1m H1 Umbrella Antenna

[Alex P]

As a follow-up to the Zoom meeting, I have attached the key slides from the presentation .

Shopping List of items can be found on photos.

Cheers,
Alex P   KK4VB

[Hugo Post]

Fantastic!!!!!

Op zo 5 mrt 2023 om 21:59 schreef 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>:

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[fasleitung3]

Hi Alex,

I very much enjoyed your presentation yesterday. Very nice experiment!

Wolfgang

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[Douglas Decker]

Great find Alex. I was thinking same thing with a patio umbrella. One question is the length of the wire element that you used?

I have tried cantennas and helix antenna . This will give me more gain. K5wmt. Doug.

Sent from my iPhone

On Mar 5, 2023, at 14:59, 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:



As a follow-up to the Zoom meeting, I have attached the key slides from the presentation .

Shopping List of items can be found on photos.

Cheers,
Alex P   KK4VB

<H1_Umbrella_photo.jpg>

<H1_Umbrella_ContourPlot.jpg>

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<H1Umbrella_forSARA..pdf>

<H1_Umbrella_photo.jpg>

<H1_Umbrella_ContourPlot.jpg>

[b alex pettit jr]

Hello Douglas,

It is a Full Wave Loop = right at 21cm.

A Patio Umbrella is not particularly Parabolic and nor is it probably sufficiently deep to shield the feed from 290K ground noise.

I eval'd a 6 ft Photo Umbrella : is too fragile to consider using it outside, and wind tie downs, as I used with the 1m

warp it .. It is also too deep ~ f/D 0.21 means the last foot in diameter extends beyond the beam shape of the loop feed.

It is not "Gain" but matching the beam pattern of the Feed to the reflector shape that is most important .

I used a tuned Cantenna on a 1.2m f/D 0.35 with results fractionally less than the Loop ..

Big Plus for the Cantenna : Its HighPass characteristics did a great job of filtering 750 MHz CellPhone Tower RFI.

Alex

=====================================================

[Douglas Decker]

I agree. Was going to  .5 dish arms and try to build a bending jig for the patio umbrella arms .  The patio umbrella is free since all the cloth rotted off.  Ham you seen the hamdish site from the Netherlands. They have some great dishes and a feedhorn. Right more  not on my budget list.

Sent from my iPhone

On Mar 6, 2023, at 13:56, 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:



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[Marko Cebokli]

The shape of an umbrella is determined by the cloth, not the spokes, so
you can "tailor" yourself whatever f/d parabola you like (within
sensible limits, of course).
More than f/d, I am worried about the arms holding the ribs apart, they
are in the maximum field region, and certainly cause some ugly
sidelobes. Could these be moved to the backside?

Marko Cebokli



On 06.03.2023 20:55, 'b alex pettit jr' via Society of Amateur Radio

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[b alex pettit jr]

Hello Marko,

Many upgrades are possible .. I wanted to design this to be constructed as simply as possible,

but still have good performance.

This particular umbrella was selected as its spreaders arms and ribs are Fiberglass ..

Thanks,

Alex

[Douglas Decker]

I have been working on Antennas for the "HL". First used a cantenna, the
a Helix. Now I am building a 1.2 meter Dish. Tried a patio umbrella but
the arms were steel not Aluminum. Put that in the trash can. I am now on
the cheap using fiberglass poles and stainless steel wire and will use a
HDPE center plate. I am attaching some pictures to show my progress.
Just thought I would share. Next is the mesh, mount and tuning. Comments
or thoughts appreciated


Doug Decker K5WMT..

[b alex pettit jr]

Hello Doug,

Looks good.. What is the planned f/D ratio ?

Ideally it should be ~ 0.30 to minimize  "spill-over"  of 290K ground noise.

An issue with small antennas is the signal level is low and minimizing ground noise reception is an important parameter.

This may be excessively deep   ( f/D~ 0.25) , but it demonstrates the concept.

 Alex  KK4VB

[b alex pettit jr]

Doug,

Consider increasing the depth of the sides from 7 to 9 inches

That will change your f/D from  0.43 to 0.31  and focal length from 21" to 14"

The diameter will decrease from 48" to 45" if you keep the current material,

but that is insignificant to the performance improvement from enhanced  ground noise shielding.

Alex

On Sunday, March 26, 2023 at 12:51:52 PM EDT, Douglas Decker <dbdec...@gmail.com> wrote: