ST2 Scantenna tested with NanoVNA

digitalanalog

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-Topic Note-
In a previous thread I did some RG6 coax testing and it was determined that the NanoVNA is a 50 ohm testing device so trying to test 75 ohm RG6 was not going to give (for lack of better terminology) Normal or Usable data as a result.

The ST2 Scantenna, This is one of the original ones with the blcak insulators
Per the Mfg Owners manual.
"Your antenna has elements which are resonant in the 30-54MHz, 108-174 MHz, 450-470 MHz, 470-512 MHz, and 800-912 MHz bands.
They work together to give you a frequency coverage from 30 MHz to 1300 MHz.
Supplied with 50' of RG-6 Coaxial Cable."

So I tested my ST-2 antenna with 25' of new RG-6 coax.

-Testing Conditions-
Sunny skies 80-85 degrees F, Using a Tripod, Using 2" dia. steel mast pipe at 10' long, ST-2 antenna mounted at 9'-11" to the center of the antenna square tube, Steel mast pipe was leveled, antenna was leveled, antenna facing North-Northwest.

-VNA-
NanaoVNA Harware Version 3.4; coverage 50k - 1.5GHz.
Test results are from the VNA and NOT from NanoVNA associated computer software.

-Testing-
Using the Resonant information from the Mfg. I tested only those area's.
I documented ONLY the starting point, any Dips (low points on the VNA) any Peaks(high points on the VNA),and the Ending Point.
Blue line on the Images is the LogMag Return Loss 10/db, the Yellow line is the SWR 1.0.

upload1.jpg

upload2.jpg

- 30-54 Mhz -
Start: 30.000 Mhz. - SWR: 7.74 - LogMag: -2.22db
Dip: 34.560 Mhz. - SWR: 2.99 - LogMag: -6.06db
Peak: 39.840 Mhz. - SWR: 8.99 - LogMag: -1.93db
Peak: 45.360 Mhz. - SWR: 9.75 - LogMag: -1.78db
Dip: 49.440 Mhz. - SWR: 4.55 - LogMag: -3.87db
Ending: 54.000 Mhz. - SWR: 6.65 - LogMag: -2.63db

upload3.jpg

- 108 - 174 Mhz -
Start: 108.000 Mhz - SWR: 1.65 - LogMag: -2.22db
Dip: 109.320 Mhz - SWR: 1.33 - LogMag: -16.79db
Peak: 114.600 Mhz - SWR: 2.56 - LogMag: -7.14db
Dip: 122.520 Mhz. - SWR: 1.12 - LogMag: -24.32db
Peak: 128.460 Mhz. - SWR: 2.54 - LogMag: -7.20db
Dip: 135.720 Mhz. - SWR: 1.13 - LogMag: -23.83 db
Peak: 142.320 Mhz. - SWR: 2.70 - LogMag: -6.72db
Dip: 150.240 Mhz. - SWR: 1.26 - LogMag: -18.68db
Peak: 156.840 Mhz. - SWR: 2.78 - LogMag: -6.53db
Dip: 164.100 Mhz. - SWR: 1.20 - LogMag: -20.79db
Peak: 170.800Mhz. - SWR: 2.41 - LogMag: -7.66db
Ending: 174.000 Mhz. - SWR: 1.92 - LogMag: -10.00db

upload4.jpg

- 450 - 470 Mhz. -
Start: 450.000 Mhz - SWR: 4.41 - LogMag: -4.00db
Dip: 458.200 Mhz. - SWR: 1.83 - LogMag: -10.57db
Peak: 466.000 Mhz. - SWR: 4.15 - LogMag: -4.25db
Ending: 470.000 Mhz. - SWR: 3.21 - LogMag: -5.58db

upload5.jpg

- 470 - 512Mhz -
Start: 470.000 Mhz. - SWR: 1.55 - LogMag: -5.58db
Dip: 474.200 Mhz. - SWR: 1.77 - LogMag: -11.08db
Peak: 481.760 Mhz. - SWR: 3.98 - LogMag: -4.44db
Dip: 490.500 Mhz. - SWR: 1.85 - LogMag: -10.46db
Peak: 498.140 Mhz. - SWR: 4.10 - LogMag: -4.28db
Dip: 506.540 Mhz. - SWR: 1.86 - LogMag: -10.41db
Ending: 512.000 Mhz - SWR: 3.63 - LogMag: -4.95db

