Strange Aerial

[mike gilbert]

I've just purchased a 1968 model year 1800S. A real old survivor its never been painted or welded and its looking a bit careworn now. Will be a lovely car in time with some TLC. Anyway it came with the original guarantee and handbook for the radio (from Southern Car Radio's Ltd) dated 7th August '68, so this aerial must the one from that date - has anyone seen one like this that runs under the floor? I never have.

[Laird Scooby]

Originally Posted by mike gilbert

I've just purchased a 1968 model year 1800S. A real old survivor its never been painted or welded and its looking a bit careworn now. Will be a lovely car in time with some TLC. Anyway it came with the original guarantee and handbook for the radio (from Southern Car Radio's Ltd) dated 7th August '68, so this aerial must the one from that date - has anyone seen one like this that runs under the floor? I never have.

That looks to me like they didn't want to remove the interior to run the aerial cable!

Never ever seen one like that and there's absolutely no technical reason for it either!

For the most part, you'd want to keep the cabling inside the car to minimise damp ingress which would alter the impedance of the cable and hence the performance of the aerial.

[mike gilbert]

Originally Posted by Laird Scooby

That looks to me like they didn't want to remove the interior to run the aerial cable!

Never ever seen one like that and there's absolutely no technical reason for it either!

For the most part, you'd want to keep the cabling inside the car to minimise damp ingress which would alter the impedance of the cable and hence the performance of the aerial.

The radio was fitted when the car was a few months old, so I suspect the idea behind it is that there was no requirement to make a hole in one of the outer body panels.

[Army]

Does the radio work?

[mike gilbert]

Originally Posted by Army

Does the radio work?

Yes works on medium wave. Nothing on long wave. I just wondered if anyone had seen this set up before. When I looked under the car it took me a minute or two to work out what it was. It's not a thing of beauty.

[Army]

Originally Posted by mike gilbert

Yes works on medium wave. Nothing on long wave. I just wondered if anyone had seen this set up before. When I looked under the car it took me a minute or two to work out what it was. It's not a thing of beauty.

I'm impressed it works as a system.

I haven't seen one like that before - only the poor distant cousin which used to be stuck on the rear window much like a retro-fitted heated rear windscreen thing that would turn yellow in the sun and eventually fall off...

[Derek UK]

Hello Mike. This is a left over from when they used to fit them under the running boards back in the 30's and 40's. Domestic radio transmission was transmitted horizontally polarised and this also sufficed for early home FM as the aerial had to be horizontal too. Split bell wire dipole behind the curtain rail anyone? In the UK the BBC moved to 'mixed polarisation' in the 70s. Apparently FM transmissions had been horizontal until then as most home listeners stretched out a horizontal wire. With the emergence of car radios capable of FM reception and the use of vertical car aerials, the decision was made to transmit both horizontal and vertical polarised signals (not strictly circular, but close enough).

[Laird Scooby]

Originally Posted by Derek UK

Hello Mike. This is a left over from when they used to fit them under the running boards back in the 30's and 40's. Domestic radio transmission was transmitted horizontally polarised and this also sufficed for early home FM as the aerial had to be horizontal too. Split bell wire dipole behind the curtain rail anyone? In the UK the BBC moved to 'mixed polarisation' in the 70s. Apparently FM transmissions had been horizontal until then as most home listeners stretched out a horizontal wire. With the emergence of car radios capable of FM reception and the use of vertical car aerials, the decision was made to transmit both horizontal and vertical polarised signals (not strictly circular, but close enough).

Interesting stuff there Derek - i was under the impression vertical polarisation for radio at least came earlier than the 70s due to the popularity of the transistor radio that often had a telescopic aerial on the top. Purely from a practical basis this worked best when vertical.

The other thing is the horizontal aerial under the car would be extremely directional and hindered somewhat by other cars, buildings and by the car itself.

[Derek UK]

Better quality transistor radios often had an aerial with a flexi joint at the base when pulled right out. This could be useful to swivel the mast to pick up the best signal. I've still got Grundig and Tandberg ones that do that. I think stereo broadcasts made the Beeb and others pay much more attention to polarisation due to the received signal having to be higher to get a good signal to noise ratio. Mono FM is more tolerant of signal level.

[Ron Kwas]

Forum;

Good info about antenna polarization, but I do need to point out that the gains from having the receiving antenna polarization same as the transmitting antenna polarization only yields big benefits when path is direct ("line of sight")...once reflections come into play, like for instance at night when MW goes long-range an bounces off the ionosphere, the polarization gets mixed and matched, and complex, so most advantage at the receiver is lost. Also, when FM came into popular use, polarization became a lot less important, because the wavelength is 1/100th as long, the Tx power is a lot less, and multipath with accompanying multi-polarization is absolutely typical...
The bottom line on an antenna under the car is...no holes in the (upper) bodywork, and IF the location of car with respect to transmitter is such that signal is strong enough with that antenna location that the radio works satisfactorily...great! Obviously, that is not an optimum location but in European countries, you are probably a lot closer to the transmitting stations than in this expansive country...the only less optimum location for an antenna I can think of would be underground...!



Cheers de KA1-RBP!