+- ARCHIVE: Australian Ham Radio Discussion Forum ( AHRDF ) (https://www.ahrdf.net/forum)
+-- Forum: GENERAL (https://www.ahrdf.net/forum/forum-29.html)
+--- Forum: General Discussion (https://www.ahrdf.net/forum/forum-9.html)
+--- Thread: Signal on 144.2Mhz from FM broadcaster (/thread-720.html)
Signal on 144.2Mhz from FM broadcaster - VK4DCM - 07-02-2019
We did some test at Mt Cotton Radio site today to see if it was suitable for the John Moyle weekend coming up.
We want to operate HF 6 2 70 23 and 13cm there is a whopping signal with modulation coming from the local FM station on 100.3 at about 100 metres away its all over the band we moved along the hill 500 metres and it was better but shouldn't they be down 80db at 40 MHz away. I think its only a 200 watt Tx. Has anyone had this problem ? Been out portable and never had anything this bad.
RE: Signal on 144.2Mhz from FM broadcaster - VK3RX - 07-02-2019
Did you try a couple of different brand transceivers?
It could simply have been front end overload, in which case an FM band notch filter might do some good.
RE: Signal on 144.2Mhz from FM broadcaster - VK4ADC - 07-02-2019
Been there. Different 2M freq but same effect.
https://www.vk4adc.com/web/general-projects/35-eqpt-repairs/131-ft1802m-fm-broadcast-fix
Also consider adding a bandpass cavity resonator at 144.15 (for SSB) or 146.5 (for FM) in line before the transceiver. I have had to do that at field day locations near communal VHF/UHF and/or FM sites - and got used to taking one with me each FD and then deciding whether I needed to put it in-line once I checked the QRM on receive.
A little loss at 2M is worth a lot of rejection in the FM broadcast band.
RE: Signal on 144.2Mhz from FM broadcaster - VK4DCM - 07-02-2019
Thanks for the reply I will take a can with me at the field day and that will do the trick.
We did see it on more than one receiver so wasn't from front end overload. Just stray signal from their TX.
Thanks hope to hear you on that weekend..
RE: Signal on 144.2Mhz from FM broadcaster - VK3PY - 08-02-2019
To VK4DCM:
If the rogue signal really is emanating from the FM broadcast transmitter, no amount of band-pass filtering at your receiver will remove it. That's because it's a real signal. However, I suggest what you're observing is more likely to be either a mixing product of the broadcast transmitter and some other signal, or possibly an image response in your receiver(s), in which case the band-pass cavity will certainly help deal with it.
Chas
VK3PY
RE: Signal on 144.2Mhz from FM broadcaster - VK4DCM - 09-02-2019
Thanks for the reply It was on a SDR dongle and my IC706 so I thought it must be on frequency but maybe not. We will have a look again and see if we can reduce it.
RE: Signal on 144.2Mhz from FM broadcaster - VK3PY - 11-02-2019
Please report your findings after the field day so we know how it turned out. It's useful for others who may experience similar issues in the future.
Chas
VK3PY
RE: Signal on 144.2Mhz from FM broadcaster - VK4DCM - 05-07-2023
Looks like they have done a fix they have replaced ther emergency power generator so may be ther UPS most of the noise has gone so will be using the site a bit more Just got to take the chain saw up and get some of those trees to the west on the ground,, Kidding..