I have a texas star dx 350 hdv and I replaced both transistors with a set of matching HG pills. With just the red button pressed on the amp it works great with loud audio but after I release the key on the mic, the amp will stay keyed up via meter light on amp and make a squeel noise in my receiver. With the red and green dial a watt button depressed the amp works flawlessly. Its only when just the red power buttom in on is when the amp stays keyed up after transmission. Any idears would be appreciated. Thanks in advanced!
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Texas star dx 350 hdv staying keyed up after transmission.
- Thread starter rflegacy
- Start date
Change jumper length between radio and amplifier.
Its probably going into self oscillation. Wait around, the pros will be here before to long
I think that did the trick. I forgot i had a longer jumper inline. Thanks! glad you guys had a good laugh. lol
just ran the amp hot for a few minutes and it didnt stay keyed up for the first time in a long time. Thanks!
When you change the jumper length, that changes the phase between the Final and the amp. This sometimes causes the amp (and Final) to go into self oscillation. Sometimes simple things like jumper length can make or break a system.
I can run a 6 inch jumper to 60ft jumper betwen my radio and amp and everything else and nothing changes. I have NEVER had a piece of radio communications equipment malfunction or self destruct due to coax length. Hmmmmm, strange.
so
So can I with certain amps/setups. I have had coax issue problems in the past, im just now getting back into it. Thanks for your concerns.
I'm pretty sure @NZ8N IS one of the pros..
There's another forum member that had the same thing happen a few months back. He changed the jumper and voila it worked perfectly.
Im not concerned in the least bit. I guess Cheap cb equipment does those kinds of things. Oh wellit happened to me with agalaxy 350, changed the jumper to a longer length 4 feet and it stop the oscillation,,,
Not strange, just lucky.
The difference between a RF amplifier and a RF oscillator is how you control regenerative (positive) feedback. Any amplifier that has a poorly-designed or botched input circuit is a potential oscillator. ALL amplifying devices will feed some of their output back to their own input, INTERNALLY. Add to this the tendency of RF to just magically travel across empty space inside the amplifier, and this just increases the overall unwanted feedback, over and above the transistor's built-in feedback.
The input circuit serves, among other things, to shunt unwanted regenerative feedback to ground, away from the transistor's input terminal. The lower the impedance at this spot the better, up to a point. The lower it is, the more feedback current it carries safely to ground, away from the transistor's inputs.
A coax jumper makes a dandy tuned circuit. Placing a tuned circuit across the input of an unstable amplifier is a good way to construct an oscillator.
Coax length should make no difference whatever to an amplifier with a perfect resistive 50 ohm input. None. Zero, Nada.
The farther an amplifier's input circuit gets above or below that one-to-one SWR impedance, the more difference coax length will make. An amplifier with a five-to-one SWR measured at its input while keyed will almost certainly change behavior as the jumper length is altered.
73