Re: How To Do A SWR Sweep on 2 Meter HT Antenna ?
On 10/20/22 8:10 PM, aackthpt@... wrote: On Thu, Oct 20, 2022 at 01:55 PM, Colin McDonald wrote:
A regular sized pizza pan with either wire or rods to extend the plane
to the right diameter for VHF would also work OK. I actually was considering building a ground plane for basically this same use of testing mobile antennas and came up with the idea of using a Harbor Freight circular saw blade (7 1/4 inch 140T plywood blade) that is $6 and 25ft mechanics wire ($1) to solder on radials. Probably cheaper than pizza pans, plus magnets will definitely stick to it. I think most pizza pans will be aluminum so that wouldn't happen.
Steel cookie sheets are easy to come by So is steel sheet at the hardware store.
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Re: How To Do A SWR Sweep on 2 Meter HT Antenna ?
On Thu, Oct 20, 2022 at 01:55 PM, Colin McDonald wrote: A regular sized pizza pan with either wire or rods to extend the plane
to the right diameter for VHF would also work OK. I actually was considering building a ground plane for basically this same use of testing mobile antennas and came up with the idea of using a Harbor Freight circular saw blade (7 1/4 inch 140T plywood blade) that is $6 and 25ft mechanics wire ($1) to solder on radials. Probably cheaper than pizza pans, plus magnets will definitely stick to it. I think most pizza pans will be aluminum so that wouldn't happen.
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Re: How To Do A SWR Sweep on 2 Meter HT Antenna ?
I direct connected my HT whip to the VNA when tuning some "Tiger tail"
ground radials for my HT antenna.
The antenna was a dual-band whip about 15" long, and I swept it attached to
nanoVNA-F which has a metal enclosure. The enclosure is just a little bit
larger than my HT, but results seem to have worked out pretty good.
I set it on edge of a table, but did not notice much of any variation when
grabbing hold of the VNA enclosure with my hand. That might be something to
watch out for if device isn't shielded.
I attached two separate radial wires to a single crimp ring connector under
the HT antenna screwed directly underneath the SMA connector, and then
trimmed one radial for 2m dip in band and the other for 440MHz dip in band.
Signals are now much better with the radials attached to the HT under the
antenna than the antenna alone had.
Maybe this removed the radio from the equation somewhat by providing a
"better alternative" return counterpoise path? I dunno.
I'd think that for adjusting the antenna itself, you could still get close
with it directly attached that way, but adding some tuned radials might
help.
I did notice resonant frequencies changed depending what counterpoise was
attached though, so the antennas may be only approximately tuned (if
they're tuned) assuming an "average" handheld as the counterpoise.
--
--Bryon, NF6M
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In my K and GMAX plot above you can see that the MMBTH10 can actually go unstable up at about 2.4GHz if given the correct input and output networks. K dips below 1 at this frequency. This vital information isn't available from the manufacturer because they only provided s2p data up to 1GHz for the MMBTH10.
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There's always the risk of damage (to the VNA) when measuring high power devices with a VNA. There are ways to minimise this risk, but this usually comes at the expense of measurement uncertainty.
The other advantage of measuring semiconductors is that you can explore beyond the typical frequency range offered by the manufacturer. This is very important when doing a stability analysis. In the MMBTH10 BJT plot below, the manufacturer only provides s-parameter data from about 40MHz to 1000MHz. I've measured from a few MHz out to about 3GHz. The agreement for GMA and K is quite good although the manufacturer's s2p data is about 30 years old. I'm not sure what equipment they would have used back then. The BJT die process may have subtly changed in this time as well. It only takes a nanohenry change in package inductance to make a notable change up at 1GHz in plots like this. My setup is generally very good, and I get good agreement with manufacturer's s2p data up to about 6GHz with faster devices.
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nanoVNA android app issue
I'm trying to get my just installed? Android nanoVNA app working with a older nanoVNA? running nanoVNA-Q. I can get the NanoVNA-Q device? to work with? the windows version of nanoVNA saver. I also have a nanoVNA-H 4 that works fine with win11 nanoVNA saver AND with the android nanoVNA app. The version of s/w I'm running on the nanoVNA-Q is 0.4.1-5bc0bde. I'm thinking the only place to look here is the software running on the nanoVNA-Q. I use the old 2.3 inch NanoVNA-Q to help tune my portable QRP setup. Using the phone for a display will be a big relief to my 73 year old eyes Does anyone have any suggestions? Thanks....
