hi steve
getting frustrated with antenna,using a inverted L and sgc auto tuner it tunes fine on bands that i use but what puzzles me is before i switch my psu on to power tuner i have 2 s points of noise when i power it on noise rises to s9 plus.am i right in thinking tuner is isolated before psu is switched on? i have a toroid wound at tuner end of 12v feed and also at psu end.i have used different types of psu but nothing changes.if i didnt need tuner it would be a quiet antenna.i feel that antenna is isolated before i switch psu on
rgds dave g0his

The SGC 230 goes into bypass mode when the power is turned on so you effectively have a direct connection to the radiating element of the inverted L therefore the noise will be a lot lower because the antenna isn't tuned. One of the portable battery powered ones latches the relays so the antenna remains tuned but as you mentioned you supply 12V to it, I am assuming its not that model.

When you power it on it remains in that state until you squirt RF down the coax and then it tunes the antenna for the frequency you select. The S9 noise is then what you hear as the efficiency of the antenna system is increased as a result and is the same as you'd hear with a resonant antenna for that frequency without a tuner.

All non-resonant antennas are quiet antennas until you tune them, that is why a non-resonant beverage antenna is often used as a RX antenna. Although the signal strengths are lower, the noise is a lot lower so you can hear more. The more efficient the antenna system is, the more the noise will rise unless you live in the middle of nowhere. That is natural and not a problem as long as the received wanted signals are also rising as well. The problem comes when the noise is but the received signals aren't. I would actually be worried if you weren't experiencing an increase in the background noise. S9 is sadly a common noise level for the lower bands such as 160m/80m/60m in an urban environment.

You say you have a toriod wound on the 12V feed but have you put a RF choke on the coax at the tuner end? What are you using as a radial system? A rod in the ground may make it tune but it doesn't mean its working properly. I used over 300ft of radials when I used an inverted L tuned by a SGC 230.

hi
think u missed the point i dont squirt rf up it just switch it on and no amount of radials or grounding makes a difference.so i am not tuning it to increase noise level.but tnx for ur input
g0his

Which model tuner, and what PSU are you using?

Following up Conor's point, if you listen to a "wanted" signal, what happens to its level when you go from tuner unpowered to tuner powered?

Steve G3TXQ

hi steve
tuner is sgc230 i use watson psu one is switch mode the other old fashioned transformer.if i hear a station about 5 s points then power up psu it 5 9 plus and station dissappears
rgds

My name is also Steve, am I permitted to comment?

I have a watson switch mode psu and it is quite noisy, can you take it out of the equation and try?

The rig will only use a couple of amps on receive, so should be happy for the test on a smaller supply.

have you tried feeding the antenna straight into the rig? What is the noise then?

I think he already tried a different supply.

You might try powering the tuner temporarily from a battery right at the feedpoint - removing the DC supply wires to eliminate pickup on them - and see if the noise is still there.

Steve G3TXQ

The SGC230 doesn't tune from power on until RF is sent to it. Definitely something seriously amiss.

I would also consider removing the lid off the SGC230 and checking for water ingress and corrosion on the earth strap inside the unit. If you don't keep them covered when they're outside the plastic case becomes a bit brittle from the sun and you can end up with cracks where the screws are on the side where the inverted L connects to from the forces exerted on the white post by the radiating element.

I don't know the SGC230. I guess a key question is: what is the difference in the signal path between the tuner being powered (not necessarily tuned) rather than unpowered?

Steve G3TXQ

yes steve that IS the question

Can you try powering it from a battery, as I suggested?

Steve G3TXQ

yes i will steve in the morning.
73 g0his

Unpowered is effectively bypass so the equivalent of connecting the centre of the antenna socket to the radiating element.

tried with a battery still the same so i believe when power off i am listening on coax feed and when on antenna is switched in circuit.i will check for water ingress when the wx improves.
rgds g0his

If I understand Conor correctly, wouldn't the antenna be connected directly to the coax in both the powered and the unpowered conditions?

It's a "long shot" but, if that's right, is it possible the processor in the tuner is not going to idle, and what you're hearing is processor "hash"?

Steve G3TXQ