Hello John,
Your warning of having the filter in the line while the ATU is tuning
is interesting.
The series coupling capacitor on my homemade 40 meter W3NQN filter
has blown twice and your warning may explain why. The series
capacitor is made up of several 1000 V capacitors in parallel and
still blows which I originally thought was due too much current
flowing through a single capacitor.
The W3NQN filter that keeps blowing is on the second radio, IC746,
connected to a EF240X. The EF240X does exhibit a reasonable SWR on
the freq. in use (<1.6 : 1 SWR). However, the 746's ATU is still
used for 40 meters. A SteppIR is used on 20 - 10 and don't use the
746's ATU. The second radio isn't used on 80 meters as I only do
SO2R in RTTY contests.
Fortunately, the W3NQN filters are homemade, but it's still a pain to
open the box as all six filters are built on a single PC board along
with the switching. Another set of homemade W3NQN filters are
installed between another IC746 and a homemade GS35-B amp. which has
a flat, <1.2 : 1 SWR, input on all the bands. The IC746's ATU isn't
used with the amp. The filters are not used for non SO2R operation.
Thanks again for sharing your filter experience.
At 10:37 AM 6/12/2006, John Laney wrote:
>While the discussion about filters is fresh in memory, let me add a word
>of caution on using Dunestar filters on 75 meters SSB. Hal, N4GG, is an
>expert on this subject and advised me not to use the stock Dunestar 80
>meter filter above 3890. He said it would fry above that frequency
>approximately. Since I have a General class license, that would tend to
>deny to me use of most of the General class SSB band and could be a big
>factor in ARRL SSB SS and a few other contests. I talked to N7EA at
>Dunestar about it and he advised that it wasn't safe to use their
>80-meter filters above 3850. That would leave out the entire General
>class band. However, he specially altered one of their filters for me
>for use on the high end of 75 meter SSB. I ordered that in addition to
>two six-packs, so I can switch to it as an alternate for 75 M SSB.
>
>Incidentally, I also ordered Dunestar single band filters for the three
>WARC bands to use on contest and DXpedition trips. I was very impressed
>with Dunestar's service and customer service. They very quickly
>repaired a couple of their filters that I had burned out components in.
> Another word to the wise, DO NOT use your ATU to tune an antenna while
>the filter is in the line. Most of them will put out too much RF at too
>high a SWR and the components will blow. If you are using an external
>antenna tuner also, do your antenna tuning with the filter out of the
>line and be sure the ATU is turned off when you put the filter in the line.
>
>73,
>
>
>John, K4BAI.
>_______________________________________________
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73,
Mike, K4GMH
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