The FET-1 "Transceiver*" ?
By Glenn Yingling
Here is the schematic for the little rig that I call the FET-1. Also
included are a few notes on building and tune-up.
I sent the full article to the 73 magazine and I am waiting for them to tell me that it is being accepted for publication.
If you decide to build this beauty, please consider calling me to set up a schedule for a rig to rig contact. I would
like to hear how it sounds and would like you to be the first one to make the FET-1 to FET-1 contact ! Hi. So
far I have worked 17 states and 2 providences with my best DX being Eagle River Wisconsin which works out
to be 36,250 miles per watt !
DETAILED ELECTRICAL CIRCUIT
-Fig. 2 shows the
electrical schematic of the FET- 1. Please note that the MPF- 102 transistor
(Radio Shack, 276-2062) is mounted directly on the 4 Pole Double Throw (4PDT)
common switch terminals. It is used for both the receiver and the transmitter sections. I selected
the FET transistor because it works good in the Regen.
MPF- 102 transistor
-For the 40 meter band, tuning is set with the
following: you set the Regen
-The 320 pf cap gets you to the 7.0 MHz range.
-The 6-70 pf cap lets you home in on the frequency of interest- -in my case, 7040 KHz.
-The small variable cap (one plate) lets you tune around 7040 KHz as a bandspread control.
-The 5-50 pf variable cap provides feedback to the oscillator for sensitivity control. Adjust it
until the Regen is on the verge of oscillation. Any squeal indicates that you have gone too far!
-This circuit works good and the layout for 40 meters is not critical, but try to keep your wires short.
-You will hear a signal on both sides of zero beat* allowing you to hear each signal twice on
your dial, unlike your superheterodyne .
-The 9 component (including the transistor) Regen receiver will bring in signals comparable to
those received by your expensive receiver. But ,the selectivity will not be as good.
-The downside of this story is that it is so sensitive that it can be easily overloaded by a strong
signal or a nearby station. ( I didnt care, so I did not try to put in any attenuation or volume
control. Also, at night with a contest on , the Regen is pretty much unusable. (If you like , you
can get some degree of attenuation by putting a variable resistor in series with the 9 volts
supplied to the Regen.)
-With the limited frequency range that I wanted ( 7040+/- 15 KHz.), once
control, you dont need to adjust it again.
you set the Regen
-Adjust the 50 K Pot and the (6-70 pf trimmer
for maximum output of the transmitter into a 50
-The transmitter puts out approximately 20 milliwatts. Power is calculated as follows:
transmitter into a 50
1 .- (Peak to Peak volts)/2 x 0.707 = volts rms
(PET- 1) 3 volts/2 x 0.707 = 1.06 vrms
2 .-(vrms squared)/50 ohms = Power in watts
(FET- 1) (1.06 x 1.06)/50 = 0.022 w = 22 mw
-The 100 micro henry rf chokes are somewhat non
critical. Try whatever values that you
have that are greater thau 100 micro henrys. I happened to have a lot of the 100 micro
henry chokes that cost me a penny each.
-The 50 k ohm pot is also somewhat non critical. Try any pot up to 500 K ohm.
-When I run this rig, I use one D cell from a flashlight for power. However, I cheat
because I use a DC-to-DC converter to boost the voltage up to 9 volts dc.
- I did not even put a power on/off' switch on the FET- 1 , instead I use the external
power supply switch.
-1 did not put a sidetone monitor on the FET- 1. I just use the sidetone from my keyer.
There is plenty of space for later addition of a sidetone to the transmitter card if so
desired in the future.
values that you
28 Lawrence Ave
Newark Valley, N.Y. 13811
* Note that the MPF-102 transistor (Radio Shack 276-2062) is mounted
directly on the 4 pole double throw
common switch terminals and is used for both the receiver and the transmitter sections. (So, would this be considered
Glen E. Yingland W2UW
Newark Valley, NY 13811-0062