Vancouver BC Former VHF TV 174-216MHz Mirroring FM Radio

Status
Not open for further replies.

freska2x

Member
Joined
May 25, 2020
Messages
10
I was scanning the frequencies that were formerly used for analogue VHF Television 174-216MHz. This range is still reserved by Industry Canada for broadcast purposes, but what I find odd is that the frequencies on there seems like it is mirroring overlapped FM radio stations from 76MHz-108MHz. The channels are about 170kHz wide and can be tuned in using SDR in WFM mode.

189.2MHz for example mirrors both FM 88.1 and FM 101.1, so you hear both radio stations at the same time, and adjacent stations like 101.1 seems to be bleeding across to other channels. If you tune 88.1 or 101.1 there is about a 1 to 2 second delay before it gets "mirrored" over onto 189.2MHz.

The range of 181-210MHz is where all the broadcasts lie. I attached a screenshot of a portion of this spectrum.

What in the world would such a broadcast system be used for?
 

Attachments

BC_Scan

Member
Joined
Aug 26, 2006
Messages
508
Location
Vancouver BC
So a mix of the two or harmonic. Could be because CFMI is using HD radio so there are two other AM carriers on there AM980 + AM730, possibly a consequence of the mix. The other issue is where the txer's are both coming from Mt. Seymour, CBC Tower being higher than CFMI,
 

mmckenna

I really ♥ Ø
Joined
Jul 27, 2005
Messages
18,096
Location
Pt. Nemo
189.2MHz for example mirrors both FM 88.1 and FM 101.1, so you hear both radio stations at the same time,
Your clue is 88.1 + 101.1 = 189.2.
2nd Order IMD product

Strong signals mixing in your receiver.
 

freska2x

Member
Joined
May 25, 2020
Messages
10
Wow thanks IMD must be it, I tuned to the 2nd order and even on 3rd order I can still hear the same signal but a lot fainter.

Is this the reason 174-216MHz is still blocked as for "Broadcast" purposes due to intermodulation so it can't really be reassigned for anything else even though analogue TV is no longer being broadcast? Also when OTA Analogue TV was in use in the past what did they do to prevent IMD products from interfering with the TV signals?
 

novascotian

Member
Joined
Oct 27, 2008
Messages
331
Location
Halifax, Nova Scotia
There still are television transmitters in the VHF-HI band (174-216 MHz), just maybe not in your area. We have one in Halifax on Channel 8 for Global. These can be analog, in the case particularly of some low power repeaters that were never changed over, or could in fact be digital transmitters. They are not all on UHF.
 
Status
Not open for further replies.
Top