Re: Audio frequency version of a NanoVNA
Since the NanoVNA covers from 10kHz up, one can use the sound system of a PC with suitable software to provide the lower frequency coverage. Even the most basic sound chip in a PC will cover 20Hz to 20kHz, and often the low frequency coverage extends to a few Hz. Some better audio cards also offer coverage beyond the audio range, to 40kHz or even more.
Software like ARTA-LIMP allows making useful measurements.
Smith charts, I don't know. I don't use them much myself, as for most situations I find standard X/Y charts more practical. But of course it's perfectly feasible to write VNA software for the PC sound system, that generates Smith charts too.
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Re: Tuning a Firestick NGP antenna
On Mon, Nov 11, 2024 at 12:06 PM, Michael Robinson wrote:
Essentially, using
RG-58 (50 ohms) at multiple half-wavelengths with zero volts at each end
removes the coax from the equation
ODD half-wavelengths of ANY impedance transmission line will repeat the impedance presented at the far end. It is not confined to RG-58 or to 50¦¸ line. 73, Don N2VGU
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Re: Audio frequency version of a NanoVNA
It's not quite what you want but the old HP 4800A Vector Impedance Meter does 5 Hz to 550 kHz. Manual (as in 'hand operated') sweeping though!
DaveB, NZ
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of John Gord via groups.io Sent: Tuesday, November 12, 2024 11:24 To: [email protected]Subject: Re: [nanovna-users] Audio frequency version of a NanoVNA Neil, The HP3577A VNA with HP35676A test set covers from 5Hz to 200MHz. Only weighs about 70lb. Some versions of the NanoVNA-H4 firmware work down to 800Hz (I don't know how well). I don't know if there is an affordable and portable unit that works below 800Hz. --John Gord On Mon, Nov 11, 2024 at 08:11 AM, Neil Preston W0NRP wrote:
Is there any practical way to make a VNA that provides the same
measurements over the frequency range of ~10 Hz to maybe 1 MHz?
Is that something that could be done with computer or cellphone apps?
I know that you can get FFT and scope apps, but I would like to see
the Smith chart for an audio network and other parameters.
Maybe with a variable normalizing impedance....
.... My Christmas wish list.
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Re: Audio frequency version of a NanoVNA
Neil,
The HP3577A VNA with HP35676A test set covers from 5Hz to 200MHz. Only weighs about 70lb.
Some versions of the NanoVNA-H4 firmware work down to 800Hz (I don't know how well).
I don't know if there is an affordable and portable unit that works below 800Hz.
--John Gord
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On Mon, Nov 11, 2024 at 08:11 AM, Neil Preston W0NRP wrote:
Is there any practical way to make a VNA that provides the same measurements
over the frequency range of ~10 Hz to maybe 1 MHz?
Is that something that could be done with computer or cellphone apps?
I know that you can get FFT and scope apps, but I would like to see the Smith
chart for an audio network and other parameters.
Maybe with a variable normalizing impedance....
.... My Christmas wish list.
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Re: Dipole antenna with Low Z0 feed point Impedance
Hi Frank,
I'm a huge fan of yours, and very grateful for your countless contributions that continue to elevate the hobby. Many many thanks! Yes, I counted your suggestion of two 1/4-wave sections of 75-ohm coax in parallel as one of the best. Regarding effective bandwidth, that method will also be dominated by that of the antenna.
