[AK-VHF] Helical Antennas

[Brandon Clark]

Hi Ed,

The helical antennas sound like a good way to go. When I get some down time I'll probably throw something together for 70 cm as a test.

I've built plenty of yagi antennas before, and they work great. But I think that setting up something with crossed elements and phasing lines would be turning fun into work. For my planned setup, with two antennas on a common mast, that also ends up being a lot of pointy sticks to run into, lol.

Brandon Clark, KL7BSC
https://brandonclarklabs.com/

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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐

On Friday, September 17th, 2021 at 21:35, Ed Cole <kl7uw at acsalaska.net> wrote:

> Brandon,
>
> For satellite comm, circular pol is better as satellites change attitude
>
> thru a pass so their linear pol signal can vary depending on whether
>
> they are aligned with a linear pol ground antenna. Some hams have
>
> crossed yagis which can switch from Right-handed to left-handed circular
>
> pol. But most just use Right-hand circular pol (RHCP). My 46 element
>
> 432 x-yagi is set up for RHCP.
>
> If you make a helical beam be sure the coil is wound in RH sense (seen a
>
> clockwise rotation) facing the satellite from behind the antenna.
>
> Impedance of a helical beam is 140-ohm so one usually makes a
>
> quarter-wave long matching section at the antenna connector. Solder it
>
> directly to the coax center pin and space it about 3/16 inch further
>
> from the ground plane reflector at connection with the helix coil. 1/4
>
> inch wide copper strap works well
>
> I made a six turn helical feed for a 30-inch dish for 2401 MHz to
>
> receive the signal from AO-40.
>
> Helical's are inheritantly wide band (15 to 20% of center frequency).
>
> 73, Ed - KL7UW
>
> On 9/17/2021 8:45 PM, Brandon Clark via ak-vhf wrote:
>
> > I was wondering if anyone in the group has experience with helical antennas?
> >
> > I am looking into designs for 2 M and 70 cm antennas for satellite communication, and would like to use something having circular polarization. I'm also considering crossed dipole style yagis, but the helical designs seem to have an advantage of much simpler feeding arrangement, and possibly wider bandwidth.
> >
> > Brandon
> >
> > Sent from ProtonMail mobile
> >
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