We had a 1550khz in town and a 1450khz moved 2 blocks away from 1550.
Yep.... mix products on 1650khz and 1350khz. ( and to some extent
1500khz )
a simple 1550 notch on the top of the 1450 transmitter eliminated the
mix products and didn't bother the 1450 transmitter.
Don W4DNR
On 2022-02-20 12:14 pm, Nick Hall-Patch via Topband wrote:
Hello Jim,
Better, I think, is this notch, found at the IRCA Reprints:
<https://www.ircaonline.org/editor_upload/File/reprints/irca-reprint-index.pdf>https://www.ircaonline.org/editor_upload/File/reprints/irca-reprint-index.pdf
Look for Reprint A-063, An RF Notch Filter by VE6JY.
You really should only need to notch the carrier of the offending AM
station, as that's where the bulk of the overload will be coming
from. It's a pretty amazing device, in my estimation.
73
Nick
VE7DXR
At 17:41 2022-02-20, jim.thom jim.thom@telus.net wrote:
Has anybody tried using a simple series L-C to notch out ONE offending
AM
broadcast station ? I'm talking about wiring from hot side of
coax...to
chassis / ground....like via a T connector etc.
On paper, it should work. Did some minor research, and one comment was
that
by using higher values of L would result in higher Q..and a deeper
notch.
Another comment stated to use some initial values, like what spits out
on a
L-C online calculator for practical values..... then multiply one
value
by the other...then take the square root of the result. Then you
ended up
with 2 x numerically equal values of L + C..... and supposedly the
greatest
notch depth.
On software, I tried several values..from one extreme to the other,
and
they all resonate on the same freq. Also tried in software, using 2
x
numerically same values..and it too, also resonates on the same freq.
The rationale behind all of this is... in some cases, there is only
one
offending AM broadcast station. Typ HP filters offer little
rejection
towards the top end of the AM broadcast band..... like 1200-1710 khz.
I would like to try it, but am still confused as to which combo (using
practical values) will result in the deepest notch. It would have to
be
wide enough to remove the 20 khz wide AM signal. A fixed coil +
variable
cap, or padded variable cap could be used to fine tune the notch freq.
Perhaps 2 or more LC filters could be used in parallel, to notch out
2 or
more offending stations ?
Jim VE7RF
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