*Quote: " My question to the group is, to best eliminate that local noise in the receiver, shouldn't* * that choke be on the receiver end of the coax, not up at the antenna feed point?"* *Yes and no. The real answer is both at the feedpoint and at the receiver or input to the matching network (a.k.a., antenna 'tuner'). * *With the choke at the transceiver all it really does is prevent whatever the transceiver is connected to from lighting up with energy on the outside of the coaxial braid. The transceivers of today are designed as a common mode / single-ended load / source. The inside of the units are designed to handle fields that end up on the outside of anything they connect to. Typically, these fields do a rather poor job of coupling into the internal circuitry - by design. Local RFI can still couple onto the outside of the coaxial braid and radiate / conduct into the antenna - still not good for received noise from the local environment. As such, the outside of the coax still becomes part of the antenna in gathering local noise. That gets into the receive path through both conduction and near-field re-rediation directly into the antenna (dipole). * *A 1:1 current choke or a common mode choke at the feed of the dipole or other balanced sources / loads solves this problem. Sure, the outside of the coax braid will still support fields generagtd by the local environment RFI, but it will be choked from conductively becoming part of the antenna and will not get into the receive path. There will still be some MINOR re-radiation through near field coupling, but it should be greatly reduced. Those fields that couple onto the outside of the transceivers will just spread to anything connected to the transceiver, as before, but the level coupled into the antenna and, then into the receiver path, will be greatly reduced. * *With a 1:1 current choke or common mode choke at both positions, both of these problems are alleviated and addressed. * *I was able to solve 95 % of my problems from the new appliances with CM chokes at the input and output of the antenna matching network. From the matching network to the 450-foot long doublet feed point, I use open wire parallel conductor line, not coax. However, we also have a steel roof and steel siding, so the house is a 'leaky' Faraday cage. I do install an additional CM choke on the output of the matching network to augment the decoupling I built into the matching network specifically when operating 160, 80, and 40-meters. That's wound on two stacked 3-inchOD #61 ferrite cores. Those I included in the home brew L-Network matching network are bifilar wound common mode choke style on red cores, powdered iron, #6 red cores of 3-inch OD. Those have the same properties as those included in the Amidon balun kit. * *Dave - W?LEV* On Wed, Aug 12, 2020 at 11:26 PM Jerry Gaffke via groups.io <jgaffke= [email protected]> wrote: Bob wrote:
This has been carried to extremes by the OCF dipoles that aren't very good antennas at any frequency, in my opinion
My end-fed half-wave is the off-center-fed-dipole concept taken to the
extreme.
Works great, in my opinion.
But it's difficult to get the matching network right, especially if
shooting for multiband use.
I simply bought an EFHW-8010 from myantennas.com, though the facebook page
referenced in my previous post tells how to clone it.
The EFHW-8010 matching network is not tuned, so works well across pretty
much all
of the HF amateur bands without adjustment and without a tuner at the
transmitter.
Some weird tricks were employed to hit desired parts of the bands that are
not exact harmonics.
A single band end-fed-half-wave with a tuned matching network is fairly
easy to get working right,
plenty of websites describing this.
The common mode choke that Dave recommended is worth trying.
I suspect the primary reason I would use one is to eliminate local noise
from getting into the receiver,
since I don't really care about the radiation pattern or a small drop in
efficiency due to radiation
from the feedline.
My question to the group is, to best eliminate that local noise in the
receiver, shouldn't
that choke be on the receiver end of the coax, not up at the antenna feed
point?
I did try one near the receiver here, but being off grid way out in the
boonies
there wasn't a noticeable difference.
Bob wrote:
If I want to operate too far from that frequency I might
use a tuner for just that although the efficiency sucks. If you have halfway decent coax that's less than 100 yards long, are
operating below 30mhz,
the antenna itself is at least as good as 4:1 SWR, and you use the tuner
correctly,
efficiency should not suck.
In Maxwell's Reflections III book I referenced yesterday, I said it needed
editing.
It needs editing because he keeps hammering away at this point again and
again and again and again.
He did so because he kept hearing from the ham community that the antenna
itself
had to be in good tune to get a decent signal out.
The power lost in the coax due to reflections between antenna feed point
and antenna tuner
can be calculated, and he shows how. And at HF, it usually isn't much of
an issue.
Many of the chapters are simply old QST articles from the 1970's, where he
felt the need to
recapitulate as readers might not have read the previous articles. But
also, the organization
of all the writing is more than a little scattered. On the other hand,
it's pretty much all correct.
In my opinion.
