Topband: Buffaloed by a bias tee

[Tom W8JI]

> Thanks to everyone for their suggestions - consensus seems to be that the 
> homebrew chokes are not enough reactance at 1.8 MHz, so I'll get some 
> store bought ones at 220 uH or more.  I tried battery power for the whole 
> system, but no difference. I'm going to try battery power for the remote 
> box and omitting the bias tee entirely, at least as a test.

That doesn't make sense for your complaint. Your choke is a little light, 
but you said it changes when you plug the supply in. That probably indicates 
you are dumping ripple or noise into the 259. I'm really surprised the 
diodes did not pop.

45 uH is  about 500 ohms, which is OK for a choke in a 50-75 ohm line. 
While it would increase SWR a bit, especially with poor bypassing (.01uF) 
and probably no additional decoupling, it is not a disaster.

Read my other post. You are running a risk with the system you have. Never 
do what you are doing with a bias T, especially when it has a .1uF isolation 
cap. A .01uF is 8 ohms on 160. That is a pathetic bypass cap, but a 
reasonable series cap. You might want to step it up to a .05 uF or larger 
when you get parts.

The bypass cap has to be a small fraction of the supply impedance and the 
choke impedance. I'd use a .33uF there, and some other decoupling. You could 
probably step the choke up a little, but don't use the 259 that way!!!