohm impedance input and 50 ohm impedance output. Variations from that will effect data accuracy. When measuring the output from a Power Amplifier be sure and use a good 50 ohm LPF, otherwise the additional output frequency harmonics will distort the observed readings.

There are six LCD display Modes; #1) shows raw Forward/Reverse voltage being sent to the ADC by the Directional Coupler board in 0.1mV increments. #2) shows the battery Voltage as x.xV, #3) shows "BBBFxx.xxxsY.Y" where BBB is the Band from 6 to 160, "F" indicates Forward Power, xx.xxx is the Wattage in 1mW increments, s is a space, and Y.Y is the VSWR from 1.0 to 9.8. #4) shows "BBBFxx.xx*x.xx" for the higher power levels and is in 10mW increments, * is a backwards "F" for Reverse "Forward" Power, x.xx is the Reverse Power in 10mW increments. #5) shows "BBBFx.xxx*.xxx" for the lower power levels and is in 1mW increments, * is the backwards "F" for Reverse Power, .xxx is the Reverse Power in 1mW increments. #6) provides some additional detail on the bands covered .....the bytes were free, what the heck.

Use Alkaline cells because of the 1.5V rating. Rechargeable NiCad cells at 1.2V are really too low for proper LCD contrast. Power consumption is about 1.25mA......not much.

The mWattmeter uses a (very familiar) 12x1 digital readout, will measure 0.25mW (actually a little lower) to 20W (that's about a 50dB dynamic range), has automatic range switching of 3 ranges (0 to 45mV, 45mV to 450mV, and 450mV to 2.0V), uses a total of 33 polynomials for curve fitting, uses matched Schottky diodes which are forward biased at 5uA, uses an 18bit differential input ADC (vs the usual 10bit or 12bit ADC), that allows temperature compensation by utilizing the differential ADC inputs, Battery operation (2-AA Alkaline, 1-AAA Alkaline for bias), draws 1.25mA so batteries should last even if it's accidentally left on, has a battery voltage indication, will store selections automatically and power up in the last state used, has a 6-pin BDM connector for reprogramming with a USB Multilink or USB Spyder, and provides 2 BNC connectors.

Most of the recent low power wattmeters have used log-amps like the AD8307, AD8310, LT5537, etc. (and there are many more, largely driven by the cell phone and RF tag industry). In addition to the obvious log curve linearization, one key advantage of the log-amps over diode detection is that they provide range "compression" resulting in a very wide dynamic range (80dBm to 100dBm). The main drawbacks are cost (in my opinion), unuseable packaging (ever hand solder an 8 pin CSP ?), and we don't really need that much dynamic range (maybe 45dBm to 50dBm).

After considerable diode specification searching (special thanks to the Crystal Radio group for some really great links), I came to the conclusion that there are basically two alternatives left for a non log-amp wattmeter, 1) use a good pair of matched germanium diodes or 2) use a good Schottky diode pair and forward bias them slightly (5uA is good). After purchasing some germanium diodes (1N60, 1N34A, 1N270, 1N277) and testing them for stability and consistency it was determined that germanium diodes have neither. The "best" germanium diodes out of this batch were those labeled "ITT 1N277". The 1N270 diodes marked "1N270" or with color bands were very good also. 1N34A diode quality (several batches) depended heavily on the supplier. Some were really bad (forward resistance varied 5x+), some were "just so-so". I was really looking for low end accuracy and settled on the HP HSMS-2815, a matched pair of low barrier Schottky diodes. The matched pair comes in handy for balancing the bias levels into the differential ADC inputs and offers temperature compensation using the ADC differential inputs.

The next step was to decide on the directional coupler values based on our constraints of <1mW to 20W and max input to the ADC of 2V. I don't want to use resistor voltage dividers with their inherent tolerance variations. The fewer the components in the bridge frontend, the better. Using 20W as max and 2V as max, we need a coupling factor of about 1:200 or greater. Since the transformers give us a 1/(N*N) coupling factor, N must be 16 or more turns (1:256). From the ARRL Antenna Handbook.. The low frequency limit of the directional coupler is determined by the inductive reactance of the transformer secondary windings. The inductive reactance should be greater than 3x line characteristic impedance to reduce loss at the lower frequencies where the circulating current will be significant. The result is heat which we don't want. For 50 ohm line that is 150 ohms and that works out to be 13uH for 1.8MHz. That is why so many designs using small powdered iron cores "cook" them at the lower frequencies. A material #2 (red) T-68 or T-80 core with 30 turns, only has an inductance of about 5uH.