Jerry, KE7ER
On Wed, Aug 12, 2020 at 03:37 PM, Bob Albert wrote:
I used to use tuners. No more. I cut my antennas so that they are in
resonance or close. If I want to operate too far from that frequency I might
use a tuner for just that although the efficiency sucks. And of course the
pi network in my amplifier does the job of a tuner. If the mismatch is more
than about 2:1 I balk even with a tuner.
So my old MFJ 986 sits in the closet. Maybe good swap material.
Incidentally I have discovered that if you only trim one end of a dipole, the
resonant frequency changes but the match at resonance deteriorates. The
upside is that the curve is a bit flatter so it covers a wider band. This
has been carried to extremes by the OCF dipoles that aren't very good antennas
at any frequency, in my opinion
Bob
-- *Dave - W?LEV* *Just Let Darwin Work*
|
On 8/13/20 11:10 AM, K2STP Chris wrote: So, when he hooks up the VNA to the coax in the shack to test, will he not need to use the TDR function to isolate the length of coax cable to the antenna? In other words, wont the long length of coax feed line affect the vna readings?
The calibration process "calibrates out" all the variations up to the "reference plane", which is where you put the short, open, load, thru cal standards. Essentially, what happens mathematically is that you put a short on the end (which has a reflection coefficient(Gamma) of -1) - you measure all the values (Tx, Rx0) and you adjust the calibration parameters so that whenever those particular values are read, the display reads Gamma=-1. it's way more complex in reality, because you have multiple "knowns" (short, open, load, thru), and multiple variables, so it winds up being a non-linear "solve multiple equations with multiple unknowns". Fortunately, it's been solved, in the generalized case, and that's what the calibration function does. It's just a more complex mathematics than calculating VSWR from forward and reflected powers on a Bird wattmeter - it can incorporate a variety of systematic effects (time delay and loss in a transmission line from test set to the reference plane) and even more important in some cases, it can allow you to know the uncertainty of the resulting measurement. If I'm testing an amplifier, and I need to know that the S11 magnitude is <-20dB everywhere, and the measurement uncertainty is 1 dB, then to "pass" I have to measure -21 dB. If the uncertainty is 10dB, then to pass, I have to measure -30dB. The problem with measuring with a long transmission line in the system is that if there is enough loss, the VNA's receiver doesn't see enough signal to make an accurate measurement. If you're measuring -20dB reflected power with a short transmission line, and I put 10dB of loss in, the receiver is now seeing -40dB (which it will "calibrate" to -20dB), but the lower you go, the more the SNR starts to affect the measurement accuracy. The other place where a long cable bites you is in the large phase shift - you calibrate at a particular frequency and temperature, and if the temperature changes, the length and the propagation speed in the cable change, and with lots of "cycles" in the cable, that could affect the phase measurement. This is more a problem with microwave frequencies - at 10GHz, a 10 meter long cable is 500 cycles. A 0.1% speed change is 180 degrees of phase. There are techniques to deal with this (put a deliberate small mismatch at the end of the coax, and *measure* the propagation constant, then use that to adjust the measured values) I just bought, haven¡¯t installed yet, the MyAntennas.com EFHW-8010-2k
I also want to connect the vna to it and document it¡¯s performance on each band using Saver. I¡¯ve done this on small antenna¡¯s (HT¡¯s...) connected directly with no feed lines. But I wonder how to perform this task with long feed lines after the antenna is installed. Thanks for the help...
|
So, when he hooks up the VNA to the coax in the shack to test, will he not need to use the TDR function to isolate the length of coax cable to the antenna? In other words, wont the long length of coax feed line affect the vna readings?
I just bought, haven¡¯t installed yet, the MyAntennas.com EFHW-8010-2k
I also want to connect the vna to it and document it¡¯s performance on each band using Saver. I¡¯ve done this on small antenna¡¯s (HT¡¯s...) connected directly with no feed lines. But I wonder how to perform this task with long feed lines after the antenna is installed. Thanks for the help...
--
Regards,
K2STP ? Chris
|
Hi Glen,
i don't understand exactly what you need.
It is possible for the nanovna-H4 to have a 40 pins LCD display which is 0.5 mm pitch or for SAA2 the SPI controlled 14 pines display it is 2.54mm pitches. I got both. The former was backed up due to damage to the center of the screen, I also tested this (see my web page). link:
While the 14-pin SPI display is sourced from:
I did not test this in the absence of a device. Both arrived in careful packaging, double protected from damage. That's how I can recommend.
73, Gyula HA3HZ
--
*** If you are not part of the solution, then you are the problem. ( ) ***
|
My first display order from Aliexpress, was unsuccessful, the seller did not pack the display at all, only in a bubble. As a result, he came overwhelmed.
Now I ordered a 7-inch module for experiments from a seller who sells only displays (but the price is a little more expensive) (I hope to get it soon, it has already passed customs).
