Australian Ham Radio Discussion Forum ( AHRDF )

General Question.

How do you report interference ? What is the ACMA process ? I've looked but cannot find a reference online.

I'm getting smashed with an S9 signal on 144.205 Mhz.
It seems to be an mixing product of a P25 DMR / Pager system installed by I suspect Sydney Rail (approx 300m away),  and a Chinese Language community radio.

The pager signal is dominant, but when it drops to carrier only the audio of the Community Radio is fully noise quieting.

I've found the Chinese language broadcast source at 152.075 Mhz.


Can anyone help with the process, or maybe the maths for how the intermixing product works.


Regards

Brian O'Gallagher

VK2XTC

Last time I looked the report interference form on the ACMA website wasn't suited to reporting radiocommunications issues, and instead I read a while back the email addresses to use were interference@acma.gov.au and FieldOperations.Mail@acma.gov.au

As regards the "maths" you can play around with the calculator here:

Calculate intermodulation products from 2 and 3 frequencies.

(06-02-2022, 02:45 PM)VK3RX Wrote: [ -> ]Last time I looked the report interference form on the ACMA website wasn't suited to reporting radiocommunications issues, and instead I read a while back the email addresses to use were interference@acma.gov.au and FieldOperations.Mail@acma.gov.au

As regards the "maths" you can play around with the calculator here:

Calculate intermodulation products from 2 and 3 frequencies.

Thanks for the link. Saved me lots of time.

It lines up perfectly to a an Intermodulation product from a +60dB pager transmission on 148.140 MHz.

(+60 dB 148.140 MHz mixed with +60 dB 152.075 MHz  = +10 dB 144.205 MHz) 

I'll try the email addresses above, but as this is a product of legal licensed transmissions do I have any hope, or is this just bad luck and I'll have to pack up and move ? (never really liked this house)


Brian

The only questions remaining are :
Is it a transmitted intermod (ie rusty bolt effect or no isolator fitted at the output of one or both transmitters) ??
Is it a receiver intermod - simply too much signal from both causing the intermod to be generated in the receiver front end (RF amp or mixer), bad RF joints in antenna or feeder ??

Transmitted intermods might interest the ACMA, receiver intermods will not.

If possibly receiver intermod, maybe try a coaxial stub filter for 152.075MHz or thereabouts.

Coaxial Stub Notch Filter Designer
Notch filter made with coaxial cable.

Regards to wether it's a receiver intermod or Transmitter intermod the signal is present on the main radio (TS-2000), the backup radios (IC-706Mk2 and FT-847) and a couple of handhelds.

(I've been actually using the handheld to chase down interference and found the Brother Printer was one nasty culprit)

I'll ask the question to the ACMA and see what they say.

The interference started when Sydney Trains placed a tower in the corridor in Chatswood. Before that it was clean.
I'll try making a notch filter and see how it goes.
Perfect excuse to buy VNA. 


I'll post an update here when available.