/"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@nbnet.nb.ca>
To: <cq-contest@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@contesting.com
http://lists.contesting.com/mailman/listinfo/cq-contest
_______________________________________________
CQ-Contest mailing list
CQ-Contest@contesting.com
http://lists.contesting.com/mailman/listinfo/cq-contest
|