[CQ-Contest] CQ-Contest Digest, Vol 151, Issue 20

[Steve London]

Bob's,

I think another way to say this is by example:

If you feed an amplifier with a pure 7 MHz signal, the 2nd harmonic at 
14 MHz will be only 6 dB down at the anode (or collector). The rest of 
the "work" to attenuate the 2nd harmonic is being done by the amplifier 
Pi or Pi-L network.

73,
Steve, N2IC

On 07/21/2015 12:59 PM, Robert Chudek - K0RC wrote:
> /"While BPFs certainly do attenuate harmonics, this is all to no avail
> when the BPF is installed between transceiver and amplifier."/
>
> I have a very hard time "buying" this statement. If a BPF attenuates a
> harmonic, let's say, 30 dB, that would be 30 dB less harmonic energy
> being fed to the amplifier. If the amplifier is truly "linear", how does
> it recoup this 30dB of harmonic power that is no longer being fed into
> the input?
>
> 73 de Bob - KØRC in MN
>
> ------------------------------------------------------------------------
> On 7/21/2015 11:47 AM, Bob Henderson wrote:
>> Mike
>>
>> Bandpass filters are likely needed for the WARC bands whenever you intend
>> to listen on those bands while transmitting elsewhere.
>>
>> Considering the value of BPFs in terms of their harmonic attenuation is a
>> common folly, except if you run barefoot.
>>
>> While BPFs certainly do attenuate harmonics, this is all to no avail when
>> the BPF is installed between transceiver and amplifier.
>>
>> A Class AB stage fed with a pure sine source has a second harmonic
>> component of anode current only 6dB down from the fundamental. This means
>> that unless the drive has a second harmonic larger than -16DB down once
>> amplified by the PA, its effect on total harmonic output will be
>> negligible.  This applies similarly to other harmonics.
>>
>> In other words: If your transceiver is FCC compliant adding BPFs
>> between it
>> and a following amplifier will yield no benefit in harmonic reduction
>> whatsoever.
>>
>> BPFs primarily act to protect receiver front ends from exposure to
>> harmful
>> levels of fundamental energy.  This is as true for a 6m transceiver as it
>> is for one at HF.  If you have a 6m yagi co located with say, a 10m
>> yagi or
>> tribander your 6m transceiver will be exposed to dangerous levels of
>> cross
>> coupled fundamental energy.
>>
>> 73
>>
>> Bob, 5B4AGN
>>
>> Date: Mon, 20 Jul 2015 19:53:24 -0300
>>> From: "Mike Smith VE9AA" <ve9aa at nbnet.nb.ca>
>>> To: <cq-contest at contesting.com>
>>> Subject: Re: [CQ-Contest] seeking 9band bandpass filter unit
>>> Message-ID: <000601d0c33e$f37e3e30$da7aba90$@nbnet.nb.ca>
>>> Content-Type: text/plain;       charset="us-ascii"
>>>
>>> Charly,
>>>
>>>
>>>
>>> Since bandpass filters are primarily used in SO2R contesting
>>> operation (or
>>> field day ie: M/M, M/2 type of operations), I have to ask..why would you
>>> need bandpass filters for the WARC bands !? (no contesting on the WARCs)
>>>
>>> Also, since nothing is a harmonic of 6m, nor is any HF band close to
>>> 6m as
>>> a
>>> harmonic,(except far far away) same query goes for SIX.
>>>
>>>
>>>
>>> I am not trying to be sarcastic...it's a serious question.
>>>
>>>
>>>
>>> I too would like to dabble my toe in the SO2R waters, but not at
>>> $2000+ to
>>> get it here to Canada.
>>>
>>>
>>>
>>> Mike VE9AA
>>>
>>> Mike, Coreen & Corey
>>>
>>> Keswick Ridge, NB
>>>
>>>
>>>
>>>
>>>
>>>
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>>
>
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