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Radio Aerial Issue

PostPosted: Tue May 21, 2019 20:48
by Ian Linden
I've put this in Chit-Chat, because the car in question is a Suzuki Ignis (2005, not the current model).

The original radio/CD player died the death, so I've fitted a new Sony radio/media player. No problem until I connected the aerial and attempted to tune stations - I could only get hissing and one very weak station.

After a lot of head-scratching, I disconnected the car aerial, and plugged a meter probe into the center terminal of the aerial lead extension (still plugged into the radio), to act as an impromptu antenna. Suddenly, everything worked. More head-scratching, and I found I could get it to work from the car aerial if I disconnected the screen conductor at the end of the adapter. Reconnecting it produced the original symptoms. With the screen disconnected, there is no interference from the car's engine, so apparently no downside.

I then insulated the screen from the adapter plug, and I'm happy enough with the outcome, but I cannot understand what the problem was, and why breaking the screen continuity solved it.

Any ideas, please?

Re: Radio Aerial Issue

PostPosted: Tue Jun 04, 2019 06:53
by Greg Ford
Ian, perhaps the co-ax antenna cable is shorted somewhere along it's length. Breaking the screen continuity then allows the inner core of the co-ax to carry the signal to the radio rather than routing the signal to earth via the screen. The outer braid of the co-ax is mainly for shielding from electrical noise, but if the car's electrical system is relatively 'electrically quiet' then you wont get more 'noise' than signal which is probably the reason it works with the screen disconnected.

Re: Radio Aerial Issue

PostPosted: Wed Jun 05, 2019 08:27
by Ian Linden
Thanks, Greg. Logical thinking, but I did try detecting a short between screen and centre conductor, and it was infinity, admittedly at dc. There may be some form of ac short e.g. capacitance.

Elsewhere, its been suggested that the aerial may have an amplifier supplied with phantom power from the original radio down the co-ax. I found an adapter which provides phantom power to the antenna, for European cars (VAG, etc) with aftermarket radios, so, thinking that the Ignis was built in Hungary, it might solve the issue.

Unfortunately, no luck - poor signal without the phantom power, and worse with it! (this was without using my modified adapter with the screen disconnected). I'm guessing that the original radio did supply phantom power, but not +12V.

I think the only solution would be a replacement aerial.