If we select type 61 Ferrite material on a FT-37 size core, 16 turns measures ~15.4uH ....close, but OK! We also want the lowest possible series inductive reactance of the single turn on the transformer. For the FT-37-61 that now measures 0.06uH.....GREAT! Note that type 43 material has a permeability 20x that of type 61 material and is not acceptable. For higher frequencies, we want to reduce the length of the transformer windings to "well below a significant fraction of a wavelength". We use a little more than one foot..... OK. We also want to reduce the turn-to-turn capacitance which can be achieved to some degree with insulated wire. Teflon insulated #30 wire is great but "slick" and a little difficult to wind. Kynar insulated #30 wire is easier to work with and has a slightly smaller diameter. I decided against using a "binocular" Ferrite core (although the board layout is wired to accept one) because the small ones are too difficult to wind with more than 10-12 turns and the larger ones have too much single turn inductance. I don't think we'll have a heat problem with FT-37-61 cores but there is always the FT-50-61 core or multiple FT-37-61 cores. The board layout will accept either one.

Milt Cram, W8NUE, ran simulations and mathmatical analysis on the design and so have I. Data indicates low insertion loss and relatively accurate SWR representations for 10 to 250 ohm resistive termination impedances. Complex impedances are more difficult to measure accurately.....tell me about it.

After all the above is said and done, MANY experiments run, MANY diodes purchased, and MANY prototype boards built (most which are now "drink coasters"), we narrowed in on an acceptable design. Two boards... a Directional Coupler board with all the RF and only the detect signals coming off the board and an ADC/Microcontroller board with no RF (that was the intent anyway). The best results for 160m to 6m were seen with two dual FT-37-61 cores with a 23 turn winding of #26 wire and a 1 turn winding of shielded wire.

Since all diodes are non-linear how do we compensate for that in order to calculate accurate Forward and Reflected power ? Well......Why not use the floating point math power of the modern microcontroller and a "few" 2nd or 3rd order polynomials to perform curve fitting ? Sounds interesting to me and I ended up with 18 polynomials. After enlisting the aid of John Fisher, K5JHF, and Milt Cram, W8NUE, to work their firmware magic, and Ben Bibb, NO5K, to make some accurate measurements in his well equipped lab, we're off to the races.

So what comes in today's mWattmeter kit ? .....Bill of Material:

The price for of this Digital QRP mWattmeter II kit #9 is $55 (just like the mWattmeter I kit) plus $5 postage in the USA and $12.75 postage for DX.

In case you were wondering about the nice Bezel, they are available from Digi-Key and are part number PRD360B-ND.


The SDR2GO Kit #10

I am out of boards/parts and have decided to retire this kit because the programming support is now directed to the STM32-SDR kit with it's color graphics touchscreen and much higher performance microcontroller. The SDR2GO kit was a really great SDR Development platform.

SDR2GO Builder's Notes V1.9x

SDR2GO Builders Notes V2.0

SDR2GO Bootloader Notes

SDR2GO Graphics Interface Notes

SDR2GO dsPIC33 HEX Code V1.9.0

SDR2GO dsPIC33 HEX Code V2.0


The ThumbTach Kit #12

The ThumbTach is the small board in the middle. It's connected to a 4.5VDC (5V) power supply and a DSO nano-Scope which is showing the 60Hz output from the overhead lamp (120Hz on the screen).

This is a little tachometer circuit developed to measure propeller speeds on model airplanes. It also has many other uses measuring rotational speeds via changes in light. The detector is a simple photo-transistor driving an Op-Amp. This photo tansistor was picked to be most responsive to visible light.

The output is pulses as can be seen on the scope. You may use it to drive a counter circuit or whatever.

So what comes in today's ThumbTach kit ? ......Bill of Material:

The price for the ThumbTach Kit #12 is $6 plus $3 postage in the USA and $4 postage for DX.


The Attenuator Kit #13

Two assembled Attenuator Kits, showing the back and front sides.

This was developed as a crude but simple HF Attenuator after I had miserable reliability problems with commercial attenuator switches. The attenuation would change depending on how the switches "felt" that day. Very difficult to get repeatable results. I also tended to stress the attenuator resistors because of their 1/4W rating. This kit provides Vishay 1W 5% resistors and uses jumper vs switches. Sure, they makes it a little more time consuming to change values, but the jumpers provide very positive contact and if they wear out .....get another jumper, they only cost 1 cent each and extras are included in the kit. Due to the "Open Design", I would not use this above HF frequencies.

