Active Car Radio Aerials

[barry wilkins]

Does any body have circuits on the amplifiers used in these car radio aerials.
The unit in my Citreon is low gain,think water got into it.
I have removed it and dried it out,but it did not make it work any better.
Now the better weather is on its way . I intend to remove it and look at it again.
Its a pig to remove bceuase of the roof lining ,so I want to fix it this time.

Barry

[stj]

Re: Active Car Radio Aerials

very unlikely,
but you finf some car stuff at radiolocman
https://www.radiolocman.com/

[CapLeaker]

Re: Active Car Radio Aerials

Are you sure it is the antennas fault and not the radio itself? What type of antenna are you talking about?

[stj]

Re: Active Car Radio Aerials

maybe it's not getting power.
french cars have a habit of letting water into places they shouldnt.

[barry wilkins]

Re: Active Car Radio Aerials

Checked the radio out of the car ,sure it ok
Bought an inline amplfier ,had to make a biased tee to get the 12 volts from the radio lead.
But its not that good.
One of the problems the freq. keeps changing as you drive .Dont think the transmiiters are very good where I live.

Barry

[stj]

Re: Active Car Radio Aerials

you dont use a T, the radio has an output for the antenna that powers down in standby or if you play a tape or cd.

you can turn off the auto-tune thing, i cant remember what it's called but Pioneer invented that.

[eccerr0r]

Re: Active Car Radio Aerials

Broadcast Transmitters in developed countries should be under strict laws to be transmitting on fixed frequencies with parts per million accuracy. So they should not be changing, unless you mean they're fading due to distance from the transmitting tower and you need to choose a different station, or you mean a low power personal transmitter (which are annoying when they drift, and really should buy a PLL transmitter that won't drift!)

Power injection is fairly common practice to reduce wiring needed to enable inline amplifiers, so that shouldn't be an issue...

[stj]

Re: Active Car Radio Aerials

car radio's dont use power injection,
the tuning thing is a function, if the signal gets weak the radio will scan for the next frequency that transmits RDS traffic data.

[barry wilkins]

Re: Active Car Radio Aerials

The cable to the radio is just 50ohm coax .
Same as sattelite ,DC voltage on the inner wire to the amp.
RF goes back to the radio.
So you use a biased tee filter to power the amp.

When the weather improves going to remove the aerial again {it aint easy to remove}
Found an intersting circuit that use an IC MAX circuit .
So might try that.

Barry

[CapLeaker]

Re: Active Car Radio Aerials

What are we talking here? FM? Frequencies only change if you are out of the transmitter range. An FM station surely does not “wander” around, they are rock solid in that aspect. However if the transmitter isn’t properly tuned it can “grow grass” on both sides of the main signal, making it dirty and prevents you from listening to other stations. Also signals can mix and could produce a weaker copy of the main signal somewhere else. However these things are regulated by the government. Chances of that happening is extremely low.

[stj]

Re: Active Car Radio Aerials

so in the u.k. you have 2 classes of FM station,
private and BBC.

private stations are usually single-site and use modern transmitters.

BBC often use mutiple frequencies from different locations and use old valve crap that has massive overspill and echo on nearby frequencies!!!
for some reason they are exempt from the regulations that prevent such crap from comercial transmitters.

the BBC really piss me off, they have very few listeners anymore, but they manage to consume atleast 25% of the available frequency space with their wideband ww2 era crap.
they dont give a fuck because they are tax-funded - even if they had zero listeners they would still keep runing to pretect their worthless jobs!

[redwire]

Re: Active Car Radio Aerials

Rare to see phantom power with a bias-tee for cars. Looked at Citroen antennas and there is a FAKRA RF connector and another lead for power, some models have more wires. There is also a dedicated RF amp module, no idea where it's located but not in the antenna or radio.

P.S> Whatever happened to AFC? FM didn't work so good without it, everything drifted.

[eccerr0r]

Re: Active Car Radio Aerials

AFC not needed with PLLs, as long as you got a good stable crystal...which usually is more than stable enough for receiver use. Transmitters, would be nice to have a TCXO.

It's those ancient radios with LC oscillators that drift badly... there I see a couple FM receivers with AFC. I have this one tube FM receiver that drifts, at least when AFC is off. When turned on...well I didn't test it much.

I also have a crappy FM transmitter that likewise also uses a LC oscillator and it drifts badly, usually off by 200-300 KHz after warming up. The PLL FM transmitters are much better, not perfect but good enough.

[barry wilkins]

Re: Active Car Radio Aerials








Hi some pictures
The active aerial from the Citreon ,only has a 50 ohm cable.
the amplifier inside the aerial
and the in line amplifier I bought on line.
I had to make a filter to power this up.
The intention is to fit this amplfier inside the aerial unit
I have seen an aerial that looks exactelty the same with two leads on line
It would mean running a cable from the radio to power it up.

Barry

[redwire]

Re: Active Car Radio Aerials

The factory antenna amp looks better than the one you bought IMHO.
The OEM has spark gaps, transient protection, 4 transistors and a bunch of inductors.
The new board has none of that, and only 2 transistors. So you might want to evaluate it before fitting it in there. I can't see it performing that great.
It looks like Citreon is using a tiny antenna and trying to make up for that with the preamp?