[Amps] tuner anomalies

[Vic K2VCO]

Dan Sawyer wrote:

> Thanks for the comments. Last one first, the signal is clean, pick up in 
> a spectrum analyzer shows the spurs are well below 40 db down.
> 
> Is there an rf conducting grease that should be used on the contacts?
> 
> I haven't checked the ground. It is simply a copper stake driven in 
> about 6 feet.

If the chassis of the tuner is hot with RF, there can be a 
power-dependent error in SWR measurements. I wouldn't expect a 'jump', 
though, this would be a smooth increase.

Also, depending on the diodes used in the SWR measurement circuit, very 
low power will often show an unrealistically low SWR because of the 
shape of the diodes' characteristic curves. 10 watts should be enough 
for most SWR indicators. This effect might appear to 'jump'.

Are there any fixed capacitors in the transmatch? Doorknob types 
sometimes break down under power.

You could have a worn or dirty spot on the roller inductor. But this 
would probably give a very high SWR with low power that would improve 
when it broke down. And it wouldn't be consistent.

Are you watching with the spectrum analyzer as you increase power?
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco