[amsat-bb] Re: Polarity switching question
hkowall at shaw.ca
Mon Jul 13 19:11:16 PDT 2009
Hello to all
You might want to check out this site for the info you may need
some good info there
----- Original Message -----
From: "i8cvs" <domenico.i8cvs at tin.it>
To: <w6zkh at comcast.net>; "amsat-bb" <amsat-bb at amsat.org>
Sent: Monday, July 13, 2009 8:23 PM
Subject: [amsat-bb] Re: Polarity switching question
> Hi John, W6ZKH
> The 2 meters KLM antenna uses two crossed folded dipoles wich are spaced
> wavelength in air over the boom so that to get circular polarization no
> delay lines are necessary.
> Each folded dipole has a wounded coax balun with ratio 4/1 wich is made
> 1/2 electrical wavelength of 50 ohm coax cable RG 303 to transform the
> balanced impedance of 200 ohm of the folded dipole into a 50 ohm
> impedance at the output of balun.
> The phasing harness coming out from the plastic barrel is made with two
> maching lines of 75 ohm coax cable type RG 302 and they are both 1/4
> electrical wavelenght long.
> Each maching line of 75 ohm transforms the 50 ohm impedance of the dipole
> about 100 ohm into the barrel but two 100 ohm in parallel becomes 50 ohm
> seen from the coax line connected to the barrel PL connector and going
> to the shack.
> The 75 ohm line connected to the polarization switching relay is also 1/4
> electrical wavelenght long but including the electrical lenght of the
> To switch polarization from RHCP to LHCP the relay only switches the inner
> conductor of it's 75 ohm coax cable from one to the other stud i.e. from
> one to the other screw of the same folded dipole.
> The 70 cm KLM antenna uses the same basic criteria but to switch
> polarization from RHCP to LHCP the relay add to one folded dipole a 1/2
> wavelenght delay line wich is included into the aluminum box and is made
> with a 50 ohm strip line over a fiberglass printed circuit.
> I hope this helps.
> 73" de
> i8CVS Domenico
> ----- Original Message -----
> From: <w6zkh at comcast.net>
> To: "amsat-bb" <amsat-bb at amsat.org>
> Sent: Monday, July 13, 2009 4:51 PM
> Subject: [amsat-bb] Polarity switching question
>> I recently obtained a pair of KLM yagi's for satellite work. They both
> have the KLM polarity switching box mounted and wired up. Since I havent
> them up yet, and not well versed in the subject, I got out my ohm meter
> to see what was what on this item. I noticed that both driven elements
> continuty to the center pin of the coax at the same time. I was under the
> impression that the relay switched back and forth the driven elements to
> give either RH or LH polarity. I havent applied the 12 volts to the box
> to check that out, but was just curious. One thing I have noticed while
> using the downlink yagi is that I get very little fade due to polarity
> I turn the antenna. I hope that is a good thing?? I havent checked the
> uplink yagi to see if it has the same results.
>> I hope someone can enlighten me abit.
>> 73 de John W6ZKH
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