|
Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is ~41.5 cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
Did you do an OSL calibration of the NanoVNA over the frequency range of interest? How is the antenna supported? How is it fed? I cannot imagine an antenna being that far off. Your length calculations for 172 MHz are correct. The third harmonic of 172 MHz IS 513 MHz. So the antenna will work at that frequency. Dipole antennas typically work well at odd harmonics of the lowest resonant frequency. What is the SWR at 172 MHz? Zack W9SZ On Mon, Mar 31, 2025 at 2:51?AM hobride via groups.io <hobride= [email protected]> wrote: Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be tuned
for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is ~41.5 cm
(1,36 feet).
When I now connect this antenna and try to measure it, the result is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord and
Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
Hello,
yes, I have also performed an OSL calibration in the 150-190 MHz range. The SWR at 172 MHz is 4.5
I made the legs from copper wire with ~1mm diameter. The legs are mounted in a plastic tube. The feed element is a BNC - 4mm connector as shown in the attached picture. The antenna is mounted in vertical position and hangs from the ceiling.
by the way, the antenna works fine at 172 MHz
|
|
|
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
toggle quoted message
Show quoted text
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride@...> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is ~41.5 cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at the antenna feedpoint to prevent the feeder from affecting the measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz, but I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
toggle quoted message
Show quoted text
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote: You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride@...> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is ~41.5 cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
Bob, Would you suggest a voltage balun or current balun at antenna feedpoint? One ham told me that if you use a voltage balun, it can bring down the high noise I have on 80m. Regarding the original question, I am tempted to think like Milt. I see a lot of harmonic resonance in NanoVNA tracings when I set the range high on purpose. In fact I use them to work higher bands. I am able to work North America from VU on 12m, using my 80m center-fed dipole mounted at just 5m height and 100W, with a little bit of touching up with the N7DDC tuner. That would be the seventh harmonic resonance! 73 Jon, VU2JO On Mon, Mar 31, 2025 at 6:29?PM Bob Ecclestone VK2ZRE via groups.io <becclest@...> wrote: Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at the
antenna feedpoint to prevent the feeder from affecting the measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz, but
I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote:
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride= [email protected]> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be
tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is ~41.5
cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord
and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
I have never seen a problem feeding a dipole directly with an unbalanced feedline. The last dipoles I had up (which were for 40 and 30 meters) were just fed by connecting the two leads of the coax directly to the antenna wires attached to an insulator at the center of the antenna. SWR in both cases, when the antenna was trimmed, were around 1.05:1. And I worked 180 countries on 40 m CW with that antenna and Japan fairly often on 30 m CW. Zack W9SZ <> Virus-free.www.avg.com <> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Mon, Mar 31, 2025 at 7:59?AM Bob Ecclestone VK2ZRE via groups.io <becclest@...> wrote: Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at the
antenna feedpoint to prevent the feeder from affecting the measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz, but
I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote:
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride= [email protected]> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be
tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is ~41.5
cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord
and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
It's measuring the 3rd harmonic which shows a nice low SWR. how far below 172 Mhz did you start your scan?
Joe WB9SBD
toggle quoted message
Show quoted text
On 3/31/2025 2:50 AM, hobride via groups.io wrote: Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is ~41.5 cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
Yup!
The Balun Craze is a new Generation thing. Got licensed in 1975, Never ever heard of a Balun.
All my dipoles were direct feed.
Only till recently has the myth of a dipole without a balun will not work.
just like a 40 meter Dipole will not work on 15 meters!
tell that to all the Novices that got their license in the 70's.
Joe WB9SBD
toggle quoted message
Show quoted text
On 3/31/2025 8:53 AM, Zack Widup via groups.io wrote: I have never seen a problem feeding a dipole directly with an unbalanced
feedline. The last dipoles I had up (which were for 40 and 30 meters) were
just fed by connecting the two leads of the coax directly to the antenna
wires attached to an insulator at the center of the antenna. SWR in both
cases, when the antenna was trimmed, were around 1.05:1. And I worked 180
countries on 40 m CW with that antenna and Japan fairly often on 30 m CW.
