Handheld VHF playing-up

[Gubbo]

Hi,

Problems with my Standard Horizon HX370.

It works fine on all channels except 71 and 84. When I tune to these I get a carrier wave hiss and the green RX light comes on. Transmissions on these channels can be heard but in a somewhat "darlek-like" manner.

These channels may be significant because, aside from 16, they are the only two channels I regularly receive on (71 for Harwich VTS and 84 for Thames CG weather forecast). I have never transmitted on either with this set.

All the other channels are clear and adjusting the squelch does alleviate this problem.

Any suggestions please?

 

[lenseman]

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It works fine on all channels except 71 and 84.

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Channel 71 = 156.575MHz (Simplex)
Channel 84 = 157.225MHz/161.825MHz (Duplex Tx/Rx)

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When I tune to these I get a carrier wave hiss and the green RX light comes on.

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I presume you mean that when you are 'listening' on these channels you get the above symptoms?

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Transmissions on these channels can be heard but in a somewhat "darlek-like" manner.

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This sounds like it is a classic example of intermodulation products (2f1 ± f2) where you have two frequencies mixing together to 'create' a third frequency. The third frequency in you case are the two receive frequencies (Ch71 and also Ch84)

Tests you can do:

Turn everything off on the boat and note whether the interference stops? If it does, obviously then a bit of electrical equipment on board is generating part of the interference and will need to be sorted.

Remove the H/H to your home address and turn on the set on the two victim channels. Do you still have interference?

If at home you still have interference, remove the antenna and note whether the interference stops. If it does, then an external interfering signal is causing the problem. If you still have the fault with the antenna removed, then there is instability within the H/H and will need to be sorted.

If you cannot remove the antenna, try putting the H/H inside a METAL biscuit tin whilst listening to the interference from the speaker.

 

[Gubbo]

Many thanks for your comprehensive reply.

I shall work through the process as you suggest. I can unscrew the antenna.

My friend has an identical radio so I'll test with his antenna if necessary too.

The main fixed VHF set doesn't suffer from any of these problems... but then again its antenna is 35' above the deck so the local interference route seems promising.

Regards

 

[Gubbo]

Followed up on local interference tack and quickly found the problem occurred when my NASA AIS "radar" was switched on.

This was the same for several handheld VHF's tested.

At least my handheld is OK and I know how to get rid of the problem if necessary.

Thanks again for advice

Gubbo