Scope-in-a-Box Antenna Upgrade

[a_pet...@yahoo.com]

FINALLY !

I began construction of this antenna a month before I found SARA and the Scope-in-a-Box .  I purchased the stock nooelec 1.7 GOES model antenna with the 100cm x 60cm reflecto, SAWBirdH1 and SmarTee to set up and test something Proven to Work before trying my  'creation'.

The difficulty : I could use the miniVNA as an H1 signal source. The Loop-Feed showed a strong +3dB reception over the Stock 1.7GHz Yagi/Dipole... BUT every time I tried to receive Milky_Way data, it just flat-lined  ZERO response .. back & forth for over a week: great data from the Stock, Nothing from the Tuned antenna .. 

Then on Saturday, out of total-frustration, I tried rotating the antenna : Signals !.  Marcus explained that these para-grid antennas are strongly  polarized and evidently I  initially had installed the antenna exactly 90 degrees out of phase creating a perfect Null !

( I still have No Idea why the miniVNA tests worked but actual H1 reception failed ? )

SO, it Works. not that great of an improvement over the stock, but with the level of effort invested, I'll keep it as my primary feed for now.

The antenna is a 21cm adaption of the OM6AA 23cm design

http://www.om6aa.eu/Loop_Feed_with_enhanced_performance.pdf

Cheers !

Alex P

KK4VB

( more info uploaded to qrz.com )

[Marcus D Leech]

It worked with your signal source because cross polarization loss in this case is probably only 10db or so. Your sig gen would still punch through. Not so much the ISM hydrogen. 

Sent from my iPhone

On Sep 7, 2021, at 9:40 AM, a_pettit_jr via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:



FINALLY !

I began construction of this antenna a month before I found SARA and the Scope-in-a-Box .  I purchased the stock nooelec 1.7 GOES model antenna with the 100cm x 60cm reflecto, SAWBirdH1 and SmarTee to set up and test something Proven to Work before trying my  'creation'.

The difficulty : I could use the miniVNA as an H1 signal source. The Loop-Feed showed a strong +3dB reception over the Stock 1.7GHz Yagi/Dipole... BUT every time I tried to receive Milky_Way data, it just flat-lined  ZERO response .. back & forth for over a week: great data from the Stock, Nothing from the Tuned antenna .. 

Then on Saturday, out of total-frustration, I tried rotating the antenna : Signals !.  Marcus explained that these para-grid antennas are strongly  polarized and evidently I  initially had installed the antenna exactly 90 degrees out of phase creating a perfect Null !

( I still have No Idea why the miniVNA tests worked but actual H1 reception failed ? )

SO, it Works. not that great of an improvement over the stock, but with the level of effort invested, I'll keep it as my primary feed for now.

The antenna is a 21cm adaption of the OM6AA 23cm design

http://www.om6aa.eu/Loop_Feed_with_enhanced_performance.pdf

<LoopFeed_NEC_Model01.jpg>

<LoopFwws_Dish_SWRchart.jpg>

<YagiDipole_vs_LoopFeed_antennas.jpg>

<Antenna_with_LoopFeed02.jpg>

Cheers !

Alex P

KK4VB

( more info uploaded to qrz.com )

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<Antenna_with_LoopFeed02.jpg>

<LoopFeed_NEC_Model01.jpg>

<LoopFwws_Dish_SWRchart.jpg>

<YagiDipole_vs_LoopFeed_antennas.jpg>

[B & MR Randall]

Wow Alex,

The feed constuiction is really nice workmanship.   I suspect the feed over illuminates the dish in the 60 cm direction.  Noise from the ground behind the dish may be limit on sensativity.  Even with the polarization aligned correctly, I wonder if a small amout of ground noise shows through the dish. 

 

Bruce Randdall 

--

[Marcus D. Leech]

On 2021-09-07 11:32 a.m., B & MR Randall wrote:

Wow Alex,

The feed constuiction is really nice workmanship.   I suspect the feed over illuminates the dish in the 60 cm direction.  Noise from the ground behind the dish may be limit on sensativity.  Even with the polarization aligned correctly, I wonder if a small amout of ground noise shows through the dish. 

 

Bruce Randdall 

I suspect that it does--the performance is surprisingly poor with the standard feed, and modified standard feed.

I have one more configuration "in the queue", which is to cover the reflector with aluminum foil.    But perhaps Alex can try that and report back.  Getting it to
  conform to the parabolic shape is easier than doing so with heavier materials.

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/005501d7a3fd%248c953100%24a5bf9300%24%40net.

[b alex pettit jr]

I can try that.  

Right now, I want to lock down a configuration and use that for future tests.

I am going to install the SawBird & SDR on the mount on a fan cooled heat sink.

The total power is ~ 2.5W, but the one time I had these components out in the Noon-time Sun, they got very hot.

I also ordered a commercial quality3 ft  LMR 240 SMA cable to run from the Loop-Feed to the 'Bird.

Many issues over the past week with intermittent Chinese Cables or Adapters added to the confusion.

FYI: I found an interesting USB extender. What's  novel  is it uses a 12VDC supply at the Tx ( PC ) end

and will power its Rx and USB powered electronics via the Cat6 cable .  12V is nice for battery powered field ops.

I have the Rx in a metal box ~ 10 feet from the antenna. Seems to work without induction of RFI into the antenna,

but I need to be aware of the 'over-illumination' potential and see if that does indeed cause an issue.

https://www.amazon.com/dp/B08Y6GYFRL?psc=1&ref=ppx_yo2_dt_b_product_details

Now that the Loop-Feed antenna non performance mystery has been solved, I can make more

accurate 'celestial'  alignments and acquire more reliable data.

The merging of  two hobbies : amateur radio ( mostly antenna design/fab ) and astronomy is Great.

 I like the ability to do some Analysis .

-ap