[amsat-bb] Re: 70cm antenna SWR problem solved? (Bird 43)
mat_62 at netcommander.com
Fri Jun 6 21:54:36 PDT 2008
Yes, I know the Bird 43 well. Years ago I worked as a shipping clerk in a
ham radio store and I remember that we sold them as well as the fact that we
had one on our test bench. I now regret not getting one back then when I
had my employee discount. As it was, I was like the proverbial "kid in a
candy store" and was lucky to get home with my paychecks intact.... hi hi
----- Original Message -----
From: "i8cvs" <domenico.i8cvs at tin.it>
To: "AMSAT-BB" <amsat-bb at amsat.org>; "Michael Tondee"
<mat_62 at netcommander.com>
Sent: Friday, June 06, 2008 11:48 PM
Subject: Re: [amsat-bb] 70cm antenna SWR problem solved?
> Hi Michael, W4HIJ
> For the velocity factor use the value given by the manufacturers for each
> type of coax cable.
> As an example a Vf= 0.66 is OK for the RG 213 and RG-58
> Don't make long run of coax without the braid in the vicinnity of the feed
> point because the inner conductor of the coax cable will add to the lenght
> of the dipole.
> When you measure the SWR slide the palm of your hand over the jacket of
> coax cable and if the SWR changes it means that part of the RF current is
> flowing over the external braid of the coax cable and so you need a balun.
> To measure the incident and reflected power to compute the SWR try to buy
> a BIRD 43 wich is a professional instrument and buy time to time the
> measuring elements to satisfy your needs.
> In a couple of years you will get the most practical and versatile
> instrument for RF measurements in the shack and over the tower.
> Have fun
> 73" de
> i8CVS Domenico
> ----- Original Message -----
> From: "Michael Tondee" <mat_62 at netcommander.com>
> To: "i8cvs" <domenico.i8cvs at tin.it>; "amsat-bb" <amsat-bb at amsat.org>
> Sent: Friday, June 06, 2008 9:47 PM
> Subject: Re: [amsat-bb] 70cm antenna SWR problem solved?
>> Thank you Domenico,
>> I've actually studied all those links before. I would build a CP antenna
>> Howard, G6LVB has done except that I have nothing with which to measure
>> velocity factor of the cable in the phasing harness. When it was working
>> the 70cm linearly polarized did a pretty good job though. At least with
>> LEO's. Unfortunately I have no experience with HEO's.
>> Michael, W4HIJ
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