"First Light" on LRO-H2 (150cm Parabolic Solar Cooker Radio Telescope at Lichfield Radio Observatory) with two orthogonal monopoles in the cantenna prime focus waveguide 27/9/2025 @ 10:35 BST (UTC+1)

[andrew....@googlemail.com]

At last! Go this 2^nd monopole installed on the cantenna at 90 degrees to first – so now I can collect vertically and horizontally polarised 1420 MHz data – given that the Milky Way does not have preferred polarisation direction, I am hoping to combine the data to improve SNR.

 

Interestingly, the slope of the data plots is in a different direction! Not sure if that means I need to adjust the data before putting it into ezRA’s ezCon – what do you think Ted? Plus, Ted, do I need to find way to average data from both monopoles together before using ezCon or will the software happily combine data from both monopoles for me?

 

Hope everyone is having a great weekend!

 

Andy

[andrew....@googlemail.com]

My apologies – I meant to include a screenshot of “fitst light” – here it is:

 

 

 

 

 

[Alex P]

If I match up the Y scales on each plot, the amplitudes are quite different

[Andrew Thornett]

Does that matter much?

Sent from Outlook for Android

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From: 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Saturday, September 27, 2025 11:56:10 AM
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: [SARA] Re: "First Light" on LRO-H2 (150cm Parabolic Solar Cooker Radio Telescope at Lichfield Radio Observatory) with two orthogonal monopoles in the cantenna prime focus waveguide 27/9/2025 @ 10:35 BST (UTC+1)

 

If I match up the Y scales on each plot, the amplitudes are quite different

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[b alex pettit jr]

It would seem logical that if you want to add/average two quantities to improve their quality, they should contain about the same data and be ~ equal to each other..

On Saturday, September 27, 2025 at 08:39:09 AM EDT, 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Does that matter much?

[Andrew Thornett]

Thanks Alex - seems strange that there is difference in Y scale as monopole made same material and same length cable and using same LNA and SDR....

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From: 'b alex pettit jr' via.

It would seem logical that if you want to add/average two quantities to improve their quality, they should contain about the same data and be ~ equal to each other..

On Saturday, September 27, 2025 at 08:39:09 AM EDT, 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Does that matter much?

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[b alex pettit jr]

You need to test each Feed System individually and ensure you get the same results .

if NOT, you have a hardware issue.

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

[Mike Otte]

Andrew,  Nice experiment!  i have often thought of putting the second element in the feed horn.  Couple years ago, when I was trying to measure the Tsys of my system, it was said that i was losing half of the power because I was only 1 polarity.    In the old John Kraus book, they were measuring the polarity and said some sources are circular and some are not.

In my thoughts, the implementation  was going to be like vhf circular  polarized antennas and hook a phasing harness to the two antennas with one side being 1/4 wavelength longer than the other. This gives one output with both phases.   You're using two complete systems.  You're not maintaining the phase, so in my mind that is like having two separate antennas.  

The level changes I see every time i work with my systems.  sma connectors are not very repeatable when connecting and f connector are worse.  Your working with very low levels so mill-ohms can swallow you signal.

Good Luck

Mike

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[Andrew Thornett]

Thanks Mike for your comments and explanation. My initial.plan was to link the 2 monopoles with a phasing cable but, after discussion on this forum and at Drakes Lounge, where concern was expressed about unpredictable effects, where the monopoles would radiate back out as result of the setup, I opted to try the 2 separate systems in the first instance - plus it allows me to test for myself the hypothesis that there is no detectable difference in polarisation between the 2 orthogonal monopoles from Milky Way data (hypothesis based on the suggestion that the Milky Way hydrogen has random polarisations), and see if this is true in all directions.

Andy

Sent from Outlook for Android

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Mike Otte <mike....@gmail.com>
Sent: Saturday, September 27, 2025 2:54:53 PM
To: sara...@googlegroups.com <sara...@googlegroups.com>
Subject: Re: [SARA] RE: "First Light" on LRO-H2 (150cm Parabolic Solar Cooker Radio Telescope at Lichfield Radio Observatory) with two orthogonal monopoles in the cantenna prime focus waveguide 27/9/2025 @ 10:35 BST (UTC+1)

 

To view this discussion visit https://groups.google.com/d/msgid/sara-list/CA%2BG65tSw3NwAELACKCBCMGrKjOQp-M2-_VUkra8WztO%2B444JLw%40mail.gmail.com.

[Don Latham]

Rotate the feed by 90 degrees and take another sample.

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From: "sara" <sara...@googlegroups.com>
To: "sara" <sara...@googlegroups.com>
Sent: Saturday, September 27, 2025 7:00:46 AM
Subject: Re: [SARA] Re: "First Light" on LRO-H2 (150cm Parabolic Solar Cooker Radio Telescope at Lichfield Radio Observatory) with two orthogonal monopoles in the cantenna prime focus waveguide 27/9/2025 @ 10:35 BST (UTC+1)

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Don Latham
PO Box 404,
Frenchtown, MT, 59846
406-626-4304

[Don Latham]

Sorry, didn't finish the thought. Should be able to drift scan the moon. Take a sample or two and then rotate the can 90m degrees, take another two or so then compare.