Zack W9SZ
<>
Virus-free.www.avg.com
<>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
On Mon, Mar 31, 2025 at 7:59?AM Bob Ecclestone VK2ZRE via groups.io
<becclest@...> wrote:
Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at the
antenna feedpoint to prevent the feeder from affecting the measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz, but
I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote:
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride= [email protected]> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be
tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is ~41.5
cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord
and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
Joe, I got licensed a decade after you and did not have a chance to use a balun or 50 ohms coax then. My 40 and 80m dipoles were fed by 75 ohms TV cable. I did not have an SWR meter either. Still I could work a lot of DX including a few W land stations with my homebrew 3 x 807 radio, 120W CW and straight key. I still have a couple of W land QSL cards in my precious collection. 73 Jon, VU2JO On Mon, Mar 31, 2025 at 7:50?PM Joe WB9SBD via groups.io <nss= [email protected]> wrote: Yup!
The Balun Craze is a new Generation thing. Got licensed in 1975, Never
ever heard of a Balun.
All my dipoles were direct feed.
Only till recently has the myth of a dipole without a balun will not work.
just like a 40 meter Dipole will not work on 15 meters!
tell that to all the Novices that got their license in the 70's.
Joe WB9SBD
On 3/31/2025 8:53 AM, Zack Widup via groups.io wrote:
I have never seen a problem feeding a dipole directly with an unbalanced
feedline. The last dipoles I had up (which were for 40 and 30 meters) were
just fed by connecting the two leads of the coax directly to the antenna
wires attached to an insulator at the center of the antenna. SWR in both
cases, when the antenna was trimmed, were around 1.05:1. And I worked 180
countries on 40 m CW with that antenna and Japan fairly often on 30 m CW.
Zack W9SZ
<
Virus-free.www.avg.com
<
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
On Mon, Mar 31, 2025 at 7:59?AM Bob Ecclestone VK2ZRE via groups.io
<becclest@...> wrote:
Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at the
antenna feedpoint to prevent the feeder from affecting the measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz, but
I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote:
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride= [email protected]> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be
tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is
~41.5
cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord
and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
Have you turned on the VNA's Smith chart? At what frequencies thru your sweep does the trace cross the chart's center (no reactance) line? Those are your antenna's resonant frequencies. The one closest to the center is your best resonance...
|
I got my Novice license in 1957 and used a single wire routed out the window and up to the brick chimney and then across the yard about 100 feet to a pole. It worked fine, with my best DX using a Knight Kit 50 watt (input) transmitter being an Argentine station in Antarctica. I worked a few Japanese stations and some South Americans from my QTH in Northern California, never realizing that my antenna was really awful.
When I upgraded from Novice to Conditional in 1958, I used a 100TH with the same antenna to work folks on AM and CW. With either transmitter, I had to stand up and throw a knife switch on the wall to go from receive to transmit.
I also still have a bunch of QSL cards from that era that bring back nice memories.
The important thing was that my Knight Kit with a pi-network and my 100TH with a swinging link coupler didn't care much about the SWR. I simply tuned for about a 10% drop in plate current and no red glow from the 100TH and everything worked fine. With a modern transmitter that wants something approximating 50 ohms, such an antenna would require a tuner and the losses in the tuner might use up a lot of the generated RF energy.
My most modern rigs here still use pi-networks, which is why I can get away with using a wire in the attic draped over air conditioning ducts and water pipes and work DX, not like a real DXer would want, but enough for a casual guy.
