Antenna Grounding

[Nathaniel Butts]

Howdy All,

This may be a stupid question, but I've gotta ask it anyways.

I am setting up a new scope using this antenna which I believe is the same as what's in the scope in a box.  I've built a can waveguide and have it attached to a pole in the ground.  Currently working on troubleshooting to get it ready for hydrogen measurements.

The spectrums I see remind me a lot of the issues I had with the pyramid horn and not having a conductive surface on the horn: lots of noise centered around a specific power, and the power seems to dip ever so slightly when it crosses the beam.

Currently the process looks like this:

I have tested conductivity of the ground from various points.  My results:

1. Waveguide can to antenna surface - not continuous
2. Waveguide can to bolts on antenna - continuous
3. Waveguide can to pole in ground -  continuous
4. Waveguide can to feed element - not continuous

Looking at my flow diagram, it seems to me that any electrical signal would flow directly into the ground, but I'm not educated enough now to know if that's how it would flow.  It's electromagnetic wave, so it make sense it would follow the path of least resistance and not actually bounce off the antenna into the waveguide to the feed.

I guess I have two questions:

1. Should there be continuity between the can and the antenna surface?  It's painted, so maybe not.
2. Should the continuity flow between the ground and the waveguide?

Anything else I might be overlooking?

Thanks,

Nathan Butts

Wannabe Astronomer

Bowling Green, KY

[Alex P]

Rotate the Feed ~ 90 degrees ..

( For test verification Only .. I do not use a Cantenna  on my system. )

[b alex pettit jr]

This simple feed uses a closely coupled LNA  and will provide better performance.

( this IS what I use )

.

[Marcus D. Leech]

On 30/10/2023 10:38, 'b alex pettit jr' via Society of Amateur Radio Astronomers wrote:

This simple feed uses a closely coupled LNA  and will provide better performance.

( this IS what I use )

Any feed that has a more-or-less direct-coupling for the LNA is going to have better performance.

The problem with this para-grid antennas is that an ideal feed would match the asymmetry of the
  reflector, and ordinary dish feeds (whether patch, loop, or "can") have a fairly-symmetric
  illumination pattern, which means that no matter what you do, you're going to have more spillover
  than for a round or offset dish.

.

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[Nathaniel Butts]

Alex and Marcus,

I believe you have hit the nail on the head.  I also got a direct message from Mike Otte stating the same thing.  I'll try that first.

Alex,  I started building that cake pan exact feed this weekend.  I've got the beginnings, maybe I'll finish this week.  I also picked up the idea of using PVC to mount it to the antenna from the Drake's Lounge discussion on Friday.  I'm going to try that first to see if it works well enough. before I redesign my ganky strut system again, lol.

One question I did have about the loop: does it matter how far from the back of the cake pan it is mounted?  

Thanks,

Nathan Butts

Wannabe Astronomer

Bowling Green, KY

[b alex pettit jr]

That is the next upgrade .. ( and over-screening the para-grid )

[b alex pettit jr]

25 mm  and that is pretty much the nominal spacing when using the SMA<>F adapter.

Start with  a 35 cm distance from the base of the reflector to back of the cake pan.  ( test 34-36cm  )

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

[b alex pettit jr]

Hello Nathan,

I cut down the original dipole feed square tube for the base,  and mounted the loop feed with an aluminum center post ..  

It does not degrade performance ... and the ability to slide the cake pan up/down the rod made finding its optimal location 'Easy.'.

Alex

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