Review of Hamtronics® T301 & R301 synthesized radio sets.
Just after the release of the new Hamtronics T301 & R301 synthesized exciter and receiver I purchased both in kit form. I also opted to purchase the TCXO stability option for each. These units can also be purchased factory assembled.
After building each I was truly impressed with the receiver sensitivity, and the exciters audio quality.
I was not compensated in any way for this review, and I pay the same price for the kits as everyone else. Hamtronics does not discount in any way. I have built lots and lots of Hamtronics kits, and kits from other manufacturers like Heathkit, Ten-Tec, Ramsey, Rainbow, and building from scratch.
I'll start with the receiver as I built it first.
The Hamtronics R301 is a totally new design as compared with the R144, the
crystal controlled receiver with helical front end. The design is similar
to the R100, but with an improved front end for better image rejection.
The receiver went together quickly, as the manual, like all Hamtronics
manuals, is excellent.
After initial tuning the sensitivity was as advertised: 0.15uV for 12 dB
SINAD, as measured with my IFR FM/AM 1200A service monitor. Tune-up is a
snap, with test points for every tuned stage.
The front end selectivity is excellent, as good as units with helical resonator front end. The squelch action is very nice, and has a wide range. Recovered audio is available from three places. One place is amplified speaker audio, one is a buffered de-emphasized, squelch gated line level audio, and discriminator audio is also available.
The recovered audio is excellent, ready to drive a controller without having to tailor the audio with capacitors or the such.
Dip switches are used to select the desired channel frequency. The PLL is not overly microphonic, and should not be a problem in most installations. The optional TCXO provides excellent frequency stability. ±2 ppm from -30°C to +60°C.
Hum and noise from the outside world (florescent lights, etc.) at first, seemed to be a problem, however when the unit was installed in a shielded enclosure, there was no problem. I don't recommend you use the receiver without placing it in a shielded box. If you are buying a REP-200, the modules are in shielded compartments and there is no hum or noise problem.
Overall, I am completely satisfied with the R301.
Now for the T301:
The T301 is a completely redesigned fm exciter. As with the R301 the channel frequency is set with dip switches. The change I liked most was the use of a varactor modulator for true fm. Older Hamtronics exciters used a phase modulator which for voice is fine, but when a PL tone was to be transmitted, the results were just unacceptable. I was forced to design a separate varactor-diode-based PL modulator for the Hamtronics TA-51 144, 220 and that information is available at the TA-51 PL Modulator web page.
The diode modulator in the T301 is used for voice / data / PL modulation. Because the new exciter uses true fm modulation, the limiter / clipper audio stages really work nicely, clipping the tops and bottoms of the audio waveform, instead of creating crossover distortion like in the TA-51. A CTCSS input is now provided and PL deviation is clean. I recommend setting the PL deviation at 500 Hz. Hamtronics recommends setting the PL level no higher than about 300 Hz deviation, otherwise a buzz will be heard at the receiver. Hamtronics also states that "Good CTCSS decoders can easily detect tones with less than 100 Hz deviation." This is true to a point. I use Communication Specialists PL decoders, (TS-32) and they will decode a PL deviated at less than 100 Hz, however the signal must be of good quieting when voice audio is also present. When a signal becomes noisy then it takes about 500 Hz deviation to get reliable PL detection.
I suppose Hamtronics made these statements because their older two meter, and 220 exciters would distort the PL tone if it was turned up to get more than 100 Hz or so PL deviation. The distortion of the modulated PL tone is what made the distortion (buzz) on the receive end. Just a little distortion of the PL tone made it sound as though it was set much higher than it actually was.
PL deviation on the new T301 can be set to a full 5 kHz without distortion of the audio. Of course, again, I recommend about 500 Hz. PL deviation.
Because there is a separate B+ input for the synthesizer, there is no start-up delay for the exciter to become active, and on frequency.
I was able to get the stated RF output (2 to 3 watts) easily. My exciter made 3.3 watts using 13.6 vdc, into a terminated Bird 43 wattmeter with 5 watt slug, and 3 feet RG-8M jumper wire. Tuning is a snap, with test points on all tuned circuits, and as with the receiver, I don't recommend using the exciter unless installed in a shielded enclosure. Shielded boxes are available from Hamtronics. All in all a very well designed exciter.
Visit Hamtronics at http://www.hamtronics.com/
Copyright ©January 6 1998 Kevin K. Custer W3KKC