But he also has the right display on sale.
|
Hello,
Been searching for a couple more displays like the H4 has.? Want the 4" with ST7796S controller,
and it would be nice to have the 2.54mm spaced single-in-line header.
Does anyone have a good source?
I see them on ebay and AliExpress but I am skeptical...
73
Glen K4KV
|
Re: Remote Operation of NanoVNA-H
Sorry, but I didn't download the firmware (I am on vacations and I was just planning how to make some measurements, so I asked if someone could implement such feature. OneOfEleven immediately did it.). But I don't understand why such a firmware version wasn't GPL compliant. Could we ask to OneOfEleven to publish it again?
Thanks,
Piero
toggle quoted message
Show quoted text
Il 13/08/2020 15:05, Larry Rothman ha scritto: Sorry, but this firmware and the repo have been deleted.due to GPL complaints from one member last week.
If you have a copy that you would like to share - please do so PRIVATELY.
Thanks,
Larry
On Thursday, August 13, 2020, 9:03:28 a.m. EDT, Piero Tognolatti <piero.tognolatti@...> wrote:
Why don't you use the recent features that? autosave on SDcard a plot
every n seconds??? I asked for such a feature and OneOfEleven
immediately implemented it.?? Look at the attached post:
Il 06/08/2020 12:18, OneOfEleven ha scritto:
I've added the ability to auto save to SD card every 'n' seconds for
those that have SD cards on their nano's.
The option is in the "SD CARD" menu. A setting of '0' seconds disables
auto save.
You can find the NanoVNA-H firmware (and windows software to upload the
firmware) in the "Release" folder here ..
I can't do H4 firmware because I don't have a H4 to test with.
Best 73
Piero, I0KPT
Il 13/08/2020 14:59, DougVL ha scritto:
WiFi dongles may be better, if you find a way.? Bluetooth specification says its range in 10 meters/30 feet.? Of course, that's the spec and it may reach farther.
As a starter, I would suggest making a cable to reach from the ground to your antenna, calibrate the vna through that cable (on the ground), and then connect cable to antenna and hoist into position.? Then you can do the actual antenna tests.
When you calibrate thru the cable on the ground, you'll find out if you can calibrate through that much cable, too.
Good luck!? I hope it works - I've wondered about the same thing.
Doug, K8RFT
|
Re: Remote Operation of NanoVNA-H
Sorry, but this firmware and the repo have been deleted.due to GPL complaints from one member last week.
If you have a copy that you would like to share - please do so PRIVATELY.
Thanks,
Larry
toggle quoted message
Show quoted text
On Thursday, August 13, 2020, 9:03:28 a.m. EDT, Piero Tognolatti <piero.tognolatti@...> wrote: Why don't you use the recent features that? autosave on SDcard a plot every n seconds??? I asked for such a feature and OneOfEleven immediately implemented it.?? Look at the attached post: Il 06/08/2020 12:18, OneOfEleven ha scritto: I've added the ability to auto save to SD card every 'n' seconds for those that have SD cards on their nano's. The option is in the "SD CARD" menu. A setting of '0' seconds disables auto save. You can find the NanoVNA-H firmware (and windows software to upload the firmware) in the "Release" folder here .. I can't do H4 firmware because I don't have a H4 to test with. Best 73 Piero, I0KPT Il 13/08/2020 14:59, DougVL ha scritto: WiFi dongles may be better, if you find a way.? Bluetooth specification says its range in 10 meters/30 feet.? Of course, that's the spec and it may reach farther.
As a starter, I would suggest making a cable to reach from the ground to your antenna, calibrate the vna through that cable (on the ground), and then connect cable to antenna and hoist into position.? Then you can do the actual antenna tests.
When you calibrate thru the cable on the ground, you'll find out if you can calibrate through that much cable, too.
Good luck!? I hope it works - I've wondered about the same thing.
Doug, K8RFT
|
Re: Remote Operation of NanoVNA-H
Why don't you use the recent features that? autosave on SDcard a plot every n seconds??? I asked for such a feature and OneOfEleven immediately implemented it.?? Look at the attached post:
toggle quoted message
Show quoted text
Il 06/08/2020 12:18, OneOfEleven ha scritto: I've added the ability to auto save to SD card every 'n' seconds for those that have SD cards on their nano's. The option is in the "SD CARD" menu. A setting of '0' seconds disables auto save. You can find the NanoVNA-H firmware (and windows software to upload the firmware) in the "Release" folder here .. I can't do H4 firmware because I don't have a H4 to test with. Best 73 Piero, I0KPT Il 13/08/2020 14:59, DougVL ha scritto: WiFi dongles may be better, if you find a way. Bluetooth specification says its range in 10 meters/30 feet. Of course, that's the spec and it may reach farther.
