I use automatic BPFs between the rig and the amp as well. Cross-band noise
seems to be well suppressed except for directly at the second and third
harmonics, thus my quest to find a good solution.
Rudy N2WQ
Sent using a tiny keyboard. Please excuse brevity, typos, or inappropriate
autocorrect.
> On Jul 24, 2016, at 2:16 PM, Kenneth Wolff <ken@k1ea.com> wrote:
>
> I put exciter power band pass filters between the exciter and the amp. They
> also get rid of some broadband noise and the TX IF cross talk.
> When we first set up our M2 with IC781s they heard each other in the pass
> band independent of frequency!
>
> - Ken
>
>> On Sun, Jul 24, 2016 at 1:07 PM, Rudy Bakalov via CQ-Contest
>> <cq-contest@contesting.com> wrote:
>> Is there a reason you wouldn't want to place the stubs between the rig and
>> the amp plus appropriate switching?
>>
>> I asked a friend of mine who makes amps to measure how much an amp
>> contributes to second and third harmonics. In his measurements he observed
>> an Icom 7800 producing more harmonics alone compared to when connected to an
>> amp. That is, the amp actually suppressed harmonics. Personally I am not
>> surprised as between the tuned input and the Pi-L output harmonics should be
>> filtered quite well.
>>
>> I have asked other hams to perform similar tests with bandpass filters. If
>> they confirm that the signal is actually cleaner after an amp, wouldn't this
>> suggest that we should make sure we clean the rig as much as possible? As a
>> consequence, this would also mean that high power BPFs are not needed if low
>> power BPFs are inserted between the rig and the amp.
>>
>> Now, the other question that has been on my mind is what happens when we
>> design stubs to be part of the RX chain (rather than TX). At the end of the
>> day N db of attenuation is the same whether or not we apply it to the TX or
>> RX paths. The end goal is to reduce the undesired signals to a certain
>> level. So, if my thinking is correct, again, shall we move the stubs to
>> immediately before the rig?
>>
>> To be clear, I am posing these questions because I don't know the answers. I
>> am genuinely curious to hear what the science says.
>>
>> Rudy N2QQ
>>
>> Sent using a tiny keyboard. Please excuse brevity, typos, or inappropriate
>> autocorrect.
>>
>>
>> > On Jul 24, 2016, at 11:52 AM, Jim Brown <k9yc@audiosystemsgroup.com> wrote:
>> >
>> >> On Sat,7/23/2016 7:39 AM, Jeff AC0C wrote:
>> >> All of these topics are covered in W2VJN's excellent book "Managing
>> >> Interstation Interference."
>> >
>> > Yes and no. In that book, George has not considered the location of stubs
>> > for optimum performance, and when he did consider it in a piece in NCJ a
>> > couple of years ago, it was poorly done (that is, technically lacking).
>> > That's why I wrote my piece on the subject for NCJ about a year ago.
>> >
>> > http://k9yc.com/LocatingStubs.pdf
>> >
>> > While my piece specifically addresses in detail stubs for suppression of
>> > second harmonic, the concepts apply to the location of all stubs for
>> > harmonic suppression.
>> >
>> > 73, Jim K9YC
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