NAT01 - Why is it flipping to mono?

I had a NAT-01 serviced in Salisbury a few months ago.


It would be useful for all of those wth NAT tuners, for you to clarify where this info orignated.
IIRC @anon70766008 has recently had a tuner serviced at HQ.

Charlie how does the flip between mono and stereo occur?
A starting pint, if you have a single run, before you do anything else, is to clean all the connections and reattach the existing coax. While it may be the tuner, I’ve had lead issues before. If you are using a wall plate at the tuner end, ensure it doesn’t have any attenuation.

Is the drop into mono occurring across the frequency range? I guess you might be using R3 - does it occur on others?

Corrosion of where the coax is attached to the antenna can ruin the signal transfer. It may be that gentle winds are making and breaking the loose-ish connection there. Worth having a gander. Also, is the tuner end of the coax terminated with a PAL or BNC. If it the latter, you may have a dodgy BNC-PAL adapter.

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I’ve had this - rust at the end of the first run of coax.

In the OPs case - it’s a loft aerial, but similar applies.

Have you tried the Nat where the creek is I know it’s not ideal but might show up something with the main install. :thinking:

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We can still service these, but if it requires adjustment of the coils it would be game over if the ferrite cores were to crack. :frowning_face:



Thanks again all. I confess I thought it was somewhere on this forum that I’d seen a remark about not servicing NAT01s any more, while I was reading through before starting this thread. So thank you graham55, that’s good news. The 4 element aerial is in the roof, so isn’t subject to the weather, and I’ve re-stripped and reattached the coax at the aerial end, and done the same at the wall plate (PAL socket) in my music room. When the flip happens, the stereo dart under the signal dart just goes out, and I’m reasonably sure it affects all stations, including Radio 4 and Classic FM, although yes, I do mostly listen to Radio 3. There appears to be no change in background noise, which is very low - i.e. the stereo doesn’t get hissier before the flip, but I think that’s a tribute to the Naim design and the threshold set for the balance between signal strength and the switch to mono. The focus on the cable in this thread makes me wonder if the coax could have been damaged somewhere along its length, e.g. by mice in the wall, which I have had occasionally (you have to take humane traps a very long way away to stop them coming back). Trying a new cable run might help identify the problem, but still wouldn’t explain why it’s intermittent. And thank you Skeptikal for the suggestion that I try the NAT where the Creek is - I’m using the DIN output on the Creek, so that would be fairly straightforward. I’ll swap them over. I suspect that might also reveal how good the Creek is, even if it doesn’t quite have the extraordinarily natural quality of the NAT.


Charlie, bear in mind that the NAT01 trades sensitivity for selectivity, so will likely need a stronger signal than the Creek to reach the stereo threshold and full quieting. This is why Naim recommended it be used with a Galaxy aerial.


Thanks Neil for clarifying here.

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Possible NAT01 issues aside, as you mention you have a Galaxy as a spare, perhaps it’s worth contacting Ron Smith Aerials (IIRC his Son runs it now) and get them to come out an install it and run a new length of coax in too. At least you know it’ll be installed and aligned correctly by someone who knows what they are doing and allow you to get the best quality signal for the NAT01.


Ron Smith disappeared off to Spain, I think, some years ago. It’s good news indeed if his son has got the business up and running again. I live right on the south coast and my aerial has taken a bit of a battering from high winds since it was installed over ten years ago.

I will buy a brand new one, if that’s possible. I’ll see if I can find them online.

PS I found the site online, and have left a message asking if they can help.

I recently bought a Nat01. Had both boxes serviced before the dealer installed it. I have a loft Ron Smith Circular 5 which is one of their smallest but nevertheless my tuner is wonderful. To me intermittent problems sounds like the Nat 01 needs servicing more than a problem with aerials cabling.

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It is a lovely bit of kit, but at ten years since its last service it may well need some TLC at Salisbury, please remember this is a piece from the last century .

Even if you want to get rid of it, have it serviced as it will be very sellable

Graham, Ron passed away in 2010. George has been based in Spain for a very long time, iirc.
Mail order is still available and the website is still live and the aerials are now available in kit form (for shipping). I can imagine being by the coast takes its toll.

