> Joe <[EMAIL PROTECTED]> wrote: > Hello to All, > I am presently working on a Hamtronics 6 meter repeater and am > finding it quite disappointing.
Sorry to read the above comment ... I've always had good luck and a lot of great learning experiences with Hamtronics gear. Dealing with Jerry at Hamtronics is sometimes a pain but other times he can be a very nice guy. > This repeater is owned by a local club and has had problems > from the beginning. The Club or the Repeater? :-) > R100 receiver. I have this working quite well, except for the > fact that it only gives 100mv of audio to the controller. The > NHRC controller I am using likes to see 1 volt of audio. I > guess I might have to add a stage of amplification. There are three or four ways to deal with the receiver audio from Hamtronics and similar Receiver Boards. Hamtronics uses two options and both work very well for what they are. The first is to tap the volume control pot on the high side for constant audio. You get what you get in level but most often deal with the level in later stages. Another method is to terminate the speaker audio output into a 22 or 27 ohm resistive load. You AC Couple the terminated audio to the next stage and simply use the volume pot as your level control. Consider the output from the above methods might contain ctcss information (any transmitted sub-audible tones) so running the repeater audio through a filter like the on-board Comm-Spec TS-32 board is a great idea. Then you simply inject the ctcss tone output from the TS-32 board direct to the transmitter for "strip (remove) and regenerate ctcss" operation. In cases of low recovered audio you can sometimes modify a Repeater Controller input op-amp stage for additional gain. All this depends on the specific controller design. A few controller mfgrs actually have input stage dip and basic pc-board jumper mods to set the controllers audio pot input range value. And the choice of adding a small amplifier circuit remains an option. You can do a simple circuit board or buy complete op-amp circuits in kit form from Jameco, Vellemum, Rainbowkits and many other locations. Check out Jameco's online catalog for more kit information. You could also use the famous LM-386 audio amplifier kit terminated as described above. Chips like the 5532 op amp make great audio buffer and line driver circuits. > TA51 transmitter. Here is the real problem. I can only get > 2.5Khz deviation of clean 1000Hz audio out of the transmitter. > I can push it to 3Khz, but it gets distorted. Using the same TA-51 tx board... I don't have that problem. You must use a low impedance, high power audio source to drive the audio input. Many repeater controller audio output stages simply don't have enough drive for a low band transmitter. I would suspect the NRHC Controller audio output circuit doesn't have enough drive for the transmitter. It's a pretty common problem... > Looking at the manual for the TA51 6 meter version, I see a note > that states the following: "Because the fundamental frequency > is only multiplied by 6 (instead of 12 for 144 MHz), the frequency > deviation is only 1/2 of what it would be on high-band. Hence the reason many low band transmitters need much more audio drive energy. > Therefore, it may not be possible to obtain a full ±5 kHz > deviation with modulation without a little distortion. This > should not be objectionable though." The distortion Hamtronics is talking about is probably not what you are or have experienced. The distortion I actually hear from my TA-51 exciter board is not very much at all. In many cases only a trained ear might object to the typical phase modulator distortion. > This seems totally unacceptable to me and it looks like it > is not fixable. Trying to Phase Modulate the transmitter > with more than 2.5Khz deviation causes it to distort and shift > frequency. Most anything is fixable... just a question of how much time you want to spend working on it. > Also, the audio stages distort at the levels that hamtronics > specifies at the test points. Only the first amplifier > stage seems to run clean. > Any comments? (except for "Don't buy Hamtronics!") I find > this disappointing because I have had other Hamtronics that > performed well, or very well, for the money. > 73, Joe, K1ike Sure... try driving the transmitter audio input from an honest low impedance source - line driver circuit. I'm using an old GE Master-Pro Line Driver circuit board (found in tone remotes and repeaters) with great results. cheers, s.
