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Brent..
I cant find a beginners guide on how to use the vna for ham radio here ..
Can you assist me on where i can find it ..
Thanks , Brian

See more info on the 50/75 transformer on the site of my friend ON6GD

I take it back... Nothing magic about bifilar. Best is a soldered tap to the desired wire. Next best is a twisted wire loop tap. Third best is bifilar and worst is two separate windings. This assumes both windings share the same ground. This can all be explained with keeping the leakage inductance as low as possible. (see attached plots).
Gary AF7NX

Hi Fred,
I appreciate the feedback. I will eventually post a link on some other forums.
I don't happen to have any mix 52 in my collection or I would have tested it. Looking at its complex permeability, I can see why it might be favored. The lower permeability allows there to be more turns on the primary, which will imply a lower B field for the same primary inductance -- That is probably a good thing for less loss. The competing issues would be larger leakage inductance and more winding capacitance...
Cheers,
Gary AF7NX

JMR,
Indeed I was using the two port S11, S21 provided by the nanoVNA. If you go through the Appendix in my post you can see how I generated the loss plots I presented. Once I established a calibrated system and a consistent method of doing the tests, the runs were quite repeatable and gave reasonably self-consistent data. It is what it is! You should be able to repeat the same experiment from what I've laid out, I would hope, if you have lingering doubts...

Gary AF7NX

Pete, I've modeled with 4NEC2 an end-fed wire with various source impedances and counterpoise lengths. The 2450 ohm source impedance seems close to optimum. You have to choose some step-up ratio. Once you do, then the match to 50 ohms becomes whatever it does and provides a good starting point for determining the properties of the transformer. Certainly the SWR will vary a lot depending on the antenna load. But one thing at a time :)

Cheers,
Gary AF7NX

Welcome to the forum, Brent.
There are several guides in the files section, including the Absolute Beginners Guide.?
Go through the forum's Wiki for additional information. There are also many YouTube videos available, just search for nanovna.?


On Thu., 1 Jul. 2021 at 7:38 p.m., Brent Sachnoff<bsachnoff@...> wrote: Hello.? I just received my H4 and I'm finding it difficult to understand the main website and getting this device to function properly.? I'm try to just start with something basic like SWR over 30-40 meters.? Can anyone help me out with calibration and then actually getting readings?

Thanks!
Brent

On Fri, Jul 2, 2021 at 12:35 AM, WB2UAQ wrote:

Many of us have been using a resistance of 49*50 for a test load as we both
have as a starting point but the real antenna is not a simple R.
Pete

I think that is one of the reasons the transformer should ideally be measured as a full 2 port device using a full two port VNA. This can also be done with a TR VNA like the nanovna with a little patience. Once this is done the s2p model can be loaded into a simulator and the load presented to port 2 can be changed to a complex load at will. To make things more realistic, a powerful RF simulator can define port 2 as an s1p model taken from a real antenna for example.

Interesting article, thanks! I think the best way to measure/model the transformer is to take a proper full two port model using the nanovna. This is a bit fiddly to do with a TR VNA but worth the effort I think. I then allows a much more detailed analysis of the transformer on a linear simulator.

I may have missed something but the insertion loss of the dual FT240 transformer looks to be very low below 2MHz. Is this taken with a 50R source and 2450R load? Or is it matched for lowest loss at 2MHz?

I did look at one of these transformers a while back using 2 x FT240 cores but I didn't wind it as an autotransformer. I wound it as a regular 2:14 transformer. I got the best performance up at 28MHz with the turns well squished together into just part of the core. With a matching cap and a 2450R load I think I achieved about 0.5dB loss at 28MHz. This setup isn't ideal for power handling but the insertion loss was impressively low across 2-30MHz. I think it was less than 0.7dB everywhere but the loss at 28MHz was optimised at just 0.5dB.

I just noticed a getting started guide under the files section. Reading thru it now.

Hello. I just received my H4 and I'm finding it difficult to understand the main website and getting this device to function properly. I'm try to just start with something basic like SWR over 30-40 meters. Can anyone help me out with calibration and then actually getting readings?

Thanks!
Brent

Gary
Have you considered what the feed point impedance of an EFHW is against the equivalent source impedance the 1:49 transformer has created? Is there a reasonable conjugate match? I have measured the feed point Z of a 66 or 67 ft wire on 40 meters (all I can use with my small lot) and recently I have worked with 4NEC2 and there is a fair agreement to the measured impedance. I have raised these question to others and get absolutely no responses. Many of us have been using a resistance of 49*50 for a test load as we both have as a starting point but the real antenna is not a simple R.
Pete

Hello,
I regularly use the Zplots.xls Download:
,
I have used it a lot with my antenna analyser SARK100, it is very versatile
and useful, now I want to use it to analyze
the results of the NanoVNA-F .
I ask.. what kind of extension is best for analyzing measurements? sp1 or
sp2?
73
Enrique LU8EFF



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Hi Dave,

Yes, the winding is tapped as an autotransformer and not a bifilar separate primary. I didn't think it would make much difference. But after seeing a couple of comments, I measured things both bifilar and as autotransformer, and indeed, the bifilar winding seems better.

Can you explain why that should be?

Cheers,
Gary

Got it.

