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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>
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