NAT02 vs. BBC R3

I live south east London on the fringe of Kent a few hundred yards I’d be in Bexleyheath. I’ve owned my Nat 101 / Snaps since 1987 and I have an aerial on a rotator that I can alter from Wrotham to Crystal Palace. This was the only way for me to get a decent signal. I can rotate and be able to receive BBC Essex if I want to. It was the only option for me to be able to achieve a strong signal.

Regards,

Martin

A rudimentary dipole ??   do you mean just a single element & no reflector or director elements & Is it mounted vertically or horizontally ??     My guess is if it is just a simple dipole  it is probably the thing to go for.

The Nat 02 may benefit from a service if it hasn't been used for a period of time. Secondly it may be worth investing in a top quality directional aerial if possible. I found that there’s occasional interference from local illegal pirate FM stations and multi path reflections around the R3 FM band in central London where I live and this can cause the problems you describe. Using a recently installed communal FM aerial in my block, a live concert of on R3 on a Nat02 can place you in the concert hall and connect you with the music like no other source in my view.

I hope the BBC also offers lossless FLAC again for the proms this year as as an alternative.  Its experiment last year also produced superb results through an ndac.

Thanks for the replies. Rudimentary in my case does mean a single vertical dipole, nothing else, and it isn’t ideally placed for Crystal Palace (although I’m not sure that CP transmits FM). And there are a ton of pirate stations around R3 bandwidth (some of them quite entertaining in small doses). I pick it up at 91.0 with a bit more interference at 91.3. Re servicing, the NAT hasn’t been mothballed for long but it is knocking on - I bought it second-hand in the mid-90s. So a few things to think about. And relatively easy to play around with positioning and even a better aerial - the aerial bracket is easily accessible (about half of the dipole sits proud of the top of the wall, about 3.5m high).

Will keep on hamming as I know the NAT02 can do a lot better, as you describe Echo Room. 

Hi again,  I'm imagining the dipole is mounted close to the wall & with the top half above the wall is not ideal,   If you are OK to fiddle around & can get at it easily & safely the first thing I would do is mount it horizontally,  Wrotham transmits mixed polarisation (V & H) & horizontal polarisation reduces interference.   A pukka 3 element aerial has to be the minimum aim to go for.    

CP does transmit FM,  but at 4kW its low power & is intended as a building shadow fill in.  Wrotham transmits all the BBC's at 125kW & is the main London area transmitter,  I can even get it near Oxford - 70 miles out - if I swing my G14 around .   This is the published coverage map

Although I no longer live in London, when I moved to the Cotswolds I installed a basic Ron Smith aerial which I use on my NAT02 and Unitiqutes.  It copes with reflection from neighbouring houses and farm buildings and trees to provide excellent reception.  Despite having five systems the Ron Smith does a brilliant job even though a pigeon has broken one of the elements.

Also worth checking that you are tuned into the right R3 transmission because you can probably hear several. Wrotham R3 is on 91.3 MHz.

best

David

Thank you all for those additional thoughts. Heartened that the topic is still of interest!

Looks like plane, placement and most likely a better aerial are the way forward. I can raise up the aerial so most of it is clear of the top of the wall. Horizontal a bit more challenging but doable.

Re frequency, 91.3 is worse than 91.0 so clearly some adjustment required. Will report back when I’ve done more tweaking.

I have an 01 Tuner which used to have "birdies" on R3 in stereo which took a decent Ron Smith aerial to cure it. R3 is a relatively weak signal. Contrast it with Classic FM or LBC who are in your face.

Some live broadcast concerts can be superb. Choral Evensong can really convey the acoustic of a large cathedral.

Please keep FM. Do NOT turn if off!

Douglas.

douglas posted:

I have an 01 Tuner which used to have "birdies" on R3 in stereo which took a decent Ron Smith aerial to cure it. R3 is a relatively weak signal. Contrast it with Classic FM or LBC who are in your face.

Some live broadcast concerts can be superb. Choral Evensong can really convey the acoustic of a large cathedral.

Please keep FM. Do NOT turn if off!

Douglas.

Totally agree re R3. My 01 comes into its own during the Proms. I have a 6 element high on the roof aimed at Wrotham from where I live in the Sussex High Weald. Totally quiet and rock steady with only the very occasional need to retune due to minor drift. I had it serviced and realigned by Naim a few years back and it’s in almost daily use. Fabulous piece of kit and long may it and the FM signal survive. It’s also useful when BT BB goes AWOL which is often around here.

Three experiments done: simple vertical dipole but a bit higher than before; same but horizontal; Magnum Dynalab S2 (on loan) extending perhaps a foot higher than the simple dipole. 

Not much difference between the first two and my starting point. A lot of stations, bright green signal and stereo lights on the NAT and R3 still noisy. 

MD S2: fewer stations, weak green lights but where it tunes in, bright, clear reception. R3 is pretty enjoyable on 91.0. Can’t get it on 91.3.

Not sure what to make of that but MD is clearly the live-withable option. Very interested if you have insights into why that difference. There must be some sort of filtering or signal selection process.

