Community radio station, pondering SDR signal analysis... - Page 1
Forum section: electronics / rf-microwave

author: oRiCLe
author_rank: Newbie
timestamp: October 23, 2019, 10:48:42 am
content: Hey all,I've been helping out a local community radio station in south of Sydney sorting out their studio hardware and learning all things radio and FM in the process, I recently purchased an SDR to do some more learning and was was doing some scanning of the station and frequencies around it from my home tonight based on a listener reporting hearing another station on the frequency at areas around town and when leaving the local area...and I thought of this forum after remembering watching Dave's video on the old analog tv transmitter tour...so hopefully I have put this in the right place, if not let me know and I can move it accordinglyThe station is 92.5MHz, transmitting at a few hundred watts, but nearby frequencies have the ABC transmitting on 92.9MHz from Gore Hill, the odd thing I found is that there seems to be a replication of the signal 2 station steps either side of the ABC's 92.9MHz signal (92.5 and 93.3-ish), which I am wondering if, in theory, the ABC transmitter transmitting at a considerably higher amount of kW the signal and its replica noise with it either side with this signal, could the community station's lack of strength actually be being further drowned/canceled out with the snow overpowering it when sub-optimal terrain conditions occur to the community Tx tower?Heres a quick screen recording with audio example if that helps make more sensestill learning all things radio but googling has not found me much other than explanations of what deviation and drift is...but if its something obvious let me know and im sure we can all have a bit of a chuckle about itthanks

author: awallin
author_rank: Frequent Contributor
timestamp: October 23, 2019, 02:58:30 pm
content: what SDR receiver are you using?from the video it almost looks like the +/- 400kHz 'ghost' signal is an artefact of something going on in your receiver.would be interesting to see the LO that you probably have for mixing down from 92.9MHz - if it has side-bands at 400kHz then that could explain things..

author: Bud
author_rank: Super Contributor
timestamp: October 23, 2019, 04:35:15 pm
content: I second this, you first of all should understand the performance of your SDR, otherwise you may be chasing a red herring.

author: oRiCLe
author_rank: Newbie
timestamp: October 23, 2019, 09:46:20 pm
content: its an RTL-SDR v3thanks I will do some more reading about LO and those effects etcand I will also do the same test around some other strong signals to see if it occurs there also.interestingly I can replicate the signal pickup as per the youtube example at those wider frequencies on my dads car stereo, but not mine

author: vk6zgo
author_rank: Super Contributor
timestamp: October 25, 2019, 01:15:42 am
content: 92.5MHz & 92.9 MHz seem to be very close allocations.My experience is that the closest frequency allocation spacing is 800KHz.With FM Stereo stations being around 200kHz or so in RF bandwidth, there isn't a lot to play with.Maybe you should have a word with ACMA.They are not infallible-----on one occasion they allocated the same frequency to the STL links for two TV stations in the same city!It may be, that because of the close spacing, your licence specifies that you have to "tolerate" imterference from full power stationsBack in the day, we had a nasty interfering signal on our TV transmission where I worked.It took the form of a signal at 800kHz in the video passband.On investigation, we found that rwo or more of the FM stations in our building & next door were mixing in the input of several of our Video Distribution Amplifiers, producing an 800kHz difference signal.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 25, 2019, 01:25:42 am
content: Are you sure about that 92.5MHZ?http://worldradiomap.com/au/sydney