Monday, February 21, 2022

Thoughts on the Penntek TR-35 QRP transceiver kit

Boards completed. Plenty of room for easy assembly
I've only had the Penntek TR-35 exactly one week, but during that time I've:

and had many ragchews (and park huntings) on all four bands. I've also made selectivity, spectrum and MDS measurements.

Be forewarned - the following may sound like an advertisement, but it is not. I paid full price for the kit and have had no other communication with the kit's designer, John WA3RNC.

Now that that's out of the way, here is a fleshing-out of the notes I took during the week.

The Build

In 40 years of building kits, I've never seen one that is designed to prevent potential problems to the extent of the TR-35.

First off, the kit arrives about 70% pre-built and pre-aligned. Numerous SMD components are already installed and even the tedium of parts inventory has been rendered as mostly unnecessary due to how the parts are packaged. They come in three sleeves - one for each of two boards, plus the final assembly components (knobs, jacks, plugs, etc).

Within each sleeve, the components for each assembly step are each in their individual pocket. There are anywhere from 1 to 5 components per pocket.

Printed instructions and schematics for assembly and operation are included. These can also be

Unboxed sandwich, ready for housing

downloaded from WA3RNC's website.

The Number 1 problem many builders have with kits is in the installation of toroidal inductors and transformers. With the TR-35, these arrive already wound and with the ends stripped of enamel and tinned. Therefore, they install as easily as any any other component. This also greatly reduces the construction time of the build.

Four crystals are numbered and are to be installed into their own specific place on the board for maximum effectiveness for receiver selectivity.

In my case, total build time was just under 4 hours. Each board took 1h20m.

There are no gotchas in the assembly procedure - just be sure to install the heat sink, insulator and final FET in the proper order. And don't omit the tiny insulator for the FET's mounting bolt. Also, pay attention to how the two banks of pins are installed onto each board. Photographs explain these steps clearly.

When I finished each board and got to the part where the two boards are mated together and fit into the case, I thought I'd done something wrong with the installation of the three LED's. They were too low to come up to the holes in the front cover. A later step takes care of this - each LED has a lens that snaps into the holes in the front panel. Fancy!


Thanks to the pre-alignment, there is very little left to be done once the boards are completed and no test equipment is needed other than a multimeter, your ears and a small tweaker to adjust the pots.

After a quick check for a short to ground of various voltage sources, the most important alignments are setting the TX bias and centering the passband frequency. Even if you've never built a kit before, you shouldn't let these steps worry you. The bias setting is done with your multimeter measuring input current; the passband can be set by ear.

Other alignments are for setting S-LED (as opposed to S-meter), Low Battery Voltage LED and sidetone volume.

That's it. With an antenna connected, you'll probably be hearing signals on the band even before you begin with alignment.


DC input vs. RF out. RX current is 90-100 mA
I like the ergonomics of the TR-35. Toggle switches and no menus were a large part of the attraction for me. The radio has a mini-Paraset look to it, yet much smaller, four bands, 10 ounces and 10 watts!

It also has a wide permissible DC input voltage, from 9.5 to 14.5 volts. This makes the radio usable with a variety of battery chemistries, at various levels of charge/discharge.

Power output is largely determined by DC input voltage.

The tuning encoder is detent-less, as it should be. In my opinion, a tuning encoder should feel like a VFO, not a circular switch.

I did replace the knob on the tuner with one of a slightly larger diameter. This small change makes a big difference in improving the feel of tuning the rig around a band.

Each band also has one memory assignable to it. WA3RNC calls these "semi-permanent". So far, mine have been permanent without the semi-. These memories simply assign the frequency, within a band, that the TR-35 will come up on when switching to that band. I can change my mind and assign a different frequency later if I want to  (thus the semi- I suppose).

Also, the tuning encoder can be locked so that you don't inadvertently QSY by hitting the knob while reaching for a nacho.

The sidetone frequency is fixed at 700Hz. The sidetone's output level is set as one of the alignment procedures and I wish there was a way that this setting could be accessed with the radio still in its case. I may well drill a small hole in the housing to make this possible.

The sidetone level is affected, to a small extent, by the settings of the RF and AF Gain controls. But it is more affected by whether headphones or an external speaker is used. At home using a speaker, one level is appropriate; at a POTA site with headphones on, a slightly lower volume sidetone was more appropriate. To access this adjustment, the cover screws and the nuts holding the front panel controls must all be removed.

Yep, I think I'm gonna drill a very tiny hole.

Another thing I wished for during my POTA op was a way to make sure my reflected power wasn't too high. I would trade the S-LED for an LED similar to that in an Emtech ZM-2 tuner whose level of illumination indicates how well the antenna is matched.

