Long wires for monitoring ,any need for counterpoise

Recently discovered I enjoy going through all frequencies I have monitoring listening . On nothing special just a old solid state 11band radio a koyo and a 90s steepletone multi band radio.
The koyo is weird ,atatch a external antenna and it just gets garbled. It's like its over sensitive and too much.I think I have read this is common on the model and best used on telescopic or with it retracted .
Interestingly enough I found that if I add a long wire and plug it into the G I believe ground plug on rear as it has 3 plug holes , vhf sw and G the G increases signal and volume of audio.
Now only a guess but G I believe is Ground ?.
So this I believe would be acting as a counterpise if I'm not mistaken ?.
On the koho it works well.

So now to the sreepletone .I connected up the long wire to a Jack plug after identifying which part of the Jack plug connected to the antenna as it is a ear phone Jack plug. .but as I was testing it I noted crackling when inserting plug so I imagine one part of the plug in the radio is grounded ? .
Or Is this wrong.

So my thought is if my thinking is correct here the plug may be able to provide 2connections ,one for the antenna element as such the other for a ground and counterpoise ?.

I think most importantly this is only for receiving signal not transmitting so is a counterpoise beneficial in any case and does my thought on the Ground make sense.
Thanks in advance

The problem with nearly every simple RX designed with a telescopic aerial is that if you plug a longer antenna in, it overloads as the longer antenna picks up more RF energy. It isn't dangerous to the receiver. It sounds as if the G is a ground terminal.

On teh steepletone if it's an audio jack plug or the antenna, these almost always short circuit momentarily because the "sleeve" bit is ground, which is why you get a crackling when you plug it in.

It's impossible to say whether a counterpoise will help or not in all honesty because in most home situations these days, the limiting factor on what you can hear is domestic noise - but there will be no harm done if you experiment with different setups. Some people find counterpoises reduce the noise, some people find they increase it. Just have a play.

Thank you , yes you have it and explained it far better than I. Glad you got my drift.
Yes on the koyo it's overload and picks up every noise from home electronics.
The steepletone however doesn't seem to suffer same.even on mains supply it's quiet and picks up little if anything.
I will try the ground and see if any improvement.
It certainly when connected to long wire alone on steepletone give no noted improvements like it does on the koyo.
However the short crackle connecting was hat I was trying to explain.
Will give it a bash.
Maybe a 20' countetpoise.
Thank you for making sense of my posting .
Cheers

All end fed antennas need a ground to work against, even for receive. There's actually no difference between setting up an antenna for RX or TX in regards to RF grounding. In both cases you're needing current to flow in the antenna, the only difference is that when you RX those electrons are sourced from the air whereas when you transmit they're supplied by the radio.

You can "get away" with not having a RF ground more with a receive only antenna because of the very low currents involved. However for say an antenna like an Imax 2000 you'll suffer from the same issues with take off angle max gain lobe being at a fairly useless high angle for DX without a RF ground as someone who is using it to transmit. You'll also suffer common mode RFI noise on receive too.