[TowerTalk] The Gremlin has been slain!

[K1TTT]

For more details, including the gremlin caught on floppy, check the latest
entry at
http://wiki.k1ttt.net/2008%20Maintenance%20and%20Upgrade%20Blog.ashx




David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
 

> -----Original Message-----
> From: K1TTT [mailto:K1TTT at ARRL.NET]
> Sent: Friday, October 24, 2008 20:02
> To: reflector cq-contest; YCCC (yccc at yccc.org); reflector -tower
> Subject: The Gremlin has been slain!
> 
> FINALLY!  The Gremlin has been slain!  With K1MK here early for CQWW SSB
> we started doing some more testing with him running the radio and me doing
> stuff.  We started with hosing down the feedlines and stuff outside.  It
> did raise the threshold from 50w to 100w or so in a couple steps, but
> nothing dramatic.  Then we started looking for higher harmonics again, we
> found an odd one at 49MHz and got a null with the 6m antenna sideways at
> the shack.  We found one just above 2m, but couldn't get any bearing on
> it.  Not having a VHF-AM receiver I tried the HT that went above the band
> and could hear it on FM in the shack.  So loud that the rubber duck was
> too much... so switch to the paperclip and scan the shack.  Its the
> strongest around the 10m station, mostly near the stubs, so disconnect
> those.  I've been here before so didn't really expect to find anything
> new... but kept disconnecting stuff and the threshold kept going up and
> up, but wouldn't go away.  It seemed to be most sensitive to the SWR meter
> being in the circuit, yes some of you did suggest those, but I had already
> disconnected all the meters from the antennas and still had the
> subharmonic... so that just couldn't be it.  Put the meter in, 100w or
> less, take the meter out 1000w or more... but it wouldn't go away.  Put
> the meter in and pull the 12v supply to it, 1000w threshold!  Pull the
> power from the 80m meter, threshold goes up some more.  Pull the power
> from the 40m/SO2R pair of meters, and it goes up more.  Pull the 15m meter
> power and it goes over 1500w... pull the power from the 20m and 160m
> meters just in case... SILENCE!  I'll test more after CQWW SSB, but my
> best guess is that something in the PEP circuit that gets 12v power was
> rectifying and resonating with the coax stubs on the different stations...
> 7 sources, all in the shack!  Well, I did get lots of ugly stuff cleaned
> up outside anyway... maybe there were some other sources outside also...
> in any case now we can have a nice quiet contest without QRM from
> ourselves anyway!
> 
> 
> 
> David Robbins K1TTT
> e-mail: mailto:k1ttt at arrl.net
> web: http://www.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
>