Q From Haynes, Hi Line diversity question

[Departed]

Originally Posted by David3807

|Suppose all the heated elements are working ??

I posted sometime ago with exactly same problem and have never got around to looking behind the trim for things and checking earths etc as suggested. However I do have a small break in one element and cleaning the whole rear window inside with a decent glass cleaner improves the radio reception no end.

A small almost break will cause major problems. It may be high enough resistance to stop the element working but the little bit of current can cause enough electrical noise to give major interference. The dirt would increase this I guess. It's a similar thing to the noise that cheap resistors can cause in audio circuits. Fix it with a dab of silver paint (real silver, not just silver coloured) before you spend too much time digging.

I've even seen it cause enough noise to cause interference on a normal antenna not on the screen (that was a 400).

[Reebs]

So to summerize my particular situation, as it was me that got the ball rolling at Haynes last week......

Doing some digging in Rave, it transpires that on 10th December 2001, ALL 75/ZT models were standardised with a Project Denied (Drive) cost cutting measure whereby from cars with SN: 240702 onwards the Diversity aerial amplifier part no: XUC100751 was deleted, and replaced with the Non Diversity unit part no: XUC100741.

Also the HRW screen was changed from part no: CQB000220(full coax) to CQB000350(single coax)

So Symphony / High-Line cars went from this:





to this:





This is all fine and dandy, but my car is a Hi-line car and still has the boot mounted DIVERSITY radio tuner part no: XQC100440 which as I understand it sends out an IF signal to the aerial amplifier to tell it to switch to an alternative element if the signal drops below an acceptable level.



Well as you can see from the picture there is a distinct lack of connection from the diversity pin to the amp in the D post (which isn't diversity and isn't able to do anything with the signal even if it got one, not to mention the lack of extra antenna cables missing from the HRW glass)

Maybe all of this is academic and there is no noticeable difference in operation but for me, ever since I collected the car the radio reception has been a real issue.

When on, the FM signal varies from being very strong and noise (hiss) free to being swamped by a high pitched buzzing whine which sounds like the cross between a hair dryer and a demented mosquito flying close to your ear.

This constantly varies as the car moves, and often will cause the tuner to start searching for alternative stations.

My wifes Beetle can easily tune to radio stations that my tuner simply doesn't find when both are parked on our driveway.

Also, the loss of signal strength causes the TMC signal to drop out on the Sat Nav, where on a recent test coming back from Haynes, "SD1Too"s car's TMC signal remained good.

Now it may be (I hear you all say) just what "Lowedb" suggested, namely my rear glass that is at fault - a poor element with a break in it, or the wire coming from the glass being faulty, but I had my local dealer REPLACE the entire HRW under warranty before MG Rover sunk, they demanded that as a warrantable claim my car had to have the same HRW glass type fitted namely CQB000350 (single coax) non diversity, and guess what? it made no difference.

I have also taken out the old NON diversity aerial amp and now replaced it with the larger diversity type in the hope that it is just a more powerful unit, but again no change.

The radio tuner in the boot was the next thing to try, so I swapped it over with the one in "SD1too"s 1999 Hi-line car, and my tuner worked perfectly in his, but his was just as poor in my car.

I live in Southampton, and in my old T reg Rover 75 which had High-Line, I was able to do a complete journey up to London listening to 2-Ten FM from Reading, all the way. My current car just about picks the signal up around halfway along the route, then looses it again, and that's just not good enough!!


My question really is, do all post project drive Symphony and High-Line cars suffer from equally poor reception and as such have MGR made a huge error through cost cutting, or is there some other reason for my bad radio.

I do know that later face-lift cars were fitted with a dual tuner unit in the boot part no: XQC000240 around 2004 onwards, but I don't know if this unit has a diversity connector on it or not.

Please could someone check and post back, as I am faced with two options:

1) purchase another HRW (full diversity this time),and an IF wire to go to the boot

2) purchase the newer dual tuner if it is non diversity.

Keith has told me that BMW tuner unit BM54 Back will work as its non diversity, but as yet I can't find one, and would rather stick with MG Rover genuine parts.

[Departed]

I have a non diversity car. It's a late Cowley car but I've retrofitted a Symphony, and reception isn't a major problem, even though I've got some major HRW problems (someone has 'cleaned' a few of the elements off). It's pretty much on a par with our other cars which have a variety of aerials.

