SSB Interference (link to audio clip)

demonboy

demonboy

Well-Known Member
Joined
11 Oct 2004
Messages
2,237
Location
Indonesia
www.youtube.com
I'm in the middle of installing my SSB, an Icom IC-M710. I am getting some rather annoying noises coming through my set and I don't know where to start looking. I have isolated all electronics on the boat except the unit itself. Here's what I have, perhaps it's something to do with any of these?


CG-3000 ATU
RG 58 from M710 to ATU, approx 10m
Insulated backstay
No stand-offs as yet
No groundplane installed from ATU as yet (but that's for TX only, isn't it?)
No ground on the 710 unit (was told doesn't need it)

Here's a link to the audio clip (actually it's a video clip):
 
demonboy said:
I'm in the middle of installing my SSB, an Icom IC-M710. I am getting some rather annoying noises coming through my set and I don't know where to start looking. I have isolated all electronics on the boat except the unit itself. Here's what I have, perhaps it's something to do with any of these?



No groundplane installed from ATU as yet (but that's for TX only, isn't it?)
Here's a link to the audio clip (actually it's a video clip):
Click to expand...

No, Not exactly.
The ATU will not work unless there is some form of groumd to ballance the long wire backstay.

In effect the ATU needs a feed from it's output (the backstay) and a return from an earth in order that there is a path for it to feed some curert into.

To recieve signals correctly there must be an earth on the ATU. This is just as critical as for the transmitter.

Iain
 
SSB Interference

Hello,

The interference is very regular and my guess is that it is locally generated...ie from within the boat or marina. The question is...is the interference being picked up on the antenna or is it coming in on the sets power supply ? There are lots of questions to be asked such as is the interference limited to certain bands or stations etc etc but personally I would do the following :

Isolate the radio completely from the boats power supply and from ac mains. This means getting a small stand-alone battery (or 2 if the radio is 24v) and connecting it to the radio. It is essential that absolutely nothing else is connected to the battery. If that cures the problem, then the interference is coming in through the supply. Then it's a matter of identifying the source. To do that you need to revert to the original situation; i.e bring up the interference, and start going round the boat switching stuff of. I would also isolate the boat from the shore supply if it is connected.

However, before doing anything I would definitely connect a good ground to the set. I don't know why they told you one wasn't needed.

Regards,

Djdiode.
 
SSB interference

Have you got a mobile phone switched on in your pocket- If 'on' mine affects my pc sound reception with series of 'ticks'. Just a thought!


ianat182
 
First thing, lose the RG58, it is not good enough for a 10 metre SSB antenna cable, use RG213 / RG8-U instead. Is your controlcable for the ATU a screened cable and grounded at both ends, if not then sort that out too. All the items should be grounded to each other.

Noise sounds like it could be your fridge.

You will need to turn absolutely everything off, including all those things you have not thought about!. My suggestion would be to disconnect the shore power and also all the battery connections. Connect the SSB to a standalone battery and try again. Then reconnect the batteries, you can then start switching things on and off one at a time untilthe noise comes back. If you are a 24v boat then also remember that there will be 24>12 droppers for things that are sometimes connected behind the scenes, so although the unit is off the dropper might not be.

Interference is a difficult one to crack, but a careful search will eventually find it.

Oh, try moving your boat too, it might be your neighbours!
 
Last edited:
Firstly the ATU DOES work on receive. It can easily make 6db improvement in signal/noise ratio.

And has was said it is essential that you have a decent earth. If you have a high resistance earth then any electrically noise kit will create a voltage across the earth resistance and that will appear as noise in your receiver.

The noise sound cylic in some way - what else did you have runningon the boat? - sounder perhaps

Try switching off everything else electrical except wireless and see if its still noisyand then go through a one at a time elimination exercise till you find the source of the noise - and then throw it overboard.
 
SSB interferecne

The sound to me seems like an actual transmitter sending data or other rubbish to lay claim to a frequency channel. If you shift the frequency of the receiver does the sound go away? If you disconnect the antenna does it diminish or go away. If you move your boat does it go way or change?

