[amsat-bb] Helical Antenna for 2-meters

[Edward R Cole]

Dave,

It helps to be multi-lingual <smile>.  Sounds as you got it under control.

I used a 16 element CC cross-yagi for AO-10 and the phasing harness 
was not according the dimensions one would calculate but it 
worked.  I traded it for a M2 436CP42UG for AO-40 (which I still 
have) and the CC 20 element 2m satellite antenna.  2m went kaput 
early so I used the 432 yagi a lot for uplink in mode-US or LS.  I 
had a 50w linear which was overkill (usually ran about 20w).  The 
dish photo I shared was my mode-S downlink using preamp to two Drake 
converters.

M2 is marketing an 8 element cross yagi CP antenna for 2m which is 
probably just right in gain.  Its pretty spendy, though.  If you have 
a couple 3 or 4 element yagi's you can combine them for CP and even 
switchable in sense using a relay or two.

I am using a 2M7 by M2 linear yagi and only have 26 elements of the 
big M2 436 antenna mounted.  Not QRV yet as I am planning major 
changes next summer.

GL on whatever you decide.

73, Ed

At 03:45 PM 2/7/2017, Dave Mann wrote:
>I just finished assembly of the Cushcraft cross-polarized yagi which 
>I bought from a fellow Ham. It was like new.  Now I remember what I 
>really didn't like like about that Antenna.  I put one together back 
>in 1978 or thereabouts.  Putting the phasing harnesses on was quite 
>the job!  I managed to remember curses in four or five different 
>languages (tnx Army language school).   Anyway it's all together and 
>I mounted it vertically on a 10 piece of pvc pipe for testing.  SWR 
>was almost 1:1 over the range 432.5 to 437.0 then rose slightly as I 
>approached 437 MHz.  I'm a happy guy now.  Next project is either 
>the 2-m Helical we've discussed here, or two 3-element yagis with 
>circular polarization.  I already have the yagis, so that would be a 
>no cost option.
>
>Thoughts anyone?
>
>73
>Dave N4CVX
>
>
>Sent from my iPad
>
> > On Feb 7, 2017, at 18:23, Edward R Cole <kl7uw at acsalaska.net> wrote:
> >
> > Just scale the dimensions proportionally (except wire diameter);
> >
> > ratio = 144/435
> >
> > I built a 14 turn 437 MHz helical back in 1996 to receive the MGS 
> beacon and built a 2.4 GHz 6-turn helical for 33-inch offset dish 
> feed for AO-40.  Plenty information in Amsat Archives.  Original 
> Kraus-W8JK design is optimistic in gain calculation.
> > http://www.kl7uw.com/Satellite%20feed.jpg
> >
> > W9EK had good construction hints in prior publications.
> >
> > For receive-only do not sweat getting a good SWR.  I used a 1/4 
> wavelength long 1/8 inch wide brass strip, run from connector to 
> beginning turn of the helix for impedance matching.  Space the 
> point of connection to the helix about 3/16 inch above the ground 
> plane reflector.  Natural impedance of a helix is 140-ohm.
> >
> > On air experience with the 432 helix was that a ten element CP 
> crossed element yagi is better.  But if you desire CP the helix is 
> a natural, though not perfect.
> >
> > 73, Ed - KL7UW
> >  http://www.kl7uw.com
> > Dubus-NA Business mail:
> >  dubususa at gmail.com
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73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
   dubususa at gmail.com