As a starter, I would suggest making a cable to reach from the ground to your antenna, calibrate the vna through that cable (on the ground), and then connect cable to antenna and hoist into position. Then you can do the actual antenna tests.
When you calibrate thru the cable on the ground, you'll find out if you can calibrate through that much cable, too.
Good luck! I hope it works - I've wondered about the same thing.
Doug, K8RFT
|
Re: Remote Operation of NanoVNA-H
WiFi dongles may be better, if you find a way. Bluetooth specification says its range in 10 meters/30 feet. Of course, that's the spec and it may reach farther.
As a starter, I would suggest making a cable to reach from the ground to your antenna, calibrate the vna through that cable (on the ground), and then connect cable to antenna and hoist into position. Then you can do the actual antenna tests.
When you calibrate thru the cable on the ground, you'll find out if you can calibrate through that much cable, too.
Good luck! I hope it works - I've wondered about the same thing.
Doug, K8RFT
|
On 13.08.20 04:20, Roger Need via groups.io wrote: Question--- In version 0.3.3 and 0.3.4 the following bug fixes were
in the release notes. "Fixed through calibration" "Fixed bug in
Through Calibration" I am currently working on an S21 to impedance
project and have made a number of calibrated S21 measurements with
the old 2.2 version and wondered what these bugs were about. If they
are serious I will have to update my conversion algorithms. That bugs where only in releases 3.0 to 3.3, due to massive code refactoring. 73 Holger, DG5DBH
|
Re: We started selling SAA2 with N-type RF connector and 4-inch display
OK, I prefer large display and N type, +1
If there is option for larger display and touch, +2
I will place my order doon,
|
Re: Remote Operation of NanoVNA-H
Nanovna use USB serial port. Serial over WiFi works with nanovna saver. Version 1: raspberry pi Zero wh + raspberry Linux lite + ser2net + PC side true port I use 18650 Li ion battery + power bank Module to Supply Nanovna Version 2: Android phone with USB otg cable + tcpuart + PC side true port Long coxial cable not the best method. Cannot corrected by oslt calibration 100¨G quality on far end. The problem for example the cable loss. Very long lossy coxial cable always close to own impedancia with or without far end short or open circuit. For example no way to correct calibration on 70cm 100 meters rg174 coaxial cable. Of course the sample is extreme. But problem exist in lower lenght cables. /g/nanovna-users/topic/70124668#11563
|
Inside the box is a 9:1
Sent from my over-rated IPhone 7 Plus. Any Mis-spellings or grammar errors are due to my IPhone auto correct feature.
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Show quoted text
On Aug 12, 2020, at 22:29, Walt M. via groups.io <wa7sdy_1@...> wrote:
? I have but one question? What is inside the box in the picture above? It has an SO-239 input, ladder line not needed, an output for the long wire on the right, and what looks like a hook to hang the box at the shack end on the left. (Or maybe it does take a counterpoise. Then it would be an OCF dipole, sorta). The match box may already have the appropriate matching network, i.e. 9:1 (or other) balun, 1:1 choke, tapped coil, or some other circuit. I have, as a reference sort of, an MFJ vertical wire antenna for 80-6 meters with a matching circuit in a box at the feed point. Matches coax thru a tapped coil and balun (not sure what the ratio is) and has outputs for the wire and radials (has a connected set of 4 radials). I can tune this fairly easily with my MFJ-948. An analyzer (VNA & MFJ-259B) shows close to res for each band tested but I still use the tuner. I suggest looking in the box, or checking the spec sheet if there is one, to see if it already has the correct matching circuit.
Walt, WA7SDY
On Wednesday, August 12, 2020, 04:26:51 PM PDT, Jerry Gaffke via groups.io <jgaffke@...> wrote:
Bob wrote:
This has been carried to extremes by the OCF dipoles that aren't very good antennas at any frequency, in my opinion My end-fed half-wave is the off-center-fed-dipole concept taken to the extreme.
Works great, in my opinion.
But it's difficult to get the matching network right, especially if shooting for multiband use.
I simply bought an EFHW-8010 from myantennas.com, though the facebook page
referenced in my previous post tells how to clone it.
The EFHW-8010 matching network is not tuned, so works well across pretty much all
of the HF amateur bands without adjustment and without a tuner at the transmitter.
Some weird tricks were employed to hit desired parts of the bands that are not exact harmonics.
A single band end-fed-half-wave with a tuned matching network is fairly easy to get working right,
plenty of websites describing this.
The common mode choke that Dave recommended is worth trying.
