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Sirio CB/AM/FM/CELL(900) Fuba Style Antenna



You have it all wrong about antenna calculation. Cable lenght is not part of
the calculation. Coaxial cable will have, say a 50 ohms impedance. It is a
constant impedance, and it matches the impedance of the outputs of the
finals, which are mostly transistors nowadays.

Antenna impedance is based on it's design. Simple designs are 1/4 wavelenght
antenna with ground plane (gain is said to be 0dB - this is the reference
other antennas are based upon). Then you have half wavelenght dipoles,
folded dipoles, 5/8, yagis, etc...

If you want to match a shorter whip (antenna) for a lower frequency
operating band, you have to tune it. Usually this is done with a L-C
network. Which is basically adding a coil or a cap in line with the 50 ohms
coaxial cable to match the impedance of the antenna at the resonnant
frequency. There is more to it tought.

1/4 wavelenght for FM broadcast in North-America is 30 inches. Does that
ring a bell? Remember the old Pinto/Comet, what was the lenght of the
antenna whip? Around 30 inches. A Fuba antenna is actually shorter than 30
inches, so they use an electrical circuit to match the lenght of the whip
(around 15 inches - can someone measure this?) with the resonant frequency
of the FM broadcast range. Then since it is workaround for the 1/4
wavelenght, you lose some signal, so they include an RF preamp to
compensate. There ain't no free lunch with physics.

AM radio is a whole different story at around 1MHz... We'll leave it for
now.

To make a story short, and I do not know if it is still possible at this
point, I would install a non amplified Fuba, along with some kit, that has
got to exist at CB shops, to adapt any car AM/FM antenna with a CB. That way
it is tuned by professionals, and you'd get a better performing system than
if you'd hack it yourself.

That is my opinion. Anybody is free to experiment for fun. It just is that
unless you have the proper tools (and knowledge), you are flying by the
seats of your pants. If you can talk to Joe across town after hacking, and
you are happy with this, then cool! 27MHz is forgiving for hacking (unlike
higher frequencies), so try it.

Cheers.

Marc
'83 Scirocco
'88 Scirocco Slegato

-----Message d'origine-----
De : scirocco-l-admin@scirocco.org
[mailto:scirocco-l-admin@scirocco.org]De la part de ATS - Patrick Bureau
Envoyé : 29 janvier, 2003 12:33
À : Julie Macfarlane; scirocco-l@scirocco.org
Objet : RE: Sirio CB/AM/FM/CELL(900) Fuba Style Antenna


Julie, you did get thinking about something you said

"Either that or extra wire is added to balance the load at either the base
or in the middle of the antenna"

well I did a little exercise in math...as per specs on the web site;

Antenna lengh = 450mm (1.476378  Feet)
cable that emerges from antenna = 215mm (0.705381  Feet)
Additional Cable = 5M = 5000mm (16.404199  Feet)

If you add it all up, 5665mm = 18.585958 Feet,  which it's 2.065958 Feet
(629,704mm) taller than Optimum.
(you quoted 16.52 ft or 5035.296  Millimeters)

Now the question is, is taller than 16FT a bad thing? I mean I have had 72"
whips with 10ft cable, which is ~16ft, but after SWR adjustements I would
like to know if there would be that much of a loss.

The other thing is since it PL-259 cable and connectors (standard CB radio)
I could just simply trim the extra 2.1 FT and splice in a new connector then
I would be in accordance to your stated rules of telecommunications.

ATS - Patrick Bureau - txrocco@sbcglobal.net


=>-----Original Message-----
=>From: Julie Macfarlane [mailto:juliemac57@hotmail.com]
=>Sent: Tuesday, January 28, 2003 9:49 PM
=>To: txrocco@sbcglobal.net; vwscir88@hotmail.com; scirocco-l@scirocco.org
=>Subject: Re: Sirio CB/AM/FM/CELL(900) Fuba Style Antenna
=>
=>
=>A transmitter antenna must be wave lenght matched. Meaning that the full
=>wave frequency for a 27 Mhz radio (cb) is 16.52 feet (both sides + & - of
=>the sinusiodal waveform). Divisors of lenght are allowed but in
=>even steps
=>only. Mismatch the antenna and the forward moving wave (energy) can be
=>reflected back to the transmitter and burn out the output stage.
=>Therefore 1/2, 1/4, 1/8 wave antennas are good. Either that or
=>extra wire is
=>added to balance the load at either the base or in the middle of the
=>antenna, and to fine tune the antenna a matcher (SWR) is added in line.
=>I didn't see this antenna matching the correct frequency for a
=>CB. Maybe the
=>hand held FM jobs on 900 mhz, but not 27Mhz.
=>Sorry boys
=>
=>
=>Julie Macfarlane
=>Menlo Park Research & Development
=>Internet Application Developer
=>Amsterdam NY
=>
=>
=>
=>
=>
=>>From: Patrick Bureau <txrocco@sbcglobal.net>
=>>To: brett cooke <vwscir88@hotmail.com>, scirocco-l@scirocco.org
=>>Subject: Re: Sirio CB/AM/FM/CELL(900) Fuba Style Antenna
=>>Date: Tue, 28 Jan 2003 19:11:03 -0800 (PST)
=>>
=>>This antenna is actually a CB antenna with an Fm and
=>>GSm coiled around the shaft, it is not a power FM
=>>antenna in any way, that is what is different
=>>and no you cannot use a standard FM antenna to
=>>transmit CB radio signal, youll just end up burning up
=>>your cb radio.
=>>
=>>Patrick
=>>
=>>--- brett cooke <vwscir88@hotmail.com> wrote:
=>> > what is the difference betwwen this antenna and the
=>> > stock antenna?
=>> >
=>>
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=>
=>
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