Best 73s,
Dave NU8A
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On Mon, Nov 11, 2024 at 01:26 PM, Frank Donovan wrote:
Dave forgot to model what is likely to be the broadest bandwidth solution
using coaxial cable: Two 90 degree lengths of 75 ohm coax in parallel
73
Frank
W3LPL
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Re: Dipole antenna with Low Z0 feed point Impedance
Dave forgot to model what is likely to be the broadest bandwidth solution
using coaxial cable: Two 90 degree lengths of 75 ohm coax in parallel
73
Frank
W3LPL
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----- Original Message ----- From: "DP via groups.io" <dpoinsett@...> To: [email protected]Sent: Monday, November 11, 2024 10:20:35 AM Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance To Bill WA2WIO: You received several good suggestions on how to transform 25 ohms to 50 ohms. Here are a few more ideas that use only coax. Method 1: Connect a 70.0 degree length of 50-ohm coax to the antenna feedpoint. Follow this with a 129 degree length of 75-ohm coax. Now you have 50 ohms. At 7.15 MHz this could be 17.3 ft of RG-58A/U (Belden 8259) and 32.2 ft of RG-59/U (Belden 8241). Method 2: Connect a 143 degree length of 50-ohm coax to the antenna feedpoint. At the other end connect a shorted stub that's 56.3 degrees long made from 50-ohm coax. The impedance at the junction will be 50 ohms. At 7.15 MHz the first section could be 35.4 ft of RG-58A/U (Belden 8259). The shorted stub could be 13.9 ft of the same. Method 3: Connect a 34.5 degree length of 50-ohm coax to the antenna feedpoint. At the other end connect an open stub 34.7 degrees long made from 50-ohm coax. The impedance at the junction will be 50 ohms. At 7.15 MHz the first section could be 8.54 ft of RG-58A/U (Belden 8259). The open stub could be 8.58 ft of the same. Notes: 1. 360 degrees equals 1 wavelength. 2. The following factors primarily determine the actual physical length of coax for each of the methods listed: the start and end impedance, target frequency, coax characteristic impedance, and coax velocity factor. 3. All these methods have less than 0.6 dB loss at the target frequency using the coax types noted. Method 3 is the lowest at 0.2 dB. 4. Although these are not broadband methods per se, they yield about 170 KHz of bandwidth below SWR 2 which is about the same bandwidth you'd get with a broadband solution. Most of that is due to the amount of change in feedpoint impedance with frequency from the antenna itself. 5. It probably goes without saying that after the 50-ohm impedance has been achieved, any additional length of 50-ohm coax can be added as needed to get to the rig. 6. All results were solved graphically in SimNEC. It took longer to annotate the attached screenshots and write this reply than it took to create the SimNEC models and get the results. Once you learn SimNEC you can graphically create impedance transformations like this (and more) very fast with no math although it greatly helps to understand the underlying principles. Dave NU8A
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Re: Dipole antenna with Low Z0 feed point Impedance
To Bill WA2WIO:
You received several good suggestions on how to transform 25 ohms to 50 ohms. Here are a few more ideas that use only coax.
Method 1:
Connect a 70.0 degree length of 50-ohm coax to the antenna feedpoint. Follow this with a 129 degree length of 75-ohm coax. Now you have 50 ohms. At 7.15 MHz this could be 17.3 ft of RG-58A/U (Belden 8259) and 32.2 ft of RG-59/U (Belden 8241).
Method 2:
Connect a 143 degree length of 50-ohm coax to the antenna feedpoint. At the other end connect a shorted stub that's 56.3 degrees long made from 50-ohm coax. The impedance at the junction will be 50 ohms. At 7.15 MHz the first section could be 35.4 ft of RG-58A/U (Belden 8259). The shorted stub could be 13.9 ft of the same.
Method 3:
Connect a 34.5 degree length of 50-ohm coax to the antenna feedpoint. At the other end connect an open stub 34.7 degrees long made from 50-ohm coax. The impedance at the junction will be 50 ohms. At 7.15 MHz the first section could be 8.54 ft of RG-58A/U (Belden 8259). The open stub could be 8.58 ft of the same.
Notes:
1. 360 degrees equals 1 wavelength.
2. The following factors primarily determine the actual physical length of coax for each of the methods listed: the start and end impedance, target frequency, coax characteristic impedance, and coax velocity factor.
3. All these methods have less than 0.6 dB loss at the target frequency using the coax types noted. Method 3 is the lowest at 0.2 dB.
