Co-ax thru engine bay

[WayneS]

I have alwas suffered with bad radio transmission while under power as well as an eratic echo sounder.

The co-ax cables happen to run thru the engine bay (Diesel Engine with factory fit alternator,hard wired to batteries thru 1-2-both switch)

the two issues may be seperate.

Radio,
1. It could be faulty (Old Shipmate 8????)
2. Could it be that I need additional smoothing on the DC side when the alternator is running
3. Could it be the fact that the aerial coax runs close to the alternator.

Echo: (Nasa Clipper with x-ducer in oil tube - yes it is full)
1.Same as above
2. or could it be that the x-ducer that goes funny after running for a while

Anyone got inspiration for me?

Regards

Wayne

<hr width=100% size=1>

 

[halcyon]

Could be No 3, if very close to the alternator, move it first, then try a capacitor. Mains used to be a problem, and switch mode battery chargers due to magnetic emmisions, you may have similar from alternator.

Could just be air bubbles, or disterbance at the hull due to moving through the water. Does it alter with speed? may need relocating.


Brian

<hr width=100% size=1>

 

[john_morris_uk]

Do you mean you get reports of poor quality audio on your vhf transmissions when talking to other boats/shore stations when your engine is running? Or do you mean that you get poor reception on your VHF radio when your engine is running.

Easier to diagnose when you say which - but whether you have oil in the echo sounder transducer tube, or where it is located will make square root of diddly squat difference to your VHF. On the other hand, the fact the the coax runs through the engine bay won't alter transmissions much either - but it could affect reception.

<hr width=100% size=1>

 

[WayneS]

Sorry, two seperate problems. I'm not saying that the echo is affecting VHF or v-v.
Just wondered if they may b suffering the same problem.

The issue with the VHF is that my transmissions are affected/distorted. Not only that, but when I transmit (Telephone type handset) I can hear clicking in the earpiece when I have the PTT pressed. This is not there when the engine is off. The speed of the clicking increases with engine RPM so it have to be alternator caused. Just not sure if it is being collected via the aerial or fed in by the power feed. BTW, we have a break in teh cable belowdecks at the mast foot that is joined via BnC plug/socket.


Wayne

<hr width=100% size=1>

 

[DMGibson]

The alternator CAN cause the effects you describe, both on the echo sounder and the VHF. It is actually caused by the regulator adjusting the charge, if it gets worse after the engine has been running for a time.

When you say the cables are "close" to the alternator, anything closer than 12" is probably too close, especially if it is near the main DC feed from alternator to battery.

If the problem is still there after separating the cables, try a capacitor across the DC output terminal son the alternator. One of the terminals could be the mounting bolts.

<hr width=100% size=1>

 

[john_morris_uk]

The two ways that the engine can cause interference on transmit are by electromagnetic interaction of the alternator/regulator charging system onto the coax outer braid which is going back down the coax and getting into (probably the audio) sections of the transmitter, or by the alternator being so badly regulated/smoothed that the nominally 12 volt supply has spikes/interference superimposed on it which then also affect both the RF and audio parts of the VHF. This could conceivably (just) not be a fault in the alternator - it would be possible for the VHF to become susceptible to interference on the 12v supply.

Simple tests:

1. Try the VHF on an independent battery not connected to the boat at all with the engine running and check results. Should disprove first hypothesis. If no/little change, move the coax further from engine. (My money is on this not being the problem)

2. Borrow another VHF and try it in your installation. If it works you can still try adding some interference suppression to your Alternator as suggested by previous post, or get the alternator checked out, but it could be that some of the capacitors in your old VHF have gone 'dry' and you then have to decide whether its is economically viable to have it repaired.

As the echosounder is affected as well, I think all serious money should be on poor alternator regulation/suppression.

If you can find an electronics engineer, I would be very interested to know what your 12v line looks like on a 'scope when your engine is running!

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by john_morris_uk on 14/02/2004 07:01 (server time).</FONT></P>

 

[Birdseye]

Sound advice. It does sound like interference up the 12v dc supply and trying a battery supply should eliminate this if you ensure a short well shieded run from the battery to the equipment.

if this works, then try buying some ferrites from maplins (theyre really cheap), and clipping them round the power supply wires to the equipment. if that doesnt work then I would be inclined to remove the alternator, take it to an auto electrician and get it checked out.

<hr width=100% size=1>

 

[LadyInBed]

A simple way to check if it is the alternator is to disconnect the alternator, run the engine and see if the problem has gone away.
If it proves to be the case, alternator suppressers can be had from any car audio shop. Alternator brushes might be worn or dirty so a service might be in order. Alternator electrical connections are loose or corroded.


<hr width=100% size=1>