73 Jeff kb2m
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On 10/20/22 3:55 PM, W0LEV wrote: Most RF devices give you an S-Parameter table or at least show you where
the input and output are placed on the Smith Chart.
Dave - W?LEV
Not necessarily - see MRF454 a venerable HF PA transistor
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Re: How To Do A SWR Sweep on 2 Meter HT Antenna ?
Hi Jim, Thanks for the advice. I will probably first try connecting it directly to my VNA.
73 Frank KF2YD
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Re: SWR measurements too high and HIGHLY unstable
Sounds like you've got some common mode RF currents coming in on your feedlines. While your radios are generally relatively narrow band devices, your NanoVNA is by design a broadband device and could be affected by strong RF fields on a lot of different frequencies. Try putting some common mode chokes/ferrite beads on your feedlines. Sometimes just a few turn loop in the coax will make a big difference.
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Most RF devices give you an S-Parameter table or at least show you where
the input and output are placed on the Smith Chart.
Dave - W?LEV
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Show quoted text
On Thu, Oct 20, 2022 at 10:30 PM Leif M <leif.michaelsson@...> wrote: Right. I think mine is some 4ohms, but I have some 30W transistors with
less than 1ohms. I think I have todo something like you said, using a 4
ohms resistor and some capacitor at first. Problem with VNAs and bipolar
transistors is that input impedance is not constant with power. I have to
use a power splitter. Output matching seems also have an effect. So, I'll
make an RF ground on output at first.
-- *Dave - W?LEV* *Just Let Darwin Work*
--
Dave - W?LEV
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On 10/20/22 3:30 PM, Leif M wrote: Right. I think mine is some 4ohms, but I have some 30W transistors with less than 1ohms. I think I have todo something like you said, using a 4 ohms resistor and some capacitor at first. Problem with VNAs and bipolar transistors is that input impedance is not constant with power. I have to use a power splitter. Output matching seems also have an effect. So, I'll make an RF ground on output at first. most of the work with active devices on a VNA is "fixturing" - spend a bunch o bux and you can get a box that hooks up to your VNA and the device that does a lot of it. I guess if you're doing production design work, and you're spending $1000/day for engineer time, and $200k on the VNA, and "time is money" it can be worth it. Think about how nice "curve tracers" were when they came out. Or for that matter, GPIB controlled test equipment.
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Re: VNA H & H4 FW version 1.2.16
Here is a screen shot showing FW Ver. 1.2.16
Clyde KC7BJE
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Right. I think mine is some 4ohms, but I have some 30W transistors with less than 1ohms. I think I have todo something like you said, using a 4 ohms resistor and some capacitor at first. Problem with VNAs and bipolar transistors is that input impedance is not constant with power. I have to use a power splitter. Output matching seems also have an effect. So, I'll make an RF ground on output at first.
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Re: How To Do A SWR Sweep on 2 Meter HT Antenna ?
On Thu, Oct 20, 2022 at 01:49 PM, Zack Widup wrote: And yet, in real operation these antennas do not have a ground plane
(unless you consider the HT a ground plane, but it's inadequate). So why
not measure the antenna as it's going to be used in the real world? Zack's got the best answer! Just putting the HT antenna right on the NanoVNA, held in your hand, is probably a pretty good simulation of the antenna in its "natural environment" on the HT. Unless you usually carry around a pizza pan with your HT. I know I don't.
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Re: How To Do A SWR Sweep on 2 Meter HT Antenna ?
Hi Zack
Done a fair amount of work in this area.My best results was transmitting then adjusting the antenna for best field strength.Because you are tweaking the antenna to an impedance the transmitter final likes.Does NOT have to be Ohms.? ?Most of the time is problem is being heard, not hearing.
One talkie company use to make their duckies using Nicrome wire.? The antenna was a?linear resistor!? ?They used the same antenna on VHF and UHF radios!? ?Since you don't know exactly how the talkie is going to be held, and how nearby dielectrics (Body parts) are going to be positioned, the Nicrome gave consistent results.? ? ?Kent
PS? ?I don't consider 4 inches of rubber to be an antenna!
