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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