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Hey ya'll? I'm a total idiot but this is my first try at this.

Kenwood ham radio 1200watt amplifier 80 meter input matching network was designed wrong, high radio SWR.

Here is the deal.? Want to match the 50+j0 radio to the amp on 80M.

Amp has known design problem.? 80M is L10.

*INPUT CIRCUIT FOR 80 METERS*

It was found that in 2 different TL922's it wasn't possible to get the input SWR down sufficiently. This isn't accidentally but a design fault. Even with a variable capacitor instead of fixed ones, the results were not consistent. If there was a good SWR at the start of the band, it was bad at the end or visa versa. Also the length of the cable between exciter and amplifier has an influence on the SWR on all bands.

It was discussed on the Internet that what was ok for one person, didn't work for somebody else. I blame this on variations in the way the input circuits were manufactured (fig?.) The circuits are in a Faraday cage and don't allow the RF current to return to ground directly. You can put an insulated tinned copper wire through the hole of where a ground pin uses to be and use this as a central grounding point (left). The best way to do this to ground all capacitors of the input filters on this earth wire. In the meantime this was only done for the 10, 15 and 80 meter input circuits.



After a bit of experimenting a better compromise was reached for 80 m by removing 2 turns of L10 and to increase a number of the capacitors in parallel to the existing ones (fig ?). The range of the inductor was changed from 2.7 – 3.2 μH to 2.5 – 3 μH. Ifyou want a different inductor value, you can calculate this with the formula L(μH) = 9n? χ1000, "n" is the number of turns.

Attention:In the circuit diagram C57 and C59 is 120 pF respectively 220 pF. In my amplifier the manufacturer had a 120 pF capacitor for both C57 and C59!


Jumped bandswitch and used a NanoVNA to look at the modded GI-46b Russian tubes input impedance directly thru input 259 connector. Here is the tube input impedance with the band switch strapped out and no parallel caps.

So tubes look like 33+j9.8.

Then designed, implemented and measured the circuit performance.

Went from 1:10 + swr to 1:1.3 first try.




Looking into tube input bandswitch matching jumped

So I take the tube input impedance and drop it in Simsmith (free)? and design a simple L filter.

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Then I cut a coil (measure with MFJ B measure inductor @ 3.822MHZ) and made the filter above.
Nano VNA measures 1.15 SWR
Radio measures 1.3-1.4 SWR

Here is NanoVNA measurement looking into the tubes but thru the L network.


Fun for a first try and usable. Seems like I missed 50 ohms but SWR is close.? I think my inductance measurements are off.

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*Cheers,* Signature

Jim Ball?? KK4NOZ

Be sure to do a reset, before doing the cal.

Is correction (based on the calibration) enabled in the menu?

--
NanoVNA Wiki: /g/nanovna-users/wiki/home
NanoVNA Files: /g/nanovna-users/files
Erik, PD0EK

Hello user group,
I just realized having a problem with calibration OPEN

Going through the device calibration process and everything goes well and I save data at Cal-x

However when I check S0 on SmithChrt it doesn't show OPEN correctly.
The marker should be far right at infinite. However it circles somewhere between 50@ and infinite.

It does not matter if I clibrate directly on the SMA connectors or having a cable in between, effect is the same.
It also doesn't matter whether I leave S0 completely open or having an OPEN-standard connected.

Is something wrong with that device, or does someone know that effect?

PHISHING EMAIL ALERT

Some entity appears to have scraped the email addresses of NanoVNA forum members and are sending emails supposedly with a link to Dropbox.

If you click the link, it asks you to login to Dropbox with one of several email addresses - IT'S ALL FAKE.

You can stick whatever garbage you want into the login fields and you will be 'logged-in' and shown a business PDF document.

Please DELETE any messages that appear to come from forum members directly unless you confirm they were sent by that member.

I just received one supposedly from Alan Victor but you might see these appear from myself or others - just delete them.

Thanks,
Larry Rothman

From: Richard Perlman

Several comments about buying the larger screen. However, all I can find are the 2.8" screen versions. Where/How can I find the larger version -- or, is the 2.8" screen the larger version?
===============================

Richard,

The large screen device is a nanoVNA-F which has a 4.3-inch screen, and their official store is here:



There are some comparative photos in a presentation I did recently:



Cheers,
David
--
SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv

The issue is not the VNA, but rather? your lack of undertsanding as to how antennas perform/function.The way you have it set up, the outside of the coax shield and your VNA are part of the antenna structure. You would be well served to get a copy of the ARRL Antenna Handbook.Dale W4OPSent from my Galaxy Tab? E

Several comments about buying the larger screen. However, all I can find are the 2.8" screen versions. Where/How can I find the larger version -- or, is the 2.8" screen the larger version?

Great thanks for you answers!! I think I understand things much better now.
Yes, the radiating emlement is parallel to the ground plane in this setup for reducing space, but it can be changed to perpendicular.
I ordered some ferrites and also will increase the distance between VNA and antenna.
I'll tell you how the modification works...

