Can anyone explain this crazy antenna analysis?

[JERRY TAYLOR]

I built an 11 element yagi  using a design calculator and it is supposed to be resonant at approximately 1420 mhz with a bandwidth of approximately 1390 mhz to 1490 mhz.

The  VSWR at 1420 mhz (red marker 1) is 2.291 which while not great should still make the antenna useable (I assume).

When I run the analysis from 1200 to 1500 mhz the VSWR is below 3 and the waveform shown on the charts looks crazy to me.  In fact if I run an analysis from 1-2 ghz the VSWR remains under 3 for most of the sweep and the waveform is essentially the same.

Is this normal for a yagi?

Is there an antenna design flaw?

The reason I question this analysis is because after multiple attempts to record H1 data I receive absolutely nothing.

[bsn...@gmail.com]

It would be helpful if you cite URL for the calculator and mention what are you using to "run the analysis"?

....bill....

[JERRY TAYLOR]

I am running NanoVNA saver connected to my NanoVNA.

NanoVNA.com

Jerry

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[bsn...@gmail.com]

And the design calcaulator, where might I find it?

[JERRY TAYLOR]

Changpuak.ch

I used the straight dipole option.

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[Alex P]

Did you run the analysis through a long length of Coax ?

I suggest you use a short cable and cal the VNA with the calibration loads at its end.

Alex

[bsn...@gmail.com]

The Changpuak.ch  software is based on the DL6WU Yagi design and I assume it properly implemented the design. The are other online DL6WU calculators and you might want to use one to verify the dimensions.

Some comments from the A.R.R.L. Antenna book to consider:

"Dimensions [for a 10 element, 1296 MHz Yagi] must be followed with great care".

"Lengths are given in millimeters to allow precise duplication."

"Element holes should be drilled +/-2 mm."

"Element lengths should be kept within +/-0.5 mm."

I'd triple check the physical construction if I were you. Good luck with a very fussy project.

...bill...

[JERRY TAYLOR]

I ran the analysis through about 10’ of rg6 coax.  Unfortunately the dipole was soldered directly to the coax.  I used stuff I had lying around.  The calibration was done without the coax.

Could this be the reason I cannot receive the H1 signal?

Perhaps a redesign of the antenna with a connector at the boom and mounting lna there at the boom would resolve the problem?

Jerry

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[JERRY TAYLOR]

Thanks Bill.  This is helpful.  

Jerry

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[b alex pettit jr]

All of the Smith Chart circles = half wavelengths of the coax.

Look  like 10' RG6 adds ~  2 dB of Loss & thus +2 dB of Noise as it is prior to the first amplification stage.

Microwaves101 | Noise Temperature

Microwaves101 | Noise Temperature Microwaves101 | Noise Temperature

Linear passive devices have noise figure equal to their loss. Expressed in dB, the NF is equal to -S21(dB). 

Something with one dB loss has one dB noise figure

Alex

[JERRY TAYLOR]

Thanks Alex.  I know just enough to be dangerous with antenna design😊. But I’m learning as I go along.

Jerry

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[b alex pettit jr]

The learning curve for microwave electronics and detecting signals barely above cold sky and

at levels which are 3 to 30  times lower than the blackbody thermal radiation of typical outdoor surroundings

is a nearly  Vertical  ... but the effort is extremely rewarding .. 

It has taken me a few years and literally hundreds of hours of time get a some level of understanding 

and reasonably good performance from my '1m'  system.

Anything  easily accomplished  quickly becomes Boring ...

Alex

[JERRY TAYLOR]

I am beginning to understand!

Thanks again.

Merry Christmas

Jerry

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[b alex pettit jr]

I will again recommend : build something Proven to Work .. get IT functioning properly and then experiment ..

The importance of reducing antenna "Spillover" ( in this case ground noise reception ) can not be overemphasized. 

Especially for small systems which can not use large choke-ring beam shaped feeds, minimization of ground noise by having the feed not 'see' the 290k ground/buildings/trees is Imperative. On my 1.2 m system, Cold Sky power level is 7.2 dB lower than the Ambient Temperature Ground and surrounding objects. Restated : The RF Noise Power from Ambient Temp Objects is 5X higher than Cold Sky and ~3.5X above the H1 signal power level.  - alexp

This Works   and is low cost and highly portable

Alex Pettit - Umbrella Antennas

Alex Pettit - Umbrella Antennas

Alex

[JERRY TAYLOR]

Sound advice. I think I will ask Santa Claus for a parabolic umbrella and faraday fabric.😊

Jerry

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[b alex pettit jr]

Get the single layer translucent umbrella with Fiberglass spreaders... Not the ones lined with aluminized mylar.

I've tried / measured several of them .. they all perform more or less equally = none are particularly parabolic.

but they Do Work when paired to a good feed.

Alex

[Stephen Thornber]

Hi, any ideas for suppliers of such ‘ parabolic umbrella and faraday’ 

Would a photographic light reflector umbrella work?

Stephen G6SGA

Sent from my iPhone

On 15 Dec 2023, at 20:51, 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:



Get the single layer translucent umbrella with Fiberglass spreaders... Not the ones lined with aluminized mylar.

I've tried / measured several of them .. they all perform more or less equally = none are particularly parabolic.

but they Do Work when paired to a good feed.

<1702673441674blob.jpg>

Alex

On Friday, December 15, 2023 at 03:44:19 PM EST, JERRY TAYLOR <gfaj...@gmail.com> wrote:

Sound advice. I think I will ask Santa Claus for a parabolic umbrella and faraday fabric.😊

Jerry

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<1702673441674blob.jpg>

[b alex pettit jr]

Hello Stephen,  here is the presentation & parts list 

Most important for the photo umbrella is to use one with Fiberglass ( non conductive ) spreaders

Alex Pettit - Umbrella Antennas

Alex Pettit - Umbrella Antennas

>>>>  More Construction Details in attached *.PDF

Alex

[Stephen Thornber]

Magic thanks. Another project :)

Stephen G6SGA 

Sent from my iPhone

On 15 Dec 2023, at 21:35, 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:



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<H1Umbrella_ConstructionDetails01.pdf>

[b alex pettit jr]

The Wescott 2005  is  the  preferred   translucent white version

Alex

[b alex pettit jr]

Hello Jerry,

Back to your Original Question

" The reason I question this analysis is because 

      after multiple attempts to record H1 data 

            I receive absolutely nothing. "

             >>  Antenna System Test <<

Here is a method to test the functioning of the antenna

1) Point the antenna towards the 10K Cold Sky and record the average signal level

2) Point the antenna towards the 290K Hot Earth ( bushes/trees/downward towards the grass ) and record the average signal level

What  Is the Difference ???

This is from the Umbrella Antenna   

 ( I used a conductive foam cover over the loop feed for the 290K reading .. not possible with the Yagi )

Alex