Hi,
I try give simplified answers ...
This should answer also Rudy's question.
2016-07-25 15:47 GMT+03:00 Joe <nss@mwt.net>:
> This also puzzles me.
> OK if an amp because of it's tuned matching circuits, block out of band
> energies
Amplifier circuits attenuate unwanted band energy.
But to a limit.
A Pi filter attenuates to some level, Pi-L attenuates more.
If that is not enough, we need additional attenuating, that is additional
filtering like a stub
>
>
The why do we have these energies at all in the first place?
>
When amplifying a signal in an amateur amplifier, the plate current when
only PTT is activated is less than a quarter of plate current with maximum
specified signal that is amplified.
It means there is plate current through most of the sine wave signal cycle,
but not all of it.
It means there is a sharp corner in the output signal .. it is not a clean
sine wave.
Such signal with such corners has harmonic energy.
This energy propagates towards the antenna connector.
It travels through the output circuit; most often Pi or Pi-L.
On an oscilloscope, the signal looks pretty much like a sine wave but it
contains harmonic energy.
Sorry, but this gets more complex when digging deeper.
Next step would require you to read some books or at least web sites.
Easy to understand information packages are ARRL hand book and Orr/W6SAI
Radio Handbook.
ARRL handbook is easy to find and purchase.
I would suggest to try and find also a paper book:
http://www.eham.net/reviews/detail/3963
W2VJN book is a must if you want to understand more about RF filtering
needs at a multi radio station.
** Encouragement, keep it simple message:
As we are hams, we can use ready made recipes for stubs, among many other
things.
That is allowed for us and us hams, we can just accept many things as given
facts.
Does not a Radio have the equivalent of an "Exciter" ( the ummm low level
> driver )
> And the "AMP" ( the final output amplifying system )
>
> So, if all this filtering is happening why do we have spurious out of the
> radio, but not an amp?
>
There are a lot more signals in the radio than the mains input and RF
connector with RXinput / TX output.
To start with, the radio's oscillator is not on your actual output
frequency.
There are other oscillators, mixers, filters, amplifier circuits, more
filters and so on inside your transmitter before the antenna connector.
All those are creating or limiting spurious signals and we need to engineer
the radios so the radios do not emit unnecessary signals and we engineer
our radios so they do not input unnecessary signals or at least the radio
does not care about the unnecessary/unwanted signals.
Emissions are emissions; intended or spurious.
The receiving side phenomena are under words immunity or susceptibility.
Together they are electromagnetic compatibility EMC.
These spurious signals propagating from device to another device can be as
bad as K1EA described about the radios they used.
The radio2radio signal propagation happened on a set of phenomena caused by
some radio internal signalling leaking through radio wiring and propagating
to another radio so the receiver of the other radio heard the transmitting
radio signal regardless the frequencies the radios were on,
That is a really puzzling situation and typically difficult to overcome.
Most likely the leaking and injecting mechanism was through antennas
connected to radios but not necessarily. That kind of electromagnetic
incompatibility should be rare, though.
After Ken K1EA et al added RF and maybe also other filtering, the radios
stopped hearing each other that badly.
Other filtering are for example ferrites we place on DC power cords, mains
wires and other .. PTT / band data and any other wiring you have at your
station. We attenuate unwanted signals until they do not bother us.
You can find a lot of information about different kinds of filtering in the
internet.
All cases are different.
Some hands-on information here:
http://wiki.k1ttt.net/Default.aspx?Page=2008%20Maintenance%20and%20Upgrade%20Blog&NS=&AspxAutoDetectCookieSupport=1
Look for words
-harmonic
-power
>
> Joe WB9SBD
>
73,
Jukka OH6LI
> Sig
> The Original Rolling Ball Clock
> Idle Tyme
> Idle-Tyme.com
> http://www.idle-tyme.com
> On 7/25/2016 5:48 AM, Rudy Bakalov via CQ-Contest wrote:
>
>> Jukka,
>>
>> It is the statement below that really puzzles me. All amp people I know,
>> including those that manufacture commercial amps, categorically state that
>> amps do not generate harmonics on their own. That is, amps merely amplify
>> them.
>>
>> To me this seemingly minor difference is huge. If amps only amplify but
>> do not generate harmonics then there is no scientific reason for filtering
>> after the amp assuming the same amount of filtering is applied before the
>> amp. In practical terms, this would mean that low power BPFs before the amp
>> are as effective as high power BPFs after the amp.
>>
>> The key point here is GENERATE vs AMPLIFY harmonics. Can the average
>> commercial, well stabilized amp generate harmonics?
>>
>> Rudy N2WQ
>>
>> Sent using a tiny keyboard. Please excuse brevity, typos, or
>> inappropriate autocorrect.
>>
>>
>> On Jul 24, 2016, at 5:14 PM, Jukka Klemola <jpklemola@gmail.com> wrote:
>>>
>>> In case you do that, you still need stubs after the amp.
>>> Amplifier creates harmonics out of the fundamental frequency.
>>>
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>>
>>
>>
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