[CQ-Contest] Band pass filters for M/M

[George, W2VJN]

The readily available band pass filters will not help between
modes on one band.  When we did W1AW/7 at W7RMs, I built a
tuneable 40 meter filter using a two large toroids wound with
heavy wire.  They were lightly coupled and tuned with a 2 gang
variable capacitor.  This simple filter produced about 25 dB of
rejection between 7025 and 7175 with insertion losses around 4
dB.  It was good enough to keep the SSB transmitter running full
power out of the CW receiver (IC-765) except when the two 3
element yagis were pointed at each other.  The SSB radio did have
a problem when CW was transmitting.

You would need to use large toroids even with QRP in order to get
a high Q in each inductor.

It's also possible to do this with crystal filters and get a lot
more attenuation.  They are expensive, however.

George, W2VJN


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>From g4piq at btinternet.com" <g4piq at btinternet.com  Mon Mar 13 00:22:58 2000
From: g4piq at btinternet.com" <g4piq at btinternet.com (Andy Cook, G4PIQ)
Date: Mon, 13 Mar 2000 00:22:58 -0000
Subject: [CQ-Contest] Re: Yaesu FT1000MP Filters


VE7NS wrote :-

>> I would appreciate some advice on the advisability of using INRAD
>> filters as opposed to the filters available from Yaesu in a stock
>> FT1000MP which I hope to acquire shortly.
>>
>> Many thanks

>> Ron
>> VE7NS

I asked a related question of the reflector a few weeks back (what INRAD 
SSB filters to take) and thanks to everyone for the responses. To 
summarise, everyone who had seen both said that the INRAD filters were a 
significant improvement and opinion was a bit divided over whether the 2.1 
kHz or the 1.8 kHz option was the best - some said 1.8 too narrow, some 
liked them. Partcularly if you're buying new, the incremental cost of 
fitting the NRAD filters as opposed to the additonal Yaesu ones is pretty 
small - even in the UK!

In the end I have gone for the 2.1 kHz option and to use the SHIFT/WIDTH 
controls to narrow down further. The skirts on the INRADs are much steeper 
than the Yaesu ones so this should be reasonably effective. Have yet to use 
the radio though.

Thanks to everyone for the points in the ARRL contests as M6T.

73,

Andy Cook, G4PIQ


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