The Triumph Dolomite Club - Discussion Forum

Hi All...

I am trying to improve the radio reception on my 1500, it has a wing mounted one. I have tried 3 now and all have been amplified.

I ensure I have got a good earth... but all is well good reception with many stations available both on DAB and FM.. until I move off the drive.. within a few hundred yards reception is lost and then very erratic. I drive to work in the car over 20 miles away and it never improves.

My VW Touran and my partners VW Polo, albeit modern cars don't experience the same issues.. perfect reception wherever I go... so I am thinking the signal is good in my area

I can only think I need a better aerial... Radio is a Bush FM/DAB one.

Just wondered if anybody had any recommendations for a good aerial that might give me a better reception... as good as listening to the engine note is.. it would be nice to have some music on the way to work..

Doesn't sound like it is the aerial itself. You shouldn't need anything special - least not for normal FM, DAB is a bit different. Never had an amplified car aerial on any car., in fact quite a few just had a bit of wire coat hanger stuffed in the aerial hole when they got snapped off. Assuming there is not an issue with the radio itself - which is entirely possible if the front end of the receiver is "a bit weak" - I would look at either the earthing or possible interference/suppression issues. Have you tried substituting another known good radio?

You say you ensure you have a good earth. Is this at both ends, i.e. the aerial end and the radio itself? The aerial base needs a very good earth straight to the car body as this acts as a "ground plane" for the aerial, it is no good just earthing the outer of the coax aerial lead, what appears to be low resistance at DC can be very high impedance at RF (radio frequencies). The body of the radio should also ideally have a good solid earth as well as a decent 12V supply that doesn't go through an old corroded fuse holder.

Interference wise there are lots of things you can do - interference is not always audible as crackling but can affect the signal the radio gets from the aerial. You can get an inline choke on the positive power lead. In addition you can fit a suppressor (capacitor!) across the radio supply, on the ignition coil and also on the alternator output. You can also get suppressor (high resistance) sparkplug leads -though I am not a fan of those for other reasons.

Roger

I've DAB radios in both the Doly and the Herald. The Doly has a windscreen DAB aerial stuck to the left side of the windscreen, which I bought of eBay for about £5, as I remember. That works very well with both the JVC Kenwood KDC-BT720DAB and the Pioneer MVH-290DAB. Only problem is I've had to re-stick the ribbon cable down twice, and it's now covered by a long strip of leather effect sticky backed plastic (still looking for where to use the washing-up bottle for a true Blue Peter fix). I've hardly ever any dropouts on DAB with that. It also has a stick on powered FM antenna in the middle of the screen behind the mirror. Again, that works well in FM with either head unit. Surprising, as it's really quite small in comparison with a 1/4 wave dipole.

The Herald has the stick on DAB aerial that came with the Kenwood. With that aerial alone, it's not good, and signal is always week. Seems to work well on the drive, but go far and it drops in and out like a fiddler's elbow. The Pioneer seems to be slightly better reception wise than the Kenwood, but not by a lot. My solution was to get a T piece from CPC (not eBay, they're a small fortune there) and put a second, magnetic antenna on the boot lid. That's the classic solution for Rayleigh fading, which I think is much of the issue, and seems to be far enough separate to make enough difference (ideally wants to be a few wavelengths between antennas). The DAB on the Herald still fades occasionally, but it's mostly acceptable around Fylde and the Lancs coast.

The Herald did have an FM antenna on the right rear wing, but it fell off and I've not bothered to fix it. As I remember, it never worked well with FM, even after being replaced. I never tried one of those FM/DAB splitter amplifiers with it. I wouldn't expect good performance on the DAB. But then I didn't expect the small dipole on the Doly to work with FM.

Graham

Thank you both for the info... I will have another look at my installation over the weekend to make sure it is optimum...

It seems as if my problem all along was a GPS speedometer plugged into a USB replacement cigarette socket.

Now removed and reception much better and consistent... thanks again for the advice..

storeyn wrote: ↑Wed Jul 01, 2020 11:38 am It seems as if my problem all along was a GPS speedometer plugged into a USB replacement cigarette socket.

Now removed and reception much better and consistent... thanks again for the advice..

Interesting, because I had exactly that problem with the FM reception in the Herald while it still had an FM antenna. That was one of the reasons for going to DAB. But I don't remember if I tried disconnecting the GPS speedo with DAB on a single DAB windscreen stick-on. So I must see whether there's any improvement in DAB reception with it off as well.

