A comprehensive review of the Penntek TR-35 four band QRP transceiver

The following article originally appeared in the April 2022 issue of The Spectrum Monitor magazine:


“Look at this, Tom! Only the stuff I need and nothing more,” cheerfully noted my good friend and Elmer, Mike (K8RAT).  It was Field Day two decades ago, and Mike was gazing at his TEN-TEC Scout. I glanced over, and agreed. “So simple and so effective,” Mike added.

I’ve never forgotten Mike’s sage words. That Scout (Model 555) was about as simple as a then-modern HF transceiver could be:  it had a total of three knobs––one for AF gain and IF bandwidth, one for RIT and Mic gain, and an encoder. It also had three mechanical switches on the front: one for power, one for TUNE and NB, and one for CW speed and RIT. It also had an analog SWR/power meter. The Scout used plug-in band modules for each HF band and featured a large segmented bright green LED frequency display that was characteristic of so many TEN-TEC rigs of the day.

And Mike was right. For those of us who appreciate radios with a simple, uncluttered, and an almost utilitarian interface, the Scout was, in vintage parlance, “the bee’s knees.”  And that the Scout also performed beautifully was just icing on that cake.

When the Scout first appeared in 1994, embedded menu options and spectrum displays were not yet commonplace among amateur transceivers. Embedded menu items can open the door to near granular level control of your radio’s functionality and features. Then again, if those embedded menus aren’t well thought out, it can lead to awkward operation practices in the field, during a contest, or even during casual operation.

As a radio reviewer, I spend a great deal of time sorting out embedded menu functionality and design. Perhaps it’s for this reason that I so enjoyed reviewing a radio that bucks this trend and reminds me of a time that was simpler, not to mention, easier.

Enter the Penntek TR-35

The new Penntek TR-35 is a four-band CW-only QRP transceiver that is available both as a kit ($279) and as a factory assembled and tested unit ($379). Penntek transceivers are designed and manufactured by John Dillon (WA3RNC).

All of his transceiver kits are available at his website WA3RNC.com.

I was first drawn to the TR-35 after reading the opening paragraph of the product description:

“Compact but powerful 4-band, 5-watt CW transceiver kit that uses no tiny push buttons, and without those seemingly endless and hard-to-remember back menus. There is a knob or a switch for every function!”

Sold!

I considered buying and building the TR-35 kit, but I wanted my eventual review––this one!––to focus on the radio’s functionality and performance. So a factory-assembled and tested unit was right for this purpose, just so that any performance issues wouldn’t be a result of any shortcomings in my kit building skills.

I decided to reach out to WA3RNC and ask for a loaner. John very kindly sent a factory built TR-35 to me along with return postage and a very flexible loan period (thank you, John!).

Look and feel

The TR-35 is a surprisingly compact radio, measuring 5 ½ X 3 ¼ X 1 ½ inches, not including the switch and knob protrusions. The chassis is made of a durable plastic and the total weight is a mere 10.6 ounces.

The TR-35 sports a small blue monochrome OLED display that’s surprisingly easy to read in the shack. Outside––in full sunlight––I have found that I needed to cover the display with my hand to read it. Still, the display works quite well and is very crisp.

Besides an encoder, the TR-35 sports four knobs:  keyer speed, transmit power, RF gain, and volume.

Yes…not only does the TR-35 have a dedicated CW speed control, but it even has a dedicated RF gain control!

As of late, I’ve tested a number of transceivers that bury keyer speed under various menu levels. It can be challenging to access when, for example, I want to slow down or QRS for a slower CW op. With the TR-35, it couldn’t be easier.  There’s a dedicated speed control accessible at all times. Same thing for RF gain; I find this an incredibly useful adjustment especially when operating during the summer when QRN manifests itself in ever-present static crashes. Tweaking the RF gain can make long listening/operations sessions much more pleasant and less fatiguing.

The TR-35 also sports three mechanical switches on the left of the OLED display: a red-capped power on-off switch, a white-capped receiver mode/AUX switch, and a white-capped band selection/RIT switch. The two white-capped switches are 3-position spring return toggle switches.

To change bands, for example, you simply flip the band selection switch upward momentarily then allow it to spring back to the center “off” position. Each upward flip of this switch cycles the TR-35 through the 40, 30, 20, and 17 meters bands, in that order. If you flip the switch up and hold it up for a couple of seconds, the current frequency and receive mode are stored in a “semi permanent” memory. The display momentarily will switch to a reverse optical mode to confirm that the current frequency has been stored. To recall the stored memory, simply click the switch upward twice in quick succession [note that this function changed slightly with the firmware update mentioned below].

As simple as the TR-35 is, it’s still worth reading through the operation manual to unearth extra features like this that might otherwise go unnoticed.