I used a resonant antenna for my most recent POTA activation but it's still nice to know, from one installation of the antenna to the next, that the SWR is not at a harmful level due to some problem with a connector, a nearby metallic awning or some other unforeseen variable encountered on portable operations.

Let's talk about bandwidth...

The TR-35 has 3 receiver "modes": CW Wide, CW Narrow and SSB.

SSB stations sound great with whatever bandwidth is used in SSB mode - I didn't measure it.

In CW Wide, the bandwidth is 1.6 kHz (measured at -6 dB points). This is very wide for CW and could more appropriately be called SSB Narrow.

In CW Narrow, the bandwidth is 250 Hz, again at the -6 dB points. However, that's only half the story. Typically, to get the full picture, bandwidth is also measured at the -60 dB points. This, along with the -6 dB measurement, tells not only the width, but the shape of the filter, ie, how steep are the skirts?

I didn't make the -60 dB measurement but, by ear, I can tell that the skirts aren't very steep - and that's not a bad thing in this application. If they were steep, 250 Hz would, to many users, be too narrow except perhaps for contesting.

Prior to the ARRL DX Contest (CW), I thought that a 250 Hz BW would allow me to hear only one signal at a time, most of the time - as it would be if I were using a 250Hz filter with my steep-skirted IC-705 or a K3, etc.

This was not the case with the TR-35 and I quickly realized that the effective bandwidth - taking into account 250 Hz @ -6 dB plus the relaxed skirts is somewhere much more appropriate for a portable multi-band QRP rig. Somewhere between the -6 and -60 dB points is an average bandwidth and I believe it's right around 400 Hz or so.

In other words, right on the money for the rig's designed application. Numbers don't lie, but sometimes they do mislead.

I do, however, wish the CW Wide was less wide.

4 continents within minutes - 5W & a dipole
Receiver performance during the DX contest was fantastic. I didn't work a single QRPer in the contest - most stations I worked were using a kilowatt, and I'm sure many of the US stations in my vicinity were too. Despite that, my receiver never de-sensed due to nearby super-strong stations, nor did the AGC prevent the receiver from coming back to full sensitivity immediately after a strong on-frequency station stopped transmitting.

MDS measurements (made only on 20m) show the TR-35 to be 8 dB better than the specs listed on WA3RNC's website for the radio. An ARRL review of the TR-25, showed that radio to be 10 dB better than advertised. WA3RNC is understating his kits' performance!

The look and color make for quite an attractive radio but I do wonder about the longevity of the labeling on a rig designed for outdoor use. Time will tell. The display is easy to see regardless of the ambient light and, like the radio itself, it has everything you need and nothing you don't.

What will the TR-35 be compared with?

For a CW op who likes POTA, SOTA, all-around QRP operation and casual contesting, sprints, etc, I can think of only one valid competitor - the SW-3B.

I owned an SW-3B for a while, had a lot of fun with it and have nothing bad to say about it. It is only available completely built and costs $188. It is a 3-bander for 20, 30 and 40 meters. Its output power is a bit less than that of the TR-35 at a given input voltage but it is half the weight of the TR-35.

For context of the TR-35's weight, it is within an ounce of that of my Samsung Galaxy smartphone. Put another way, I could detect the weight difference between the TR-35 and the SW-3B only if I were holding them both at the same time.

Each radio sips power. I wish I'd measured the receive current on the SW-3B when I had it. Anyone know? On the TR-35, it's 90-100 mA.

With the TR-35, you get an additional band - 17 meters, which is coming to life as the sun finally grows more and more spots. I'm seeing more POTA activity than ever before on 17m and I was glad to have it on my own recent outting.

QSY'ing around any band is so much easier with the TR-35. Three tuning rates are selectable and they are easily accessed with a push of the tuning knob. Unless, its firmware has been improved, the SW-3B has an awkward scroll order in which the tuning rate is changed from one digit to the not-so next. I describe that minor(?) annoyance in more detail here.

The lack of an ability to buy the SW-3B in kit form is disadvantageous in a way. Having built the TR-35, I'm familiar with its innards and how to align or adjust any of the parameters to my liking. If ever a switch or the display need replacing, I'm on it - no intimidation factor at all.

And the more recent SW-3B's have CW memories (they didn't when I had it) - the TR-35 does not. However, the SW-3B has to resort to menus in order to have this - the very thing the TR-35 is designed to avoid.

And, unlike the SW-3B, the TR-35 will drive an unamplified speaker to room-filling volume.

