Ten-Tec’s RX-350 DSP HF Receiver.

Total lockups and other operational gremlins were normal and plagued the set to the end (from our testing and other reports). Was the last straw bad LCD's and or display boards from China ? Sync detection performance was like the expensive RX-340 model that is " Poor ". Plastic bezel mold was used for other Ten Tec transceiver models, check out blocked spot in the lower left hand corner (for a 8 pin mic connector). (Photo : N9EWO)

Discontinued Receiver

I do NOT own a Ten-Tec RX-350. Two test samples were used for the report below from 2001 and 2002.

A Set With True DSP Bandwidth Filtering

I’m not sure if one dares to compare this RX-350 with its much more expensive cousin RX-340 set. But there are parts that are similar. But lets face it, the overall parts count is far less than what a RX-340 contains and perhaps the reason it has some major problems with it’s microprocessor operations and total lockups ?

Coverage / Display and Spectrum Scope / Tuning Steps and VFO’s / Memories

RX-350's coverage is supposed to be from 150 kHz to 30 MHz. In practice it will tune down to “0” and on the top end up to 30.015.999 (using the tuning knob).

Display is a very nice size LCD with 4 LED’s used for backlighting. There is no display brightness control, but a contrast level adjustment within the “MNU” list is provided. The display also features a spectrum scope, but as comment will be made later, it’s not very useful.

The large display has excellent big numbers for frequency, but the end effect of this LCD it has a “light” look to it. The contrast control has little effect to the problem at hand, it’s still comes out to a light gray look.

2 very handy VFO’s will be found and 128 memory channels with 8 banks each (0 to 7) for a total of 1024. Alpha Tags are also found with each memory and reminded me of the Icom R-9000 the way they are displayed and entered. The only problem I have with the memory channels is that as you do not have wrap around, that is when you reach # 128 in the bank. It will not wrap around, will just stop and you have to rotate the control and go backwards and just go the other way back down. This is really a sad way to do this in my view and makes the memories less useful. Update: Another strange gremlin, certain banks did have wraparound, others did not...WEIRD !

A way to scan the memory channels is also provided. To be able to select the “Bank” one MUST be in VFO mode (another point the manual misses).

Frequency slewing and broadcast band presets are a couple more pluses. One will find no direct keypad entry on the body of the RX-350. This is provided with the optional “Model 302” accessory and is very much recommended.

Construction / Power Supply

Cabinet is made of steel with an inner aluminum chassis. The cabinet is held to the inside chassis with self-tapping screws.

Front bezel is of painted plastic, paint was also is used on the front of the 4 little spin wheel knobs. Thank goodness, it was not used on the body of these 4 smaller knobs. It is not a good idea to have paint on a knob that will be “pawed” all the time.

A switching power supply is used in the RX-350. It seems to work just fine with no excessive noises or heat. It’s made by Autec (model UPS50-2002). Just be aware that using any indoor antennas (or loops) near the set may not work so well with added RF noise.

Spartan Owners Manual / No schematics included

The 38 page owners manual might get the job to get it going, but it lacks explaining functions in any detail and I found contradicting info in regards to the “hard” reset procure (more later). It does have a table of contents.

No schematics or block diagrams are included with the set.

Knobs / Encoders / Tilt Bail

All front pushbuttons have a very good feel and are of the desired hard plastic variety. Mode selection is done with dedicated buttons, but a “ALT” key is used for many of the other RX-350’s functions. So we have double duty buttons with this set.

We have 4 Bourn’s mechanical encoder “spin wheel’s” that are used for AF / RF gain, Bandwidth , PBT (Pass Band Tuning), and one marked “Multi” that is used for a variety of functions.

I found that a couple of these controls had a ruff feeling when rotated. But not all of them. A fix on the ones that were rubbing on the case, After pulling the “chrome” outer ring off the knobs, use a hex key wrench to loosen the knob (these plastic knobs actually have set screws). Move the knob slightly back on its plastic shaft away from the cabinet. Re-tighten, replace the little chrome outer ring. It only goes on one way, don’t get it backwards. After this simple fix and it was much easier to rotate these controls.

A large and weighted metal tuning knob with a finger spin hole is the main attraction that hits your eyes first before turning it on. It has a nice rubber track, and uses a “optical encoder” made by “Agilent Technologies” .

Also felt that it too was too much of a “friction feeling” with the main tuning knob as I rotated it. At first I was thinking that it was the encoder at fault, it was not. The same cure as with the 4 other spin wheels, but use a bit larger hex key wrench to loosen the knob. You have to remove the rubber track first however. Actually behind and attached to the knob it has a couple of felt pads that are made to add friction. But again after backing this knob slightly away from the case it was a lot better for my liking. There is nothing in the manual about this, which is not a real shock.