Hi PF, your dipole should be more effective in terms of gain  (less lossy) than your Magnum Dynalab antenna, assuming your dipole is set up correctly and spaced away from wall or chimney, in fact the gain of the dipole should be nearly twice that of the Magum, which is effectively a loaded whip antenna from what can I see,

There is a big gotcha however.... a half wave dipole has an optimum impedance of 75 ohms into a balanced feeder, great you say, I don’t need a transformer. Coax is however unbalanced feeder, therefore attention is required so as not to negatively affect the gain and pattern of the dipole  antenna when using coax. Your antenna designer or antenna fitter should have fitted some sort of BalUn where the coax joins the antenna... this could something like a series of reasonably substantial chokes around the coax at the feed-point, or even coil of half a dozen turns of the coax just before the feed-point or some other method. The Magnum being unbalanced can directly connect to the coax, and it’s loaading coil will be designed to provide a 75 ohm impedance for around the middle of 87.5 to 108 band.

Therefore properly set up the Dipole should be more effective in terms of gain  but require more space and a BalUn, the Magnum is more lossy but easier to locate. In vertical polarisation both should offer a reasonably consistent 360 degree gain strength pattern. So if the dipole is not more effective it most likely hasn’t been setup or installed correctly.

Hi again PF.  The MD St-2 whip antenna is telling us lots:  they do a good job when in what seems like your location,  I had one when I was living in an apartment in USA, after a lot of frustration playing with dipoles the St-2 just did the job.  But don't let it kid you,  its got no gain as such & is beaten hands down by a pukka correctly installed multi element.   

Your dipole I suspect is picking up a reflections off the wall,  as I said in my first post wall mounting is not ideal,  I would normally have it on a stand off aprx 18 inches away from the wall.    But it does seem like the dipole is the more effective aerial, per your description,  as its picking up more, but that includes the reflections by the sound of it.  

The fact that the St-2 is only picking up CP only on 91.0MHz & not 91.3MHz from Wrotham would normally indicate you are in a Wrotham shadow, & if so your original post's 'compass bearings' don't make sense.  But as the dipole giving you stronger light indications that says its not,  maybe the Wrotham signal & reflections are too much & the St-2 is selecting the cleaner signal from CP. 

I would be tempted to ask a local aerial installer for advice.

I agree with Mike as to how to interpret what you are telling us. And I also agree with him that it's well worth paying to get a proper aerial put up in the right way. You will be surprised and delighted how much better it sounds.

best

David

Love this forum, its a treasure trove. Thanks Simon and Mike for the thoughtful, articulate responses.

I’m sure of the orientation versus Wrotham but I do live in a built up area and Crystal Palace is a stone’s throw. So the two key points for the dipole, if I’ve understood your advice: 1) instal a balun (there isn’t one - the cable connects directly to the dipole); 2) move the aerial away from the wall and if possible a bit higher. I can keep the MD for a bit so have a serviceable solution while I ham away with the dipole.

Re balun: any recommendation (there seems to be a thriving cottage industry) and can it be installed anywhere on the cable run or is closest to aerial source best? I’d have thought the latter.

Re placement: I could instal a mast 20-30” away from the wall. It’s at the end of the back garden and won’t be particularly visible from the house. Let me try that and if I still can’t solve it, local expert it is!

Thanks again gents. PF 

And thank you David. We crossed. Agree, I’m sure about the potential results, hence I’m persevering. 

The big advantage of a multi-element aerial, which means 3 elements at band II (or 4 but you won't need 4 being that close to Wrotham) is that it reduces multipath and so the wanted signal becomes much larger than the various reflections. This alone makes for a much simpler job for the tuner and will likely give a much cleaner sounding audio signal than you are likely to get with a dipole, however carefully you site it. Anyway enjoy!

best

David

Hi PF, both your option 1 and 2 are the right ones...as far as BalUns themselves, if you don’t really know what is going on or how to measure their effectivess, best ask your competent radio antenna installer to fit or loop the coax just prior to the antenna, whilst they are repositioning in a clearer and higher position. Looping three to five turns of the coax through three to five ferrite chokes placed together or looping the coax three times in an approx 28” diameter loop could work right by the antenna feed point of you have nothing else..if the dipole is vertical, ensure the coax BalUn loop is horizontal to minimise coupling..

David Hendon posted:

The big advantage of a multi-element aerial, which means 3 elements at band II (or 4 but you won't need 4 being that close to Wrotham) is that it reduces multipath and so the wanted signal becomes much larger than the various reflections. This alone makes for a much simpler job for the tuner and will likely give a much cleaner sounding audio signal than you are likely to get with a dipole, however carefully you site it. Anyway enjoy!

best

David

But being in a location such as PF is, the best thing about a dipole is that you will have the greatest diversity of radio stations (and some of the new low power community radio stations are offering some great live music)... if the main station you listen to is relatively strong, then the AGC of your tuner will adjust and reduce the effect of multipath signals by reducing the overal level of those signals just like a Yagi would do, so the dipole will effectively enable the signal to be cleanly demodulated. Now if there are stations interfering with each other , and you are sort of between them, then yes I would recommend a Yagi in that situation even if you are in a strong signal strength location.

The OP's problem Simon is that he can't get an acceptable R3 signal. See his original post.

best

David