4. Although these are not broadband methods per se, they yield about 170 KHz of bandwidth below SWR 2 which is about the same bandwidth you'd get with a broadband solution. Most of that is due to the amount of change in feedpoint impedance with frequency from the antenna itself.
5. It probably goes without saying that after the 50-ohm impedance has been achieved, any additional length of 50-ohm coax can be added as needed to get to the rig.
6. All results were solved graphically in SimNEC. It took longer to annotate the attached screenshots and write this reply than it took to create the SimNEC models and get the results. Once you learn SimNEC you can graphically create impedance transformations like this (and more) very fast with no math although it greatly helps to understand the underlying principles.
Dave NU8A
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Re: Tuning a Firestick NGP antenna
Good morning, y'all. There is a fundamental feature of the physics involved in this particular antenna installation. No ground plane indicates a colinear antenna. But, the issue is, from the radio, through the SWR meter, to the antenna feed point requires specific lengths of coaxial feed line. That length can be any number of *electrical* half-wavelengths of coax from radio (or SWR meter with a very short jumper coax) to the antenna feed point. The point is to make each end of the feed system at zero volts! Essentially, using RG-58 (50 ohms) at multiple half-wavelengths with zero volts at each end removes the coax from the equation allowing for maximum power transfer from source to load minus the resistive losses within the lumped constants of the feed line. Just voicing my experiences; take it for what it is worth. Best Regards, Michael L Robinson, KC0TA ¡°In the beginning of a change the Patriot is a scarce man, and brave, and hated and scorned. When his cause succeeds, the timid join him, for then it costs nothing to be a Patriot.¡± ¨D Mark Twain When Tyranny becomes Law, Revolution becomes Duty! On Mon, Nov 11, 2024 at 7:42?AM Daniel Brown via groups.io <daniel.h.brown= [email protected]> wrote:
On Nov 11, 2024, at 8:21?AM, Andrew Harman via groups.io <Nexus9d9= [email protected]> wrote:
Yes, the coax is understood to be part of the antenna so an external
meter would have to be at the coax end and not the antenna feed point.
Also, Firestik says not to trim the length as it is factory matched.
They do say you can add coax but only in 9ft increments and on the radio
side. They specify it is resonant through 30mhz, my target will be 10m
at 28.4. (fingers crossed). So, it's being said that a VNA will work to
"time" the antenna leaves me wondering what the commenter was talking about
in his review. Another thought is that if this is like a sleeve dipole
that the SWR will vary if the coax is run horizontal, vertical or
diagonal. Diagonal runs tend to require a longer length - so the
placement during testing is critical.
But.....contrary to what was just said: You DO tune the antenna at the tip; You DO NOT ground the antenna mount. You should normally isolate the
bracket from a metallic mast if used. You can ground the remainder of the
mast for lightning protection if that's your choice. In this app the
shield is not bonded to the mounting bracket and it will be attached to PVC
pipe, there is no need to add a ground wire from the bracket.
Would be marginally interested (as in probably not enough to go buy one of
these ham-stick clones for myself) to see what happens if you tried running
the antenna against a ground plane with and without the OEM feed line. My
un-educated guess is it will be fine, maybe even better than the magic feed
line - though highly dependent on both the overall installation, as well as
the adjustment of the tuning stud. I used a set of Hamsticks for a while -
they¡¯re similar - fiberglass blank, wrapped with a loading coil, adjusted
by a stinger at the top end. Worked best against a decent ground plane - I
used 4 radials with the ¡¯stick on the end of a painters pole. The whole
setup was very frequency dependent since there is a very high ¡°Q¡± factor
with these types of dummy loads¡ errrr antennas.
--
Daniel Brown
daniel.h.brown@...
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Audio frequency version of a NanoVNA
Is there any practical way to make a VNA that provides the same measurements over the frequency range of ~10 Hz to maybe 1 MHz?
Is that something that could be done with computer or cellphone apps?
I know that you can get FFT and scope apps, but I would like to see the Smith chart for an audio network and other parameters.
