FM radio strange behaviour

Phil_aka_Pip

I have an "indoor aerial" plugged into a tuner. The aerial consists of a rather rude looking vertical plastic thing about 12" high mounted on a base out of which sprouts the coax you plug into the tuner, 2 wires with spade connectors (which you connect to the AM inputs if you have any), and the power supply lead. There is a little pot for adjusting signal strength. Tuned to R4 the pot does nothing (ie makes no difference to audio quality or volume) - probably because where I am the signal is plenty strong enough without needing to boost it but if you click the control off, you get noise behind the signal. Tuned to R3 you get loadsa noise almost obliterating the music, even when the signal strength leds on the tuner indicate max signal and the stereo led is also on, but if you nobble the frequency on the tuner until (i) the strength and stereo leds all go out (ii) the frequency indicator suggests you aren't tuned to R3 (or at least shouldn't be) you get audio that is crystal clear, but mono.

I don't get it. Does anyone else?

CHRISB50

No

FX_Munkee

Check for "innocuous looking" van outside your property.

Flanging_Fred

The alien invasion has begun. They take coms first apparently. They then start to attack th₹#_8$46* गजुर्रतु।  डकलsty865℅¥π ]]]]]]]●●● ....666.

Grunfeld

Phil_aka_Pip said:

Tuned to R3 you get loadsa noise almost obliterating the music...

Are you sure that's not just R3's latest avant-garde offering?

Ravenous

Phil_aka_Pip said:

...but if you nobble the frequency on the tuner until (i) the strength and stereo leds all go out (ii) the frequency indicator suggests you aren't tuned to R3 (or at least shouldn't be) you get audio that is crystal clear, but mono.

This sounds like typical stereo FM behaviour when there's interference or reflections or an otherwise bad signal for that particular station.

The signal strength isn't the problem in other words. (My guess.)

Try the aerial in a different place, say temporarily set the gear up upstairs (higher up), or close to a window...

Sassafras

Get DAB.
I never have trouble with that.

exocet

It'll be multipath or multiplex distortion - direct and indirect signals being picked up at the same time. The booster is boosting the weaker indirect signal and making matters worse.

FM stereo is transmitted using at least two signals multiplexed onto the RF Carrier (Mono and Stereo or Sum & Difference). 

These signals will be at different frequencies so it is possible to tune into the mono only part if the signal. The stereo part is usually lower level signal and is where the noise is introduced. 

boogieman

Sounds like you need a better aerial. Is your tv signal a decent strength ? You might be able to split the coax lead from the tv aerial and use that for your tuner too

RandallFlagg

“They're he-ur”

Emp_Fab

Sassafras said:

Get DAB.
I never have trouble with that.

Surely you mea..... Get...B.  I.........trou...............that. ?

Phil_aka_Pip

Thank you @exocet and @Ravenous ... seems like I should get a feed from my rooftop VHF aerial: I already have a 4 way splitter that feeds 4 tuners on the 1st floor. If I replaced that with a 6-way, I could take a feed though the first floor into the ground floor where this kit is

btw lol@Grunfeld

RiftAmps

exocet said:

It'll be multipath or multiplex distortion - direct and indirect signals being picked up at the same time. The booster is boosting the weaker indirect signal and making matters worse.

FM stereo is transmitted using at least two signals multiplexed onto the RF Carrier (Mono and Stereo or Sum & Difference). 

These signals will be at different frequencies so it is possible to tune into the mono only part if the signal. The stereo part is usually lower level signal and is where the noise is introduced. 

This.

My valve-tuner in the shop picks up two separate R2 signals, one around 89.5mcs and the other at 91mcs. Depending on the time of day one signal is stronger than the other although the higher one is mono only.

57Deluxe

Then the loud sound did seem to fade, came back like a slow voice on a wave of phase haze - that weren't no D.J. that was hazy cosmic jive!

ESBlonde

This wouldn't be anything to do with all the notices on TVs about needing to retune after the 7th February would it? Could just be a coincidence.

Phil_aka_Pip

ESBlonde said:

This wouldn't be anything to do with all the notices on TVs about needing to retune after the 7th February would it? Could just be a coincidence.

I have no idea mate. The TVs are all digital these days, aren't they? so isn't "re-tuning" just a case of switching to a different channel to get the broadcast you want?