The TR-35 even has a RIT control which can be very useful if you’re rag-chewing with a friend who has a drifty transmitter, or if you would like to operate split in the field. RIT can be adjusted for +/- 5 kHz. There is a dedicated yellow lens LED light under the RIT toggle to indicate that it’s engaged.

The receiver mode switch toggles the filter between narrow CW, wide CW, and SSB. Keep in mind that while the TR-35 does have an SSB filter setting, this is only for listening purposes; it has no other SSB functionality.

The tuning encoder is also a push button, and like many small transceivers, pushing it will allow the user to toggle between tuning rates. The TR-35 can change frequency in 10 Hz, 100 Hz or 1 KHz steps. Short presses of the tuning knob will toggle between 10 and 100 Hz tuning steps. A long press will enable 1 KHz steps.

There are a total of five internal adjustments that require opening the radio chassis:  PA Bias, sidetone level, signal-level LED sensitivity, audio bandpass filter frequency, and a low battery detector threshold. Other than when building the kit, the only one I suspect might need to be tweaked at some point would be the sidetone volume.

Besides the RIT indicator, there are two other LED indicators:  one with a red lens for a low battery warning, and one with a blue lens that serves as the signal level indicator. The blue LED, when tuned to a strong CW signal, gives a visual indication of the CW that’s being received. I’ve actually enjoyed trying to copy random code and callsigns with the volume turned down and simply watching the blue LED flashing code. While I’d never attempt this during a park activation (I mean, how could you handle a CW pileup?) it’s fun to do this at home.

One other thing very unique to the TR-35? It has both a dedicated straight key and a paddle port. That’s right:  there’s no menu item to switch the key input from “straight” to “electronic” keying; you simply put your key into a dedicated port. What a fun little luxury!

A note about the TR-35 kit version

In my first unit, I noticed a bit of noise from the OLED display. Turns out, this was an issue with a small number of John’s earliest units, and there was a very simple fix:  adding a capacitor to the amplifier chip bypass pin. For anyone with a unit thus affected, John offered to send a capacitor––or, if preferred, the owner could send in their unit to him and he would add the capacitor himself (with free shipping! Excellent customer service). As I already had a capacitor that fit the bill, I neither needed one of his, nor John’s kind offer to install it.

I opened the TR-35 to solder in the capacitor, and it was then I discovered the superior quality of this kit’s boards and components. (I instantly regretted not ordering the kit version!)

I’ve heard from a number of my blog readers who built the kit and many have told me it’s one of the best radio kits they’ve ever built. The boards are of a good quality, all of the SMD components are pre-installed, and the toroids are all pre-wound! Does it get any better than that? Why, yes, it does:  all of the kit’s component groupings are separated into individual poly bags, making it easy to quickly identify the components needed during each stage of the build. This is such a luxury for those of us who are used to receiving a “bag-o’-parts” in our kit boxes.

In summary:  if you’re looking for a low-stress kit building experience, look no further!

On the air

At the end of the day, a radio’s design and ergonomics only carry it so far. For a radio operator to enjoy the whole package, the radio needs to perform.

Over the past few months, I’ve given the TR-35 a thorough workout on the airwaves. I’ve used it at the QTH for casual contacts, and for hunting park and summit activators, for working DX, and even participated in a CW contest. I’ve also taken the TR-35 to the field and used it during park activations of my own.

How well does it perform? In short:  beautifully.

If you’ve been reading my TSM reviews lately, you might have noticed that I’ve pointed out an unpleasant tendency for low-cost radios to overload easily and produce harsh, unrefined audio. Being completely transparent here, I worried the TR-35––also being a small, affordable radio––might fall into this category.

Fortunately, that did not turn out to be the case! Indeed, quite the opposite.

The TR-35 has very pleasant audio. The noise floor is quite low and I’ve found I can operate it for extended sessions with no listener fatigue.

In my view, the filter selections are also a particularly nice addition. I primarily keep the narrow CW filter engaged unless I’m hunting for signals on the air and want the “blinders” off. The narrow CW filter is 250 Hz, but to my ear, it sounds much more like 500 Hz or so. Indeed, the narrow filter sounds almost identical to the 500 Hz Collins filter in my FT-817ND. To me, it’s the perfect bandwidth because I rarely use extremely narrow filtering.

The most surprising thing to me––and to my buddy John Harper (AE5X)––is how well the TR-35 receiver could handle the RF density of a CW contest. He and I both participated in the ARRL DX Contest with our TR-35s. To be clear, I’m not actually a dedicated contester; I simply (and rather selfishly!) participate in contests for the DX. It gives me a small thrill to poke through a big gun pileup with my meager 5 watts of flea power. And I did this numerous times with the TR-35, and even logged one all-time-new country!

