The third harmonic of 50.313 is 150.939, there is probably enough energy to
cause problems. A good LPF on the 6m station might help and a good bandpass
filter on 2m should help. A brute force method is a shorted
quarterwave stub at 150MHz on the output of the 6m amp but a good LPF is
still the best bet. There are many designs out there for homebrew or buy
one already tuned by W6PQL.
Also make sure all your connectors are tight, I've seen MANY times at K8GP
where interference was just a loose connector. This past weekend, we ran
1500w on both 6m and 2m and the antennas were about 100ft apart with no
issues, that is a K3 on 6m driving a Harris SSPA with a good LPF on the
output (all harmonics are at least -70dB) and a DEMI 2m transverter with a
4 pole helical filter between the rx input and the LNA. Be VERY careful
using LNA's on 2m, too much gain is the kiss of death to all receive
Is it coming in through the coax at an RF level or is it audio
rectification in headphones or the radio? I keep a box full of clamp on
ferrites from Amazon on hand and use them liberally. 6m just has a way to
get into everything!!
Last make sure your matching components on the antennas are good and tight
and free of oxidation. This can cause all kinds of problems. On transmit it
might act as a capacitor and couple the RF just fine so you won't see an
SWR issue but on rx, it could act as a diode and cause any high RF received
to generate spurs.
Terry Price - W8ZN
Directive Systems and Engineering
On Mon, Jan 18, 2021 at 1:11 PM Chuck Dietz <firstname.lastname@example.org> wrote:
> I tried dueling CQs for 6M and 2M during the VHF contest. 6m was totally
> quiet when 2m was transmitting, but 2m had S9 white noise when 6m was
> transmitting. Antennas are 130 feet apart. Happens with even 50 watts on
> 6M, although "only" S7 then. Using FT8 for both bands. Rig is Flex 6700
> with a DEMI 2m low drive amp with receive preamp. When I transmit SSB on
> 6m, it sounds like splattering on voice peaks.
> I need advice on what to try.
> Chuck W5PR
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