Ham Repeater Sounds

[rothackerben8]

Hi everyone,

I am using my scanner to listen to my local ham repeater (Mount Kerang) the repeater outputs on 147.0250 and inputs on 147.6250. When I listen to it I can hear a control channel, the ambulance pager tone and the police in the area, but all on top of each other. I don't see how this could be a useful repeater if it has so much interference. Also there is a morse code that comes through, which is a callsign of some kind. Can someone please explain what is going on here?

Cheers

Ben

[Phantom]

The morse would probably be the repeater ident (roughly every 10mins?) and would be its ident or callsign.

As for being "useful" - it probably would be utilising CTCSS.
It sounds like the site may be high in RF so I hope they are using good filters to help the site
You could also be hearing "harmonics" but the question is:

Is the "interference" always present or at specific times?

[Yipyip46]

Good Afternoon Ben, as Phantom said is the interference there all of the time? Is the repeater retransmitting the interference or does it appear randomly? If the interference is there only when the repeater is keyed then it is most likely getting into the input and would likely be site related. This would mean that the owners of the repeater would need to look at the issue. If it appears randomly when the repeater is off air it is likely to be image frequencies or harmonics. I have also seen where an some older scanners that do not have a good front end filtering or they use a 10.7 mHz I.F. which can allow image frequencies through. These sorts of problems can get complex and take some sorting. I hope this post has helped. Regards Yipyip

[Vkfour]

I thought that I had replied to this, but I must have pressed the wrong button, (put an empty drink can in the fridge the other day). Many repeaters are in high RF locations and with the mixing of frequencies and close proximity of others, (pagers are a real problem), there can be a major issues. As Phantom said, they can eliminate this by using CTCSS. I did have a look and this repeater is not showing as having a CTCSS frequency attached, but there is a note saying that they are waiting for riggers to reposition the antennas.

[rothackerben8]

Okay, so the sounds happen whenever the ambulance pager tone comes through. The repeater's input is close to the frequencies i said above, and all of them are transmitting on the same site. I'm wondering if because the pager signals are so strong, they are overlapping onto the repeater's input. As for the morse code, i ran it through a decoder and it is a callsign of the group who manage the repeater

[Vkfour]

Repeaters are required to identify themselves when first activated and then regularly there after until people stop using it. There have been a few voice ones over the years, but morse code is the usual way. The interference is because they are very close in frequency and filtering the pagers out is quite difficult.

[rothackerben8]

Yeah thats what i was thinking. Why did they put the repeater so close to such strong signals then?

[Vkfour]

It is possible that the amateur repeater was there first. Up where I am, the amateur repeater was the first and only one on the mountain, then the landlords found that they could make a fortune hiring their mountain out. It is also possible, because of other equipment at the site, or when the pager was installed, or frequency changed, that this problem has only just arisen. We are seeing more and more amateur repeaters being equipped with CTCSS just to stop interference. A sign of the times I'm afraid.

[Yipyip46]

Good Morning again, one issue with pagers is there are only a fixed number of frequencies available in Australia and most of them are in the 148 mHz section. The repeater frequency allocation is done with a set criteria of location, adjacent repeaters, coverage and power just to name a few. As Vkfour alluded to, first in does not protect you from future allocations. Another issue with pagers is their output power. This can be as much as 1kW and that can be very difficult to filter out as the level at the input frequency of the repeater on a co-sited setup will be extremely high. The CTCSS does not remove the interference but stops the interference from opening up the repeater as there is not a matching tone on the pager signal. If you had CTCSS on and a weak amateur signal into the repeater you would still hear the pager noise. The above reasons are why there is a comment about waiting for riggers to re-position the antennas. My 5 cents worth to add to the conversation. Regards Yipyip

[Vkfour]

Your 5 cents worth is really worth 10 cents YipYip, you explained it clearer.

[rothackerben8]

Yeah that sounds like the problem. The ham repeater was installed in 1989 and the pager transmitter in 2006. This makes sense, and the crowd who maintain it probably wouldn't have enough money to install CTSS equipment