??? Mikek

On 7/1/2021 3:22 PM, Jim Lux wrote:

On 7/1/21 12:18 PM, Mikek wrote:

On 7/1/2021 9:18 AM, Jim Lux wrote:

On 7/1/21 7:13 AM, Joe WB9SBD wrote:

I do not understand why a good 75 ohm calibration load would not make
the thing be a 75 ohm test.

Isn't that what the 50 ohm one is doing when you calibrate the dead
short and the 50 ohms load?

exactly.

I'd do the cal at the end of the coax, too.

Ok, but I can't do both, the cal is which ever one I do last. Yes, there
are memories, but then which cal means what?

Mikek

You don't need a cal without the cable.

Essentially, calibrating at the end of your test cable makes the cable
"part of the instrument"

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Would you please take multiple pictures out of the box so we
can see the winding technique and how things are connected!
It appears the secondary is center tapped. Please - out of the bos!

Dave - W ?LEV

On Thu, Jul 1, 2021 at 8:29 PM Fred, W9KEY <fred.schwierske@...>
wrote:

Gary - very interesting!
I would urge you to also post notice of your work on QRZ.com. There is
active discussion of EFHW 49:1 technology in the "Antennas, Feedlines,
Towers & Rotors" forum, with significant contributions by retired EE
professor Mike Mladejovsky, WA7ARK.
* This should provide a link to the Forum:

* This should provide a summary of posts from WA7ARK:


Have you yet had opportunity to evaluate FT-240-52 mix cores? It's my
understanding a triple stack of 52 cores offers better performance (versus
43 mix) for higher power HF applications - reference this 2019 YouTube
video from Steve Ellington:

It would be very interesting to specifically compare FT-240-43 versus 52
mix cores for HF use with EFHW transformers.

--
*Dave - W?LEV*
*Just Let Darwin Work*

Gary - very interesting!
I would urge you to also post notice of your work on QRZ.com. There is active discussion of EFHW 49:1 technology in the "Antennas, Feedlines, Towers & Rotors" forum, with significant contributions by retired EE professor Mike Mladejovsky, WA7ARK.
* This should provide a link to the Forum:
* This should provide a summary of posts from WA7ARK:

Have you yet had opportunity to evaluate FT-240-52 mix cores? It's my understanding a triple stack of 52 cores offers better performance (versus 43 mix) for higher power HF applications - reference this 2019 YouTube video from Steve Ellington:

It would be very interesting to specifically compare FT-240-43 versus 52 mix cores for HF use with EFHW transformers.

On 7/1/21 12:18 PM, Mikek wrote:

On 7/1/2021 9:18 AM, Jim Lux wrote:

On 7/1/21 7:13 AM, Joe WB9SBD wrote:

I do not understand why a good 75 ohm calibration load would not make
the thing be a 75 ohm test.

Isn't that what the 50 ohm one is doing when you calibrate the dead
short and the 50 ohms load?

exactly.

I'd do the cal at the end of the coax, too.

Ok, but I can't do both, the cal is which ever one I do last. Yes, there
are memories, but then which cal means what?

Mikek

You don't need a cal without the cable.

Essentially, calibrating at the end of your test cable makes the cable "part of the instrument"

Ya, I have not looked it over real well, but it does give signal
strength, S/N and IF-AGC %.

?Also the station frequency, and physical channel.

The signal strength indicator is under, Product Support-- Signal
Diagnostics. (Sony)

??????????????????????????????????????? Mikek

On 7/1/2021 11:52 AM, Joe WB9SBD wrote:

Most TV's this "SIGNAL STRENGTH" is not a true signal strength but a
signal to noise measurement.

You could have a very weak signal but if it's channel is free and
clear of any noise, co-channel stations, cell phone, etc.
interference, it could show a better signal strength than a station
that is ten times stronger, but is plagued with all those interference
issues.

Joe WB9SBD

On 7/1/2021 11:41 AM, Fred, W9KEY wrote:

Well I suppose you are looking to have fun with your NanoVNA --- but
there is likely a much easier way to directly accomplish your goal.
Many modern TV's (with digital tuners) have a diagnostic mode that
will display received signal strength (along with other parameters).
So look up your model on the internet, or interrogate the internal
Help File, or even check the User Manual.
Using that mode will allow direct comparison of your various antennas.

For example, many Sony TV's use something like this:



And I recall the (now decades old) Digital TV Converter boxes
included the same feature.

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Yep, I have had my Sony TV for 10 years and never saw the signal meter,
I finally found it a week ago.

Yesterday, I went to pull it up and had do go through the whole search
again. it's not clearly labeled.

?It does display a lot of information!

???????????????????????????????????? Mikek

On 7/1/2021 11:41 AM, Fred, W9KEY wrote:

Well I suppose you are looking to have fun with your NanoVNA --- but there is likely a much easier way to directly accomplish your goal.
Many modern TV's (with digital tuners) have a diagnostic mode that will display received signal strength (along with other parameters).
So look up your model on the internet, or interrogate the internal Help File, or even check the User Manual.
Using that mode will allow direct comparison of your various antennas.

For example, many Sony TV's use something like this:


And I recall the (now decades old) Digital TV Converter boxes included the same feature.

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