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On Thursday, October 20, 2022 at 03:49:17 PM CDT, Zack Widup <w9sz.zack@...> wrote: And yet, in real operation these antennas do not have a ground plane (unless you consider the HT a ground plane, but it's inadequate). So why not measure the antenna as it's going to be used in the real world? Zack W9SZ On Thu, Oct 20, 2022 at 3:28 PM Colin McDonald <colinrmcdonald@...> wrote: Most HT antennas are some form of compromised quarter wave radiator.
Meaning they really need a ground plain of some kind to get the correct
feed point impedance.
Not a counter poise, but a ground plain. Remember, you are dealing with
a wave length of 2 meters or so. and once you are beyond a quarter wave
above ground, about 18 inches, a quarter wave radiator needs a ground
plain because the actual ground is no longer providing that.
So, simply connecting the HT antenna to the NanoVNA directly or sticking
the antenna on the end of a cable isn't going to give a very accurate
measurement of the antennas electrical characteristics as far as
impedance and VSWR.
To properly test HT antennas you should have some kind of ground plain
jig to mount the antenna to. You can calibrate the NanoVNA with the
cable and ground plain mount connected to provide a calibrated reference
point for any HT antenna.
I have had some limited success by tightly holding the metal adapter at
the bottom of an HT antenna to provide some form of ground plain to work
with but those results vary quite a bit depending on how tightly I grip
the body of the connector and how far I hold the antenna away from myself.
You will find that even with a proper ground plain, HT antennas are
rarely resonant on the ham bands and impedance can vary wildly depending
on the frequency.
Interestingly enough, out of about 10 different stock rubber duck and
after market whip style antennas that I've tested so far, the original
Nagoya 701 that I bought way back when they were about 3 bucks measures
the lowest SWR on the VHF and UHF ham bands and is the closest to 50
ohms impedance at those frequencies. It's still around 1.5 to 1.7 to
one, but at least it's not 4 or 5 to one with a 80ohm feed point
impedance like most of the stock rubber duck style coil antennas that
come with a handheld.
A large cheap metal baking sheet can suffice as a ground plain for VHF
or UHF. You can mount both types of SMA connectors to it and feed with a
couple pieces of RG174 as long as you keep the run under 10 feet.
If you want to get ambicious? you can build a decent ground plain out of
a piece of plywood with 4 20 inch wires at 90 degrees to each other and
a fifth wire circling the perimeter electrically connecting the ends of
the 4 wires. Then a connector of your choice at the center tying the
wires together. You are now looking at a piece at least 40 inches by 40
inches though or a 40 inch circle. Unwieldy for most hobbiests.
But, if you really want to know how the HT antenna is going to measure
when used on a plastic cased HT, probably connecting it directly to the
NanoVNA and holding the Nano it in your hand while conducting the sweep
will give you the closest approximation of real world operation.
Another work around is to get a small magnet mount with the appropriate
SMA antenna mount and do your tests in a vehicle with the antenna stuck
to the roof. This will provide a pretty decent ground plain as well. Or
stick the magnet mount on the top of a fridge or metal stove top etc.
When I test and tune my quarter wave magnet mount antennas I just slap
them on top of my fridge and it seems to work great. Sitting on a wooden
table the same antenna will show a very high swr and feed point
impedance, but once stuck to the fridge those usually drop right down to
expected parameters. Tuned that way, they usually exhibit just about the
same VSWR and impedance when mounted to the vehicle roof.
Lot's of ways to get to the end goal without getting too technical or
fiddly.
Regards
Colin VA6BKX
On 2022-10-20 1:16 p.m., Jim Lux wrote:
On 10/20/22 11:45 AM, Frank wrote:
How To Do A SWR Sweep on 2 Meter HT Antenna ?
Whats better: Should I connect the 2 meter HT antenna directly to the
VNA or should I connect the 2M HT antenna to the end of a SMA cable
then to the VNA ?
The VNA is sort of like an HT and you're holding it in your hand, so
I'd say that's closer.