Maybe with a variable normalizing impedance....
.... My Christmas wish list.
|
Re: Dipole antenna with Low Z0 feed point Impedance
k3eui. Barry;
Dipole is center fed 1/2 wave 66ft #18 stranded insulated in a rt angle horizontal V. The shape is necessitated by the complicated and crowded attic construction. Interesting idea. I need to read up on it. Thank you.
Kirk, NT0Z: I bought a copy of your book. "Stealth Amateur Radio" some time ago. Great resource. I can see I am not alone in my quest. Thank you
Bill WA2WIO
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Barry K3EUI via groups.io Sent: Sunday, November 10, 2024 7:10 PM To: [email protected]Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance I have a MUCH MUCH less messy solution. Is the dipole (center fed) 130 ft (80m) or 66 ft (40m) or 33 ft (20m)? Center feds will work on the 3rd harmonic, so a 40m can also tune to 15m. So¡. try this ¡ for $1. Put a small inductor (say 5 turns of wire 1 inch diam) across the dipole where it attached to the coax. If you have a 1:1 balun, leave it in place. This will RAISE the input impedance (just like the method to couple a mobile whip to 50 ohm coax. You MAY have to then shorten the wire a bit at each end ( try 1 ft at first) to get it back to the resonant freq you want. I often do this on a very low 80m dipole (130 ft) when it is low to the ground. Impedance at 20 ft above gnd is often about 20 ohms. But if you try to change the impedance by changing the LENGTH of your coax, the SWR will not change. You will only move the impedance around the Smith Chart, so you may get a higher impedance than 50 ohms, but the SWR will still not change. If on 80m you may need more inductance across the dipole input¡. so try 10 turns of wire, 1 inch diameter. Eventually the inductance in parallel with the dipole will raise the impedance to where the 50 ohm coax will match a bit better. Let us know if that works. Messing with 1:2 baluns is kind of silly and expensive when a simple inductor across the input will work. de k3eui. Barry
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Re: Tuning a Firestick NGP antenna
On Nov 11, 2024, at 8:21?AM, Andrew Harman via groups.io <Nexus9d9@...> wrote:
Yes, the coax is understood to be part of the antenna so an external meter would have to be at the coax end and not the antenna feed point. Also, Firestik says not to trim the length as it is factory matched. They do say you can add coax but only in 9ft increments and on the radio side. They specify it is resonant through 30mhz, my target will be 10m at 28.4. (fingers crossed). So, it's being said that a VNA will work to "time" the antenna leaves me wondering what the commenter was talking about in his review. Another thought is that if this is like a sleeve dipole that the SWR will vary if the coax is run horizontal, vertical or diagonal. Diagonal runs tend to require a longer length - so the placement during testing is critical.
But.....contrary to what was just said: You DO tune the antenna at the tip; You DO NOT ground the antenna mount. You should normally isolate the bracket from a metallic mast if used. You can ground the remainder of the mast for lightning protection if that's your choice. In this app the shield is not bonded to the mounting bracket and it will be attached to PVC pipe, there is no need to add a ground wire from the bracket.
Would be marginally interested (as in probably not enough to go buy one of these ham-stick clones for myself) to see what happens if you tried running the antenna against a ground plane with and without the OEM feed line. My un-educated guess is it will be fine, maybe even better than the magic feed line - though highly dependent on both the overall installation, as well as the adjustment of the tuning stud. I used a set of Hamsticks for a while - they¡¯re similar - fiberglass blank, wrapped with a loading coil, adjusted by a stinger at the top end. Worked best against a decent ground plane - I used 4 radials with the ¡¯stick on the end of a painters pole. The whole setup was very frequency dependent since there is a very high ¡°Q¡± factor with these types of dummy loads¡ errrr antennas. -- Daniel Brown daniel.h.brown@...
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Re: Dipole antenna with Low Z0 feed point Impedance
Using a NanoVNA or a MFJ 259 either is the source of the RF... whereas using a transmitter then a short length of coax to a SWR bridge, changes the length of the source of RF to the antenna..