We have a nice “Tilt Bail” that raises the set to proper height. It lacks any protection for the table top, so as with the Icom IC-R75 , a couple of pieces of slit hard rubber tubing would fix this. 2 rear “real” rubber feet are found on the bottom, which helps the set from roaming around in use.

Reception Died When Microprocessor Reset Was Done, But Not all the time. Also died this same way during testing.

As with all my receivers that I have owned or tested, I always do a “hard” reset of the radios microprocessor. This is to reset all parameters to factory defaults and also to be sure that something within the software/firmware was not spooked in shipment.

Let me say that the manual does a confusing job in explaining the CORRECT procedure on reset. This will certainly buffalo most new people to the hobby. It appears, that to be done correctly one should see the “Reset Complete” appear on the LCD. One section of the manual (page 3) indicates nothing about holding the “MNU” when doing a “hard” reset, another on page 18 does.

For a “Hard” reset one is supposed to push and hold the “STORE” button while powering up the set. But then a comment on the version on page 18 is made that the “MNU” button is to be held until “Reset complete” appears. It does not say when one is to let up on the “STORE” button and then switch over to the “MNU” button. This leaves you in the dark, like being in the middle of a jungle without a flashlight.

Learned that right after the version and date are finished displaying (just the globe is shown), THEN one lets up on the “STORE” button, moves quickly (takes a bit of practice) over to the “MNU” button and continues to hold this button until “Reset Complete” shows up. Then the owner can release it (once “Reset Complete” is shown) and the set should come to life. I’m guessing that this is the correct method to do a hard reset?

I say the word “should”, as a number of times I tested this “Hard” reset procedure we had a problem. While all the screen displays came up correctly, the radio did not. Some times it did work just fine and other times it did not. When I’m hearing nothing, we just experienced radio hiss just like there was no antenna connected.

Found the cure was to just turn the set off for say 10 minutes (go have a sandwich) , then turn it back on and it does come back to life.

If that was not enough, it also did this in normal operation. It just died just as above when I was zipping through memory channels. Switching the receiver off , waiting another 10 minutes again (another sandwich) and turning back on cured this “dead state” but there is simply no excuse for this.

And to even top that one, another “once in awhile thing”. Going from the memory channel mode (after zipping through them) and returning back to VFO mode, once in awhile the set would show some way out frequency, say in the 40 to 95 MHz area (was not receiving this just displaying it). As soon as I turned the tuning knob, the display would show 30.000.00. One time it locked up doing this and could control nothing on the radio. Yep, you guessed it another 10 minutes (run around the block this time and burn off the 2 sandwiches you just ate).

These are very serious problems that Ten Tec never took serious. I had a gut feeling the receiver's firmware was running over the hardware's limit (like trying to cram 3 pounds of sand in a 1 pound bag) ?

Once in awhile the RX-350 would lock up or display some weird frequency in the 40 to 95 MHz area. Here it is during one of its odd frequency fits. The cure is to turn it off (go have a sandwich) for about 10 minutes. Early Yaesu VR-5000's had lockups too, but at least they fixed it (Ten Tec never did).
(N9EWO Photo)

Setting of the Clock Very Strange

The RX-350 has a very nice "real time" clock that displays seconds and not sharing the frequency display. Also the Day, Month and Year are also part of the scheme.

Well I had a difficult time setting the clock in the 24 hour mode ( has 12 and 24 hour modes ). The only way I could set the minutes and display 24 hr (UTC) time was to set the minutes while still in 12-hour mode. The go over to the 24 hr mode and set the hours. If I did not, it simply would not allow me to select minutes while in 24 hour mode. Perhaps this is way it was meant to be, but nothing in the manual to reflect this.

Frequency Display Off Up to 30 Hz

Not a real serious problem here, but I found the frequency display on the test samples to be off by 20 hz (high) at 10 MHz and 30 hz (high) at 15 MHz.

WARNING : Don’t ground that Audio Output !

Manual does make a strong point NOT to ground the speaker output. If you do, damage will occur (bridged amplifier). This sounds like what Drake did with a number of lower end sets in the 1990’s (and Palstar as well) and for a receiver of today to have this is a drawback to me.

Sensitivity Equal To Other Sets / No Images or Major Spurious Signals

As it seems to be the case with most sets these days , sensitivity is not an issue (at least above 4 MHz , see text below on the added "High Pass" filter). Pretty equal to any other table top receiver that I have used. Could not detect any major spurious signals

True DSP Bandwidth Selection – But AM wider than displayed?

We indeed have “True” DSP being used in the bandwidth chain. 34 bandwidth filters from 300 hz up to 8000 hz.

When I’m receiving signals in AM mode it sounds like the actual filter you end up with is wider than what is displayed. Like perhaps 75% wider? But I like a receiver that offers wide bandwidth filters anyway , so good on that front with me.