While the narrow CW filter of the TR-35 doesn’t have sharp skirts or the surgical precision of a contest-grade radio, the receiver made up the difference. I compared the TR-35 with the new Xiegu X-6100 (click here for my review of the X6100) in the ARRL DX contest, and the TR-35 simply wiped the floor with the X-6100. Where the X-6100 overloaded in the dense RF environment, the TR-35 front end seemed relatively stable and pretty darn bullet-proof. Frankly, I never expected a QRP portable radio in this price class to have “contest chops,” but the TR-35 really does.

In the field, the TR-35 has been a sheer pleasure to use. It’s compact, the chassis is rugged and feels sturdy, not to mention, it does the job.

The TR-35 operates from 9.5 to 14 volts, thus my 3Ah LiFePo4 battery is an ideal power source. Since the TR-35 consumes no more than 100 milliamps in receive, even a modest battery will power it for hours at a time.

Any cons?

No radio is perfect, but I’ll admit that it’s difficult to come up with a list of cons for the TR-35 because the whole design philosophy is built around simplicity, performance, and a successful kit building experience.

What the TR-35 does, it does exceptionally well. I’ll admit, I’ve very few criticisms.

That said, as with my Mountain Topper MTR-3B, I wish the TR-35 had even a basic SWR meter. Since I’ve primarily used either resonant end-fed half-wave antennas, or paired the TR-35 with my Elecraft T1 or Emtech ZM-2 portable tuners, it hasn’t really been an issue.Yet I do like a little feedback in the field to let me know if, for example, I’ve damaged the antenna in deployment and it has negatively affected the SWR.

Also, as I previously mentioned, the OLED screen may need a little cover to be read in full sunlight.

Again, minor criticisms.

I also like built-in CW message memory keying in my field portable radios, and as the TR-35 originally did not have this, I initially listed it as a “con.” However, one week before this issue of TSM went to print, John WA3RNC sent me a prototype TR-35 firmware chip to Beta-test. The new firmware adds two CW message memories. I used it heavily during a Parks On The Air (POTA) activation on Wednesday, April 20, 2022, and can confirm that it works very well indeed! On April 23, 2022, John announced that the upgraded chip will ship with all new TR-35 orders. The upgrade is also available for existing TR-35 owners, although due to chip shortages, upgrading one will require sending the TR-35 back to John for reprogramming. He will do this for free, and is only requesting $15 for return shipping and insurance.

Summary

If you haven’t gathered, I really love the Penntek TR-35.

Why? For the same reasons my buddy Mike loves that Ten-Tec Scout:  it’s “so simple and so effective.” Like the Scout, it doesn’t offer a deep feature set, but it has “everything [you] need,” and it packs meaningful performance with great audio characteristics, stable AGC, and has those all-important controls readily accessible. It’s not complicated, and that’s the point; it’s really a joy to use.

And the fact that it’s available as a kit? Woot! All the better.

The Penntek TR-35 is truly a keeper, and if all of this sounds appealing to you, I highly recommend it.

Click here to check out the Penntek TR-35 at WA3RNC.com. 

Thank you!

I’d like to send a special thanks to those of you who have been supporting the site and channel through Patreon and the Coffee Fund. While certainly not a requirement as my content will always be free, I really appreciate the support which allows me to open up my work life to write more reviews, field reports, and film more activation videos. I really appreciate it!

15 thoughts on “A comprehensive review of the Penntek TR-35 four band QRP transceiver”

  1. Good morning Thomas. Couldn’t agree more with you about this little gem!

    The Penntek TR-35 has become my grab and go radio and shares a spot in my heart with the KX-1. The KX1 has an ATU, but honestly most times I’m using resonant wire antennas and the atu is not necessary. Plus, I fuss over the KX1 given it’s age and the fact they’re rather rare to find now.

    Building the kit was an absolute pleasure. John Dillon, WA3RNC, did a superb job of packing/organizing parts and writing the assembly instructions, not to mention the fantastic design.

    One little simple mod I did to allow me to lean the rig up against, say for example my battery pack, was to place two small/wide rubber bands (the kind grocers use to hold broccoli or asparagus together) around the two side of the rig. These rubber bands can be placed right at the very edge and they provide a nice non-slippery contact and keep the rig from sliding and laying flat.

    I agree, it’s a keeper!

    73,
    Brent VA3YG

    1. That’s exactly how I feel about the KX1, Brent. I don’t even want to take it out of the shack now. I bought the TR-35 to take its place in my activities, although I haven’t given it a proper workout yet.

  2. Great review Thomas! I have had this radio for a few months now, and I completely agree with your assessment. This little radio is a joy to take into the field. The cons that you list are accurate, but do not distract from operations. I sent my radio back for the firmware upgrade, and it was quick and painless. The new message memory keying function was really welcome to improve this operator’s workload during pileups.

