During receive mode try to measure the by-passed PA DC voltage if it exists
then it may cause self oscillation within the PA disconnect this DC voltage and
see.
Aland
Nate Duehr <[EMAIL PROTECTED]> wrote:
Hi guys,
Built a link radio out of a MASTR II mobile a while back. 444.575 TX,
447.575 RX.
It is NOT duplexed and the RX section turns off during TX, just a normal
MASTR II mobile setup. The only modification done was to by-pass the PA
and run the exciter output over to the Low-Pass Filter board in the PA
section directly -- didn't need much power to make this link work with a
6 or 7 element yagi mounted outside, pointed at the repeater it's
linking into.
After having the link installed in my basement for a few days, I
realized that it's throwing a fairly strong dead carrier on VHF at
145.460 or thereabouts, but ONLY when it's sitting idle in Receive.
When the radio is transmitting the carrier generated by the receiver
disappears.
It's not strong enough to receive it further than about one house away
on an HT down the street, and I don't hear it one block over, but there
in the house... permanent carrier on 145.46. (Unfortunately this is the
output frequency of one of our club repeaters that's over 40 miles and
behind a ridge from my house, and the repeater "loses" completely to the
carrier coming from the link radio in the basement.)
I attempted to figure out the mix math to see if that would be a
"normal" thing to see when using that particular UHF RX frequency, but
I'm honestly not very good at that. I figured I'd post and see if any
of the list's gurus might have an explanation of why it might be doing
this. Any thoughts?
I might (just to see what happens) stuff the crystals in another MASTR
II, tune it up, and see if the same thing happens, but if this could be
explained mathematically, that would be more "interesting".
Hmm, what other info might you need... ahh... thinking back, the
crystals might not have been ordered with high-side injection... I'd
have to look at the ICM packing sheet, and it's at home.
Nate WY0X
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