It has served my needs, does what I need an attenuator for, and will work for you too.

The kit can be provided with BNC connectors as shown or SMA board edge connectors. Your choice to specify, same price.

OK, OK, so the jumpers are a little cumbersome if you change them often so we'll offer an option to replace the 9 2x3 Headers and 25 Jumpers with 9 nice APEM 2P2T slide switches for an additional $5.

What the one with the switch option looks like.

Ben Bibb, NO5K, checked this Attenuator in his lab and was very impressed. The SWR at 6m is only 1.2 and the SWR at 2m is only 1.4. Lower frequencies are, of course, better with a SWR of 1.0 to 1.1. Ben also found the accuracy of the attenuation to be within 1-2% and the Return Loss levels are very acceptable. Insertion loss is a fraction of a dB. Those 1W Vishay 5% resistors are good ones and cost $0.16 each. Overall not bad for a $20 open board Step Attenuator. Those slide switches are made in the USA and good for 50,000 cycles.

So what comes in today's Attenuator Kit ? ......Bill of Material:

The price for the Attenuator #13 is $15 (or $20 with slide switches) plus $4 postage in the USA and $9.50 postage for DX.


The 20W HF Amplifier II Kit V1.5 #15

The 20W HF Amplifier II shown. The SMA connectors (board has the footprints) were installed for my testing, the kit is provided with 50 ohm coax to connect to the BNC/SMA/HF connector of your choice. Normally the Ampifier would be mounted inside an enclosure with a hole so the MOSFETs can be bolted directly to the outside heatsink.

Shows some more detail of T2 and T3 mounted on the Amplifier board.

Shows some detail of T3 assembly steps.T3 is made up of two sleeve ferrites on 3/16" copper tubes soldered to a 1/32" copper plate on one end. The secondary is 2 turns of #20 stranded and Teflon coated wire. The 1 turn primary is connected to power via a Phasing Choke, T2.

T2 is the phasing choke and is made using a BN43-302 Binocular core with 1 hairpin turn of #20 bifilar wire. The bifilar wire is made from two 2" sections of #20 enameled wire (not twisted) throught 1-1/8" of 3/32" shrink tube. The shrink tube holds the wires tightly together in parallel and forms the bifilar turn. The turns are connected in series with power connected to the center terminal. The picture ought to clear up questions.

Never wanting to leave well enough alone, the 20w Amplifier I has been replaced by the 20W amplifier II. The main differences are adding some surface mount components, replacing the two output transformers with a single homebrew OPT as shown above, much better (lower DC loss) RF chokes, reducing the SOX timeout by changing the capacitor from 10uF to a lower value, and providing an optional drilled and tapped heatsink (no fan required) from HeatsinksUSA. The new OPT does not run hot at all.....even with 25W+ applied and efficiency, although not measured, appears "better" than previous designs.

20W Amplifier I, V1.3B, Construction Hints

20W Amplifier I, V1.3B, Schematic

20W Amplifier II, V1.4, Construction Hints

20W Amplifier II, V1.4, Schematic

20W Amplifier II, V1.5, Construction Hints

20W Amplifier II, V1.5, Schematic

When it comes to Amplifiers, the Radio Amateur is responsible for making sure his amplifier operates within the guidelines established by the FCC and that it does not cause unwanted ipassnterference. This is a Broadband Amplifier and will require some sort of Low Pass Filter (LPF) or Band Pass Filter (BPF) on the output to attenuate harmonics. You may already have one you intend to use.

Amplifiers have been around a long time and continue to evolve, one design being based on another, etc. I want to give credit to some who “plowed the ground” before me: G6ALU, KE9H, WA2EBY, TF3LJ, K5OOR and above all NO5K who provided all the testing in his extensive lab. The question may come up, “Why ANOTHER Amplifier ?” To that I say, “Looks like fun, why not ?”

