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

[Robert Chudek - K0RC]

/"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
>>
>>
>>
>>
>>
>>
> _______________________________________________
> CQ-Contest mailing list
> CQ-Contest at contesting.com
> http://lists.contesting.com/mailman/listinfo/cq-contest
>