[CQ-Contest] Bandpass filter

Joe nss at mwt.net
Tue Jul 3 06:35:12 PDT 2012

This whole filtering thing....

Can they not make front ends rugged enough to survive these situations? 
Or for that matter, Now I have not had the blessing of playing with a 
K3, so do not know what it is like using one of them,

But when it comes to front ends,, now I'm dating myself here,  I love 
Field Day, loads of fun. Great opportunity to get new people into 
contesting.  But I have to say again I don't know what a K3 would be 
like in a similar situation,  but these new rigs SUCK when it comes to 

I remember in the 70's at Field day rigs,  Collins, Drakes, etc.  all 
Glow tubes. And I remember fully having three stations at the same time 
on severl bands.

Like there was 40 CW,  40 Novice (Novice CW band)  And 40 SSB. all three 
at the same time, and all three never even noticed the others were even 
on the band unless they got like 10Kc apart from each other.

Now days at every Field day I hear the great sucking sound. when on 20 
SSB  you hear the band getting sucked down by the 20 CW station. Even 
when the 40 SSB station was transmitting the 20 meter station would 
"Hear" his LSB modulation EVERYWHERE on 20.

This sucks.

The Original Rolling Ball Clock
Idle Tyme
On 7/2/2012 8:24 PM, Timothy Coker wrote:
> If you are going to use two radios then bandpass filters (BPF) will be
> needed to protect each of them when one or the other transmits, assuming
> enough coupled power. Coupled power occurs with power output, antenna
> polarization, and antenna proximity in mind. Bandpass filters pass whatever
> frequency they are meant to pass and do nothing to stop in band
> frequencies. I bought two sets of W3NQN filters for my home SO2R setup and
> didn't fully appreciate why one would have a filter on the RX and the TX. I
> just bought them because that is what so many experts told me was needed. I
> now understand that say a 40m TX filter passes 40m signals to and from my
> 40m radio. If I have another radio on 20m then I will need a 20m BPF to
> reject the 40m signals produced by my TX and pass any 20m signals to my
> second radio.
> My understanding is that the main function of my 40m BPF (when thinking of
> my second radio on 20m) is to reduce the second harmonic on 20m produced by
> my 40m TX. So if I am on 7.025 running, I will create a very strong second
> harmonic signal on 14.050. Depending on my TX power, antenna proximity, and
> antenna polarization, that signal might be enough to couple enough power on
> my 20m line to fry my second radio front end. It may only be enough to
> create a large amount of interference heard over a large swath of 20m
> frequencies. I can further protect the radio and reduce the interference
> (that big second harmonic produced on 20m) with a good quality BPF on the
> TX... possibly by up to 80dB. The RX 20m BPF does nothing to stop this
> second harmonic because it is a 20m signal which is passed by design of the
> 20m BPF... no different than everyone else's signal your trying to hear.
> The place for the RX BPF is in reducing out of band signals that are strong
> and might cause phase noise. Without the RX BPF you might be completely
> fine or you may be so bad that your RX transceiver gets it's front end
> fried. Every station is different, but it is safe to place a BPF on each
> radio to prevent unwanted phase noise and to reduce TX harmonics. Then you
> will also have the freedom to TX on either radio whenever you want, within
> the limitations of your station design and whatever contest rules your
> operating under.
> George's (W2VJN) book, Managing Interstation Interference, is a great read
> on this subject. It's available from Inrad directly. I finally spent the
> money on it and consider it an invaluable resource for a SO2R or Multi-op
> station designer.
> Further details on your plans would be helpful if you want to proceed in
> design and / or learning.
> 73,
> Tim / N6WIN.
> On Mon, Jul 2, 2012 at 12:54 PM, Roberts, Will <Will.Roberts at pgnmail.com>wrote:
>> If you are single op/1 radio and never listen on a band other than the one
>> you are transmitting on, a bandpass filter isn't necessary. If you have a
>> second receiver, then a bandpass filter could be helpful if you are trying
>> to receive on a different band than you are transmitting on. For example,
>> you are running on 40 meters and tuning for multipliers on 20m. If you had
>> interference on 20m from your transmitted signal on 40, a bandpass filter
>> could make a big difference in being able to hear 20m as you transmit on
>> 40m.
>> There is a lot of expertise here on the reflector for station design. It
>> sounds like you are just asking fundamentally if it would help out in your
>> situation.
>> 73,
>> Will AA4NC
>> From: "James" <jms_k1sd at verizon.net>
>> Subject: [CQ-Contest] Bandpass Filter
>> To: <CQ-Contest at contesting.com>
>> Message-ID: <000601cd57d5$62abcfd0$28036f70$@net>
>> Content-Type: text/plain;       charset="us-ascii"
>> If I operate single op and never transmit on two bands at once, is a
>> bandpass filter necessary?  Is it helpful?
>>       73 / James / K1SD / Rhode Island
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