Hi everyone, here is the most puzzling issue I ever encountered. I just bought a lp-100A watt meter and I checked my output and swr with a dummy load in line with amp on. My swr on ch1 - ch20 - and ch40 are all 1.1 now when I put my antenna in line, my swr on ch1 - and ch40 are low, 1.1 BUT....on ch20 it climbs over 4.0, on a dead key....but...if I audio check the swr then drops down to 1.1. I am stumped on what this is all about. If the amp is off, the swr is low on all 3 test channels. But like I mentioned if the dummy load is in line I dont have this problem. Any ideas???? Thank you.
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Craziest swr question ever??
- Thread starter D. koenig
- Start date
Could be CMC issue or amp on ch20 goes into parasitic oscillation for unknown reason.
Ya it's the craziest thing I ever had happen. I dont know. Thanks for the reply though.
Then reduce the drive power to the amp and/or have the amp repaired.
73
David
Yes sir, they are at 1.1 with it off. And 1.1 with it on but going into a dummy load. Only when the antenna is in line and amp on is when 20 is very high swr. But antenna still in line and amp off, swr is good.
Have you checked the antenna coax/ mounting? Bad coax can cause all kinds of crazy readings and issues.
Yes I actually upgraded the coax from lmr 240 to lmr 400 and check the continuity and is good. So I did my best to cover all my ground so I wouldn't have issues. But got one anyway. Go figure. Thanks for the advice.
Have you tried checking your SWR between the radio and amplifier terminated in a dummy load on Ch. 1, Ch. 20 & Ch. 40?
73
David
73
David
Shadetree Mechanic
Delaware Base Station 808
The amplifier is going into oscillations at that frequency. The negative feedback can be increased to keep the amp from running on the edge of it's acceptable operation.
Check your coax jumpers to be sure the connection between the shield braid and the plug is secure. If you can twist the cable any amount where it comes out the rear of the plug this suggests a questionable connection that can cause stability problems.
This is about the only external fault I know that can get you that symptom. All the other possible causes are inside the amplifier. More than one way to make a RF amplifier unstable.
73
This is about the only external fault I know that can get you that symptom. All the other possible causes are inside the amplifier. More than one way to make a RF amplifier unstable.
73