Aside from its excellent performance, the TR-35 will see much use from me for two reasons: I like the easy accessibility of its functions and I like the 17m band. Its inclusion allows me, not one, but two WARC bands with which to avoid contests if I'm not feeling the spirit. And 17m has been a good QRP DX band recently - and will continue to improve.




W1AND said...

Venus website for SW-3B states: "receiving: about 45mA(backlight on), and less than 40mA(backlight off)."
So, roughly half of what TR-25 takes. Not that it is really a problem with modern LiFePO batteries.

John AE5X said...

Thank you, sir.


Thomas Witherspoon said...

Excellent assessment, John.

I appreciate your insight as a builder because the tR-35 I have at the QTH now was pre-assembled and is only only loan for a few weeks. I did pull it apart though to do a small mod per WA3RNC's request (a few units had noisy display chips and the fix required soldering one cap across the chip to ground--very easy). The boards are top quality.

I agree with you about the performance aspects of the TR-35. I used mine in the contest a bit (I logged maybe 10 DXCC entities?) and I found it had quite good contest chops! The receiver handled the RF density without any problem.

I also agree with you about the CW Narrow filter--to my ear, it's maybe between 400-500 Hz. Perfect. And, yes, the wide filter is too wide.

Thanks again for sharing your thoughts! I'm planning to purchase the TR-45 when it's available, although I do love the form factor and weight of the TR-35.


John AE5X said...

Good morning Thomas,

I like the looks, the analog meter and the additional functionality of the TR-45 and will think about buying one but I'd never use it on 80m and it lacks 17m. If only it covered 17-40m. For now, the TR-35 is ideal and I'd have no qualms about putting it in the kayak or taking it out in iffy weather - situations where I wouldn't take my IC-705, cage or no cage(!).

The recent DX contest was an eye-opener...not just in terms of the TR-35 but in how much receiver performance has improved over the years, even in inexpensive rigs. Many years ago, I bought a Yaesu FT-840 - their bottom-of-the-line rig. It cost $550 in 1996 dollars and fell apart, receiver-wise, during CQWW. I had no context at the time in how a receiver should behave in such conditions, so I thought "this mush must be normal with all this RF around". Not until I bought my next rig, a K3, did I realize what a dog the FT-840 was in contest conditions. The TR-35 is certainly not a K3, but it most certainly is not an FT-840 either, fortunately.


W4GER said...

Thank you very much for your detailed review. I am thinking about this radio or the MTR4B from LNR. I was wondering, if you used MTR4B, or other MTR radios, if you could post some comparison in usability and functionality?


John AE5X said...

Hi Alex,

No, I've never used an MTR-4B but did build an MTR-3B years ago when they were offered by their designer Steve KD1JV. They are fantastic kits, super-lightweight and great for SOTA ops. But for casual QRPing I prefer tuning around a band with a rotary encoder rather than up/down switches.

The MTR series have no protrusions and therefore pack almost anywhere without much chance of damage - but at the cost of some inconvenience in how the various controls are accessed.

As we speak (type) I'm working on a rudimentary cover to protect my TR-35 when packed into the bag for travel.

It really depends on how you feel about the two methods of manipulating each radio's functions (switches vs. rotary) and what bands you prefer.


Goathiker said...

Building the TR35 was a blast I then took it on summit in CO's bright sunlight and the display was impossible to read thus band/freq were?? flipping the memory switch reverses the display for a brief half second but not a real solution for me ...maybe better if I lived in WN where there's less sun?

John AE5X said...

Hi Steve, maybe a future firmware update could make the reversal permanent. As you know, it only happens now when the memory is being written to. I had no problem seeing the display on my recent outdoor activity, but it was partly overcast those days.


W4GER said...

Thank you John. I am wondering if Thomas has some comparisons that he would be willing to share?

Jeff Bauer, WN1MB said...

Thanks for the detailed review, John. Excellent. I first learned of PennTek only recently on the SKCC io groups board. Their rig design philosophy is what I've been looking for going on two years now. I'm tempted to wait out the "45" but may very well go with the "35" for the time being.

Being a CW only guy, 70 years old and semi-retired, the "45" may very well be that elusive forever rig I've been looking for!



John AE5X said...

Jeff, I was doing the same thing but then read of the parts availability affecting the further development of the TR-45 and decided then to get the TR-35. I really like the look of the '45 and hope to have one eventually. But the TR-35 has the four bands that I use the most.

I just played with the rig a bit in today's CW Sprint and will post a short video of the rig in action soon.


Greg Graham said...

Thank you for this review; I've decided the TR-35 is the next radio for me. I've built a 40m QCX+ and a 20m QCX mini, and I've enjoyed them, especially the mini. However, I don't want a bunch of QCXs to cover 4 bands. I also like the no-menu philosophy and the smooth tuning on the TR-35, so I'm glad to see that it works as good as I hoped.

