Strange Radio Issue

[SVNeko]

We have a Standard Horizon 2100 with AIS reception that has been great for 4 years. However, recently it has been doing something funky which I have NO IDEA how to diagnose. A few seconds after a transmission by us, we hear our own message again sounding a little faint and scratchy. The recipient doesn't hear it and just talks over it, but it interferes with us hearing them. Any idea what this could be? It has happened over a span of hundreds of miles, so I don't think it is some local phenomena. We have the usual panoply of electronics on when it happens, but they are the same electronics that were on when it was working well in the past. thx

[F51]

Ok, I think you're pulling our leg, but I'll try. Turn off everything electrical/electronic on the boat except the radio. Does it still do it? Then measure exactly how long the delay is. Is the moon above the horizon? Then maybe it is some kind of moon bounce, but the signal would be so low coming back as to be unreadable. Hams use EME moonbounce to communicate, but it takes some pretty sophisticated gear. Let us know what you find.

[Paul Elliott]

Zero point zero zero chance of moonbounce!

There are some VHF radios with a "replay last-received message" capability, but not the SH2100 (and this would not fit the problem as described). Moonbounce would give you about a 2.6 second delay, but the losses are so huge that your marine radio gear could *never* pick up the reflection. Sometimes HF signals can propagate around the world and back (giving about a 0.15 second delay), but not VHF.

I am stumped.

[rwidman]

Standard Horizon has some of the best customer service in the industry so my suggestion is to call them and talk to them about it.


I'm assuming you're not transmitting on channel 26 or 27 which in some areas have a SeaTow radio check feature that plays back your transmission.

[BigJohn]

Originally Posted by SVNeko

We have a Standard Horizon 2100 with AIS reception that has been great for 4 years. However, recently it has been doing something funky which I have NO IDEA how to diagnose. A few seconds after a transmission by us, we hear our own message again sounding a little faint and scratchy. The recipient doesn't hear it and just talks over it, but it interferes with us hearing them. Any idea what this could be? It has happened over a span of hundreds of miles, so I don't think it is some local phenomena. We have the usual panoply of electronics on when it happens, but they are the same electronics that were on when it was working well in the past. thx

sounds like you are picking up the harmonic for some strange reason ...

does your Tx have a gain control? if so, try reducing it ...

[S/V Illusion]

A "harmonic" is a radiated signal usually on a multiple of the frequency. It has nothing to do with a delayed transmission. An increase in gain would serve only to distort the audio or increase deviation on FM. Nothing related to the described delay.

Sounds more likely this is either a delusion or a dysfunctional hearing aide.

[Tx J]

Originally Posted by SVNeko

We have a Standard Horizon 2100 with AIS reception that has been great for 4 years. However, recently it has been doing something funky which I have NO IDEA how to diagnose. A few seconds after a transmission by us, we hear our own message again sounding a little faint and scratchy. The recipient doesn't hear it and just talks over it, but it interferes with us hearing them. Any idea what this could be? It has happened over a span of hundreds of miles, so I don't think it is some local phenomena. We have the usual panoply of electronics on when it happens, but they are the same electronics that were on when it was working well in the past. thx

If it were simultaneous crosstalk it might be explicable, but hearing a presumed radio echo "a few seconds after", with RF traveling at close to 186K miles per second (speed of light), kind of rules out any reasonable external factor.

Sounds like the VHF has developed a fault that is mimicking something called an Analog delay line - Wikipedia, the free encyclopedia , which could possibly reproduce your 'delayed' voice transmission in the receiver/audio circuit.

Suggest you plug in another VHF and see if this perceived audio "delay" problem goes away. If it does, somebody, like SH, should be mighty interested in playing around with that VHF unit.

(Have you looked for a UFO overhead at these times? Any faint woo-woo Twilight Zone music in the background? )

[Tx J]

Originally Posted by rwidman

Standard Horizon has some of the best customer service in the industry so my suggestion is to call them and talk to them about it.


I'm assuming you're not transmitting on channel 26 or 27 which in some areas have a SeaTow radio check feature that plays back your transmission.

Certainly plausible, and if the Sea Tow repeater were defective and echoing other channels too. But the OP wouldn't be the only one in the area having this problem.

[Tx J]

Originally Posted by S/V Illusion

A "harmonic" is a radiated signal usually on a multiple of the frequency. It has nothing to do with a delayed transmission. An increase in gain would serve only to distort the audio or increase deviation on FM. Nothing related to the described delay.

Sounds more likely this is either a delusion or a dysfunctional hearing aide.

Exactly, "harmonics" travel at exactly the same speed, contemporaneously with, the fundamental/base frequency transmission; as even multiples of that frequency, subject only to any propagation differences of the (always weaker) higher harmonic being in a different 'band'.

[Paul Elliott]

Originally Posted by rwidman

I'm assuming you're not transmitting on channel 26 or 27 which in some areas have a SeaTow radio check feature that plays back your transmission.

This is by far the most likely explanation (a SeaTow or similar playback station). I'm embarassed that I didn't think of it, since I've got a friend who operates one of these on channel 28 up here in Friday Harbor.

[colemj]

Assuming it isn't just a new voice in your head, does it happen only near land? Only on certain channels?

I have no explanation for the following thought, but as a WAG, could it be triggering a 2M repeater somewhere because its tx and rx bandwidths have become way out of spec?

If you key the mic while listening to other (different) channels on a handheld, do you hear any noises?

Mark

[SVNeko]

Its happening in the remote islands of Belize. There is hardly any equipment here at all, let alone a SeaTow station. It happens on 14 and 16, but I haven't really tested many channels. At first I thought it only happened when I was monitoring two channels, but that clearly now is not the case. Mark, what's a 2M repeater? And, no, no noises on different channels when the mic is keyed. When keyed on the same channel the closeby handheld squeals of course.

[colemj]

Two meter repeaters are ham stations set up to repeat radio signals to allow for longer distance communications. Two meters also covers the VHF bands, which is why I suggested that your radio may be out of spec.

The whole thing was a WAG, though. It is unlikely there are any 2M repeaters in Belize, or in range of you. Your problem is certainly a new one for me.

You sure it isn't just a new voice in your head?

Mark

[SVNeko]

No, not a new voice in my head... and all the old ones are accounted for.

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[gilgsn]

Ham repeaters "repeat" signals instantly and most require a tone to trigger them; no way. The simplest explanation would be that the signal is repeated by some automated system within range. Why? No idea. I doubt a hardware problem could do this, and the signal bouncing on something with such a long delay is very unlikely..

Gil


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