73,
Maynard
W6PAP
toggle quoted message
Show quoted text
On 3/31/25 08:07, Jon via groups.io wrote: Joe,
I got licensed a decade after you and did not have a chance to use a balun
or 50 ohms coax then. My 40 and 80m dipoles were fed by 75 ohms TV cable. I
did not have an SWR meter either. Still I could work a lot of DX including
a few W land stations with my homebrew 3 x 807 radio, 120W CW and straight
key. I still have a couple of W land QSL cards in my precious collection.
73
Jon, VU2JO
On Mon, Mar 31, 2025 at 7:50?PM Joe WB9SBD via groups.io <nss=
[email protected]> wrote:
Yup!
The Balun Craze is a new Generation thing. Got licensed in 1975, Never
ever heard of a Balun.
All my dipoles were direct feed.
Only till recently has the myth of a dipole without a balun will not work.
just like a 40 meter Dipole will not work on 15 meters!
tell that to all the Novices that got their license in the 70's.
Joe WB9SBD
On 3/31/2025 8:53 AM, Zack Widup via groups.io wrote:
I have never seen a problem feeding a dipole directly with an unbalanced
feedline. The last dipoles I had up (which were for 40 and 30 meters) were
just fed by connecting the two leads of the coax directly to the antenna
wires attached to an insulator at the center of the antenna. SWR in both
cases, when the antenna was trimmed, were around 1.05:1. And I worked 180
countries on 40 m CW with that antenna and Japan fairly often on 30 m CW.
Zack W9SZ
<
Virus-free.www.avg.com
<
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
On Mon, Mar 31, 2025 at 7:59?AM Bob Ecclestone VK2ZRE via groups.io
<becclest@...> wrote:
Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at the
antenna feedpoint to prevent the feeder from affecting the measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz, but
I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote:
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride= [email protected]> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be
tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is
~41.5
cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord
and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
Maynard and others:
You and we were most fortunate to be initiated with one of the most robust sunspot cycles of modern times in 1957!!
Same story at pre-Nano VNA KN1CJO in southern Maine. Worked all over the place, including all TV sets in the neighborhood.
Antenna was classic Windom, usual length, but fed with 300 feet of single wire to bannana plug into the DX-20 antenna port, me serving as T-R relay.
We are equally fortunate to still be able to remember all that, and be alive to write about
Ed McCann
AG6CX
Sausalito
toggle quoted message
Show quoted text
On Mar 31, 2025, at 8:45?AM, Maynard Wright, P. E., W6PAP via groups.io <ma.wright@...> wrote:
?I got my Novice license in 1957 and used a single wire routed out the window and up to the brick chimney and then across the yard about 100 feet to a pole. It worked fine, with my best DX using a Knight Kit 50 watt (input) transmitter being an Argentine station in Antarctica. I worked a few Japanese stations and some South Americans from my QTH in Northern California, never realizing that my antenna was really awful.
When I upgraded from Novice to Conditional in 1958, I used a 100TH with the same antenna to work folks on AM and CW. With either transmitter, I had to stand up and throw a knife switch on the wall to go from receive to transmit.
I also still have a bunch of QSL cards from that era that bring back nice memories.
The important thing was that my Knight Kit with a pi-network and my 100TH with a swinging link coupler didn't care much about the SWR. I simply tuned for about a 10% drop in plate current and no red glow from the 100TH and everything worked fine. With a modern transmitter that wants something approximating 50 ohms, such an antenna would require a tuner and the losses in the tuner might use up a lot of the generated RF energy.
My most modern rigs here still use pi-networks, which is why I can get away with using a wire in the attic draped over air conditioning ducts and water pipes and work DX, not like a real DXer would want, but enough for a casual guy.
73,
Maynard
W6PAP
On 3/31/25 08:07, Jon via groups.io wrote:
Joe,
I got licensed a decade after you and did not have a chance to use a balun
or 50 ohms coax then. My 40 and 80m dipoles were fed by 75 ohms TV cable. I
did not have an SWR meter either. Still I could work a lot of DX including
a few W land stations with my homebrew 3 x 807 radio, 120W CW and straight
key. I still have a couple of W land QSL cards in my precious collection.
