[Amps] Titan 425 Reflected Power

[Michael Tope]

----- Original Message ----- 
From: "Michael Tope" <W4EF at dellroy.com>
> From: "Jim Brown" <jim at audiosystemsgroup.com>

>> I'm encountering a strange problem with my Titan. If I follow 
>> standard practice and achieve a 1:1 match with the exciter, then 
>> take the amp out of standby, the amp typically shows mismatch on 
>> the order of 1.5 or 2:1. 
>> 
>> If I then re-tune the antenna for minimum reflected power on the 
>> Titan, the VSWR at the tuner, and also at a Bird inserted right 
>> after the Titan, shows a mismatch of 1.5 - 2:1. The mismatch seems 
>> to be greater at higher frequencies. 
 
> Jim, 
> 
> Sounds like you may have a load impedance that varies with 
> applied power. Try the following experiment - put the the Titan 
> in operate mode at full power, make the adjustment with the 
> external tuner for minimum VSWR (as you describe above) and 
> then slowly start backing off the exciter drive to see if the VSWR 
> changes slowly or abruptly as the output power of the Titan is 
> lowered. IOW, right now you have two data points - exciter 
> only and amplifier at full power. Try plotting the points in 
> between. 
> 
> 73, Mike W4EF.............
> 

Nevermind my previous suggestion, Jim. It doesn't apply here. 
I misread your original post and was somehow thinking that the 
Titan meter matched the reading on the Bird and the antenna 
tuner bridges and that the readings just differed between high
and low power. You clearly state that the Titan meter does 
not agree with the Bird and the tuner bridges. Sorry for the 
mixup. I'll try to read more carefully next time. 

BTW, have you tried driving a 50 ohm dummy load with the 
amplifier. It would be interesting to see if you could get a 
good tuning solution (high output power, low grid I) using
a 50 ohm dummy load connected through a short piece of
50 ohm cable to the amplifier output. 

73, Mike W4EF.................................