Bernd

Hi,
I am facing similar in fact worst situation. Just using the same coaxial cable you showed in your picture and connecting to its end a 20 cm bare copper wire (that I am planning to use as an antenna) to measure its impedance, or even connecting this bare copper wire directly to CH0 through an SMA connector. Moving my hand around the nanoVNA, and trying to tap on the LCD changes significantly the readings on the nanoVNA. My nanoVNA has no shielding inside it. So, may be this is making things worst.

Seems from the replies that this an expected behavior, and I should connect the antenna under test through a long cable to keep it away from the nanoVNA.

With the antenna that close to the VNA, ferrites are a must at both ends of
the connecting coax. Install ferrites and move the antenna structure
several wavelengths away from the VNA.

Also, for an instrument like this, the antenna is far too close to the
VNA. We know early models indicated additional shielding was required.
This is not a piece of HP/Agilent/Keysite test gear. Even the 8753C
exhibits this problem to a much lesser extend when I measure antennas at
the H1 frequency, 1.420 GHz.

A vertical monopole must be perpendicular to the ground plane. In the
first picture, it appears the vertical radiator is in the plane of the
ground plane. It should be perpendicular to that plane. It is the ground
plane perpendicular to the monopole that renders it an unbalanced
source/load - coaxial feed.

Dave - W?LEV

--

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

A better picture would help. Seems like your ground plane is tiny compared to the radiating part. And its hard to see but it looks like your ground plane is parallel to you radiating element.

Both those things are making you test equipment part of the antenna.

Dave
VE7HR

Looks like your feedline is radiating and your USB connection becomes part of the antenna. Try using ferrites over the outside of the RF cable right at the antenna to decouple your cable.

The email is K2RMA <at> arrl.net

73s

Marco

Hi,
I try to use NanaoVNA for measuring a vertical ground-plane antenna at 170MHz for later impedance matching.
A picture of the test setup is attached.
Connecting NanaoVNA to USB affects the measurement quite much, as you can see on the pics (max scale for VSWR here is 10).
Does anybody made the same experiences, as I never read about this being a problem?

The NanaoVNA has been calibrated with the same wire, as attached to the antenna and all calibration points (open, close, load) show the same values on the display, no matter if USB is connected or not. But attached to the antenna, the measurement shows quite different results.
And I'm not really sure if the results are reliable, even with unconnected USB.
The antenna should physically (length of the whip) have an VSWR minimum at 170MHz and not a peak (USB not connected).
Connected to USB, the result makes more sense to me, but I don't know which result to trust.
Any ideas what I'm missing or what I can do?

I have two NanoVNA devices from different suppliers, which both show the same results.

Many thanks!

On Fri, 29 Nov 2019 at 12:30, Dejan Corovic via Groups.Io <Dejan.Corovic=
[email protected]> wrote:

Agreed.

So is there a seller on UK eBay or Amazon that you bought before and he
wasn't selling fakes?

If you intend using the unit without a PC attached, I would get one with a
larger screen, rather than the standard screen.


Dave.

--

Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom

On Fri, Nov 29, 2019 at 04:30 AM, Dejan Corovic wrote:

So is there a seller on UK eBay or Amazon that you bought before and he wasn't selling fakes?
==============================================================================
I bought mine on eBay, , from seller shuangtai-elec. His positive feedback is very high and delivery time was shorter than estimated by a week. UK and US ebay usually have parallel offerings.

Besides some of its latest enhancements, the reason I purchased the NanoVNA-H is I wanted to support hugen's efforts by purchasing one of his units. Its hard to do that with the original open case design because the cloner's have gotten so good. At this point in time, I have not seen a clone of the NanoVNA-H that is not an obvious fake. Hugen has packaged the NanoVNA-H in a very distinctive box with molded plastic inserts to hold and protect the unit and its various accessories. The enclosed case design for the NanoVNA-H itself is also distinctive. If the unit you purchase is as pictured in the ebay auction that I referenced, then you can be fairly certain it is a hugen product, in this case probably second sourced from him.

- Herb

The known official store of Hugen is here

The other sellers on ebay, aliexpress, amazon, etc are usually selling
clones. Very rarely, some are reselling originals from Hugen.

In my opinion, is better to get the original, which has the latest hardware
upgrades and firmware, and also supporting the developer in this way.

Ady YO2NAA


On Fri, Nov 29, 2019 at 2:30 PM Dejan Corovic via Groups.Io <Dejan.Corovic=
[email protected]> wrote:

Agreed.

So is there a seller on UK eBay or Amazon that you bought before and he
wasn't selling fakes?

Agreed.

So is there a seller on UK eBay or Amazon that you bought before and he wasn't selling fakes?

Owen cannot compare a $10k VNA against a $50 one

I am happy with the cheap and cheerful H version for basic understanding
and experimentation

To expect lab grade performance is ridiculous

John ve3ips
--
Sent with a Palm Pilot. Ve3ips.wordpress.com
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