Poor Aerial performance ?

jp928

Well-Known Member
If I am in my local area (15km from CBD) the radio works fine on FM. if i pull the plug out of the unit, no sound. If I go another 10-15kms out of town the fm signal starts to break up. The aerial is on the roof, and is extended, lying flat. Have not tried with AM yet, next trial. The lead seems to be OK, coming down the A pillar. Is it worth exploting the connection to the actual external aerial, or...?
thanks
 
I've no idea if the angle of the aerial improves reception, but I know they simply look wrong lying flat on the roof! I have to resist the temptation to touch other peoples cars whenever I see a limp aerial atop a P6 at a meet!
 
The roof acts as the ground plane for the aerial, so yes the angle is important. The more vertical it is the better.

But how much better is a real question.

Yours
Vern
 
OK, seems I need to try with the aerial more upright. Next outing....will raise it once out of the garage, cost it wouldnt clear the entrance if higher than 45d.
 
They do extend like the old school ones. I extend mine for country driving and reduce it when I'm home, so it doesn't hit he garage door. best to park the car in nose first so if it does hit it'll bounce off...
 
I believe In the UK most FM is slant polarizes , having the aerial at about 45 degrees is the best position for optimum reception. The screening braid in the aerial lead needs to be grounded both ends , ie to the radio via its plug and the roof at the aerial end . The centre feeder wire must not touch the braid. May be worth checking its not corroded at the roof end, accessible by taking off the mirror , sun visors, then the small forward trim panel
 
Here is what I find. I suspect that the external aerial metal should NOT contact the roof metal, and that the toothed washer teeth SHOULD have good contact with the roof? hole does not look like factory? Needs enlarging a tad? Only 2 screws holding the mirror mount, I think cos it was upside down. The underside of the rubber between the aerial and the roof is marked as though the toothed washer was previously pressed into it. Dont see any point in having the teeth on the washer/spacer contact the roof, as there is nothing to contact it to earth to..?
zmeQcb0.jpg

w9RP4Wc.jpg

thanks.
 
Last edited:
Think its fixed, but time will tell. Enlarged the roof hole to suit the ridge in the external side rubber. none of this easy single handed. Where before I could not get any AM stations now they tune fine. Sadly the refitting has not gone well -my local octopus was not available so getting the piece of headlining in place was a real PITA! Same for getting the mirror mount back in place - multiple hands needed, lots of swearing involved. Having done driver's side visor, taking a break before doing the other side.

Now I know why the pass side visor keeps coming out of the holder/socket in center - the mounting holes are compromised, and its at an angle that wants to leave the center holder. I am NOT going to pull the whole lot down to investigate!
 
Last edited:
My driver's side visor had that problem, screw holes worn out or twisted. I tried thicker screws but they stuck out and looked aweful. Eventual solution was to cut a small piece of sheet and slide it up under the panel. I then pop riveted it in place and drilled new holes in it. Finally I worked the pin out of the visor then greased and replaced it so it came down without twisting the mount. Eventually had it all back together and working properly. All that did require at least two hands and some small/long vise grips to hold the plate in place prior to riveting. Allow a whole day and a case of beer.
 
"Allow a whole day and a case of beer. " Sounds about right, sadly. will have to put up with it as it is for a while, until I get used to the idea.
 
hmmm interesting about lack of reception. I (had) only 70's Motorola radio in but could only get 2 stations (am no fm) no LW . it works now and again. checked Ariel connections at radio /leads = good. not thought about checking roof aerial . currently trying out a more modern radio I was given but nothing at all on that! so might put of radio back ( at least it worked now and again) had radio apart but no visual issues such as debris/corrosion/loose/broken wires etc does get a buzzing sound though so suspect picking up signal from somewhere on a circuit. ( or possible radio itself generating it) will try and have another go during week at sorting it and might even be brave enough to check out roof connections. many thanks posting pics. Update: fitted more modern (80's) radio and it works very well indeed. thus showing to me old radio on AM wasn't up to the job. New uses FM and is superb. ideally I would like old radio updated at some stage for FM and re-fit.
 
Last edited:
My pic of the hole wasnt very clear, but its edges were ragged, not cleanly drilled, and it was much too close a fit on the metal of the aerial base. The ragged edges made it hard to get a drill to spin, in fact I cut some metal with the drill bit stalled, and twisting the whole drill&bit by hand. Once the hole was round it was easier to enlarge. Re-engaging the inside bolt with the aerial base can be a 2 person job - I jammed the inside bolt in place through the hole with a piece of rag, dismantled the aerial base off the aerial and then I was able to start the base screwing onto the bolt. Getting the interior trim back in place is a real PITA single handed.
 
Probably too late now, but here is a copy of what I posted in the Factory Antenna thread in December. I believe that the headlining support panel is integral to proper earthing of the antenna.

"Having dislodged my antenna solid mount by adjusting it too forcefully a few weeks back I went through the process of removing the mirror, sun visors, "A" column finishers and screws at each end of the front headlining section, which was simple enough.After re-securing the antenna the radio reception was rubbish, so removed the radio and antenna connection at the back to check it and almost concluded that the cable was fractured, so left it to heal for a couple of weeks.
We had an electrician doing some work in our home so I asked his opinion. Reception was ok when one of us was holding the cable and earthing it.
He thought that perhaps the jagged washer was not earthing to the roof properly because (after 51 years) the paint was too thick so I sanded that back. Partly fixed the problem but reception varied.So sprayed WD40 on and sanded the antenna rods, to not much avail.
Then when cleaning the visors and headlining section I noticed a dent/impression in the mild steel headliner support panel where the screw section of the solid mount had been resting so sanded that and as they say in various aftermarket service manuals "offered it up" to the antenna. Reception immediately improved and when everything was re-installed and all the screws tightened reception is again perfect.

Conclusion: The headliner support panel is an integral part of the earthing circuit.
Could have saved a lot of fiddling and thinking time and frustration if I'd realised that earlier, so hope some-one else can benefit from this experience."
 
Mike,
Curious, all this talk of earthing. The round body of my cable (where it attaches to the aerial) has recessed copper faces (just visible in pic2) on both sides, one of which is in contact with the bolt that attaches it to the aerial . The cup washer with teeth sits on the rubber body of the cable end, but has no contact with any metal part of the cable end- I cannot see anything that can be earthed up there. My problem seems to have been that the hole in the roof panel too small (and jagged)and was shorting the aerial to earth. Enlarging the hole so there was no metal to metal contact seems to have fixed the issue I had. The outer of the plug into the radio seems to be earthing the cable shielding.
 
The jagged cup washer should be connected to the braid . Its all crimped and moulded together. One could check with a meter, set at resistance range. Should be a connection between the jagged washer and the outer part of the plug into the radio and no connection between the centre pin and the washer or jagged cup. . On my P6 aerial the plastic top hat portion insulating the aerial bolt to the body had disintegrated allowing a short. Turned up a new one on my lathe from Delrin and now has good reception.
 
There is no braid visible at the aerial connection end at the roof to connect to the jagged washer, the whole connector is rubber except for the recessed copper that contacts the aerial base. The side of the connector under the jagged washer is the same as the visible side - rubber with a recessed copper disc.
 
my feeling (only) is that having the head of the through bolt in clean contact with (earthing through) the metal header support panel fixed the issues I was having.
 
Back
Top