"Greg_False" wrote in message
...

I don't think there's anything wrong with the radio, it is fairly new, I
was
hoping to snatch the last bit of a fading signal from the ether.

It is a very simple radio, the only controls are channel selection,
squelch
and volume.

I know, get a more professional bit of kit, but I'm always challenged to
try
and improve things, which eventually costs more than buying the correct
thing in the first place.

I thing I've got the message, don't waste my time:((

Greg

Amidst all the quotes and suggestions, I didn't see an explanation of why
people are saying what they are saying. Here's an attempt at an
explanation.

There is noise in the air, and more noise at lower frequencies. Meanwhile,
especially with transistors, it is easier to get gain at lower frequencies
than at higher. Once you can hear the noise, no additional gain is going to
help. The signal that was below the noise will still be below the noise,
only the noise and the signal will be louder.

At 40 meters, there is so much noise that it borders on impossible to make a
receiver that doesn't have more than enough gain. At 2 meters and above,
the noise is very low, and gain is hard to get. So hard, in fact, that
noise in the transistors becomes an issue. It isn't an issue at lower
frequencies. At VHF and above, if you want to increase the gain you need to
do it at the first stage, otherwise you will be amplifying the noise in the
earlier stages. Furthermore, at VHF and above, coax losses tend to be high,
so it makes sense to amplify the signal before it has been attenuated by the
coax, and possibly fallen into the internal noise of the amplifier. At HF,
coax loss isn't much of an issue (except for antennas operated at very high
SWR), so if you would need a preamp, putting it at the antenna end of the
coax isn't the big advantage that it is at VHF/UHF.

Now, the reason for a little waffling is that 10 meters is kind of in
no-man's land. Band noise is quite low, and it does take some work to get
the gain you need. It tends not to be expensive to get that gain, so even
cheap radios will sometimes have enough gain, but not always. Back thirty
years ago, it was hard to get enough gain on 10, so many older radios could
use a little help. But today, two bucks will buy a chip with ten times the
gain you can use on ten meters.

The reason for the suggestion on unplugging the antenna should now be
obvious. If you can hear the difference in background noise with the
antenna plugged in versus not, then you have enough gain in your receiver
that a preamp will do no good. This is a worthwhile experiment, given that
you have indicated it is a low end rig. I'm sure you hear "band noise", but
if it's a sufficiently low end rig that noise could be coming from inside
the receiver. Not likely, but still possible. The antenna experiment will
put that question to rest.

The reason for the idea of going into the radio to locate the preamp was
simply one of convenience - the relay you need is already there. Unlike at
VHF, there really isn't a big advantage to putting the preamp at the end of
the coax, so why not mount it near the radio where you already have power
and don't have to waterproof it, and taking it a step further, why not take
advantage of the relay that's already there.

Oh yes, and if you do build a preamp, don't sweat the SWR bump at the relay.
As long as you keep all the connections reasonably short and straight it
won't be an issue.

Hope this helps a bit

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