73
Jon, VU2JO
On Mon, Mar 31, 2025 at 7:50?PM Joe WB9SBD via groups.io <nss=
[email protected]> wrote:
Yup!
The Balun Craze is a new Generation thing. Got licensed in 1975, Never
ever heard of a Balun.
All my dipoles were direct feed.
Only till recently has the myth of a dipole without a balun will not work.
just like a 40 meter Dipole will not work on 15 meters!
tell that to all the Novices that got their license in the 70's.
Joe WB9SBD
On 3/31/2025 8:53 AM, Zack Widup via groups.io wrote:
I have never seen a problem feeding a dipole directly with an unbalanced
feedline. The last dipoles I had up (which were for 40 and 30 meters) were
just fed by connecting the two leads of the coax directly to the antenna
wires attached to an insulator at the center of the antenna. SWR in both
cases, when the antenna was trimmed, were around 1.05:1. And I worked 180
countries on 40 m CW with that antenna and Japan fairly often on 30 m CW.
Zack W9SZ
<
Virus-free.www.avg.com
<
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
On Mon, Mar 31, 2025 at 7:59?AM Bob Ecclestone VK2ZRE via groups.io
<becclest@...> wrote:
Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at the
antenna feedpoint to prevent the feeder from affecting the measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz, but
I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote:
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride= [email protected]> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be
tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is
~41.5
cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord
and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
You need to calibrate your coax SOL at the far end, so your readings look like your antenna is at the vna and not some distance away.9 On Mon, Mar 31, 2025, 12:58 AG6CX via groups.io <edwmccann= [email protected]> wrote: Maynard and others:
You and we were most fortunate to be initiated with one of the most robust
sunspot cycles of modern times in 1957!!
Same story at pre-Nano VNA KN1CJO in southern Maine. Worked all over the
place, including all TV sets in the neighborhood.
Antenna was classic Windom, usual length, but fed with 300 feet of single
wire to bannana plug into the DX-20 antenna port, me serving as T-R relay.
We are equally fortunate to still be able to remember all that, and be
alive to write about
Ed McCann
AG6CX
Sausalito
On Mar 31, 2025, at 8:45?AM, Maynard Wright, P. E., W6PAP via groups.io <ma.wright@...> wrote:
?I got my Novice license in 1957 and used a single wire routed out the
window and up to the brick chimney and then across the yard about 100 feet
to a pole. It worked fine, with my best DX using a Knight Kit 50 watt
(input) transmitter being an Argentine station in Antarctica. I worked a
few Japanese stations and some South Americans from my QTH in Northern
California, never realizing that my antenna was really awful.
When I upgraded from Novice to Conditional in 1958, I used a 100TH with
the same antenna to work folks on AM and CW. With either transmitter, I
had to stand up and throw a knife switch on the wall to go from receive to
transmit.
I also still have a bunch of QSL cards from that era that bring back
nice memories.
The important thing was that my Knight Kit with a pi-network and my
100TH with a swinging link coupler didn't care much about the SWR. I
simply tuned for about a 10% drop in plate current and no red glow from the
100TH and everything worked fine. With a modern transmitter that wants
something approximating 50 ohms, such an antenna would require a tuner and
the losses in the tuner might use up a lot of the generated RF energy.
My most modern rigs here still use pi-networks, which is why I can get
away with using a wire in the attic draped over air conditioning ducts and
water pipes and work DX, not like a real DXer would want, but enough for a
casual guy.
73,
Maynard
W6PAP
On 3/31/25 08:07, Jon via groups.io wrote:
Joe,
I got licensed a decade after you and did not have a chance to use a
balun
or 50 ohms coax then. My 40 and 80m dipoles were fed by 75 ohms TV
cable. I
did not have an SWR meter either. Still I could work a lot of DX
including
a few W land stations with my homebrew 3 x 807 radio, 120W CW and
straight
key. I still have a couple of W land QSL cards in my precious
collection.
