Band Pass Filters for QRP

[Jack Nelson-3]

Good afternoon all. I have a question and would appreciate everyone's
thoughts. I've started trying to get to the field with a buddy of mine. We
take a popup camper and have a day or two operating event. We keep running
into a problem if we both decide to set up stations.

We are generally using K3s and W3EDP antennas or maybe a Buddipole. The
antennas are 20-30 feet apart, so as you might guess, If one of us is on 40,
the guy operating on 20 knows it and visa versa. While the K3 can do alot to
minimize the interference, it's not something you'd want to listen to for
very long.

What options might be out there. We are aware of W3NQN bandpass filters, at
$105-$125 a band, that can get expensive quick. But that's not the real
problem. 6 of them is almost the size of them is almost the size of the
radio. I don't really need filters capable of 200W. I'm looking for
something closer to QRP levels. Even 20-30W would probably work, as it would
allow for some of the backpacker type amps.

I know the W3NQN filter, or some of their cloans would do the job, but I'd
like something smaller....IF I don't have to compromize too much in
performance.

Any suggestions would be appreciated.

73's Jack  K5FSE
Treas  QRP ARCI

[hidden email]



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[David Gilbert]

W3NQN wrote a nice series of articles for QST on bandpass filters, a
couple of which were targeted specifically for QRP operations during
Field Day.  The design I liked uses a band reject element at the next
harmonic frequency.  You can make your own filters from those articles,
and they are quite small in size due to the use of small ferrite cores
for the inductors.

73,
Dave   AB7E



On 10/27/2011 2:21 PM, Jack Nelson wrote:

> Good afternoon all. I have a question and would appreciate everyone's
> thoughts. I've started trying to get to the field with a buddy of mine. We
> take a popup camper and have a day or two operating event. We keep running
> into a problem if we both decide to set up stations.
>
> We are generally using K3s and W3EDP antennas or maybe a Buddipole. The
> antennas are 20-30 feet apart, so as you might guess, If one of us is on 40,
> the guy operating on 20 knows it and visa versa. While the K3 can do alot to
> minimize the interference, it's not something you'd want to listen to for
> very long.
>
> What options might be out there. We are aware of W3NQN bandpass filters, at
> $105-$125 a band, that can get expensive quick. But that's not the real
> problem. 6 of them is almost the size of them is almost the size of the
> radio. I don't really need filters capable of 200W. I'm looking for
> something closer to QRP levels. Even 20-30W would probably work, as it would
> allow for some of the backpacker type amps.
>
> I know the W3NQN filter, or some of their cloans would do the job, but I'd
> like something smaller....IF I don't have to compromize too much in
> performance.
>
> Any suggestions would be appreciated.
>
> 73's Jack  K5FSE
> Treas  QRP ARCI
>
> [hidden email]
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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[k6dgw]

Jack,

20-30 feet separation puts your antennas in each others' near fields,
and they become coupled together [i.e. you're trying to receive on
conductors that are actually parasitically part of your partner's
transmit antenna].  Invest in a roll of coax and get them at least a
couple of wavelengths apart, more is better.  It'll make a big
difference, and may get the QRM down to levels the K3 can handle.  You
may still need a couple of filters for 80/40 operation, the the higher
frequency bands may turn out OK.  Don't even think about 80/75
operation, we fried the T/R switch diodes in a K3 when someone tried
that at our M/2 CQP expedition.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org

On 10/27/2011 2:21 PM, Jack Nelson wrote:

> We are generally using K3s and W3EDP antennas or maybe a Buddipole. The
> antennas are 20-30 feet apart, so as you might guess, If one of us is on 40,
> the guy operating on 20 knows it and visa versa.
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Please help support this email list: http://www.qsl.net/donate.html