Sydney - "Noise" on 70cm repeaters

[VK2FABS]

New to the local repeaters and noticed that during the day, there's frequent noise/interferences on the various 70cm repeaters around town. Are these so called city RF pollution? I note that some of them have a voice in the background. Where are they all from? 2M is so much quieter but little activities.

One other question. I've read that VK2RCG Sydney repeater on 439.800MHz is listed as a digi only repeater but regularly it's being used for voice comm. Is that an issue?

[VK2HRX]

It is a P25 digital voice repeater.

[VK4DU]

Hello Weiyun

The noise you can hear is interference from other commercial services on the repeater sites. Some of the repeaters are sited on very busy commercial sites, with lots of transmitters. Mixing products from the multiple transmitters sometimes appear on the repeater receiver.

439.8 is an analog repeater, located in the Sydney CBD - it needs a CTCSS tone of 91.5 Hz to access. It is linked to the Horsley Park repeater on 439.75.

Both repeaters provide excellent coverage, and are probably the most active 70cm machines in Sydney.

There are a number of P25 digital repeaters in Sydney - there is one in the CBD on 438.2. Alas, as an F call you can't use P25.

There is also one at Paddington on 438.575 - this a dual mode machine, and often is connected to IRLP/echolink nodes.

73
Glenn VK4DU

[VK2FABS]

Thanks Glenn and got it! I just want to make sure that voice access of the 439.800 CBD repeater is permitted. Yes, noticed the interference to be particularly bad during the working hours, as a matter of fact, right across all the 70cm repeaters I hear. I suspect they aren't even coming through the repeaters but directly onto my HT. That's when driving through and around the CBD.

[VK2AVR]

You're quite likely to have direct break-through on a handheld, because handhelds don't have the circuit board real-estate for good filtering compared with a mobile rig. If you have added an external antenna onto your HT then this issue can get really bad. I noticed a massive difference upgrading to a proper mobile rig.

You can usually tell if it's coming through the repeater because when it stops the repeater will have a perfectly quiet tail for a fraction of a second before the carrier drops. If there is no clear tail then you are getting local interference on your HT. Also, check the HT's signal strength meter. local interference will have a different signal level to a real transmission from the repeater.

[VK2FABS]

Yep, confirmed. It's local interference in and around the CBD. The difference b/n 70cm and 2M bands is really quite something.

[VK2LK]

New to the local repeaters and noticed that during the day, there's frequent noise/interferences on the various 70cm repeaters around town. Are these so called city RF pollution? I note that some of them have a voice in the background. Where are they all from? 2M is so much quieter but little activities.

One other question. I've read that VK2RCG Sydney repeater on 439.800MHz is listed as a digi only repeater but regularly it's being used for voice comm. Is that an issue?

VK2RCG has several repeaters under the one license.

439.8000 is NFM analog voice
438.2000 is P25 digital voice (linked internationally to P25 network)

and there is another repeater in the pipeline

[VK2LK]

Thanks Glenn and got it! I just want to make sure that voice access of the 439.800 CBD repeater is permitted. Yes, noticed the interference to be particularly bad during the working hours, as a matter of fact, right across all the 70cm repeaters I hear. I suspect they aren't even coming through the repeaters but directly onto my HT. That's when driving through and around the CBD.

Most of these repeaters transmit a 91.5Hz CTCSS tone. This can be used in your receiver to prevent some of the issues you are experiencing with commercial services bleeding through.

[VK2FABS]

Most of these repeaters transmit a 91.5Hz CTCSS tone. This can be used in your receiver to prevent some of the issues you are experiencing with commercial services bleeding through.

Thanks for the suggestion. As was pointed out, it would appear those interferences were actually direct interferences onto my HT. They weren't going through the repeater as their signal strength were different and affected a number of 70cm repeater frequencies at the same time. All gone on the weekend.

[VK2LK]

Those interferences were actually direct interferences onto my HT.

Yep thats exactly why the tone on the repeater output is there - it ensures your HT won't unmute unless its actually hearing the repeater

Hope to catch you on there sometime mate, the more the merrier

[VK2FABS]

Thanks VK2LK. Catch up at some point. 73