upload6.jpg

- 800 - 912 Mhz -
Start: 800,000 Mhz, - SWR: 1.55 - LogMag: -13.24db
Peak: 803.360 Mhz. - SWR: 1.72 - LogMag: -11.50db
Dip: 810.080 Mhz. - SWR: 1.22 - LogMag: -20.05db
Peak: 819.040 Mhz. - SWR:2.18 - LogMag: - 8.58db
Dip: 828.000 Mhz. - SWR: 1.24 - LogMag: -19.13db
Peak: 835.840 Mhz. - SWR: 2.01 - LogMag: -9.44db
Dip: 843.680 Mhz. - SWR: 1.45 - LogMag: -14.62db
Peak: 851.520 Mhz. - SWR: 1.70 - LogMag: -11.71db
Dip: 861.600 Mhz. - SWR: 1.38 - LogMag: -15.72db
Peak: 871.600 Mhz. - SWR: 1.65 - LogMag: -12.11db
Dip: 880.640 Mhz. - Swr: 1.28 - LogMag: -18.02db
Peak: 889.600 Mhz. - SWR: 2.04 - LogMag: -9.27db
Dip: 898.560 Mhz. - SWR: 1.12 - LogMag: -24.77db
Peak: 906.400 Mhz. - SWR: 2.18 - LogMag: -8.61db
Ending: 912.000 Mhz. - SWR: 1.31 - LogMag: -17.42db

The fact that most of us do not have high dollar antenna testers and the availability of the NanoVNA as seen time and time
again in many locations this is what is being used to test antennas and other antenna related components.

No, the ST-2 people did not use a Nano to test with, But by today's standards it's what people can afford and what they are using.

While some of these numbers may not agree with the Mfg Resonant points, the NanoVNA has done the testing. I simply installed
the antenna and the coax.

Will others get the same numbers if they test with a NanoVNA, The answer I believe is NO, every situation is different and no 2 test results
will be the same, close yes, the same I doubt it.

I simply turned the antenna after testing was done and looked at a few numbers I had documented, and just by turning the antenna it changed the numbers........
 

W9WSS

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Now, will there be an equivalent available to the scanning enthusiast through normal retail channels without jumping through hoops via Scantenna 030519-01.jpgwholesale or off-shore vendors? I own two of them, and wouldn't part with 'em for the world!
 

W9WSS

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Mine came down in an ice storm about a year ago. I thought it was obliterated, but fortunately, only one element bent. I put out a "want ad" for another ST-2, and a local CARMA member in Chicago had one that he had never put up outside. I paid a fair price for it along with the 50' of cable and transformer. It will go back up in place of the previous ST-2 which was put on another corner of my tower for further monitoring.

If you find one, and it's available, grab it before it disappears! Works hands-downScantenna 030519-01.jpg better than a discone!
 

AZMONITOR

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A great antenna for monitoring, I have three of them on my roof, superior to discones.
 

vagrant

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A great antenna for monitoring, I have three of them on my roof, superior to discones.
I agree that the ST2 performs better than various discones I tested in the frequency ranges it advertises. (30-50, 148-174, 440-470, 470-512, 800-912)

If one enjoys 118 - 144 MHz for civil/mil aircraft, or 225 - 400 MHz for military aircraft, a discone wins. Well, at least in my testing and day-to-day use. To solve this I run an ST2 and a discone. Sometimes I will overlap and I can clearly hear the difference when two scanners are both sitting on the same mil air freq.
 

digitalanalog

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I must admit I was looking for better numbers when I tested this antenna.
I have test results from a lot more professional analyzer and the results
are way different, especially in the return loss numbers.

Although i have no doubt that the nearly $30,000. test equipment will
provide much better results, I would still think the NanoVNA would
show better results then it did.

It is easy to get different readings by simply changing certain aspects of the test like turning the antenna,
mounting it on the mast at different heights, landscape placement like pointing it towards trees or pointing it away,
and even pointing it at a slight angle up or down, all these things will provide a different out come as far as the numbers go when testing.

I did learn somethings so all in all it was a great learning curve, I plan on testing more antennas I have, I think the AT-197 will be a great test as we know it's narrow band of 200-400MHz.
 

prcguy

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I've used and tested AT-197 Discones and they cover roughly 175MHz on the low end to over 1.2GHz on the high end. They will have a pattern shift upward mid range starting maybe 700-800MHz but over the 225-400MHz range they are great with a low angle at the horizon.

I did learn somethings so all in all it was a great learning curve, I plan on testing more antennas I have, I think the AT-197 will be a great test as we know it's narrow band of 200-400MHz.
 

digitalanalog

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I've used and tested AT-197 Discones and they cover roughly 175MHz on the low end to over 1.2GHz on the high end. They will have a pattern shift upward mid range starting maybe 700-800MHz but over the 225-400MHz range they are great with a low angle at the horizon.
 

Ubbe

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It could be some pitfalls with cheap VNA's like lack of interference rejection. There's a lot of RF signal in the air and the VNA will receive those, it is a RF receiver, and if it doesn't have any protection for it, I guess a $50 device doesn't have any, it will influence all readings if you do not do the test in a faradays cage, or at least in a garage. Expensive analyzers use different tecniques to isolate interferencies and get proper results.

If you get different readings when turning the antenna and tilting it, then also do a test by moving the coax around. If that also change the reading it would be a sign of that the coax are not properly decoupled from the antenna.

