Home |
Search |
Today's Posts |
#4
![]() |
|||
|
|||
![]() "Dave Hall" wrote in message ... On Tue, 15 Feb 2005 09:57:06 -0500, Vinnie S. wrote: While I solved one problem on SSB, another continues. I am still having that "carrier" problem on SSB. For some reason, as soon as I speak into the mic, the radio holds power, as if it were on AM. The TX meter on the radio shows this, and the SWR/power meter shows this. The power is not fluctuating with modulation. The ALC was not cranked up. The power is not high, about 20 watts peak. Like I said, it seems to do this as soon as I speak into the mic. Even a subtle noise will send it to max, and stay there. Changed mics, and have the same problem. So then I tried this. I took this radio and put it in my car (it's my only radio). When I connect it directly to the Wilson 1000 barefoot, I get the same problem on SSB. However, when I go thru the amp, it works perfectly, no power unless I modulate. This is also true if the amp is turned on or off. It appears to be an impedance mismatch. Since the amp input is a perfect match, the problem goes away, whether or not the amp power is on or off. Here is the kicker. The SWR on my home antenna is about 1.3-1.5 across the band. The final oscillation is most definitely related to output load impedance. When I first stumbled onto this problem (In some older dual final Galaxy radios), the problem would never show up on the bench when I used my dummy load. It also didn't show on my base antenna. But the problem would happen on the customer's antenna. I managed to force the problem on my antenna by using a tuner and de-tuning the match until the oscillation occurred. The cover of the radio acts like a capacitor, and it's very sensitive to it. Did you see any bottom mounted caps connected to the final transistor? If not then you might have to mount a piece of grounded shield plate over the final or experiment with bypass caps until you kill the oscillation. But try setting the bias first. If I remember right, the bias for the final should be set at somewhere in the 30 - 40 mA range. I'll check the manual and give you the exact value. Dave "Sandbagger" I kinda figured oscillation also. Bad bias can cause it. Make sure that's correct. See if any one had hinkeyed around in there, Check serial numbers, did these not use 2 different finals at different times? When changing finals did they change drive components? Unfortunately I do not have a schematic here to look around. Did anyone do any "coil spreading"? Chad |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
Choke Balun Impedance Recommendations? | Antenna | |||
Tx Source Impedance & Load Reflections | Antenna | |||
impedance mismatch? | Shortwave | |||
A Subtle Detail of Reflection Coefficients (but important to know) | Antenna | |||
Reflection Coefficient Smoke Clears a Bit | Antenna |