Texas star dx 350 hdv staying keyed up after transmission.

[snippits75]

On the other hand, I have experienced just changing radios will make the amp happy with the same length jumpers.

For what ever reason, I have had more trouble with high powered radios causing problems. Hook up my Cobra 142 GTL, and problem goes away using the same length jumpers. And on high powered radios that do cause problems, a half wave length jumper of RG-8X makes the amp behave.

 

[groundwire]

I use a two full wavelengths jumper for my amp, then it works.

 

[linearone]

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.

It only matters sometimes. It usually occurs when the load is not perfectly 1.0 50 ohms.

As a rule of thumb, I like to look up the vf for my coax and cut them in even multiples of a wavelength, usually 1/4wave. Sometimes I use 6fts too. Typically never 3 fts.
The last time I saw something weird was with a three ft jumper a few weeks ago.

 

[linearone]

Also, if you have an MFJ or one of those fancy vnas you can measure exact multiples instead of relying on a tape measure