RS rigged my G17 a quarter of a century ago and it is still going strong, I had met him a few times for different rigs, a Puccini fan, iirc. The coax lead has subsequently been replaced after water ingress, which George suggested might have occurred when we discussed the matter by phone. I eventually found a great guy locally, well experienced with radio aerials.

Thanks, I’ve amended my earlier post to say that I found the site and I have left a message asking for their assistance.

Rowridge is undergoing essential maintenance at the moment and is on reduced power.
I am line of sight of Rowridge and it has been up and down of late.

Below is from BBC check transmitter faults.

|From 10:02AM on 7th May 2024|BBC Radio 1|Slightly reduced power due to essential engineering|
|From 10:01AM to 11:46AM on 4th May 2024|BBC Radio 1|Slightly reduced power due to essential engineering|
|From 10:02AM on 7th May 2024|BBC Radio 2|Slightly reduced power due to essential engineering|
|From 10:01AM to 11:46AM on 4th May 2024|BBC Radio 2|Slightly reduced power due to essential engineering|
|From 10:02AM on 7th May 2024|BBC Radio 3|Slightly reduced power due to essential engineering|
|From 10:01AM to 11:46AM on 4th May 2024|BBC Radio 3|Slightly reduced power due to essential engineering|
|From 10:02AM on 7th May 2024|BBC Radio 4|Slightly reduced power due to essential engineering|
|From 10:01AM to 11:46AM on 4th May 2024|BBC Radio 4|Slightly reduced power due to essential engineering|
|From 10:02AM on 7th May 2024|BBC Radio Solent|Slightly reduced power due to essential engineering|


I was in touch with George Smith in Spain as recently as last year - as responsive and helpful as ever. I bought the G17 when I acquired the NAT01, but never installed it as the tuner worked perfectly with my old 4-element aerial - until late 2022.

NeilS thank you for confirming it can still be serviced. Worth doing while it can still be done. I never mind a trip down to Salisbury, as it reminds me of the happy days when I was able to drop down and chat with the great JV himself - including about folding bikes, yachts etc… And a service now will probably see it through until the fateful day when they do go ahead with switch-off.

I’d love to get the G17 up, but it won’t fit in the loft where the 4-element is. We built our house in a period style, and it is so far unadorned with aerials, so there’s a WAF issue here. I’d have to send her off on a boozy lunch with her chums and hope she didn’t notice when she got back; though there’s one gully I might be able to partially hide it in.

In the meantime I’ll try a run of new WF100 - George warned me it’s hard to get “real” CT100 any more, as much of it is fake and uses inferior metal.

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Kend I think you might have nailed it for me. I was about to suggest that the NAT01 flips to mono when the sky is clear: I’ve had good stereo reception all weekend, during the cloud and rain, and this beautiful clear blue morning it’s mono again. I couldn’t understand that. But I can understand the impact of reduced power!

Justin at aerialsandtv is another gem of the industry - and thank you Skeptikal, that’s indeed where I’ll get the WF100.

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Google ATV poles.
They do the real cable.

Here is an anectdotal story about my NAT-01 experience when I relocated to South Florida.
When I first moved here about 12 years ago, there was only one FM station worth listening to…a classical station in Miami. But it was a good distance away.

Nevermind, I have a G17.

…Home owners Rule #5…no roof mounted antennas.

Well there was no rule about sticking them on a ladder and putting it in the backyard, which is exactly which I did. But the line of sight was partially obscured by trees and after ages, the best I could do was to get a relatively hiss-free mono signal and that stereo ‘dart’ indicator would not light up.

But one day, after a strong windstorm…the stereo indicator lit up for the first time, and I was getting glorious stereo sound. So I went outside to see what had changed.

The wind had blown the antenna and turned it by 90 degrees. It turns out the radio station was vertically polarized and I had set up the antenna for standard horizontal polarization. By a stroke of serendipidy my fortunes were reversed.

Of course 6 months later, the radio station shut down and was replaced by a Christian music station.

At which point I removed the G17, the ladder and the NAT01, which now has now been on long term loan to someone I know for the last 4 years.

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