The high-Z coaxial cable is more for the AM portion of the radio. On AM
frequencies, especially the European version, the "stinger" antenna is
nothing but a capacitive probe. Consequently, it presents an extremely
high impedance. The loss in the 93-ohm line is considerably less at the AM
broadcast frequencies than a standard 50-ohm cable would offer. However
at FM broadcast frequencies, the external "stinger" antenna is a reasonable
portion of a wavelength, although still a bit short. Therefore, it offers
something more manageable considering losses. If you're just doing FM
alignment, 88 to 108 MHz, a 50-ohm source/load is appropriate. Some older
units may have a 300-ohm balanced input. In that case you need a
transformer/balun to convert from 300-ohms balanced input to an unbalanced
50-ohm load.
That's the purest approach and theoretically correct. HOWEVER, if its
300-ohmsbalanced input, just take a visit to Home Depot, Lowe's or any
big-box distributor and buy a cheap 300-ohm to 75-ohm converter and use
your 50-ohm equipment.
Dave - W?LEV
On Mon, Apr 7, 2025 at 2:43?PM AArnaud via groups.io <a.cabiyaud=
[email protected]> wrote:
Hey everyone,
True beginner in RF here for a classic alignment question. Sorry if this
is inappropriate or the wrong group, I'm not sure where to ask such
question. I suppose the NanoVNA would be a great tool to solve the question
and you guys seem to know a thing or two about RF.
I'm working on FM alignment for Citro?ns car radios from the late 80s and
early 90s. For this I would suppose matching the alignment to the OE
antenna and cable are ideal for best tuner performance and sensitivity.
Therefor I also suppose it would mean making something such as a dummy
antenna/aerial or a network so that the RF generator looks exactly like the
antenna does to the radio, right?
I have the cable, base and antenna of the car taken out. I also have
access to a bunch of cars if averaging is necessary.
My particular generator is 50ohm. I have no clue what the OE antenna and
cable impedance are, as nothing is printed on them. Reading online it seems
most automotive radio cable are 93 or 100ohms?
For the extra information: there are two models I would like to align, a
Blaupunkt which would have a 150ohm impedance, but the other which is a
Clarion does not give any information regarding its impedance... it just
says to plug the generator into the radio and voila.
Thanks for looking into my question.
--
*Dave - W?LEV*
--
Dave - W?LEV
