In article , "Greg_False"
writes:

"Avery Fineman" wrote in message
...
In article , "Greg_False"

writes:

Thanks for the prompt and very helpful response.

I do not know enough about radio circuits to fiddle with installing
additional preamps directly into the radio it' self.

Okay. How old is the radio you want to use in the Land Rover?

For those made since around 1970 in HF use, the sensitivity
of the receiver section is already near optimum. Won't be
much improvement by adding an outboard preamp.

I want to improve my reception as I normally travel with a group of other
Land Rover owners who also have 29MH radios but they are not as fussy as I
am about their installations and in many cases they can hear me but I cannot
hear them.

Then I would look into the connections and possible corrosion
on your existing mobile antenna mounting. If you are traveling
with others no more than perhaps 10 miles or so distant, your
transmitter output may be enough, even though attenuated, to
break the others' squelch and they could hear you.

Chances are that the receiver of your transceiver is just off-tune
and some alignment is needed. I'd check that first, can be
done on-air, receive only with a friend's transmissions.

I'd begin with the mobile antenna mount and connection to the
coax, even the coax itself. Use an ohmmeter and check for
low but finite resistances there. Take apart the mobile antenna
mount and wire-brush (rotary on a drill is my recommendation)
the conductor surfaces. Some corroded contact surfaces may
look clean but an ohmmeter may show otherwise. If there are
lock-washers there, a dab of silicone grease (the thermal
conductivity grease used on power transistor mountings works)
will cut down on future oxidation. The teeth of lock-washers
assures a positive metal-to-metal contact even with grease.

I was thinking of using a double pole double throw relay.

No problem there.

I could fit a micro switch to the mic which activates before the press to
talk switch activates the transmitter?

I like Tim Wescott's suggestion of using a lower-power relay coil
and detecting the RF from the transmitter first...saves having to
run a line from the transceiver for the PTT coil energization...but
that has a danger in the build-up time of transmitter power output
being faster than the detector-relay switchover time. If so, the
preamp will be fried before the relay has time to switch over.

Nearly all PTT transceivers of any kind have a line already there
inside from the PTT switch. Bring that one out and get an RF
detector to measure the transmitter RF output. Accuracy not
needed here. Use an oscilloscope with a slow time base, say
around 0.1 Sec, with a DC input capability, and compare the
timing of the PTT line and the detected RF output. The PTT
line MUST operate FIRST. With at least 0.1 Sec lag of RF
output versus the PTT line, the relay idea has a chance to work.

To be honest, I would suspect you might have some
misalignment in the receiver front end that's giving the
problem of low sensitivity. An outboard receiver preamp may
not help that condition much.