An HF receiver will receive on almost any antenna however a good shielded cable to the tuner with a very short lead to the antenna will ensure that only signals from the antenna ie external to the boat get into the receiver. Perhaps more so on a metal boat.

I don't agree with the statement that RG58 is no good for SSB. It should be very adequate the transmitter voltage will not exceed the rating of the cable and losses only appear at VHF /UHF.

Other wise if it is a local interference do as suggested disconnecting every thing. Watch out for mobile phones and computers although I don't think it sounds like them. good luck olewill
 
William_H said:
If you shift the frequency of the receiver does the sound go away? If you disconnect the antenna does it diminish or go away. If you move your boat does it go way or change?
Click to expand...

Those are the questions I would ask too. But don't despair yet. Any installation will produce that kind of noise at some time on some frequencies, it does not sound like locally generated interference to me.

Harbours/marinas are always very radio noisy places IME. I have sat in the middle of an active harbour and heard nothing, not even the BBC. But just 1 mile outside everything was crystal clear.

You should ground your ATU before expecting to be able to diagnose this kind of thing.

RG58 is perfectly adequate and by itself will certainly not account for the interference.
 
Firstly thank you all for your replies. I'm not sure where to start, so in no particular order:

- I'm at anchor so no neighbours or marina interference
- All electronics were switched off including laptop, instruments and fridges
- When I disconnect the aerial from the SSB unit the sound does stop
- When I change frequency the sound changes. There might be a delay in the sound starting again and sometimes the clicking changes pitch

Hightech - you say "Is your controlcable for the ATU a screened cable and grounded at both ends, if not then sort that out too. All the items should be grounded to each other." Which is the control cable, the cable from teh ATU to the backstay or the 710 to the ATU? How do you mean grounded at both ends?

I'm a little confused by the responses. Was the consensus that the ATU SHOULD have its groundplane installed before trying to isolate this noise? That's my next job to install the ground so perhaps I should do that next and come back to you.
 
Even if you run any thick piece of wire from the earth terminal on the ATU to one of the keelbolts that will give you something. (as a temporary measure)

The wire could even be the braiding and the inner of a piece of coax joined together. Copper foil would be much better as it is surface area that is important. But any wire should give an improvement.


This will allow the ATU to tune and you may find that much of your interference disapears.

For SSB frequencies the type of coax you use between the Tranceiver and the ATU will not be the cause of your problem.

Iain
 
You may not have a "Control Cable" - I don't. I just have the coax going from TX to ATU. ATU tunes automagicly when it gets a signal from TX (evidenced by clicking noises coming from it, which eventually stop). The "tune" function on the TX sends a signal down the coax to do this. Having said that, I don't think I would fire up the TX, even on "tune" unless the ATU was grounded and if you don't do that then the ATU won't be tuned and so will not help, even when Rx'ing.

By the way a "grounding plate" is not the only way to do it. You can use 75mm wide copper strips laid out under cabin soles, or under the headlining. So long as you have one strip cut to 1/4 wavelength for each frequency you plan use it will work fine. Bring them all together at the ATU grounding post.
 
You have had all sorts of advice so far, and the truth is that finding the source of your problem is a bit of detective work. So to try and help:

1/ Start by taking the boat to an anchorage and then trying again on a range of frequencies from (say) 3mc/s to 30 mc/c. Where I am at the moment (Swansea marina) there's so much electical activity going on that my ham radio is unuseable, but 1 mile out and its completely quiet.

2/ Dont expect the same sort of quiet reception from SSB that you are used to from FM. You wont get it. And noise will vary wildly from band to band.

3/ If you still have the noise in the anchorage then the culprit is on board. Switch the radio on and then switch off all the onboard kit item by item. Batter chargers and power supplies like inverters are partciular culprits as is the fridge

4/ Dont worry about things like cables or grounding if you are just receiving. The idea that using RG58 could cause that noise is technical nonsense.
 
You must log in or register to reply here.

Share this page

Top