My idea was to provide a good and low cost Amplifier for the HF bands (160m to 6m) which can be driven by a SoftRock SDR or any other low power driver and provide ~20dBm of gain. Low power being defined as less than 1W. Some of the new SDR units supply less than 50mw and really need a little “boost”. This Amp uses well received RD16HHF1 RF MOSFETs which are each rated at 16W output for 12.5VDC at 30+MHz. These parts are quite robust and much better than the IRF510 Switching Power Supply MOSFETs used earlier, largely because of their low cost and availability. The other advantage of the RD16HHF1 is that the mounting tab is attached to the “Drain” pin which is at ground potential …so no mica insulator is required. The Amplifier has a Signal Operated Switch (SOX) for CW QSK. I didn’t really put it there for SSB …..but who knows (still better to use PTT). Did I mention good and low cost ?

The design and components which have been selected require that the operational criteria of 1) an Input of 1W max –AND-- 2) an Output of 20W max ………whichever comes first, NOT be exceeded. To allow some adjustment, the input to the Amplifier has places for a Pi network Input Attenuator of your selection (Rx, Ry, Ry) ….3dB, 6dB, etc. Parts for a 3dB (50% power reduction) attenuator are provided in the kit. The purpose of the attenuator is to reduce input power and to provide proper 50ohm matching for the driver. This design has been extensively tested and optimized to provide good matching to 50ohms without the attenuator. If you elect to not use an attenuator, replace Rx with a jumper and do not install either Ry.

1Mhz to 61Mhz Power Profile of 20W Amplifier II showing relatively flat output..... 43dBm is 20W. This was with a 3dB on board attenuator so the Amplifier is driven by a constant 500mW (1W into the attenuator). The lower line is with a constant 250mW drive (500mW into the attenuator) and shows lack of compression indicating great linearity. Try that on some of the other Amps out there. To attain "20W", you can crank the drive up slightly while maintaining the 1W max input to the Amp and 20W max output from the Amp as specified.

The design provides Class A/B linear operation for (all Modes). This means that both MOSFETs -MUST- have their gate bias adjusted and balanced so they are the same on both devices. The actually current required is between 250mA and 500mA. You determine the optimum level for your application, power supply voltage, etc. Do not exceed the 500mA gate bias per MOSFET. This is simple to set up. After assembly, with the MOSFETs screwed to the heatsink and the Bias switch closed (shorts R2), turn the bias potentiometers fully counterclockwise, connect a 50ohm load to the input connector and to the output connector, put 12V on the PTT input to pick the Rx/Tx relay and and turn on the 6V bias regulator. Now measure the current. There should be a small current draw. Turn one bias pot clockwise until the current increases by 300mA, then turn the other bias pot until the current increases an additional 300mA. Now the bias levels are balanced and set for Class A/B operation for your Amplifier. Since linearity gets worse at the higher power levels, you may want to experiment with R/C FeedBack values .....the footprints are on the board. Be sure to use 1KV rated capacitors, not 25/50V rated capacitors, for "C" to protect the MOSFETs. That's experience talking.

The design also provides Class C operation (CW only). This allows lower power consumption when you really don’t need linear operation. A single resistor reduces the Gate Bias current on both MOSFETs to around 25-35mA each. Testing has shown them to remain adequately balanced. You can also use the potentiometers to adjust this if you prefer and only want to run Class C (for CW).

Many MOSFET Amplifier circuits do not use a feedback circuit but I thought it would be good design practice to do so and added one. It's not used but, at least, the component footprints (C,R) are there if we need them later. The T3 compensation capacitor is made up of Qty 2, 249pF Mica capacitors in series.

Another design parameter which seems to help on all the bands, especially 6m, is to further reduce spurs by paralleling capacitors of different values to reduce the capacitor self resonance effects. You will see that in many cases a 100nF cap is in parallel with a 47nF cap or 10nF cap and also a 1nF cap.

So what comes in today's 20W amplifier Kit ? ......Bill of Material:

I now offer 2 heatsink alternatives for the 20W Amplifier (board measures 2.5" x 3.5").

#1) No Heatsink/fan, Just the 20W Amplifier II for $55, you come up with your own AM-2 Heatsink/fan or whatever Heatsink you want to use. The amplifier was originally designed for a computer type AM-2 heatsink .....or whatever heatsink you have laying around.

#2) A 4.23" x 2.90" x 1" Heatsink from HeatsinksUSA. This Heatsink has 11 fins and is drilled and tapped to match the board. I am the driller/tapper. Price will be an additional $15. Postage will go up because of the added weight.

Shipping for one kit with option #1 (NO heatsink) is $5 First Class Mail in the USA and $9.50 First Class Mail for DX. Shipping for a kit with a Heatsink option in the USA will be $6 for a small Priority Mail Box. DX shipping costs are determined by location.