/Ubbe
 

digitalanalog

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It could be some pitfalls with cheap VNA's like lack of interference rejection. There's a lot of RF signal in the air and the VNA will receive those, it is a RF receiver, and if it doesn't have any protection for it, I guess a $50 device doesn't have any, it will influence all readings if you do not do the test in a faradays cage, or at least in a garage. Expensive analyzers use different tecniques to isolate interferencies and get proper results.

If you get different readings when turning the antenna and tilting it, then also do a test by moving the coax around. If that also change the reading it would be a sign of that the coax are not properly decoupled from the antenna.

/Ubbe
I used a new 300/75 transformer and the connection was good and as mentioned new
coax so that part I have think is good. I started testing with a different transformer and the numbers were all over the place,turns out one of the new transformers was bad.
 

popnokick

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So after everything that was explained in the other thread about using the NanoVNA with 75 ohm coax (RG6) and not 50 ohm coax (for which it is designed).... you used 75 ohm RG6 and tested the ST-2 with the NanoVNA anyway? Here's the thread -
NanoVNA RG6 Test Results
 

prcguy

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You should be able to calibrate the Nano VNA with a 50 to 75 ohm minimal loss pad on the instrument, then it will in effect be a 75 ohm instrument. See if its instructions mention using an open, short and load for a single port cal and S11 or S22 measurement. If so you would need a 75 ohm reference open, short and load and they are available with F type connectors. Not cheap however.

With all that you would just use a good quality RG-6 cable with F connectors on the antenna to test for VSWR and impedance changes, which would include the effects of the 75 to 300 ohm transformer at the antenna.

So after everything that was explained in the other thread about using the NanoVNA with 75 ohm coax (RG6) and not 50 ohm coax (for which it is designed).... you used 75 ohm RG6 and tested the ST-2 with the NanoVNA anyway? Here's the thread -
NanoVNA RG6 Test Results
 

Ubbe

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A short it just a short, 0 ohm resistance and impedance. An open calibration tool are just that, open with as high impedance as possible. There's plenty of 75 ohm loads to have. I have both BNC and F types and costs a dollar or two. It doesn't matter much if it is 72 or 78 ohm in those cheap loads with the measurements you are going to do. The issue is if the internals of the VNA can handle a 75 calibration without using the impedance matching that prcguy mention.

But at the end the scanner is supposed to be 50 ohm (well, it isn't really) so using a 50 ohm VNA seems to be the logical way to go, as it will represent what a scanner sees.

/Ubbe
 

prcguy

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I would think the original version of this antenna would have been designed and factory verified at 75 ohms since it uses TV coax to the radio and terminated with 75 ohms at the radio. That would give repeatable testing anywhere. If you terminate the coax with 50 ohms then different lengths of coax would give different results.

I have not run across a 50 ohm VNA that could be properly used and calibrated at 75 ohms without using resistive matching or a minimal loss pad to do the impedance conversion.

A short it just a short, 0 ohm resistance and impedance. An open calibration tool are just that, open with as high impedance as possible. There's plenty of 75 ohm loads to have. I have both BNC and F types and costs a dollar or two. It doesn't matter much if it is 72 or 78 ohm in those cheap loads with the measurements you are going to do. The issue is if the internals of the VNA can handle a 75 calibration without using the impedance matching that prcguy mention.

But at the end the scanner is supposed to be 50 ohm (well, it isn't really) so using a 50 ohm VNA seems to be the logical way to go, as it will represent what a scanner sees.

/Ubbe
 

k9wkj

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where they make the cheese
there is a 75 ohm firmware for the Nano
its hosted in the groups.io nanovna-users group
but to my thinking if you calibrated on the end of the test coax for each segment as you go along
remember you only get 101 data points, so keep your calibrations as narrow as the bands you want to look at
then you should get fair numbers
but this is at worst a minor mismatch, and for a receive antenna I would never worry one bit about it
 

digitalanalog

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a 75-50 ohm matching pad would cost twice the amount I paid for the Nano and in so cases 3 times as much.
So what would be worse, testing with a 50 ohm coax going to a 300/75 ohm matching transformer? or testing
or using a 75 ohm coax to a 75/300ohm transformer going to a 50 ohm testing device?

All in all the way I have done it provides a means of testing and if i have to have adapters and different coax for each type
of antenna depending on it's impedance i may as well not test at all, but being as this is what I like to do and being as it's a HOBBY
my means seem to fit my HOBBY, as acturate as a high dollar analizer....NO..... but shows me the points of resonance in an antenna YES,

Besides as mentioned above, what's the scanner impendance verses the coax verses the antenna verses the test device, this ain't
rocket science, it's testing and having a hobby with variables that I can live with. It will show me what I need to know to perfect and fine tune
a home built antenna that may some day soon be a big success.

I appreciate everyones comments, there are smarter people then me when it comes to all this, but I'm in it for FUN and the HOBBY
so let the testing continue and please continue with your comments, but don't beat me up for what I am doing and the way I'm doing it.
 
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