Commercial Radio Station Being Picked Up On 447.2375 MHz

How far away is the broadcast transmitter antenna? My brother used to get the local radio station on his electric coffee pot.

The frequencies, 95.2 MHz, 96.1 MHz, 96.6 MHz, 105.4 MHz, 106.3 MHz are much lower. Maybe a harmonic?

It would be strange how a broadcast station could be picked up so clearly if it was a harmonic. The audio quality is also close to that of our local station. If it were a harmonic from the local transmitter, Ofcom might be angry.

Also, the transmitter is about 4 miles away, but I am really not all that sure.

What's the call sign and freq of the FM station? Could also be mixing with some other signal and coming out on 447.2375. Do you get it on more than one receiver?

I can get it on the two radios I mentioned which are the only ones with that frequency range. I have no idea about its call sign. Kingdom FM is on 96.1 MHz and is being re broadcast at 447.2375MHz at broadcast quality with mono sound.

Is the image you are receiving always there or does it sometimes turn off

Do you pick up any thing at 351.1375MHz?

Kingdom FM also transmits at 95.2MHZ. Can you receive that?

Doe your USB defined radio have a spectrum analyser feature like Winradio or similar? If it does look for a big carrier that is always on.

It sounds like they are broadcasting their radio to be received on T.V.

I would also check cable television equipment near your house. This could be a radiation from damaged cable if it's running at the old 450 MHz.

DAB? or DTV sideband, where the radio stations are transmitted from. Most DAB signals are 128 bitrate, and mono.

It can not be digital or cable. The signal is there all the time.

I don't know where you are located but it is possible that you are picking up the remote feed from a control center to the actual transmitter location. The UHF band is often used for this purpose, your best bet is to Google on the frequency and see who the licensee is. For example in Manchester UK this entry indicates to me a "control link" between this particular communications tower and another location:

"447.2375 TOWER FM TALKBACK BOLTON GREATER MANCHESTER FM Nov-06"

But he has identified, the station as the local FM broadcasting station. Check the local oscillator and the IF frequency of the radio. The harmonic of local osc. heterodyning with some interferring carrier may be the cause of this fenomena.

Sounds like an signal being translated by another strong signal. Rusty joints in the vicinity might be the culprit. I've also seen corroded antenna connections rebroadcast. You will need to play detective.

you know the output frequency and one of the input frequencies. output= input1 +/- input2 the other input could be a 3rd harmonic.

good luck

Joshi, perhaps you can explain to us how you would tell the difference between the feed and the broadcast signal, especially since they are identical except for the carrier frequency, power level and a few microseconds of delay as the signal is amped up to broadcast levels.

And let's rule out any weird harmonic stuff, both the 4th and 5th harmonic of 96.1 are very far away (in RF terms) from this UHF channel, even when IF shift, sidebands, and signal detector deviation are accounted for.

A quick look shows two broadband tuned filter mosfet preselector stages (one for each of the two receiver bands) which connect to the RDA 1486 radio chip at pin 15 RF In. Notice that there are no IF transformers since all of the decoding and processing of the RF signal takes place on the chip, exiting at pin 9 as Audio Out.

Bottom line is there is no IF to tweak, swamp, overload, intermodulate, generate spurious harmonics, etc. The other chips are the microcontroller, power controller, and audio power amplifier.

Also note that there is a separate Broadcast FM receiver chip, and that it's audio output is mono, not stereo.

There are a number of King radio stations broadcast all over the world, when OP reveals his approximate location and/or the call sign of the FM station that he is receiving, and the make and model number of his other SDR, we will be in a better position to answer this non-mystery.

I am not in touch with the current technology. The circuit appears to be using broadband amplification of received signal. Must see the application notes on RDA 1486 before commenting. The TX freq. and the offset freq. for repeater operation are generated on RDA 1486. Pin 5 & 6 allude to XTAL-1 & XTAL-2, also there are few more XTALs on the module. What is Y1 - 13M ? Without knowing how the TX/RX works, I am afraid to venture further.

Have you had a look at the ether around you with a spectrum analyser yet?

Use a yagi antenna and see which direction it is radiating from. You can possibly do this without a specan as well just rotating till you had the "best" signal. Easier with a specan though.

Does your USB SDR have a specan feature?

I don't have a yagi antenna. I wish I did though. The signal does come up clearly on the spectrum analyser but there are no other signals around.

Crikey mate! You were contemplating construction of a quadrifilar helix at one stage...

Do you not have a UHF TV antenna lying around?

Yes, we have one in the garden that was taken off the roof.

Seems you do have one then.

Hook it up and faff around a bit.

Yagi antennae have directivity and polarisation. The received signal level, as shown on your specan will vary both with the direction and orientation.

You do know which way the front of the Yagi is?

Eventually you will be able to determine which direction it is coming from. You can even take it on the road and triangulate to the source.

The antenna is huge and heavy. It would be useful. If I removed some of the elements on the front to increase the spacing, would it then be suitable for picking up the weather satellites?

If there is antenna mismatch, the RF output transistors/module may get damaged. You can use it only for receiving though. Never ever press the PTT switch.

Hydrogenhead is messing with receivers right now. So not critical. A balun would improve the transmission line link budget considerably if he really needs all the gain he can muster.

Good general caution re transmitting into a mismatched antenna. Not really an issue with the type of (generation of) handheld transceiver he has though. There is a circulator at the RF output and a load on the reflected port. They can work reliably even without an antenna though the rx sensitivity and EIRP are down you can still use it if required.

My only warning re the PTT is don't press the PTT if you have your finger in the antenna socket. Even 5W gives you a bit of a nudge.

Step by step mate. Hydrogenhead is an enthusiastic learner.

Big and heavy? Not UHF then.

Maybe you have a dual band antenna?

Don't remove any elements. Trim the length of the elements to suit the band you want to receive. You can google the lengths yourself.

That weather sat was VHF right? If the yagi is setup correctly it will be better than the long wire you are using now.

I was thinking that it would be easier to drill holes in a length of wood at the correct spacing for 137.5MHz and then put thin metal rods through the holes to make a yagi antenna.

Something like this, but this one is for 900 MHz.

Absolutely.

Plenty of resources to guide you on the internet mate.

Have you at least attempted to connect the yagi you already have to your receiver?