The other approach is to make a test fixture, use coax with a LOT of
appropriately chosen ferrite beads (probably not 31 for 140 MHz) to
decouple it and put the VNA 10-20 feet away (so the operator is not in
the near field of the antenna.
Test fixture should then replicate the operator's effect. i.e. that
you've got a lossy arm holding the HT next to a lossy body. For what
it's worth human muscle, bone, and vessel tissues are about 1.5 S/m
and epsilon 40.? So a bag of salt water with the right conductivity
with some polyester fiber or flakes (fake snow, pillow stuffing)that
is about half the volume (to bring epsilon down from 80 for water))
Sea water is about 3 S/m and about 3.5% salt.? So that will get you
started.
(ProTip, add a preservative so mold doesn't grow in your RF simulant -
it's really, really gross)
Or, test in a fixture that replicates "free space" - accept that it's
not what the thing looks like in real life, but does provide something
to compare against.
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Re: How To Do A SWR Sweep on 2 Meter HT Antenna ?
I was thinking of aluminum foil as well.
One would have to insure a good electrical bond between the various pieces of foil as I've not encountered aluminum foil a meter wide yet :)
Copper tape with conductive adhesive would work as well.
A regular sized pizza pan with either wire or rods to extend the plane to the right diameter for VHF would also work OK.
Sorry for the awful spelling in the last post. That's what happens when one texts too much and proofs too little.
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On 2022-10-20 2:33 p.m., Jim Lux wrote: If you don't care about replicating the human half of the HT antenna, then a pizza pan or large cookie sheet works well. It's repeatable, etc.
FWIW it should be 1/4 lambda *radius* not diameter. so for 70cm band, you're looking at 35cm diameter (call it 14" or so..it's not going to make much difference)
For 2m, that makes your pizza pan a bit bigger than is practical (a 1 meter diameter pizza pan is a specialty item). A big circle cut out of hardware cloth, or a couple pieces of plywood, MDF, or foam core, covered with aluminum foil works.
With all these things, it's the mechanical aspects you'll spend most of your time figuring out.
|
Re: How To Do A SWR Sweep on 2 Meter HT Antenna ?
And yet, in real operation these antennas do not have a ground plane (unless you consider the HT a ground plane, but it's inadequate). So why not measure the antenna as it's going to be used in the real world? Zack W9SZ On Thu, Oct 20, 2022 at 3:28 PM Colin McDonald <colinrmcdonald@...> wrote: Most HT antennas are some form of compromised quarter wave radiator.
Meaning they really need a ground plain of some kind to get the correct
feed point impedance.
Not a counter poise, but a ground plain. Remember, you are dealing with
a wave length of 2 meters or so. and once you are beyond a quarter wave
above ground, about 18 inches, a quarter wave radiator needs a ground
plain because the actual ground is no longer providing that.
So, simply connecting the HT antenna to the NanoVNA directly or sticking
the antenna on the end of a cable isn't going to give a very accurate
measurement of the antennas electrical characteristics as far as
impedance and VSWR.
To properly test HT antennas you should have some kind of ground plain
jig to mount the antenna to. You can calibrate the NanoVNA with the
cable and ground plain mount connected to provide a calibrated reference
point for any HT antenna.
I have had some limited success by tightly holding the metal adapter at
the bottom of an HT antenna to provide some form of ground plain to work
with but those results vary quite a bit depending on how tightly I grip
the body of the connector and how far I hold the antenna away from myself.
You will find that even with a proper ground plain, HT antennas are
rarely resonant on the ham bands and impedance can vary wildly depending
on the frequency.
Interestingly enough, out of about 10 different stock rubber duck and
after market whip style antennas that I've tested so far, the original
Nagoya 701 that I bought way back when they were about 3 bucks measures
the lowest SWR on the VHF and UHF ham bands and is the closest to 50
ohms impedance at those frequencies. It's still around 1.5 to 1.7 to
one, but at least it's not 4 or 5 to one with a 80ohm feed point
impedance like most of the stock rubber duck style coil antennas that
come with a handheld.
A large cheap metal baking sheet can suffice as a ground plain for VHF
or UHF. You can mount both types of SMA connectors to it and feed with a
couple pieces of RG174 as long as you keep the run under 10 feet.