Diversity is only really a help in areas where there is multipath interference. This sounds technical but isn't. Please forgive me if this is too detailed but some people seem interested.

If you are in an area where there are buildings or anything that will reflect the radio signal, the signal gets to you two ways: directly from the transmitter, and via a reflection. (OK this is a bit of an over simplification because there are always lots of paths). It's a similar thing to ghosting on analogue TV (I nearly put 'old' analogue TV)

Now depending on the extra distance the reflected signal has to travel, it can either add to the main signal or cancel it out. This leads to peaks and troughs in the signal. The distance between these peaks and troughs depends on the wavelength, and at FM is quite small, small enough so that if one antenna on a car is in a trough, another stands a good chance of not being. Diversity switches to the antenna that isn't in the trough, so you don't get a fluttering noise as your'e antenna dips in and out of the troughs while you drive.

This is also why it's done on FM and not AM. AM is broadcast on a lower frequency which means the wavelength is much longer (100s of metres rather than metres) so diversity wouldn't help.

Back to the point, if you have just a plain weak signal diversity doesn't help, it only helps in particular areas with lots of refelctions such as the A45 just outside Birmingham airport where the lamposts cause really bad Multipath even on strong signals.

Hope this is of interest.

[colinjyates]

Hi,

just reading this thread with interest as I have just replaced the hi line radio XQC100440 for a BMW BM24 dual tuner.

I have an 04 ZTT and also the diversity pin was not connected up. I totally agree that the radio signal quality is unacceptable.

On another note, the CD player quality sound and sound from the radio (not reception) is now much better with the BM24. Anyone know why this is?

Regards

Colin

[Keith]

Reebs cracking photos I assume the second one is your car?

What is interesting is you have the chokes in the two earth leads I don't have these in my V8. For you it would make adding the full diversity set up a breeze if you look at the bottom two wires from the diversity amp they go to connectors which are hard wired to those black wires although you don't have the connector on the hrw you can easily piggy back off the black wires

The top two wires go to the same point on either type of Hrw

I reckon the reason TMC reception is improved with the full diversity is simple, one of the other elements is simply better than the one used for non diversity reception.

[John Robins]

I am begining to think that one of those black things at either end of the roof or a chrome one on the wing is a good idea !

[Keith]

Yes hence why I am looking for a glass coulpled one as I don't want to drill any holes. Lots available for Dab but none so far for AM/FM

[HarryM1BYT]

Originally Posted by lowedb

However, I've just spoken to our antenna Engineer, who had been told the same, but he did some digging, and it seems you are right that it's not as I (or he) believed. However he tells me that it's not the IF at a varying level either (he had a scope on it and there was no RF. He tells me that its a low level signal at close to DC. I can only assume it is a voltage corresponding to signal strength. Sorry if this is getting a bit deep.

That will be an amplified AGC output. Basically a radio tunes to a signal, the IF output of which is converted to a DC voltage which is then fed back to the RF stages to control the amount of gain - called AGC or automatic gain control. So the AGC voltage depends upon the received signal strength of the station it is tuned to. Tune to a weak station - the gain is turned up to improve the strength, tune to strong station and the gain is turned down. That AGC voltage is also fed into the diversity amp, which can then try either of the two antennas, to see which provides the stronger reception for the station you are tuned into.

On a rather more specialised radio set, the AGC voltage might also be fed to a meter, to give an indication of the signal strength of a received signal.

[denboy]

hi
i have a 2004 75 saloon cdti auto ,its great but the radio signal keep's on fadeing. is there anything that can be done to correct this .could you put a aerial on the car and disconnect the diversty aerial amplifier,would this help stop the radio fading.your's denboy

[HarryM1BYT]

Originally Posted by denboy

hi
i have a 2004 75 saloon cdti auto ,its great but the radio signal keep's on fadeing. is there anything that can be done to correct this .could you put a aerial on the car and disconnect the diversty aerial amplifier,would this help stop the radio fading.your's denboy

A 2004 is unlikely to have the diversity type antenna / amp system.

If you think a better antenna would help, try it, but most modern radios seem to expect the antenna to be fed to it via an external amp.