NAT05 problem, please help

Yes, it sounds like three possibilities;

• a drop of signal strength due to wind damage on the coax, elements or direction ... hard to confirm without a signal meter or an aerial rigger checking.... but it is worth checking internal coax cabling and plugs... is it firmly inserted into the back of the NAT?
• a local source of intermittent interference such as from home adapters (networking over mains) devices or similar etc... you might be able to correlate this with noise from a portable stereo receiver.
• damage or maintenance being carried out on your transmitter where power has been temporarily reduced.

Stereo FM requires more spectrum and a requires a cleaner and less noisy modulated signal.. as stereo modulation  uses AM within the FM station bandwidth.

Chris, it may be odd atmospheric conditions. Last few weeks I noted that on some radios around the house Radio 4 was noisier and more prone to interference than normal.  A quick scan around and I noted that suddenly there were loads of french FM radio stations that had appeared and were coming in quite strong, some of them were very close in frequency to the main UK FM stations.

Apart from that, if you're concerned then maybe worth asking one of the radio boffins at the factory.

Yes it may be ionospheric conditions .. typically Sporadic E .. that can effect VHF and UHF signals (radio, mobiles, TV etc) ... and this time of year is more prone, but will be short lived over say 24 hours or less and will be quite consistent whilst it occurs... (effectively signals travel significantly further than line of sight as they are reflected by the ionosphere or occasionally the troposphere and therefore interfere with each other)... I can sometimes pick up Russian CB/taxi  operators  on FM with my (specialised ) radio equipment here in the UK sometimes when it occurs ..   but only for a few hours..  

To check on your local transmitter health,  use http://www.bbc.co.uk/receptionsearch

If thats OK, which I suspect is the case,  my first item to check would be the coax & its connections.  Its been a hot summer & sun heat can cause the coax to loose shape i.e. the centre core can creep towards the outer on bends, its more liable with the air-spaced type coax & water ingress is another possibly with air-spaced.  The wind may have caused a broken connection in the aerial's terminal block.    As its a roof aerial I would get an aerial installer to check it out.  

Thank you all for replying so promptly. It's a bit like going to the doctor isn't it?! it's not done it since I posted.

I can confirm that the connection is firm at the back. My transmitter is Rowridge on the IoW, I now know, thanks Mike, and they had some low power on Thurs 20th which affected R2, they say, since put right. Friday morning was when I first noticed it, but on R4 during 'Today'.

Which leaves me with the ionosphere and the 'Sporadic E', an idea that I like the sound of since we can sort of sense the world turning at this time of year.

I have a Tivoli Model One in the bedroom. If it ever happens on the NAT again, I will see if it is affected too, and if not see about checking connections on the roof.

So I'm keeping an eye on it. Thanks.

Hi Christopher,  you are receiving one of the most powerful FM transmitters in UK, Rowridge is pushing out 250kW on the four main BBC's.   If you are in the service area as shown on the map,  your are in a good place with a roof aerial (assuming its not defective) 

I would put the problem being related to ionosphere at the bottom of the list. 

You idea of checking out the Tivoli next time you get the problem is a good one,  that will show a low power event from Rowridge.  My Tivoli has difficulty with distant and/or low power stations when the NAT-05 will suck in lower power & further distant stations with ease.   

Thanks Mike. I'm definitely in the green area, and had no idea I had such a major league transmitter.

I'm glad you like the idea of me checking on the Tivoli the next time it happens, and understand your reasons.

My NAT03 picks up Rowridge very nicely with a cheap & crappy “squarial” from Argos., but then I can almost see the mast on a good day (the old joke in Sarf Ampsheer is “If you can see the Isle of Wighit, then it’s going to rain. If you can’t see it, then it is already raining”).

However I’m hoping to acquire a Ron Smith jobbie from a chap up county, surplus to his requirements as he’s bagged himself a ND555! Total overkill for our current location, I know, but SWMBO has designs on moving to the wilds of Wales when we retire in a year or so........

Christopher_M posted:

Thanks Mike. I'm definitely in the green area, and had no idea I had such a major league transmitter.

I'm glad you like the idea of me checking on the Tivoli the next time it happens, and understand your reasons.

Aren’t you up around C Ford? Or am I thinking of somebody else.....

@Mike_B

History Question.........I have a vague memory that there used to be another Tx on the IoW. One for the Beeb, and the other for ITV?

Suzy Wong posted:

@Mike_B

History Question.........I have a vague memory that there used to be another Tx on the IoW. One for the Beeb, and the other for ITV?

Chillerton Down,   it was the ITV VHF service until the end of VHF ITV in 1985.   Its still transmitting local FM services & DAB.

Suzy Wong posted:

Christopher_M posted:

Thanks Mike. I'm definitely in the green area, and had no idea I had such a major league transmitter.

I'm glad you like the idea of me checking on the Tivoli the next time it happens, and understand your reasons.

Aren’t you up around C Ford? Or am I thinking of somebody else.....

I'm a bit off the Avenue.

The weather's calmed down, reception top notch.

Let's see what happens in the Autumn gales. Thanks all.