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

[Michael Tope]

Neal,

Get one of those MFJ noise cancellors for each station and
then sample off a little bit of the transmit signal from the
adjacent mode station (e.g. sample off a little of the 40 CW
transmit signal and feed it into the 40 phone tent with some
coax). Assuming that the interfering signal level coming down 
the main antenna isn't so high that it overloads the noise 
cancellor, you should be able to null it out.

Mike, W4EF.................

----------
From: 	N7RX[SMTP:n7rx at arrl.net]
Reply To: 	N7RX
Sent: 	Sunday, March 12, 2000 9:46 AM
To: 	CQ-Contest at contesting.com
Subject: 	[CQ-Contest] Band pass filters for M/M


W7LT runs 4A QRP M/M for Field Day. We typically split modes 2 & 2. One of
the stations runs 40 & 20 CW, while another runs 40 & 20 PH (a 3rd and 4th
run 80/10/15 CW and PH, respectively). Problem is that the 40 CW station has
been blanking the 40 PH station, practically disabling it entirely. We've
tried different rigs, antennas and spacing:

1998: CW Icom 725 with a 40M loop; PH Kenwood 440 with a double extended
zepp. The stations and antennas were about 20 feet apart. 40M blanking was
really bad and I don't remember about 20.

1999: CW Icom 706mkII with a 40M loop; PH Icom 765 with a bobtail curtain.
The stations were 100 feet apart. 40M blanking was semi-tolerable; 20M
blanking intolerable.

2000: CW Icom 706mkII with a 40M loop; PH Elecraft K2 with Lazy H on 40.
(This station will go to 10M CW during the day this year with a 10M monoband
yagi. The 20 PH station will be about 150 feet away with a tri-band yagi).

We've got to eliminate this problem. The following has been suggested:

1. Bandpass filters to reduce intra-band mode interference - we don't have a
cross band problem
2. Improve earth grounds at each station (we've had none to speak of).
3. More spacing.

I'm particularly interested in #1. How does/can a bandpass filter be tuned
to deal with mode interference? Bear in mind that we're running QRP, and I'm
having a hard time understanding what's cause this in the first place. I
think its the 40M loop.

The good folks at the Portland Amateur Radio Club thank you.

73 Neal N7RX
W7LT FD Site Boss





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>From Eric  Raub" <ki0mi at earthlink.net  Sun Mar 12 23:52:55 2000
From: Eric  Raub" <ki0mi at earthlink.net (Eric  Raub)
Date: Sun, 12 Mar 2000 17:52:55 -0600
Subject: [CQ-Contest] Band pass filters for M/M
References: <200003122220.RAA27195 at contesting.com>



Don't know about bandpass filters but have you considered using standard 40
meter dipoles instead.  Line them up end to end and you will GREATLY reduce
your interference (to the point where the interference is either negligible
or completely gone) Right now your omnidirectional 40 meter loop is
transmitting directly into the face of your zepp and visa versa.  We've had
great success with dipoles for 80/40 with our local club and have also been
able to stay reasonably competitive (top 3% in 2A).   I know we've been able
to get a 40 meter Phone and CW station on the same band.  Seems like I
remember last year having a Novice station (mid 40), CW (low 40), and Phone
(high 40) station on for a brief time without interference.  Pretty nice for
only 100 feet separation between stations! Just make sure and get the
dipoles up 35 feet or more.

73, KI0MI
>
> W7LT runs 4A QRP M/M for Field Day. We typically split modes 2 & 2. One of
> the stations runs 40 & 20 CW, while another runs 40 & 20 PH (a 3rd and 4th
> run 80/10/15 CW and PH, respectively). Problem is that the 40 CW station
has
> been blanking the 40 PH station, practically disabling it entirely. We've
> tried different rigs, antennas and spacing:
>
> 1998: CW Icom 725 with a 40M loop; PH Kenwood 440 with a double extended
> zepp. The stations and antennas were about 20 feet apart. 40M blanking was
> really bad and I don't remember about 20.
>
> 1999: CW Icom 706mkII with a 40M loop; PH Icom 765 with a bobtail curtain.
> The stations were 100 feet apart. 40M blanking was semi-tolerable; 20M
> blanking intolerable.
>
> 2000: CW Icom 706mkII with a 40M loop; PH Elecraft K2 with Lazy H on 40.
> (This station will go to 10M CW during the day this year with a 10M
monoband
> yagi. The 20 PH station will be about 150 feet away with a tri-band yagi).
>
> We've got to eliminate this problem. The following has been suggested:
>
> 1. Bandpass filters to reduce intra-band mode interference - we don't have
a
> cross band problem
> 2. Improve earth grounds at each station (we've had none to speak of).
> 3. More spacing.
>
> I'm particularly interested in #1. How does/can a bandpass filter be tuned
> to deal with mode interference? Bear in mind that we're running QRP, and
I'm
> having a hard time understanding what's cause this in the first place. I
> think its the 40M loop.
>
> The good folks at the Portland Amateur Radio Club thank you.
>
> 73 Neal N7RX
> W7LT FD Site Boss
>
>
>
>
>
> --
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> Administrative requests:  cq-contest-REQUEST at contesting.com
>
>


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