Tuning Steps / SAM modes Disappoints But Manual ECSS works OK / Very Good SSB

Selecting tuning steps I felt were done well on the RX-350. Push the “step” button and along the bottom 1 , 10 , 20 , 50, 100, 1K , 5K and 9 K appear. Pushing the button right below this selects the tuning step. Simple and easy with not a merry-go-round chore. You can also program one of the F1/F2/F3 buttons on the Model 302 Keypad to select tuning steps as well.

With the set tuning and displaying excellent 1 hz increments, makes for hair splitting resolution.

Now I wish the SAM mode actually worked on this set. It simply works as about as good as it does on the RX-340 super set. It looses lock more than it holds it. Pretty much worthless. Does not matter if you use SAM in the Upper, Lower or Both..it simply just disappoints.

If you use manual ECSS, it works well. Equally the SSB modes also work well…but not so fast as we cover next.

Audio good and bad / FAST AGC makes for Harsh listening / WARNING : Watch the + 12 vdc jacks in the rear

When using manual ECSS or if you can find a signal that allows for the SAM mode that will work (just about NO fading at all)..A strange background noise appears when listening on STRONGER signals. I guess a “Whoosh” sound I would call it is mixed in the background. I heard this using any AGC setting. Not good.

Also forget about using “Fast” agc setting in any mode. Excessive distortion sets in and for me really made me want to grab the off button. AGC “FAST” is even worse in any SAM mode (can get downright painful). But just switching to MED or SLW helped a great deal. Note : A firmware update (1.15) helped with this nasty problem.

For general SSB signals (Hams etc), the RX-350 sounds pretty good. The 350 has a much punchier audio output than its costlier cousin RX-340 does . Drives an external speaker better.

The Line output to my ears sounds fine with no strange sounds, (other than with the noises as above). The only caveat when using the rear “line out” jack, you will find two 12 +vdc connections right next to the “line output” jack. One should take great care NOT to accidentally plug into one of these when intending to connect a tape recorder or other device. I do not think Ten Tec should not have used a RCA plug for a voltage output.

MW Crossmod With Signals Below 4 MHz

Tec Tec uses a preamp in the antenna line "full time" with the RX-350 (sorry you cannot switch it off). MW cross modulation was a issue with early samples below 4 MHz (first test sample lacked this which was a pre-production unit). Ten Tec added a high pass filter that cured this issue. Unknown how many (if any) were sold without this added filter ?? Look for a small internal "double backed taped" circuit board about the size of a soda cracker. The downside : This reduces MW and LW sensitivity and pretty much kills any REAL use below 500 kHz.

MW cross modulation did happen with the RX-350 below 4 MHz (prototypes and perhaps with some production units ?). A "High Pass" Filter Board was added with double backed tape to cure this, however it reduced sensitivity as well. In fact forget any Long Wave use.
(N9EWO Photo)

The Model 302 keypad Wired Remote Keypad..A Must

Without a way to enter frequencies directly on the front of the RX-350…the Model 302 optional Remote Keypad is really a must have for this radio.

It of course allows for direct keypad entry, but there are 3 keys marked F1, F2 and F3 that are semi programmable. This allows you to program the tuning step, select A or B VFO (a bit of a chore on the front panel), select mode, or engage the sweep display to any one of these keys.

But even better it has a weighted tuning knob for “lazy-sit back” in your chair tuning. Well as long as the cord reaches…It uses the same tuning optical encoder as what is in the 350.

2 bug-a-boo’s here: On some occasions during testing the frequency entry button would have to be pushed twice for it to take, It does not act like it the button itself but more with the sets electronics. This is a bit annoying, and does not do it all the time. The other gremlin is that you are required to enter the frequency in MHz ,one additional button to have to push. I feel also was a bit overpriced.

But a great gadget and I wish more set manufactures would work with this idea.

S-Meter and “Sweep” Spectrum Scope a Bomb

I will have to say that I was not pleased with the RX-350’s s-meter. It also has a numeric indication. The whole meter scheme jumps around like a grasshopper in a wheat field. Just not enough area shown to be of any use. The displayed bar also has a tendency to flicker as moves back and forth. Annoying.

Almost as annoying is the “sweep” spectrum scope. It has hardly any vertical rise on super strong signals. Another great idea and I think the proper way to do it, but it does not work well in practice. If the band displayed does not have too many strong signals and the proper sweep range is chosen, then I found it can be somewhat useful.

The RX-350.....A Real Stinker It Was

Even with the RX-350 able to accept firmware upgrades, Ten-Tec never corrected the excessive lockup and other operational problems the set had in its life on the market. Near the the end we heard of bad LCD boards (these were made in China). Was this the last straw as it was discontinued rather quickly. It COULD have been a very nice DSP HF receiver, but it was just not to be.

Dave N9EWO
© N9EWO
Ver. 2.2

Discontinued Receiver

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