I never got to working out what the incompatibility was, as I don't have access the equipment. I was assuming it was probably at the intermediate frequency level on the FM receiver, since it applied to a good range of stations, maybe from the processor clock in the GPS receiver. So I never thought about it affecting DAB reception in the same way - even if DAB receivers use a superhet like the FM, I never thought about it being the same intermediate frequency and susceptible to the same source of interference.

Graham

storeyn wrote: ↑Wed Jul 01, 2020 11:38 am It seems as if my problem all along was a GPS speedometer plugged into a USB replacement cigarette socket.

Now removed and reception much better and consistent... thanks again for the advice..

I very much suspect that it was not the GPS speedo itself but the USB power socket. This has to convert the nominal 12V car supply to a regulated 5V. Unfortunately a lot of them originate in China where they use a cheap, quick and very electrically dirty switch mode voltage converter design with little or no filtering. This has the potential to produce loads of interference across the radio spectrum which radiate not only directly from the circuit but also from any leads/cables connected to it - they effectively acts as transmitting aerials. Many years ago the E.U. introduced the EMC Directive (Electro Magnetic Compatibility) which ALL electrical and electronic devices were supposed to be comply with. It was designed to stop exactly this sort of thing. Trouble is some manufacturers just put a CE sticker on their product but don't bother testing, the Far East being the worst offenders - in many cases with product from China CE stands for China Export !!

Buying a higher quality USB socket and/or moving it further away from the radio and fitting some filtering to the cables may let the two live in harmony.

Roger

marshman wrote: ↑Wed Jul 01, 2020 1:34 pm

storeyn wrote: ↑Wed Jul 01, 2020 11:38 am It seems as if my problem all along was a GPS speedometer plugged into a USB replacement cigarette socket.

Now removed and reception much better and consistent... thanks again for the advice..

I very much suspect that it was not the GPS speedo itself but the USB power socket.
Roger

Wasn't a DC-DC converter in the USB adapter in the Herald affecting FM reception and maybe explaining why it has poorer DAB reception than the Doly when it has what should be a better (Kenwood vs something off ebay) stick-on antenna. That's because the Herald's GPS receiver is a 12v unit and hardwired off the ignition supply. It is about 15" directly over the radio head unit though and I don't think there's any metal in the way.

I would put my money on something like a clock in the GPS and bugger all shielding. But EMI/EMC is a true black art; especially, when you get to the level of TEMPEST testing.

Graham

I agree that EMC is real Dark Art stuff

I was really responding to storeyns comment that his was powered from a USB power socket. I have had exactly that issue of interference from a plug in USB power adaptor for a sat nav, totally obliterated the radio, it was a cheap eBay one I had in the car for phone charging, when I used the proper Tomtom one all was OK - even though the cheapo one was well within its rated output power. I would have thought the GPS unit should have been quite good, The GPS signals themselves are quite weak and GPS location usually requires at least four satellite signals, preferably more to work, not sure if a speedo needs the same level of accuracy, so one would think it would be electrically quiet, however it seems a little strange that you both had GPS speedos - one USB powered and yours direct 12V and they both caused issue with the radio.

Interesting discussion though, one to file away for the future!

I hate EMC, especially susceptibility, I have spent many a week around test chambers in the past trying to make units "bomb" proof in terms of surviving high field strengths and also static discharge - really difficult on price sensitive products, easier on military gear where money is no object by comparison. I have great admiration for those that really understand it!

Roger

Jut tried taking the power lead out of the GPS, where it plugs in the side, and went for a bit of a drive around. Can't see any change with the GPS on or off and, as said, there's no FM in the Herald. But that's with the two DAB antennas, one on the screen and one on the boot lid. So it still might have been a localized effect on the front antenna that the rear one is masking.

Question for storeyn: Are you sure your GPS speedo was powered off 5v from a USB port, e.g. out of an adapter, not 12v from a plug straight into the cig lighter socket - not sure what the "USB replacement cigarette socket" bit means?

Graham

I replaced the cigarette lighter with a two port usb socket with two 5v usb sockets in it..

I agree with Roger, it was one off eBay, so suspect it’s wasn’t complying the EMC regs... the interference appeared as soon as I plugged the gps speedo in to it, I checked after my last post and exactly the same happened when I plugged my phone it to it. So as soon as it started to draw any current it caused interference.

I never noticed when I originally tried the radio as there was nothing plugged into the socket... it was only when I plugged in and drove off I noticed.. I should have put two and two together sooner...