I suspect the primary reason I would use one is to eliminate local noise from getting into the receiver,
since I don't really care about the radiation pattern or a small drop in efficiency due to radiation
from the feedline.
My question to the group is, to best eliminate that local noise in the receiver, shouldn't
that choke be on the receiver end of the coax, not up at the antenna feed point?
I did try one near the receiver here, but being off grid way out in the boonies
there wasn't a noticeable difference.
Bob wrote:
If I want to operate too far from that frequency I might
use a tuner for just that although the efficiency sucks. If you have halfway decent coax that's less than 100 yards long, are operating below 30mhz,
the antenna itself is at least as good as 4:1 SWR, and you use the tuner correctly,
efficiency should not suck.
In Maxwell's Reflections III book I referenced yesterday, I said it needed editing.
It needs editing because he keeps hammering away at this point again and again and again and again.
He did so because he kept hearing from the ham community that the antenna itself
had to be in good tune to get a decent signal out.
The power lost in the coax due to reflections between antenna feed point and antenna tuner
can be calculated, and he shows how. And at HF, it usually isn't much of an issue.
Many of the chapters are simply old QST articles from the 1970's, where he felt the need to
recapitulate as readers might not have read the previous articles. But also, the organization
of all the writing is more than a little scattered. On the other hand, it's pretty much all correct.
In my opinion.
Jerry, KE7ER
On Wed, Aug 12, 2020 at 03:37 PM, Bob Albert wrote:
I used to use tuners. No more. I cut my antennas so that they are in
resonance or close. If I want to operate too far from that frequency I might
use a tuner for just that although the efficiency sucks. And of course the
pi network in my amplifier does the job of a tuner. If the mismatch is more
than about 2:1 I balk even with a tuner.
So my old MFJ 986 sits in the closet. Maybe good swap material.
Incidentally I have discovered that if you only trim one end of a dipole, the
resonant frequency changes but the match at resonance deteriorates. The
upside is that the curve is a bit flatter so it covers a wider band. This
has been carried to extremes by the OCF dipoles that aren't very good antennas
at any frequency, in my opinion
Bob
|
I have but one question??What is inside the box in the picture above??It has an SO-239 input, ladder line not needed, an output for the long wire on the right, and what looks like a hook to hang the box at the shack end on the left. (Or maybe it does take a counterpoise. Then it would be an OCF dipole, sorta). The match box may already have the appropriate matching network, i.e. 9:1 (or other) balun, 1:1 choke, tapped coil, or some other circuit. I have, as a reference sort of, an MFJ vertical wire antenna for 80-6 meters with a matching circuit in a box at the feed point. Matches coax thru a tapped coil and balun (not sure what the ratio is) and has outputs for the wire and radials (has a connected set of 4 radials). I can tune this fairly easily with my MFJ-948. An analyzer (VNA & MFJ-259B) shows close to res for each band tested but I still use the tuner. I suggest looking in the box, or checking the spec sheet if there is one, to see if it already has the correct matching circuit.
Walt, WA7SDY
toggle quoted message
Show quoted text
On Wednesday, August 12, 2020, 04:26:51 PM PDT, Jerry Gaffke via groups.io <jgaffke@...> wrote: Bob wrote: ? This has been carried to extremes by the OCF dipoles that aren't very good antennas at any frequency, in my opinion My end-fed half-wave is the off-center-fed-dipole concept taken to the extreme. Works great, in my opinion. But it's difficult to get the matching network right, especially if shooting for multiband use. I simply bought an EFHW-8010 from myantennas.com, though the facebook page referenced in my previous post tells how to clone it. The EFHW-8010 matching network is not tuned, so works well across pretty much all of the HF amateur bands without adjustment and without a tuner at the transmitter. Some weird tricks were employed to hit desired parts of the bands that are not exact harmonics. A single band end-fed-half-wave with a tuned matching network is fairly easy to get working right, plenty of websites describing this. The common mode choke that Dave recommended is worth trying. I suspect the primary reason I would use one is to eliminate local noise from getting into the receiver, since I don't really care about the radiation pattern or a small drop in efficiency due to radiation from the feedline. My question to the group is, to best eliminate that local noise in the receiver, shouldn't that choke be on the receiver end of the coax, not up at the antenna feed point? I did try one near the receiver here, but being off grid way out in the boonies there wasn't a noticeable difference. Bob wrote: ? If I want to operate too far from that frequency I might
? use a tuner for just that although the efficiency sucks.? If you have halfway decent coax that's less than 100 yards long, are operating below 30mhz, the antenna itself is at least as good as 4:1 SWR, and you use the tuner correctly, efficiency should not suck. In Maxwell's Reflections III book I referenced yesterday, I said it needed editing. It needs editing because he keeps hammering away at this point again and again and again and again. He did so because he kept hearing from the ham community that the antenna itself had to be in good tune to get a decent signal out. The power lost in the coax due to reflections between antenna feed point and antenna tuner can be calculated, and he shows how.? And at HF, it usually isn't much of an issue. Many of the chapters are simply old QST articles from the 1970's, where he felt the need to recapitulate as readers might not have read the previous articles.? But also, the organization of all the writing is more than a little scattered.? On the other hand, it's pretty much all correct. In my opinion. Jerry, KE7ER On Wed, Aug 12, 2020 at 03:37 PM, Bob Albert wrote: I used to use tuners.? No more.? I cut my antennas so that they are in
resonance or close.? If I want to operate too far from that frequency I might
use a tuner for just that although the efficiency sucks.? And of course the
pi network in my amplifier does the job of a tuner.? If the mismatch is more
than about 2:1 I balk even with a tuner.
