[TowerTalk] TH7 puzzle

[Michael Tope]

----- Original Message ----- 
From: "Steve Lawrence" <SMLX at earthlink.net>

> TH7 Puzzle:
> 
> I have an FT1000D driving a legal limit amp to a TH7DX. The FT1KD  
> tuner is left off when driving the amp. Occasionally, the FT's Hi SWR  
> light will flicker or stay on but only when the amp is off line. The  
> FT's power setting can be anywhere from the 3 watt minimum to full.  
> This happens only on 20m, not 15m or 10m and not all of the time. If  
> I put the amp on, the antenna takes the full legal limit without any  
> problems. Immediately after that, if I put the amp on standby, the  
> rig's Hi SWR light no longer reacts and there is no indication of  
> reflected power.
> 
> I can make the light go out when I have the Hi SWR indication and the  
> amp is off line by switching the FT's tuner in but I'll still see the  
> same reflected power as if the Hi SWR light is on.
> 
> I have connected the FT directly to a dummy load and the Hi SWR light  
> remains off. Connecting the TH7 directly - no switches, power meters,  
> coax elbows, no amp in standby - and the light comes on. This is  
> repeatable. Unless I run the amp and then everything is normal until  
> some time passes - hours, days or not for some time.
> 
> Best guess is that there something going on with the TH7. Loose  
> hardware? Critters in traps? But why only 20m and why would high  
> power clear it but not blow it out.
> 
> Experiences and thoughts appreciated.
> 
> 73 - Steve WB6RSE

Steve,

I've seen this on the TH7 at the local club station. The antenna system 
was doing this last year. I used it last weekend at it was okay. I never 
did any tests to try to determine whether the poor connection was
in the antenna or the feedline, but it was acting very similar to what you 
describe (higher than normal VSWR with exciter - 2:5:1 -, and then 
very good SWR - 1:1 - after I would bang it with 1500 watts). 
There was no noticeable change on receive as you sometimes get with 
a dirty relay contact. 

Sorry that I can only offer another data point and not a diagnoses. 

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