EXTERNAL LOW PASS FILTERS.....7 Band Relay Switched LPF Board.

Shows the bare 7 band LPF board and a partially built LPF board

I have a limited quantity (12) of 7 band Relay Switched LPF boards (board only) available for $12 plus $2 postage in the USA. The boards measure approx. 3" x 4". I also have 5V relays available for $1 each plus postage. Toroids and capacitors are listed below. I suggest using one of the free programs like Jim Tonne's, ELSIE, or other filter program (AADE, etc) for the appropriate values for your needs.

ERATTA: Pin 11 on the CD4028A is wired "high" to 5V. The pin should be "low" and connected to ground for proper operation of the CD4028A. Cut the trace to the pin and ground the pin to a ground point.

The board schematic is shown here:

7 Band LPF Board Schematic


EXTERNAL FILTERS ......Individual Plug-in BPF and LPF filters.

Shows several BPF and LPF boards

These boards all have a 2.5" x 0.6" form factor and come in two varieties, BPF or LPF. Redundant header pins are located at both ends (or you can solder directly), The designs are symetrical so the boards can be reversed or flipped without effect. The boards can be used standalone and plugged one at a time or used with a switcheable host board of your design or mine (available later). I have the bare boards only and header pins available for $2 per board plus postage in the USA. Toroids are listed below (the capacitors are all 630V or 1KV NPO 1206/1210 size SMT. You would use one of the free programs like Jim Tonne's, ELSIE, or other filter program (AADE, etc) for the appropriate values for your needs.

The schematic is shown here:

BPF and LPF board schematic


Toroids for external Low Pass Filters are not very expensive and W8DIZ suplies a wide variety at reasonable cost. If you need 25-100 of those you are better off to order directly from W8DIZ. Since I've had some requests and if you only need a few, here is my list. They all came from W8DIZ:

AVAILABLE TOROIDS Feb 31st, 2013


500V Mica caps for Low Pass Filters are pretty expensive so I'm offering these out of my stock.

AVAILABLE MICA CAPACITORS Feb 31st, 2013


The Graphics Interface for the SDR2GO Kit #17

I am out of boards/parts and have decided to retire this kit because the programming support is now directed to the STM32-SDR kit with it's color graphics touchscreen and much higher performance microcontroller. The SDR2GO kit and the suporting Graphics Interface kit was a really great SDR Development platform.


The WB6DHW Band Pass Filter Kit #20

The WB6DHW BPF Kit with toroids, top view. Note that I mounted the toroids on the bottom of the board to reduce interference with other components. The SMA connector in the picture is for my testing, the kit does include 1 ft of RG-174 coax.

The WB6DHW BPF Kit with toroids, bottom view. That's a lot of little toroids to wind ....but it does have higher "Q" (less insertion loss). You can adjust the turns spacing to get closer to the "target inductance" on the provided sheet.

The WB6DHW BPF Kit with chip inductors top view. This shows one type of chip inductor, your kit may vary. I tried to select the highest "Q" chip inductors which were easy to solder and reasonably priced.

The WB6DHW BPF Kit with chip inductors bottom view. This particular board uses one of Dave's earlier versions without the extra holes for toroids. All boards now being shipped have the extra holes (R1 level).

The idea here is to offer a complete BPF kit based on the board offered by Dave, WB6DHW. I know it's difficult to buy all the various parts in small qtys so this is an attempt to help out. As you know, the values Dave selected, using the great L/C filter program from AADE, provides 6 overlapped BPFs which cover from 1.5MHz to 30MHz. Note that none of the passbands include harmonics. In other words, the highest passband frequency is less than 2X the lowest passband frequency. I refer you to Dave's, WB6DHW, website for schematics and additional details.

I have made a few minor modifications which are detailed in the instructions which come with the kit. Basically for the larger inductances, I use 2 stacked cores to cut down the turns count, a different 1:1 RF transformer is used, and you have the option to install L44 or a 1N914A diode for "accidental 5V power reversal protection" which will cost you both FETs.....been there, done that.