    I would also note that there is a new TR-35 thread over at the new QRPer.net discussion board.

  3. Great review! You didn’t mention it but I think it will drive a small external speaker for those of us that don’t like earphones.

    Did your unit have the optical encoder?

    Max – WG4Z

    1. Mine drives a small, external, rechargeable speaker; the kind you’d use with your smart phone. I’ve always preferred such a setup vs earphones.
      73 Brent VA3YG

  4. i had my Penntek TR-35 QRP rig on the air for a few hours operating Pedestrian Mobile Today using a 10 foot whip and a drag wire on 14061 kHz.
    Had a great time out on a warm sunny day.

    i worked 9 stations:
    W7JCF John WA,
    WB9HFK Mark IL,
    n9ru ? Lost,
    WA9PWP Paul WI, (he also heard me on 17M),
    AB5X Bob TX,
    K5MUG Cray TX,
    WN9U Gary WI,
    WB4LAL Ike AL,
    W1PID Jim NH (stuck inside becuz of rain),
    AF8E John OH,

    My ERP was around 3W.
    This operation was a little like my KX1 operation on Pikes Peak,
    See the picture of me standing next to the big 5 foot Oshkosh snow blowers holding the KX1. The TR-35 is similar but it has no built in key. See http://www.qrz.com/db/w0rw/
    i set the TR-35 on 14061.00 (the display is a bit hard to see in bright sunlight) and i set the “Lock” to keep it there.
    i used my old Whiterook single lever Paddle.
    i used my regular 10 foot, center loaded whip, and a drag wire that connected to my Elecraft T1 tuner. The tuner then went to the TR35.

    Got a SWL report from N6CC said he just barely heard me in SF, CA.
    i didn’t work any CA stations either.

    Another SWL report from Bob K2YGM who is in FL.
    He saw my announcement and used his iPhone and set it up for getting WEBSDR. Using the Washington DC SDR of NA5B, he put in 14061 and heard me calling CQ.
    My signal was about a 339 and he copied many of the stations who worked me.

    The RBN’s that copied me were coast to coast, VE6, VE7 and TI7.
    Cool radio…Thanks to all the callers.
    Paul w0rw
    Colorado

  5. Thanks for the review! I _just_ took my TR-35 out to a park event yesterday, and managed to work a POTA and a SOTA station. The receiver is great, and the only complaint I have about the radio is that the display really is unreadable in direct sunlight – I was even struggling to see it with my hand cupped over it to make a shadow.

    I feel that the audio is a little on the weak side as well, and I’ve been experimenting with various combinations of headphones, speakers, and little micro headphone DACs/amps to get reasonably loud audio out of the radio.

    1. … and somehow I managed to submit my comment before I was done typing…

      Otherwise, the radio is great, I feel like it’s a bit more “rugged” with the case, and it’s a fun little addition.

  6. FWIW, I just designed a 3D printed stand for the TR-35 and posted it on Thingiverse. It makes it easier to use in the shack. The TR-35 is a great radio and a sheer joy to operate. And John, WA3RNC really supports his product. I can’t wait for the TR-45.

  7. I notice John WA3RNC has updated his TR-45 page with photos and a note that the kit version won’t be available until some time after the pre-built version has been released. Bummer! Oh well, at least progress is being made regarding parts availability.

    73,

    John AE5X

  8. I’ve had the factory built radio for several months , used primarily for pota, activating and hunting using 1500mah lipo batteries from rc sailplane days. running about 4 w out, I’ve yet to deplete a battery. I’m not a backpacker,so it with operating accessories fit nicely into an old plastic tray.

    luv the knobs!
    72s de randy, k8zfj

  9. Love this radio – my first kit build in about 40 years. I screwed up one of the components and John replaced it for free. I can’t say enough good things about that level of customer service. I added a pair of keyboard/laptop foldable feet from Amazon to be able to prop it up for a better viewing angle. Works well. I do wish it had a break-in feature but that is my only minor quibble.
    John, K9BRS

  10. I bought the kit after Thomas’ video dropped a few months ago. It is the first transceiver build I have completed and it has set the bar pretty high. I have a QCX mini sitting on my bench but the bag-o-parts is a bit intimidating. Great instructions on assembly and pre-field tuning. The bubble packaged parts are in order of the build steps, so as long as you do the steps in order and don’t open anything until you need it, it would be hard to loose anything.

    I’ve done a couple of field activation (SOTA and POTA) since building the radio. It is very fun to operate. I’m not very experienced with CW but this little radio reduces the stress. The keyer memories are easy to program and use, though I do wish there was a repeat function. The programmed patterns follow the keyer speed adjustment, which surprised me but makes a lot of sense.

    All in all a great value and super fun kit to build, I’ll be very interested to see how the QCX mini stacks up.

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