[CQ-Contest] SO2R Technical Question - Round II

[Igor Sokolov]

You can use one set of filters because each of you rigs is on different band 
at any given time. 2 SIX PACKS from WX0B and one set of filters (W3NQN 
filters are the best choice) can do the job. But second harmonic from 40m 
will only be suppressed if filters are used between the TX and antenna. If 
you filter is between the transceiver and amplifier the amplifier will 
generate second harmonic on 20 which will not be suppressed by 20m filter 
since the harmonic is in it's passband.
In  "filter between the TX and antenna" scenario you only get 40 db 
separation (and not 80 db, as in your example) since 40m filter does not 
attenuate 40 m signal and 20 m filter does not attenuate second  harmonic 
from 40m TX. Many people therefore use coax stubs at the output of the 
linear amp to fight second and other harmonics (see K1TTT site for that). It 
is advisable to automate switching of all those filters, stubs, linears and 
antennas because in the heat of the contest you will inevitably make 
mistakes sooner or later.


73, Igor UA9CDC

> After reading quite a bit on the WWW about SO2R....
>
> I am assuming that you place band pass filters (what ever ilk) in line 
> with BOTH radios.  That being the case (if it is) then using bandpass 
> filters on 40 you would be knocking down (but not eliminating) the 
> harmonics on 20 meters.  In addition if you have a 20 meter filter on your 
> second radio, that do would have attenuation on the 7 Mhz energy.  So if 
> the transmit filter on 40 is...say....40 db down and the receive filter on 
> the 20 meters station is another 40 db down....would not those figures 
> combine?  That is a question!  So, you are protecting the 20 meter radio 
> from the 40 meter radio.
>
> That means you would have to have filters for 6 bands times 2 or 12 
> filters. if you were running 160, 80, 40, 20, 15, and 10 meters.  I guess 
> you could use a manual six position switch to select the Radio 1 filter 
> and the Radio 2 filter.  That would mean using passband filters...that you 
> would need to switch the filter to the band you were on and all is well. 
> Now, alot of S02R ops use automatic switchers (I am sure they found that 
> to be less expensive in the long run that sending in the radio for 
> repair)...but one could get away with the manual switch if you were 
> "careful."  This is only a good way of doing things if it is a bandpass 
> filter.
>
> Is the logic OK....I know I am running in the dark with a pair of 
> scissors?
>
> I hope I am not showing my stupidity here....but I am learning.
>
> Lee - K0WA
> "I think I barefoot too"
>
>
> In our day and age it seems that Common Sense is in short supply.  If you 
> don't have any Common Sense - get some Common Sense and use it.  If you 
> can't find any Common Sense, ask for help from somebody who has some 
> Common Sense.  Is Common Sense divine?
>
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