Since many of you have ordered the board from Dave already and may not have gotten around to ordering all the remaining parts (or like me, couldn't find it), I offer the option of buying the BPF Kit with or without the board. OPTION #1

The lowest BPF insertion loss will be if you use handwound toroids. This is not easy, there are 42 of them, and it requires a steady hand, good magnifier, and patience, patience. You may want to enlist the aid of a young type person. The cores come with 20ft of Belden #28 Thermaleze wire. OPTION #2

Some of you may not want to undertake the task of winding 42 REALLY SMALL toroid cores, and you have the option of selecting 0805 size chip components which are easy to solder and no winding is required. Although I have selected chip inductors with high "Q" levels, they still have slightly higher insertion loss as shown by the comparison BPF plots on the AQRP website on yahoogroups.com (under my call and BPF #20).

We are trying to find a local person to wind the toroids and provide pre-wound sets....but that has not been worked out yet and I have no idea of the costs involved. The only thing that is certain is that it won't be me.

CONSTRUCTION and TESTING HINTS:

It's best to unpack the envelopes and especially the capacitor/inductor sheets over a large piece of white paper so you don't accidentally "ping" small parts into the carpet. Remove only one capacitor/inductor value at a time and get it soldered in place. It's also best to put the cat in an isolated room.

For initial testing, check continuity across each filter from the filter side of each 100nF DC blocking capacitor on the input and output. The resistance should be less than 1 ohm. To check the 3-bit filter selection for the 8 possibilities, measure the voltage on the outside of the DC blocking capacitors. When a specific filter is selected you will see +2.5V on the 100nF DC blocking capacitors for that filter. Don't forget to measure the two filter positions which will be used later.

So what comes in today's WB6DHW BPF Kit ....other than a --LOT-- of small parts ? ...Bill of Material:

OPTION #1 Bill of Material:

OPTION #2 Bill of Material:

OPTION #3 Bill of Material:

The price for the WB6DHW BPF KIT #20 is $15, plus $9 for OPTION #1 (if you don't already have the board ....or can't find it), plus $10 for OPTION #2, plus $10 for OPTION #3, plus $4 for postage (for 1 or 2 kits) in the USA and $9.50 for DX postage. You can order option #2 AND/OR option #3, but you only --need-- one of them. Options can only be ordered/shipped with a kit.


The 5W HF Amplifier Kit #21

The 5W HF Amplifier shown with the new optional Heatsink. The SMA connectors were installed for my testing, the kit is provided with 50 ohm coax to connect to the BNC/SMA/HF connector of your choice. Normally the Ampifier would be mounted in an enclosure with a hole so the MOSFET can be bolted directly to the outside heatsink.

Picture of the optional drilled and tapped heatsink.

It would be nice to have an Amp with a little less power than the 20W amplifier Kit #15, so here is a 5W version using a single MOSFET with an optional drilled and tapped heatsink (no fan required) from HeatsinksUSA.

When it comes to Amplifiers, the Radio Amateur is responsible for making sure his amplifier operates within the guidelines established by the FCC and that it does not cause unwanted ipassnterference. This is a Broadband Amplifier and will require some sort of Low Pass Filter (LPF) or Band Pass Filter (BPF) on the output to attenuate harmonics. You may already have one you intend to use.

My idea was to provide a good and low cost Amplifier for the HF bands (160m to 6m) which can be driven by a SoftRock SDR or any other low power driver and provide ~20dBm of gain. Low power being defined as ~100mW. Some of the new SDR units supply less than 50mw and really need a little “boost”. This Amp uses the RD06HHF1 RF MOSFET which are rated at 6W output for 12.5VDC at 30+MHz. These parts are quite robust and much better than the IRF510 Switching Power Supply MOSFETs used earlier, largely because of their low cost and availability. The other advantage of the RD06HHF1 is that the mounting tab is attached to the “Drain” pin which is at ground potential …so no mica insulator is required. Just like the 20W HF Amplifier Kit #15, this Amplifier has a Signal Operated Switch (SOX) for CW QSK. I didn’t really put it there for SSB …..but who knows (still better to use PTT). Did I mention good and low cost ?

The design and components which have been selected require that the operational criteria of 1) an Input of ~100mW –AND-- 2) an Output of 5W max ………whichever comes first, NOT be exceeded. To allow some adjustment, the input to the Amplifier has places for a Pi network Input Attenuator of your selection (Rx, Ry, Ry) ….3dB, 6dB, etc. Parts for a 3dB (50% power reduction) attenuator are provided in the kit. The purpose of the attenuator is to reduce input power and to provide proper 50ohm matching for the driver. This design has been extensively tested and optimized to provide good matching to 50ohms without the attenuator. If you elect to not use an attenuator, replace Rx with a jumper and do not install either Ry.