So my old MFJ 986 sits in the closet.? Maybe good swap material.
Incidentally I have discovered that if you only trim one end of a dipole, the
resonant frequency changes but the match at resonance deteriorates.? The
upside is that the curve is a bit flatter so it covers a wider band.? This
has been carried to extremes by the OCF dipoles that aren't very good antennas
at any frequency, in my opinion
Bob
|
I was looking over the improvements made to NanoVNA Saver by the new development team.
A few bugs have been fixed and I wondered if any of the developers might have time to answer a question.
Question--- In version 0.3.3 and 0.3.4 the following bug fixes were in the release notes. "Fixed through calibration" "Fixed bug in Through Calibration"
I am currently working on an S21 to impedance project and have made a number of calibrated S21 measurements with the old 2.2 version and wondered what these bugs were about. If they are serious I will have to update my conversion algorithms.
Thanks - Roger
|
I am trying to use this end fed so I can work all frequencies 80-10m. I have limited space and can¡¯t put up a tower or beam.
Darrell
Sent from my over-rated IPhone 7 Plus. Any Mis-spellings or grammar errors are due to my IPhone auto correct feature.
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On Aug 12, 2020, at 17:30, Dave <dave@...> wrote:
?Darrell:
I initially make a wire antenna a little longer than the formula calls for(it's easier to cut than to add wire). Put up without the autotuner. Check with the nanovna or an SWR meter(the vna gives more info). Then trim so the lowest SWR is where you will be operating. If the lowest SWR is at a freq below where you want, cut a little wire off each end. If the SWR is above the freq you want to operate at, you will need to add wire. Once the trimming is done, then you can add the auto tuner if needed.
Dave - WB6DHW
On 8/12/2020 3:07 PM, Darrell Carothers wrote:
Thank you. Excuse my beginner questions but it seems I have a lot to learn. I will be using a auto tuner. I was just trying to find out what my SWR would be on the different bands and where it would be resonant on each band so I could attempt to find out if I need to trim it to tune it a bit. I guess I need to do more research before I attempt to put it in service.
Darrell
Sent from my over-rated IPhone 7 Plus. Any Mis-spellings or grammar errors are due to my IPhone auto correct feature.
On Aug 12, 2020, at 16:59, David Eckhardt <davearea51a@...> wrote: ?As far as a counterpoise goes: As a single-ended, common mode source/load,
the fields must go somewhere. They don't just abruptly stop at the feed of
the EFHW (end fed half wave). Yes, the coaxial feed WILL participate in
radiation as it forms the counterpoise to the EFHW. Some form of
decoupling must be supplied before it connects to the radio or matching
network (a.k.a., 'antenna "tuner"') or there will be "RF In the Shack". A
current choke or common mode choke installed before the coax connects to
the radio or matching network would be appropriate. Then you can connect
the VNA to that point AFTER the current balun or common mode choke.
Without that, the VNA and anything holding onto the VNA or capacitively
coupled to the VNA will become part of what you measure and part of the
antenna.
Dave - W?LEV
On Wed, Aug 12, 2020 at 9:37 PM David Eckhardt via groups.io <davearea51a=
[email protected]> wrote:
Not quite correct! Ladder line is a transmission line just like coaxial
line. However, they perform their function differently.
1) The center fed dipole is a balanced source/load - differential
source/load.
2) Ladder line is a balanced transmission line - differential
transmission line. It is the correct transmission line to connect directly
to a balanced/differential source/load (dipole). It does NOT participate
in radiation. As a transmission line, fields close onto themselves
(between the two parallel conductors) and do not open onto free space, so
no radiation occurs.
3) Coax is an unbalanced transmission line - common mode transmission
line. Fields are intended to close between the inner conductor and the
inside of the outer shield/braid. It is NOT the correct transmission line
to connect directly to a balanced/differential source/load (dipole).