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From: "Don Latham" <d...@montana.com>
To: "sara" <sara...@googlegroups.com>
Sent: Saturday, September 27, 2025 1:48:58 PM

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[Stephen Arbogast]

I  am  very confused  which is not unusual.   So  a  thought  experiment.....    Suppose we have one E&M  wave front  being  captured  by  our  small  dish  and entering  the circular wave guide  with two mono-pole pickups placed  at 90 degrees to each other..  Let's assume  that no  unknown weirdness  is happening in the  circular wave guide and zero  loses in all  conductors.   I am assuming  that  both  mono-pole  feeds are being  fed into one lna  and   lna  output  goes into   sdr.

 Wouldn't  the  signal random polarization  cancel out  the  at the input  to the lna?

[joe...@alpine-club.dk]

Good effort Andrew!

I think your problem is the Nooelc LNA and its performance when its NOT seeing 50 ohm clean. Have done a lot of experimentation with this LNA and it is sensitive to impedance, ohm value not phase angle. If it is under 50 ohm, your ezCol will show a slope and for higher than 50 ohm still a slope but in the other direction. Your ezCol is set to RefDiv and this is enhancing the slope.

Have 3 Noelec LNAs and they are all behaving similary, its not a faulty LNA.

In your case Andrew, the precise reason is the the LNA gain ripple caused by the antenna inpedance is not 50 ohm at one or both frequencies in play here. 1420 and 1417 will have different slopes and ezCol presents the difference as shown.

In my own case i use a relay and a good 50 ohm load and gets.... the same result.

From my experimentation, VSWR has to be better than 1:1,2 or better than 20 dB return loss to avoid the slope and of course on both frequencies in play. As you can see on my graph i havent reached 50 ohm myself.

A bare cantenna can easilly be 50 ohm and on the reflector, be far from 50 ohm wich is the case for me.

Any experience on how we achieve 50 ohm when we are using the reflector?

Joergen

[tedcl...@gmail.com]

I agree with Joergen, I think that slope presented by ezCol is enhanced by the difference in frequency gain responses of the Antenna and Reference sample frequency ranges.

ezCol's RefDiv and RefSub settings simply emphasize the presented Galactic hydrogen signal.

ezCol's RefDiv and RefSub settings do not change the recorded data values.

ezCol's RefDiv presents the Antenna sample values divided by the Reference sample values, frequency by frequency.
ezCol's RefSub presents the Reference sample values subtracted from the Antenna sample values, frequency by frequency.

I do not worry about that slope.
ezCon tries to remove it.

While creating the AntXT signal inside ezCon's plotEzCon081antXT(),
ezCon linearly levels the slope between the 2 frequencies defined by the 2 ezConAntXTFreqBinsFracL values
(by default, 0.15 and 0.85, meaning at 15% and 85% of the increasing range of frequencies).
The ezConAntXTFreqBinsFracL values are adjustable.
Outside of that ezConAntXTFreqBinsFracL frequency range, the AntXT sample values are set ("Trimmed") to 1.0 .

ezConAntXTFreqBinsFracL is a convenient setting to remove some constant-frequency RFI,

and is the first of the TVT (Trim-VLSR-Trim) post processing.

After the VLSR adjustment, there is second frequency Trim (ezConAntXTVTFreqBinsFracL).

The interesting spikes on Joergen's screen above are from his
      large setting of ezColIntegQty (384,000 for 163.9 seconds = 2.7 minutes),
      and his setting of ezColAntBtwnRef (I am guessing 5).

---
Ted Cline
TedClineGit at gmail.com

On Sunday, September 28, 2025 at 3:39:10 AM UTC-6 joe...@alpine-club.dk wrote:

...

[joe...@alpine-club.dk]

Like Ted I am not to worried because ezCon is only using the central part of the shown spectrum when it creates the EZB file. When the slope is tilting around 1420 MHz in a nice way EZB file should be ok but not perfect. The signals are not in balance (dobler shift) around 1420,408 MHz so there will an error but not bringing me into panic! But next operation including the Cantenna will require attention on the VSWR so the LNA performs to its best.

A little on my system, using a Raspberry 5 for the sampling and as Ted noted one referance + 5 samples. I prefer 1024 point FFT because i get a better idea what the spikes are if there are any. The 

antenna is a solar coocker.

Joergen

[Alex P]

If you get the two  channels working equally, you may not have a problem.

Until you get the two channels performing equally, No Software will work as you wish.

[Marcus D. Leech]

On 2025-09-29 13:02, 'Alex P' via Society of Amateur Radio Astronomers wrote:

If you get the two  channels working equally, you may not have a problem.

Until you get the two channels performing equally, No Software will work as you wish.

I've not been following closely---what is the goal?

If it's just to improve sensitivity, without wanting to do polarimetry or anything, then simply combining the two channels together post-detection will improve sensitivity,
  even if the levels aren't well matched.  Remember SNR is set very early in the reception chain.  Small differences in gain in the two chains make very little difference to
  the overall SNR.

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[b alex pettit jr]