The design also provides Class C operation (CW only). This allows lower power consumption when you really don’t need linear operation. The Gate Bias current on the MOSFET is set to around 20mA with the potentiometer if you prefer and only want to run Class C (for CW)....much less heat generated.

Many MOSFET Amplifier circuits do not use a feedback circuit but I thought it would be good design practice to do so and added one. The T2 compensation capacitor is a 249pF Mica capacitor. This value seems to work best for 160m to 6m (emphasis was put on working well at 6m), and Mica capacitors are very stable across a broad range of frequency and temperature.

Another design parameter which seems to help on all the bands, especially 6m, is to further reduce spurs by paralleling capacitors of different values to reduce the capacitor self resonance effects. You will see that in many cases a 100nF cap is in parallel with a 47nF cap or 10nF cap and also a 1nF cap.

Here are the assembly Instructions for the 5W Amplifier

5W Amplifier Construction Hints

So what comes in today's 5W amplifier Kit ? ......Bill of Material:

I offer two heatsink options:

#1) No Heatsink, Just the 5W Amplifier for $35, you come up with your Heatsink

#2) A 4.23" x 2.90" x 1" Heatsink from HeatsinksUSA. This Heatsink has 1 hole drilled and tapped to match the MOSFET and 2 mountin holes. I am the driller/tapper. Price will be an additional $5. Postage will go up because of the added weight.

Shipping for one kit with option #1 (NO heatsink) is $4 First Class Mail in the USA and $9.50 First Class Mail for DX. Shipping for a kit with Heatsink option in the USA will be $6. DX shipping costs are determined by location.


The Si570 Low Frequency and I/Q Output Adapter Board Kit #22

This board was designed to be used with an Si570 Frequency Controller (Kit #2) or any Si570 (SoftRock for example) to provide outputs lower than 3.5MHz by dividing the input signal by 10 or 100 AND provide I/Q signals for mixer experimentation. The board show is set up for Divide by 100 AND Provide Quadrature QSD/QSE I/Q signals

This little board was designed to be used with an Si570 Frequency Controller (Kit #2) or a SoftRock to provide outputs lower than 3.5MHz. Jumper selection of divide by 1 (bypass), 10, or 100 will provide down to 35KHz. This is something useful for the LF guys. You would then feed that signal to a QSD or QED for detection at ¼ of that frequency.

You can also jumper select an I/Q output in addition to divide by 1, 10, or 100. This could be used with your own external mixer or other experimentation.

The construction is pretty simple ….solder all the parts on the board and pay attention to where you have all the jumpers set. All the resistors are the same, except for the 0 ohm "Jumper", and all the capacitors are the same. The 16 pin smt IC goes on the 16 pin footprint and the 14 pin smt IC goes on the 14 pin footprint. The #1 pin on the connectors is shown as a square pad on the footprint.

Power/Ground is taken from the Si570 Controller output connector which has 3.3V or you can attach it externally to 3.3V or 5V on a SoftRock or whatever you are working with. Both chips on this board will run off 3.3V or 5V and have slightly better performance at 5V.

So what comes in today's Si570 Low Frequency and I/Q Output Adapter Board ? ......Bill of Material:

Kit #22 sells for $12 and shipping is $3 First Class Mail in the USA and $7.50 First Class Mail for DX.


The Octal Swizzle Board Kit #23

This board can be used to transform any Octal (3 bit) pattern to any other Octal (3 bit) pattern. The color jumpers are for testing purposes and will be replaced with #30 teflon wire on the back side for normal use.

What is it ? A board which can be used to transform any Octal (3 bit) pattern to any other Octal (3 bit) pattern using the brute force of a 74LV138 Decoder and a 74HC148 Encoder. All the signals have 10K pullups. You are given multicolor jumpers to experiment with and some #30 wire to finalize the job since the #30 wire on the bottom of the board looks much cleaner. You will want to experiment because of Hi active and Low active devices. It's only 8 wires but you will have to scratch your head.

Why this board ? Makes the 3 control lines from your SDR2GO, STM32-SDR, manual switch, etc much easier to wire if the BPF control lines and the LPF Band control lines for the boards you are using are different.....for whatever reason.

This can be readily demonstrated for those using Dave's WB6DHW BPF for "Receive" and some other LPF board for "Transmit" on your transceiver.....or if you are just using a junkbox switch.