Larry W8LM
ARRL Life Member Licensed 59 years
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Re: Tuning a Firestick NGP antenna
Yes, the coax is understood to be part of the antenna so an external meter would have to be at the coax end and not the antenna feed point. Also, Firestik says not to trim the length as it is factory matched. They do say you can add coax but only in 9ft increments and on the radio side. They specify it is resonant through 30mhz, my target will be 10m at 28.4. (fingers crossed). So, it's being said that a VNA will work to "time" the antenna leaves me wondering what the commenter was talking about in his review. Another thought is that if this is like a sleeve dipole that the SWR will vary if the coax is run horizontal, vertical or diagonal. Diagonal runs tend to require a longer length - so the placement during testing is critical.
But.....contrary to what was just said: You DO tune the antenna at the tip; You DO NOT ground the antenna mount. You should normally isolate the bracket from a metallic mast if used. You can ground the remainder of the mast for lightning protection if that's your choice. In this app the shield is not bonded to the mounting bracket and it will be attached to PVC pipe, there is no need to add a ground wire from the bracket.
Regards,
/a
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Re: Tuning a Firestick NGP antenna
Perhaps my ignorance is showing, but It occurred to me that the linked "documentation", , makes it fairly clear why the Firestick NGP is named as such, why a customized feedline length, and the propriety of an swr tuning procedure with a NanoVNA or MFJ259, at the transmitter end of that customized length.
The Ol' Dog
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Re: Dipole antenna with Low Z0 feed point Impedance
I have a MUCH MUCH less messy solution.
Is the dipole (center fed) 130 ft (80m) or 66 ft (40m) or 33 ft (20m)?
Center feds will work on the 3rd harmonic, so a 40m can also tune to 15m.
So¡. try this ¡ for $1.
Put a small inductor (say 5 turns of wire 1 inch diam) across the dipole where it attached to the coax.
If you have a 1:1 balun, leave it in place.
This will RAISE the input impedance (just like the method to couple a mobile whip to 50 ohm coax.
You MAY have to then shorten the wire a bit at each end ( try 1 ft at first) to get it back to the resonant freq you want.
I often do this on a very low 80m dipole (130 ft) when it is low to the ground.
Impedance at 20 ft above gnd is often about 20 ohms.
But if you try to change the impedance by changing the LENGTH of your coax, the SWR will not change.
You will only move the impedance around the Smith Chart, so you may get a higher impedance than 50 ohms,
but the SWR will still not change.
If on 80m you may need more inductance across the dipole input¡. so try 10 turns of wire, 1 inch diameter.
Eventually the inductance in parallel with the dipole will raise the impedance to where the 50 ohm coax will match a bit better.
Let us know if that works.
Messing with 1:2 baluns is kind of silly and expensive when a simple inductor across the input will work.
de k3eui. Barry
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Re: Tuning a Firestick NGP antenna
Actually the firestick NGP does indeed time at the antenna, and it does use the coax as a counterpoise. It does not use the vehicle as ground plane. I have one on a fiberglass bodied vehicle and used a VNA to time the tip of the antenna for best return loss at center operating frequency. 30dB return loss on CB channel 20 is as good as it gets.. and yes, extending the coax made it un-tunable on CB freqs. On Sun, Nov 10, 2024, 12:43?PM Clyde Lambert via groups.io <clyde.lambert= [email protected]> wrote: Hello,
The Firestick NGP is a mobile CB antenna designed to be mounted on a
vehicle. That is why it has NO radials.
The vehicle is supposed to make up the ground plane, not the coaxial lead.
Without knowing where, to what or how the antenna is going to be mounted,
the worry of RF on the coaxial lead may not be a concern unless, it is used
as a fixed station antenna or one does not properly ground the antenna
mount to the vehicle.
