[CQ-Contest] ICE 419 Bandpass filters

[Dave Hachadorian]

----- Original Message ----- 
From: "W0MU Mike Fatchett" <w0mu at w0mu.com>
To: <cq-contest at contesting.com>
Sent: Sunday, March 18, 2007 1:30 AM
Subject: [CQ-Contest] ICE 419 Bandpass filters


>I have a unit that keeps failing on 20 meters.  Not sure 
>why.  I also
> noticed that my FT-2000 will not put out the same amount 
> of power while the
> 419 is in the line with a 1:1 swr.  Anyone else seen this? 
> Not sure why
> that would happen either.

Where are you measuring the power and swr, between the radio 
and filter? If so, I don't understand why the FT-2000 would 
throttle back.

If you are measuring the power and swr between the filter 
and antenna, then here are some thoughts. Insertion loss in 
a bandpass filter is about 15% of applied power. In other 
words, 100 watts in, 85 watts out. SWR presented to the 
radio through an ICE filter can be adjusted by squeezing the 
coil and rearranging the capacitor leads for each particular 
band. Just tweak for min swr. If you keep the power down to 
about 20 watts, or the minimum to make your swr bridge work 
reliably, then you can wear a rubber glove and squeeze the 
coil while "hot." Slide the innards out of the enclosure 
just enough to get your hand in there, because replacing the 
cover causes the swr to change somewhat.

My buddy W7WW has two of the ICE filters, and I've been over 
there on numerous occasions to help him replace 10 and 15 
meter capacitors that had significantly changed value. You 
can find the bad caps by putting them on a capacitance 
meter, which most antenna analyzers have. It's easy to find 
the bad caps, because they are WAY off value. We finally 
replaced his 10 and 15 meter caps with "snubbers." I'm not 
sure of the derivation of that word, but snubbers are mica 
caps that are more rugged than the regular micas. We got 
them from www.mouser.com keyword "snubber mica." The 
snubbers still get very hot (will boil spit), but so far 
they haven't changed value or otherwise failed. The caps 
that have failed so far have all been on the radio side of 
the coil.

Another thing I don't like about the ICE design is that the 
signal path goes through 12 sets of relay contacts, 10 of 
which are in the relay-relaxed position, and intermittent 
receive signal dropouts can occur, requiring one to "whack 
the box" or "transmit a dit" to get the receive signals 
back. My other buddy K6AM tells me that he solved this 
problem by replacing all of the relays with Omron Brand 
relays, but we haven't done that at W7WW, so he still has to 
"whack the box" every now and then. ICE will probably tell 
you that they have never heard of any of these problems. At 
least, that's what they told us.

If you need to know the capacitor values, drop me a line. I 
think I have them around here somewhere.

Dave Hachadorian, K6LL
Yuma, AZ