4) If coaxial cable it is connected directly to a dipole, the outer
portion of the shield/braid WILL participate in radiation and gather noise
on receive that will couple into the antenna and receiver.
5) The correct manner in which to connect a coaxial transmission line
(unbalanced transmission line) to a dipole (balanced source/load) is
through a 1:1 current balun or common mode choke. This will prevent the
outer layer of the coaxial braid from participating in radiation and
coupling local noise into the antenna/receiver.
6) 4:1, 2:1, 9:1,.......are NOT appropriate for the purpose stated in
(5). These are TRANSFORMERS and NOT BALUNS.
7) If you MUST use a transformer for impedance transformation, follow it
with a 1:1 current balun or common mode choke.
Dave - W?LEV
On Wed, Aug 12, 2020 at 9:20 PM Darrell Carothers <rescuemedic1@...>
wrote:
I am slowly getting parts in to try my end fed long wire antenna. Correct
me if I am wrong. With a center fed dipole, the 300 or 450 ohm ladder line
feeding it is part of the antenna. I would think I would use my NanoVNA at
the end of the feed to check where it would be resonant and for SWR. If so,
would the coax feeding the end fed long wire antenna also be considered
part of the antenna and use the NanoVNA to measure accordingly? I am told
this doesn¡¯t need a counterpoise.
Am I correct or am I missing something?
Thanks
Darrell
N5FTW
Sent from my over-rated IPhone 7 Plus. Any Mis-spellings or grammar
errors are due to my IPhone auto correct feature.
--
*Dave - W?LEV*
*Just Let Darwin Work*
--
*Dave - W?LEV*
*Just Let Darwin Work*
|
Bob wrote: This has been carried to extremes by the OCF dipoles that aren't very good antennas at any frequency, in my opinion My end-fed half-wave is the off-center-fed-dipole concept taken to the extreme. Works great, in my opinion. But it's difficult to get the matching network right, especially if shooting for multiband use. I simply bought an EFHW-8010 from myantennas.com, though the facebook page referenced in my previous post tells how to clone it. The EFHW-8010 matching network is not tuned, so works well across pretty much all of the HF amateur bands without adjustment and without a tuner at the transmitter. Some weird tricks were employed to hit desired parts of the bands that are not exact harmonics. A single band end-fed-half-wave with a tuned matching network is fairly easy to get working right, plenty of websites describing this. The common mode choke that Dave recommended is worth trying. I suspect the primary reason I would use one is to eliminate local noise from getting into the receiver, since I don't really care about the radiation pattern or a small drop in efficiency due to radiation from the feedline. My question to the group is, to best eliminate that local noise in the receiver, shouldn't that choke be on the receiver end of the coax, not up at the antenna feed point? I did try one near the receiver here, but being off grid way out in the boonies there wasn't a noticeable difference. Bob wrote: If I want to operate too far from that frequency I might
use a tuner for just that although the efficiency sucks.? If you have halfway decent coax that's less than 100 yards long, are operating below 30mhz, the antenna itself is at least as good as 4:1 SWR, and you use the tuner correctly, efficiency should not suck. In Maxwell's Reflections III book I referenced yesterday, I said it needed editing. It needs editing because he keeps hammering away at this point again and again and again and again. He did so because he kept hearing from the ham community that the antenna itself had to be in good tune to get a decent signal out. The power lost in the coax due to reflections between antenna feed point and antenna tuner can be calculated, and he shows how. And at HF, it usually isn't much of an issue. Many of the chapters are simply old QST articles from the 1970's, where he felt the need to recapitulate as readers might not have read the previous articles. But also, the organization of all the writing is more than a little scattered. On the other hand, it's pretty much all correct. In my opinion. Jerry, KE7ER On Wed, Aug 12, 2020 at 03:37 PM, Bob Albert wrote: I used to use tuners.? No more.? I cut my antennas so that they are in
resonance or close.? If I want to operate too far from that frequency I might
use a tuner for just that although the efficiency sucks.? And of course the
pi network in my amplifier does the job of a tuner.? If the mismatch is more
than about 2:1 I balk even with a tuner.
So my old MFJ 986 sits in the closet.? Maybe good swap material.
Incidentally I have discovered that if you only trim one end of a dipole, the
resonant frequency changes but the match at resonance deteriorates.? The
upside is that the curve is a bit flatter so it covers a wider band.? This
has been carried to extremes by the OCF dipoles that aren't very good antennas
at any frequency, in my opinion
Bob
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On 8/12/20 2:37 PM, David Eckhardt wrote: Not quite correct! Ladder line is a transmission line just like coaxial
line. However, they perform their function differently.