73
Jon, VU2JO
On Mon, Mar 31, 2025 at 7:50?PM Joe WB9SBD via groups.io <nss=
[email protected]> wrote:
Yup!
The Balun Craze is a new Generation thing. Got licensed in 1975, Never
ever heard of a Balun.
All my dipoles were direct feed.
Only till recently has the myth of a dipole without a balun will not
work.
just like a 40 meter Dipole will not work on 15 meters!
tell that to all the Novices that got their license in the 70's.
Joe WB9SBD
On 3/31/2025 8:53 AM, Zack Widup via groups.io wrote:
I have never seen a problem feeding a dipole directly with an
unbalanced
feedline. The last dipoles I had up (which were for 40 and 30 meters) were
just fed by connecting the two leads of the coax directly to the
antenna
wires attached to an insulator at the center of the antenna. SWR in
both
cases, when the antenna was trimmed, were around 1.05:1. And I worked
180
countries on 40 m CW with that antenna and Japan fairly often on 30 m
CW.
Zack W9SZ
<
Virus-free.www.avg.com
<
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
On Mon, Mar 31, 2025 at 7:59?AM Bob Ecclestone VK2ZRE via groups.io
<becclest@...> wrote:
Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at
the
antenna feedpoint to prevent the feeder from affecting the
measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz,
but
I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote:
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride= [email protected]> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be
tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is
~41.5
cm (1,36 feet).
When I now connect this antenna and try to measure it, the result
is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried
DiSlord
and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
The SWR for a 50 Ohm cable will depend on the feedpoint impedance at the end of the cable. The impedance will depend on the antenna dimensions, its height, and its proximity to the environment. If the antenna is supported horizontally, its impedance at resonance could vary from a few Ohms to a maximum around 90 Ohms and then down to about 72 Ohms as the height is increased. If you are seeing a minimum SWR at your operating frequency, the length of the antenna is at or very close to a half-wave. Sometimes you can bend the ends of the antenna towards the ground and reduce their length to bring the impedance to 50 Ohms and an SWR of 1.0.
|
I suspected the 50 Ohm calibration resistor and ordered two new ones.
After recalibration and measurement, the SWR is 1.26 at 172 MHz and 1.65 at 522 MHz.
Both measurements with SOL calibrated center frequencies 172 span 50 MHz and center 522 MHz span 50 MHz
that is much more plausible to me, i'm right?
I think that was the reason.
thanks for your support
|
Yes,a dipole will work without a balun. But it is not a dipole anymore. The outer surface of your coax shield becomes part of the antenna system. This can give inaccurate results with the VNA. In real world usage it will distort the radiation pattern of the antenna and can provide a path for RFI in unexpected places. It's not rocket science but it *is* radio science.
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I have never seen a problem feeding a dipole directly with an unbalanced
feedline.
--
73
-Jim
NU0C
|
Hello Jon,
As you wish to use the antenna on the higher harmonics as well as 2M, I would suggest you use ferrites to create a Common Mode Choke (CMC) as noted by Roger.
I suspect (but do not know, I am no expert here) that it would be difficult to build a broadband balun to cover your frequency range (x5, x7) at TX power levels.
As for some of the other comments to this thread, I did not say that your antenna would not work without a balun or CMC.
What I said was that without a balun or CMC, the connection of an unbalanced VNA to a balanced dipole would not give correct measurement results of the antenna because the feedline would become part of the antenna measurement as also noted in other responses in this thread.
Your experience when you used a replacement "load" to do your calibration just emphasises how critical it is to do calibrations correctly and to treat your calibration SOLT "standards" with care and respect.
We can measure antennas till the cows come home and hypothesize on the results for twice as long, but we all know that the most unlikely collection of bits and bobs will form some sort of antenna that may, or may not, enable QSOs one way or the other. However a successful QSO is not scientific evidence of a "good" or "bad" antenna.
