FM car aerial tech /hidden

[steveo3002]

doing some bodywork and decide to fill in the aerial hole on my car , old 80s car with the chrome mast

any ideas on the workings of these? i was hoping to extend it and shove under the dash or wiper tray area , does it matter if the chrome mast touches earth ? guesiing the base wasnt earthed as it was bolted on through paint

or any proven ideas on a hidden FM aerial , yes ive seen ebay has some but google suggests theyre poop

 

[dobbslc]

@ajlelectronics might have some info.
I'd say put it back in as I've had loads of trouble messing around with car aerials in the past. I ended up buying a brand new genuine Toyota electric aeria £££l for my Surf after lots of wasted time and money trying to get a generic one to work.

 

[ajlelectronics]

doing some bodywork and decide to fill in the aerial hole on my car , old 80s car with the chrome mast

any ideas on the workings of these? i was hoping to extend it and shove under the dash or wiper tray area , does it matter if the chrome mast touches earth ? guesiing the base wasnt earthed as it was bolted on through paint

or any proven ideas on a hidden FM aerial , yes ive seen ebay has some but google suggests theyre poop

Ye cannae change the laws of physics Cap'n.

It needs to be in a metal panel, as high as possible and away from the ignition system as far as practicable. Anything else you do will render it merely ornamental. Happy to make your eyes glaze over with chapter and verse, should you be interested in the science.

To sum up, the aerial was installed where it is for good reason.

 

[steveo3002]

hole is welded up its not going back , appears to work waving it about by hand

how do fibre glass cars go about the mounting , im not convinced it was earthed by the mount , the wings paint was intact and thick sealer underneath , it wasnt making much earth through that , i can easily add a wire if needed , what about the mast? sleeve it or no?

 

[ajlelectronics]

hole is welded up its not going back , appears to work waving it about by hand

how do fibre glass cars go about the mounting , im not convinced it was earthed by the mount , the wings paint was intact and thick sealer underneath , it wasnt making much earth through that , i can easily add a wire if needed , what about the mast? sleeve it or no?

Fibreglass vehicles have a ground plane added to the mounting point. Not having a ground plane reduces its efficiency and leaves reception prone to picking up interference from the car. It is difficult to visualise, but the part that you can hold in your hand is only half of the aerial. The other half is (electrically) in the ground plane. Wire is no good, the word 'plane' gives it away and should be just over a quarter wave in all directions. That having been said, receiving aerials are not as demanding as transmitting aerials, so impedance matches etc don't need to be worried about unless wanting the very last drop of gain from it. Make a good solid connection into the metalwork.

If you screen the mast by hiding it in metal bodywork, it will do nothing useful. It needs to be in free air where it can get line of sight. Earthing the mast just shorts it out of course.

Bodge solutions (which are better than nothing but still rubbish) include using the rear screen heater as an aerial, or those silly shark fin types on the roof. I appreciate your intentions but I refer you to my first sentence.

 

[Nomad]

A powered stick on one at the top of the front screen worked well for me (same era as your car - expect poor results with modern cars that have wires in the glass for heaters etc), the ariel wire and 12 volt feed connected up at the rear view mirror area, running the wires from there down to A post took some thinking about.
Add a green or smoke tinted strip at the top of the screen for added retro cool points and to hide the ariel, it's not very noticable but you can see it if you look.

The shark fin ones are on my to-do list at some point to see what they're like (it was a common choice for a lot of cars & different manufacturers for many years - they must work "ok" or better)

One of the best I had a was a 7ft fibreglass whip ariel fitted to a 60s Ford, not seen any around for a long time so guess they're out of fashion or illegal on the grounds of something or other

Others may have different opinions, it's all good

 

[sako243]

Contradicting @ajlelectronics slightly but what he is describing is the perfect solution and more of a requirement for vintage era radios. Modern head units have vastly more signal processing and devices such as LNAs (Low Noise Amplifiers) which were not available back in the day. If you wanted to keep a period correct radio I'm sure you could find an inline device that cleans up the signal for you.

To put modern signal processing in perspective I had a project recently working down in the HF territory (we were in the 1.8 to 30MHz). Transmit antenna was a decent match but the receive aerial which would have ideally been 80m long was about 2ft and inside an almost fully enclosed room with foil back cellotex. Didn't have any significant problems seeing things. Yes making the aerial bigger and locating it outside would have improved things but the point was it worked well enough because the signal processing was able to compensate for it.

As an aside I did some signal processing about 15 years ago where we had some quiet audio and then various noises were mixed in - such as a fighter jet taking off in the background drowning out the audio. Yet relatively simply we could use some signal processing to in realtime (<2ms delay in this instance) cancel out the different noise sources with no prior knowledge of the form the noise was taking.

I'd just shove the aerial where you want and try and keep it from running in parallel or touching grounded surfaces.

 

[steveo3002]

yeah i will have to suck it and see i think , i cant be the first to have welded an aerial hole lol

 

[Islander71]

The stick on ones at the inside top of the windscreen with 12v feed do work, i have one on my '91 Transit campervan.

 

[steveo3002]

The stick on ones at the inside top of the windscreen with 12v feed do work, i have one on my '91 Transit campervan.

name brand or a ebay cheapie?

 

[ajlelectronics]

If you take a poor aerial which gives weak, noisy signals and then amplify it; you get lots more weak, noisy signal plus the noise of the amplifier. There is no substitute for effective aperture.