If you want to get ambicious you can build a decent ground plain out of
a piece of plywood with 4 20 inch wires at 90 degrees to each other and
a fifth wire circling the perimeter electrically connecting the ends of
the 4 wires. Then a connector of your choice at the center tying the
wires together. You are now looking at a piece at least 40 inches by 40
inches though or a 40 inch circle. Unwieldy for most hobbiests.
But, if you really want to know how the HT antenna is going to measure
when used on a plastic cased HT, probably connecting it directly to the
NanoVNA and holding the Nano it in your hand while conducting the sweep
will give you the closest approximation of real world operation.
Another work around is to get a small magnet mount with the appropriate
SMA antenna mount and do your tests in a vehicle with the antenna stuck
to the roof. This will provide a pretty decent ground plain as well. Or
stick the magnet mount on the top of a fridge or metal stove top etc.
When I test and tune my quarter wave magnet mount antennas I just slap
them on top of my fridge and it seems to work great. Sitting on a wooden
table the same antenna will show a very high swr and feed point
impedance, but once stuck to the fridge those usually drop right down to
expected parameters. Tuned that way, they usually exhibit just about the
same VSWR and impedance when mounted to the vehicle roof.
Lot's of ways to get to the end goal without getting too technical or
fiddly.
Regards
Colin VA6BKX
On 2022-10-20 1:16 p.m., Jim Lux wrote:
On 10/20/22 11:45 AM, Frank wrote:
How To Do A SWR Sweep on 2 Meter HT Antenna ?
Whats better: Should I connect the 2 meter HT antenna directly to the
VNA or should I connect the 2M HT antenna to the end of a SMA cable
then to the VNA ?
The VNA is sort of like an HT and you're holding it in your hand, so
I'd say that's closer.
The other approach is to make a test fixture, use coax with a LOT of
appropriately chosen ferrite beads (probably not 31 for 140 MHz) to
decouple it and put the VNA 10-20 feet away (so the operator is not in
the near field of the antenna.
Test fixture should then replicate the operator's effect. i.e. that
you've got a lossy arm holding the HT next to a lossy body. For what
it's worth human muscle, bone, and vessel tissues are about 1.5 S/m
and epsilon 40. So a bag of salt water with the right conductivity
with some polyester fiber or flakes (fake snow, pillow stuffing)that
is about half the volume (to bring epsilon down from 80 for water))
Sea water is about 3 S/m and about 3.5% salt. So that will get you
started.
(ProTip, add a preservative so mold doesn't grow in your RF simulant -
it's really, really gross)
Or, test in a fixture that replicates "free space" - accept that it's
not what the thing looks like in real life, but does provide something
to compare against.
|
Re: How To Do A SWR Sweep on 2 Meter HT Antenna ?
If you don't care about replicating the human half of the HT antenna, then a pizza pan or large cookie sheet works well. It's repeatable, etc.
FWIW it should be 1/4 lambda *radius* not diameter. so for 70cm band, you're looking at 35cm diameter (call it 14" or so..it's not going to make much difference)
For 2m, that makes your pizza pan a bit bigger than is practical (a 1 meter diameter pizza pan is a specialty item). A big circle cut out of hardware cloth, or a couple pieces of plywood, MDF, or foam core, covered with aluminum foil works.
With all these things, it's the mechanical aspects you'll spend most of your time figuring out.
|
Re: NanoVNA-saver crashes on calibration
Understood.
Maybe 1.2.16 is Alpha code.
Maybe DiSlord can comment.
Mike N2MS
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On 10/20/2022 12:36 PM Ho-Ro < homuth-rosemann@... > wrote:
On Thu, Oct 20, 2022 at 04:46 PM, N2MS wrote:
Isn't DiSlord's latest version 1.2.16?
DiSlord posted version 1.2.16 in message # 4004 on September 30, 2022.
Mike N2MS
At least in his GitHub repo the version is still at 1.2.15 (I get the
version info by grepping for this line):
#define VERSION "1.2.15"
Martin
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Re: How To Do A SWR Sweep on 2 Meter HT Antenna ?
Most HT antennas are some form of compromised quarter wave radiator. Meaning they really need a ground plain of some kind to get the correct feed point impedance.