If it works, great. But do not use this as evidence of optimum antenna performance:-)
The "suck it and see" approach may not quite equate to measured results:-) Just my 2 cents worth.
Cheers...Bob VK2ZRE
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On 1/04/2025 12:25 am, Jon via groups.io wrote: Bob,
Would you suggest a voltage balun or current balun at antenna feedpoint?
One ham told me that if you use a voltage balun, it can bring down the high
noise I have on 80m.
Regarding the original question, I am tempted to think like Milt. I see a
lot of harmonic resonance in NanoVNA tracings when I set the range high on
purpose. In fact I use them to work higher bands. I am able to work North
America from VU on 12m, using my 80m center-fed dipole mounted at just 5m
height and 100W, with a little bit of touching up with the N7DDC tuner.
That would be the seventh harmonic resonance!
73
Jon, VU2JO
On Mon, Mar 31, 2025 at 6:29?PM Bob Ecclestone VK2ZRE via groups.io
<becclest@...> wrote:
Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at the
antenna feedpoint to prevent the feeder from affecting the measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz, but
I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote:
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride= [email protected]> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be
tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is ~41.5
cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord
and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
On Mon, Mar 31, 2025 at 03:20 PM, Joe WB9SBD wrote: The Balun Craze is a new Generation thing. Got licensed in 1975, Never
ever heard of a Balun.
All my dipoles were direct feed.
Only till recently has the myth of a dipole without a balun will not work. When I started in ham radio, 46 years ago, indeed almost nobody used baluns with dipole antennas. Nowadays instead it's very common to use them, and there are at least two good reasons for this change! One reason is interference between radio equipment and other stuff in the home. Computers, switching power supplies, TVs, even refrigerators and lamps. When no balun is used, the feedline is part of the antenna, so the antenna extends into the shack and the home's electrical wiring, severely worsening the interference situation. With a balun that's working ideally, the feedline does not radiate, and does not receive signals, so is not part of the antenna. That moves the actual antenna out of the home, away from the switching power supplies and other stuff, reducing the interference both ways. Back before the 1980s this wasn't such a big factor, because there were no switching power supplies, no computers, no LED lamps, no CFL lamps with electronic ballasts, no LAN, and so on. TVI was the only point of concern, and sometimes handled by establishing time schedules for ham operation and for TV viewing. But today it's an important factor, because there are so many interference-causing and interference-sensitive things that it's not acceptable to turn them all off by a schedule. The other reason is how hams assess the condition and usability of their antennas. In the "good old times", the test was whether the transmitter could be loaded up into that antenna, without arcing, and how many contacts it produced. The antenna would be cut by trial and error to such a length that it worked well enough with that one specific feedline, in its fixed position. At most a ham might measure the SWR, but many didn't even have an SWR meter. Today instead, with instruments like the nanoVNA, hams have become scientists, trying to understand exactly what's going on, and will discover things like the antenna being resonant outside the band and operating on one the sides of the resonance dip, or that moving around the coax cable will change the SWR, or that adding even a little piece of coax will drastically change the impedance, shifting the resonant frequency. So they prefer to use baluns, to reduce the sensitivity of the antenna's parameters to feedline conditions, in order to be able to at least begin to understand what's happening with their antennas, and to achieve a setup that works more like theory tells. I began using baluns in 1989, when I got into packet radio, and needed to run a computer at the same time as a radio, and interconnect the two, hopefully without causing feedback loops. About that 172MHz dipole, I would expect it to measure differently according to its position relative to the nanoVNA and other stuff, to be sensitive to feedline length, etc. The usual stuff. If a balun is added, I would suggest a current balun, since we don't know how the antenna will be oriented, what will be close to it, but we do know that we want the lowest possible common-mode current on the feedline.
|
hobride
Ken
Jim Shorney