In my 60 years of civilian, military and commercial, mobile communications
installations, I have never had a problem of using an external SWR meter to
tune a antenna installed between the coaxial lead and radio. NOT at the
antenna feed point.
You DO NOT tune the antenna itself.
Clyde Lambert KC7BJE
Retired Electronics Manufactureing Engineer
U.S. Army Signal Corps Veteran
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Re: Tuning a Firestick NGP antenna
Hello,
The Firestick NGP is a mobile CB antenna designed to be mounted on a
vehicle. That is why it has NO radials.
The vehicle is supposed to make up the ground plane, not the coaxial lead.
Without knowing where, to what or how the antenna is going to be mounted,
the worry of RF on the coaxial lead may not be a concern unless, it is used
as a fixed station antenna or one does not properly ground the antenna
mount to the vehicle.
In my 60 years of civilian, military and commercial, mobile communications
installations, I have never had a problem of using an external SWR meter to
tune a antenna installed between the coaxial lead and radio. NOT at the
antenna feed point.
You DO NOT tune the antenna itself.
Clyde Lambert KC7BJE
Retired Electronics Manufactureing Engineer
U.S. Army Signal Corps Veteran
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Re: Tuning a Firestick NGP antenna
I'm using a NGP antenna in a camper for reasons. While an in-line SWR meter can cause issues, the VNA is the perfect tool for tuning. Got mine tuned to over 30dB return loss. Chris Smith NK9W On Sun, Nov 10, 2024 at 7:39?AM Mike N2MS via groups.io <mstangelo= [email protected]> wrote: These "No Ground" antennas use the coax feeding it or the ground
connections to the radio as the counterpoise to the radiating element hence
the recommendation to use the radio's SWR meter. I would stay away form
these antennas if your don't want RF in your shack..
All of these "no ground" antenna are descendants of the Gotham Antennas
sold when I was young:
<>
Mike N2MS
On 11/10/2024 7:12 AM EST Andrew Harman via groups.io <nexus9d9= [email protected]> wrote:
I have a Firestick No Ground Plane antenna on order that I'm going to
install for a friend. Reading through the reviews there are comments that
you cannot use an external SWR meter to tune it. That you use the radio's
internal SWR meter. I'm not sure why this would be or if that also means
I cannot use either my NanoVNA or MFJ259. Does anyone have any background
with these?
Thanks again,
/A
in the following forum areas:
Documentation & Update Files: /g/nanovna-users/files Knowledge-based Wiki: /g/nanovna-users/wiki
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Group Owner: [email protected]
Unsubscribe: /g/nanovna-users/leave/11823847/89811/742747392/xyzzy [
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Only 9 vertical graduation on 4'' H4 version !!
Hi all
It seems there is only 9 vertical graduation lines on the 4'' H4 version , if it can be configured to 11 graduations as with 4'' F version ??
73's Nizar
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Re: Tuning a Firestick NGP antenna
These "No Ground" antennas use the coax feeding it or the ground connections to the radio as the counterpoise to the radiating element hence the recommendation to use the radio's SWR meter. I would stay away form these antennas if your don't want RF in your shack.. All of these "no ground" antenna are descendants of the Gotham Antennas sold when I was young: <> Mike N2MS On 11/10/2024 7:12 AM EST Andrew Harman via groups.io <nexus9d9@...> wrote:
I have a Firestick No Ground Plane antenna on order that I'm going to install for a friend. Reading through the reviews there are comments that you cannot use an external SWR meter to tune it. That you use the radio's internal SWR meter. I'm not sure why this would be or if that also means I cannot use either my NanoVNA or MFJ259. Does anyone have any background with these?
Thanks again,
/A in the following forum areas: Documentation & Update Files: /g/nanovna-users/files
Knowledge-based Wiki: /g/nanovna-users/wiki
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Group Owner: [email protected]
Unsubscribe: /g/nanovna-users/leave/11823847/89811/742747392/xyzzy [mstangelo@...]
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Donald S Brant Jr
Larry Macionski
Barry K3EUI
Clyde Lambert