Radio has a usb socket too, so I tried the gps speedo in that one and made no difference to the signal.

I’ve removed the socket now to avoid any future issues....

Clearly a different problem from mine then, as my GPS speedo is 12v and only seems to affect FM not DAB. Like I said, EMI/EMC's a real black art.

So I suppose I should look elsewhere for why what should be a better screen antenna in the Herald gives a weaker DAB signal, and needs a second on the boot lid. It's especially odd, because the Herald's a convertible, and I'd expect to get more signal than the Doly in certain orientations without the roof acting as a partial shield. But maybe the cabin's acting as a waveguide - the 226Mhz of the BBC's ensemble would be above the cutoff of a waveguide that width, though it's a bad shape to analyse.

I won't look though, because the second antenna fixes the problem.

Graham

I realize this is off topic, though the original topic appears solved, but why are people fitting secondary GPS speedos? They are not legal as a primary, so it's not a replacement for the original (I spent a small fortune getting the electronic speedo and signal generator for the Dolomega to MAKE it legal)

So what's the point? Original speedo erratic/inaccurate? That's never bothered me, a quick ride out with the satnav to quantify the error and I remember it! Can't think of another reason! I have enough trouble keeping up with one speedo, let alone having 2 telling me different things!

Another thing, for an electronics philistine, whats the gig with DAB? In fact what IS DAB? It seems to be a load of expense and bother, for what exactly? Explanation at a 5 year old level please! I have to admit, I rarely listen to the radio, the Carledo doesn't even HAVE one, let alone a posh one. On shorter journeys I prefer the "straight through orchestra" anyway and on longer journeys the local nature of FM means regular retuning, a CD stacker or memory stick is easier (no adverts either)

But i've bought a very flashy unit for the Dolomega (though I don't THINK it's DAB) which does just about everything but change your nappies, its got touch screen, Sat-nav, bluetooth, a built in hard drive, wi-fi, reversing camera, hands free, voice activated phone, Video player and probably more that I haven't worked out yet. Pretty sure it does the traffic report update thingy that I can't remember the acronym for too. And THREE ariels! (Radio, GPS and Wi-fi) I'm a little disappointed that I can't seem to connect it to my Pioneer CD stacker, but it's got 3 USB sockets and an SD card holder so don't think i'll go short of tunes!The radio is probably the least of my worries, but i've selected a swanky chromey roof arial (as much for aesthetic reasons as anything else) I guess it will work OK with FM. Back in the old days when radio was a big thing, transistors replaced valves and FM was in it's infancy, a roof ariel was reckoned to be best because it was never in "shadow" from the roof. But they were stonkingly expensive due mainly to high fitting cost of removing part of the headlining and routing the co-ax. Nowadays they are making a comeback, but as OE only and mainly as "bee-sting" or "sharkfin" which to me look out of character. It took me ages to find my old fashioned looking one, wasn't cheap either at almost £30 with carriage! But allegedly UK made, and to my mind, it looks the mutts nuts!

Steve

I did have somewhere a radio aerial adapter that uses the rear window demister
Off a Ford Granada MK2 although I think fords around the same year used them.

Was originally going to fit on my Sprint.
Sure I still have it somewhere
So will be on the build list.

Carledo wrote: ↑Thu Jul 02, 2020 10:09 am I realize this is off topic, though the original topic appears solved, but why are people fitting secondary GPS speedos? They are not legal as a primary, so it's not a replacement for the original (I spent a small fortune getting the electronic speedo and signal generator for the Dolomega to MAKE it legal)

So what's the point? Original speedo erratic/inaccurate? That's never bothered me, a quick ride out with the satnav to quantify the error and I remember it! Can't think of another reason! I have enough trouble keeping up with one speedo, let alone having 2 telling me different things!

Steve

In the case with the Herald, the magneto-mechanical one was badly off, I didn't have (still don't) have a satnav for it, and fixing it looked a problem as the Herald is a right mishmash with various Spitfire Marks in the transmission - overdrive, etc. So I didn't want to just buy a replacement Herald one if it was the diff ratio or speedo drive off the box that was at fault.

It did turn out that it was just the speedo head that was in error, as I got a spare with some other stuff, and when I swapped it, it worked fine. However, me and the missus have got used to the head up display from the GPS one. It's also covering the unsightly mess on the dash where the stickum pad it came with has melted. So, at least while it works, it's staying.

Graham