Unknown said...

Thank you John, I just ordered me one.

Dave KN4OK

John AE5X said...

I know what you mean - I have a 20m QCX-mini waiting to be built but with the TR-35 on-hand, it may be a very long while before I can justify the effort to build it only to do 1/4th of what the TR-35 is already doing (although the QCX series have WSPR capability).


John AE5X said...

FB Dave - it looks to be well on its way to becoming a very popular rig/kit.


Vic Kieffer WA0USA said...

I built the kit and did the noisy IC mod.I love the radio. Worked 42 DXCC entities in the ARRL DXCCcontest 40m SO QRP. The rig was right at home in KW alley. Handled the strong signals with aplomb. My reference rigs are Orion II and FT 1kD for contesting. I would say the 400 hZ figure on narrow is about right but I find "wide" perfect for getting an idea of band condition. I contacted John about the arrangement of rx modes and the inability to change cw filtering after entering RIT mode. He sent me a new software chip. Doesn't get any better than that. Great radio. Tons of fun to build and operate.

John AE5X said...

Hi Vic - it's good to know that John is responsive to issues (or even requests) on firmware updates and changes. I've heard from a few other owners regarding the noisy IC mod...maybe a bad batch affecting only some of the kits? I guess if you need to make the mod, it's obvious? I must have lucked out. Thomas K4SWL mentioned the need in his pre-built kit as well.


Unknown said...

Hi John: I noticed the 90 hZ hum when changing power supplies with no antenna on the rig. I thought it was the different supply that I had switched to, a 3.5 A computer style supply. I started out with an Astron RS 70m that I use to power my HF rigs. I never heard the hum with an antenna attached and would not have worried about it until I received a note from John saying that the condition existed on some of the radios. He offered to pay for round trip shipping and make the fix himself. It was waaay easier to have him ship me a cap and do it myself. Problem solved.Another example of his customer service. On another note, after buying and building a QRPoMeter I noticed that the power output of the TR35 tapered off and then quit after 7 to 15 seconds of keydown at full power out. I took notes of time and power levels and sent him an email. His response was that the radio was operating as designed. The poly fuse that he incorporated to protect the radio from reverse polarity also protects the final FET from high SWR, extended keydown situations. I never noticed the power issue until I started fooling with the QRPoMeter with its built in 16w dummy load. I use a scope on the output of my station and never noticed any degradation in power output in normal use at full power or contest use at 5w out. John said that he would rewrite the manual to include an explanation of the protection circuitry. Another undersold feature in the radio! The noisy IC was evidently not even to the batch level but rather a scattered few chips.



John AE5X said...

Thanks for the info, Vic. Maybe that explains why I never heard the hum - I've only used a battery to power my TR-35, never a PS. Like you, I also have an Astron (35M). I'll try it out on that supply but don't think my rig will ever see any real use other than from batteries. In fact, I need to buy a smaller one - the 12AH one I have is overkill for QRP rigs.

Thanks again and 73,
John AE5X

Unknown said...

By the way, my TR 35 displays reverse display illumination as long as you hold the band switch up in the memory write position. Don't know if he rewrote that feature in the chip he sent me or not.



Anonymous said...

Hey John AE5X, thanks for the write-up! I pulled the trigger on a TR-35 just the other day. I really like your larger-knob upgrade, and have tried to find the knob you used (since it matches), but I’ve been unable to locate it. Would you mind sharing a link or a part number?

Chuck KI5JUB

John AE5X said...

Hi Chuck,

It is part number 41004-4:

Amazon or Mouser probably have many similar that would work (25 to 30mm diameter).


C.L. Stearns said...


C.L. Stearns said...

John - I acquired a larger knob and it is THE BEST modification - makes navigating the bands so much easier. Thanks!

John AE5X said...

Ergonomics of radios should be rated right up there with rx specs, IMO. Enjoy!


Dave AG7TX said...

John, I put my TR-35 in a small Pelican case. I might put a small piece of foam on top of it but I'm not sure it is necessary. The small Pelican cases are not very expensive, either.

There's room inside for a couple of doodads, too.

The Elecraft T1 is a nice addition to the radio and complements it nicely. In fact, I'm thinking about taking this rig out today and trying to activate a park or two.

John AE5X said...

Hi Dave - my problem with Pelican (and similar) cases is that I keep changing what I want to, what at first seemed the ideal case, now becomes too big, small or incompatible with what I later decide to include with a rig. They are nice though and offer the best protection available.