Not a counter poise, but a ground plain. Remember, you are dealing with a wave length of 2 meters or so. and once you are beyond a quarter wave above ground, about 18 inches, a quarter wave radiator needs a ground plain because the actual ground is no longer providing that.
So, simply connecting the HT antenna to the NanoVNA directly or sticking the antenna on the end of a cable isn't going to give a very accurate measurement of the antennas electrical characteristics as far as impedance and VSWR.
To properly test HT antennas you should have some kind of ground plain jig to mount the antenna to. You can calibrate the NanoVNA with the cable and ground plain mount connected to provide a calibrated reference point for any HT antenna.
I have had some limited success by tightly holding the metal adapter at the bottom of an HT antenna to provide some form of ground plain to work with but those results vary quite a bit depending on how tightly I grip the body of the connector and how far I hold the antenna away from myself.
You will find that even with a proper ground plain, HT antennas are rarely resonant on the ham bands and impedance can vary wildly depending on the frequency.
Interestingly enough, out of about 10 different stock rubber duck and after market whip style antennas that I've tested so far, the original Nagoya 701 that I bought way back when they were about 3 bucks measures the lowest SWR on the VHF and UHF ham bands and is the closest to 50 ohms impedance at those frequencies. It's still around 1.5 to 1.7 to one, but at least it's not 4 or 5 to one with a 80ohm feed point impedance like most of the stock rubber duck style coil antennas that come with a handheld.
A large cheap metal baking sheet can suffice as a ground plain for VHF or UHF. You can mount both types of SMA connectors to it and feed with a couple pieces of RG174 as long as you keep the run under 10 feet.
If you want to get ambicious? you can build a decent ground plain out of a piece of plywood with 4 20 inch wires at 90 degrees to each other and a fifth wire circling the perimeter electrically connecting the ends of the 4 wires. Then a connector of your choice at the center tying the wires together. You are now looking at a piece at least 40 inches by 40 inches though or a 40 inch circle. Unwieldy for most hobbiests.
But, if you really want to know how the HT antenna is going to measure when used on a plastic cased HT, probably connecting it directly to the NanoVNA and holding the Nano it in your hand while conducting the sweep will give you the closest approximation of real world operation.
Another work around is to get a small magnet mount with the appropriate SMA antenna mount and do your tests in a vehicle with the antenna stuck to the roof. This will provide a pretty decent ground plain as well. Or stick the magnet mount on the top of a fridge or metal stove top etc. When I test and tune my quarter wave magnet mount antennas I just slap them on top of my fridge and it seems to work great. Sitting on a wooden table the same antenna will show a very high swr and feed point impedance, but once stuck to the fridge those usually drop right down to expected parameters. Tuned that way, they usually exhibit just about the same VSWR and impedance when mounted to the vehicle roof.
Lot's of ways to get to the end goal without getting too technical or fiddly.
Regards
Colin VA6BKX
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Show quoted text
On 2022-10-20 1:16 p.m., Jim Lux wrote: On 10/20/22 11:45 AM, Frank wrote:
How To Do A SWR Sweep on 2 Meter HT Antenna ?
Whats better: Should I connect the 2 meter HT antenna directly to the VNA or should I connect the 2M HT antenna to the end of a SMA cable then to the VNA ?
The VNA is sort of like an HT and you're holding it in your hand, so I'd say that's closer.
The other approach is to make a test fixture, use coax with a LOT of appropriately chosen ferrite beads (probably not 31 for 140 MHz) to decouple it and put the VNA 10-20 feet away (so the operator is not in the near field of the antenna.
Test fixture should then replicate the operator's effect. i.e. that you've got a lossy arm holding the HT next to a lossy body. For what it's worth human muscle, bone, and vessel tissues are about 1.5 S/m and epsilon 40.? So a bag of salt water with the right conductivity with some polyester fiber or flakes (fake snow, pillow stuffing)that is about half the volume (to bring epsilon down from 80 for water))
Sea water is about 3 S/m and about 3.5% salt.? So that will get you started.
(ProTip, add a preservative so mold doesn't grow in your RF simulant - it's really, really gross)
Or, test in a fixture that replicates "free space" - accept that it's not what the thing looks like in real life, but does provide something to compare against.
|
BryonB
Jim Allyn - N7JA
Clyde Lambert