1) The center fed dipole is a balanced source/load - differential
source/load.
2) Ladder line is a balanced transmission line - differential
transmission line. It is the correct transmission line to connect directly
to a balanced/differential source/load (dipole). It does NOT participate
in radiation. As a transmission line, fields close onto themselves
(between the two parallel conductors) and do not open onto free space, so
no radiation occurs.
3) Coax is an unbalanced transmission line - common mode transmission
line. Fields are intended to close between the inner conductor and the
inside of the outer shield/braid. It is NOT the correct transmission line
to connect directly to a balanced/differential source/load (dipole).
4) If coaxial cable it is connected directly to a dipole, the outer
portion of the shield/braid WILL participate in radiation and gather noise
on receive that will couple into the antenna and receiver.
5) The correct manner in which to connect a coaxial transmission line
(unbalanced transmission line) to a dipole (balanced source/load) is
through a 1:1 current balun or common mode choke. This will prevent the
outer layer of the coaxial braid from participating in radiation and
coupling local noise into the antenna/receiver.
6) 4:1, 2:1, 9:1,.......are NOT appropriate for the purpose stated in
(5). These are TRANSFORMERS and NOT BALUNS.
7) If you MUST use a transformer for impedance transformation, follow it
with a 1:1 current balun or common mode choke.
Dave - W?LEV By the way - if you need a transformer - MiniCircuits sells transformers in various turns ratios for about $5. for a 1:1 try the T1-1T-X65+ (it's a 6pin dip, so easy to solder wires to it for banana jacks or coax) Choke on the coax, use 31 mix cores with the right number of turns SInce most VNAs are made to work best with 50 ohm loads, a transformer might not be a bad idea. A 4:1 turn (16:1 impedance) would turn your VNA into an 800 ohm VNA. You can cal with 50 ohms, then hook up the transformer, and trust that it works fairly well, or you can make a set of cal standards - short, open, 800 ohm non-inductive resistor. On Wed, Aug 12, 2020 at 9:20 PM Darrell Carothers <rescuemedic1@...>
wrote:
I am slowly getting parts in to try my end fed long wire antenna. Correct
me if I am wrong. With a center fed dipole, the 300 or 450 ohm ladder line
feeding it is part of the antenna. I would think I would use my NanoVNA at
the end of the feed to check where it would be resonant and for SWR. If so,
would the coax feeding the end fed long wire antenna also be considered
part of the antenna and use the NanoVNA to measure accordingly? I am told
this doesn¡¯t need a counterpoise.
Am I correct or am I missing something?
Thanks
Darrell
N5FTW
Sent from my over-rated IPhone 7 Plus. Any Mis-spellings or grammar
errors are due to my IPhone auto correct feature.
|
Re: Remote Operation of NanoVNA-H
On 8/12/20 1:16 PM, Jerry Gaffke via groups.io wrote: This doesn't answer your question, but I believe you could achieve the same result
by calibrating the VNA through your run of coax to the antenna feed point.
So perhaps have an assistant up on the roof, they attach the short, open, and load
calibration standards to the coax while you run the VNA at your operating desk.
Alternately, detach the high end of the coax and bring it in through a window to your
operating position for the calibration procedure.
Or have a relay box at the far end (Antenna Under Test) with open, short, load, antenna. At HF, the distance through the box is negligible. However, there are cases where you don't want "wires" near the AUT - fiber optics and wireless w/batteries are your friends in this case. Jerry, KE7ER
On Wed, Aug 12, 2020 at 12:12 PM, Steve Dightman wrote:
I am going to be working with wire antennas in the 3 to 30 MHz range. I would
like to attach the VNA at the antenna feed point and have the antenna at
operating height. Therefore I would like to use NanoVNA-Saver connect via the
NanoVNA USB-C port to the PC connected by replacing the USB cable with some
sort of a RF link, (wifi or bluetooth). I have a couple of Bluetooth-to-usb
dongles but don't yet see a way to have them connect to each other and pass
the bi-directional data. The connection range needs to be in the 60 ft
(possibly up to 100 ft range).
Any experience or suggested approach for doing this?
I've seen somewhere a spec name for the data exchange that NanoVNA-Saver to
NanoVNA uses, but have not been able to find it again. Anybody know off the
top?
Will the nanoVNA USB-C port provide battery power out to operate a dongle
device?
The NanoVNA looks like a serial port to the host computer. I don't think it can "supply" current, but I don't know. You can load NanoVNA-Saver on something like a Rpi and VNC to it. However, I'm not sure *all* front panel functions of the NanoVNA can be done over the serial port.
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Chris K2STP
Gyula Molnar
oakkar7
Darrell Carothers
Walt WA7SDY
Roger Need