The logic will work with 2V to 6V signals. If you are connecting to a 3.3V interface which already has pullups, remove the three 10K to 5V pullups on this board.

Example:

Using Dave's, WB6DHW, suggested values and schematic you have the following BPF board controls:

For this example I have a pushbutton switch which reads "0" to "7" and has a 3 bit output to ground as follows: Since everything has pullups, an open switch bit will be "Hi" and a closed one will be "Lo"

I want the pushbutton octal switch with 3 bit output to control the BPF as follows:

So I map (jumper/wire) the two connector rows which are labeled 1-8

Hope that does not confuse anyone (may require some paper and pencil). There is some ERATTA (Murphy is ever present). One of the three input pins is not connected to it's pullup resistor (1/8" trace missing). This is easy to correct by bending that lead and soldering it directly to the 10K resistor pad. You can see the 'fix" in the picture.

So what comes in today's Octal Swizzle Board ? ......Bill of Material:

Kit #23 sells for $15 and shipping is $3 First Class Mail in the USA and $7.50 First Class Mail for DX.


The T/R Switch Kit #24

This is a simple T/R Switch board.

What is it ? A board with a nice G6H-2F 5VDC Omron relay with dual, bifurcated, and gold plated contacts which can be used to switch a coax line between Receive (Normally Closed) and Transmit (Normally Open). The coax connectors are SMA type connectors or you can solder coax directly to the board (SMA connectors are a much better idea). The control signal is 5V active. If you want to use 12V for the relay, put a 270 ohm resistor is series with the power.

So what comes in today's T/R Switch Board ? ......Bill of Material:

Kit #24 sells for $10 and shipping is $3 First Class Mail in the USA and $7.50 First Class Mail for DX.



So what else are those AQRP guys up to ?? Well, lets see.........

This is the 6 band, manually switched, Band Pass Filter and Low Pass Filter board.

It consists of a 2.5" x 3.5" host board with up to 6 individual 2.5" x 0.6" BPF filters or LPF filters. It has multiple coax attach methods on the board: Coax cable directly with strain relief, BNC connectors, or SMA connectors.....your choice. Signal traces on the board are 50 mils and kept as short as possible with all wiring over a solid ground plane to minimize transmission line problems on the board.

The 6 bands on the switch are plug-in and can be any 6 BPF or LPF filters. The assumption being that for Tx you would probably want LPFs. However, if you want to use pluggable BPFs for both Receive and Transmit, that's OK too. The board can be configured so that the onboard Tx/Rx relay can be connected to either end of the symetrical plug-in filters.

In Mode 1 the relay armature switches the Antenna between the 6 plug-in filters and the Receive input. This assumes the receiver has it's own filters ......like Dave's, WB6DHW, broadband BPFs). In Mode 2 the 6 pluggable filters are connected to the Antenna at one end and the armature of the Tx/Rx relay at the other end. The relay selects between Receive and Transmit/Amplifier and the filters are inline to the antenna for both.

The relay is powered by 12V or 5 V, at 28mA and is controlled by external (Voltage active) PTT input. It has gold, bifurcated and redundant contacts for reliability.

The little 2.5" x 0.6" BPF/LPF filter (shown in the Kit #15 section, above) form factor is not a "standard" yet but they seem to fit in well with the size QRP SDR units around here (AQRP). I measured a couple of LPFs for 40m and 20m on my MiniVNA-Pro and the Transmission Loss was <0.1dB with a very respectable Return Loss so the SWR is low. Of course, all these maeasurements are into 50 ohms. BPF data looks good too but I haven't built them up and tested them for all the bands.

Some pictures showing more detail of the switch. The filters are symetrical and can be plugged right side up or upside down. You can locate the header pins on either side of the board and can come up with some very compact implementations. This compact technique works great for T37 cores. For T44/T50 cores, use additional spacers where needed.


This is the Si570 Controller II. You will note that it's just the bottom half of a SDR2GO board (above).

This is the Si570 Controller II which offers the same features described in the SDR2GO section. The main ones are "standard" backlit 16x2 display, keyboard input (as well as rotary encoder input), ability to display some user defined text, scanning capability, and enhanced frequency/display offset capability.

This kit is waaaaay on the back burner at this time .........and the burner is "off". I do have several boards available for $10 each, postpaid in the USA or $20 for a board and programmed microcontroller (only, no other parts), postpaid in the USA.