Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
- Nanovna-Users
- Messages
Search
|
Re: Diagnose unresponsive ch1 port on the nanovna
#repair
#circuit
#fix
#hardware
#internals
Yes you are right, I had just spent a while reading posts between Eric and a couple of users on the tinysa site and had forgotten that I had switched sites before replying.
________________________________ From: [email protected] <[email protected]> on behalf of Roger Need via groups.io <sailtamarack@...> Sent: Saturday, November 16, 2024 10:28:55 PM To: [email protected] <[email protected]> Subject: Re: [nanovna-users] Diagnose unresponsive ch1 port on the nanovna #repair #circuit #fix #hardware #internals On Sat, Nov 16, 2024 at 02:17 PM, M0CNL wrote: Erik has nothing to do with VNA products - he manufactures the tinySA... Th OP has a product which is an owocomm design. |
|
Re: Diagnose unresponsive ch1 port on the nanovna
#repair
#circuit
#fix
#hardware
#internals
On Sat, Nov 16, 2024 at 02:17 PM, M0CNL wrote:
Erik has nothing to do with VNA products - he manufactures the tinySA... Th OP has a product which is an owocomm design. |
|
Re: Diagnose unresponsive ch1 port on the nanovna
#repair
#circuit
#fix
#hardware
#internals
Firstly any nano vna advertised as performing up to 30GHz is making false claims about its specifications.
Secondly it sounds like you didn¡¯t discharge any static from the antenna before connecting the nano vna and have blown the input stage. You may have gotten away with just the input switch which is documented on wiki. Further than that you should probably wait for Erik to respond once you have posted those pictures you said that you had attached, along with pictures of both front and back of your nano vna. |
|
Diagnose unresponsive ch1 port on the nanovna
#repair
#circuit
#fix
#hardware
#internals
Hello, I recently purchased a nanovna s-a-a-2 (hardware version v2_2, 50k-30ghz, owocomm design), and after around 2 weeks of work the measurements on the s11 port decided to malfunction.
At the time of the s11 port breaking a simple v dipole was connected to the s11 port of the analyzer, and the nanovna was plugged into a usb port on my computer, where i was getting my measurements from using vna_qt. After the malfunction I tried the following: 1) inspect my sma ports to make sure the little spring contacts weren't bent or out of place 2) connected all the different types of calibration loads directly to the s11 port with no change in any parameter 3) I connected a regular sma connector to both ports at once and observed the s21 logmag value change, which seems to imply that something is wrong with the s11 port only 4) disassembled the vna to check if there was some obviously blown up component (there arent any, even under the metal shielding) 5) cleared Please help diagnose and potentially fix this problem. I attached 3 pictures of the analyzer: one with no connections, one with the 50ohm load, and one with an sma connector connecting the 2 ports. |
|
Re: Dipole antenna with Low Z0 feed point Impedance
The antenna, being in the attic, is already influenced by very close-by
objects. The best you can do is isolate it from the measurement setup - the NanoVNA, the laptop, and anything the laptop is connected to (charger and house wiring). The ferrites on the coax will accomplish that. As far as far field is concerned, the usual criterion is: Far Field Distance (about) = 2[D^2] / Freespace wavelength While this is only an approximation, it's pretty good. D = largest dimension of the test article. For 40-meters, D would be 280-feet. The attic is clearly in the nearfield, but so be it. You are a small portion of a wavelength at 7 MHz, so don't bother isolating yourself. The attic takes care of the "near field" and is not an option in your installation. Dave - W?LEV On Sat, Nov 16, 2024 at 12:15?AM Bill WA2WIO via groups.io <sla= [email protected]> wrote: Dave - W?LEV;-- *Dave - W?LEV* -- Dave - W?LEV |
|
Re: Choke measurement
Why do you want to measure that choke?
Is there a problem with it? If you can't loosen that choke, measuring with a VNA is almost impossible because of the correct connection to be made and the own impedance of the VNA, which you have to take into account. A photo of the choke would already say a lot. Herman ON1BES |
|
Re: Dipole antenna with Low Z0 feed point Impedance
The loss attributable to a 2:1 VSWR can be stated as a constant,; the reflection loss from a 2:1mismatch is 0.512dB. Wwhat is variable is the loss before the incident power hits the mismatch, and what happens to the 0.11% of the incident power that goes backdown the cable, some of which is re-reflected again back up the cable from the transmitter. Those are cable type dependant.
73 Jeff G8HUL ________________________________________ From: [email protected] <[email protected]> on behalf of Warren Allgyer via groups.io <allgyer@...> Sent: 15 November 2024 14:42 To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance Joe The loss attributable to a 2:1 VSWR cannot be stated as a constant. It is a function of the length and characteristic loss of the coax cable used. The additional loss in 100 feet of cable that is a consequence of having a 2:1 SWR load would be 0.33 dB for RG58 and about 0.11 dB for LMR400. This is far less than 11.1% however none of the calculated additional loss are significant and overcoming those losses by searching for a perfect match will solve no problem that the author is experiencing. Warren Allgyer - WA8TOD |
|
Bugs in the source code of NanoVNA-D-v1.2.29
I was using the NanoVNA-D-v1.2.29 source code, and found that there is a bug in exti_v1.c.
Because I added PA8 as an external interrupt, but when I enable the relevant code, I found that after triggering the PA8 interrupt, the program would go into an endless loop, and when I checked the code, I found that this piece of code is missing: EXTI->PR = pr; The problem was fixed with the addition of this piece of code |
|
Re: Dipole antenna with Low Z0 feed point Impedance
there's a bunch of definitions? ?there's also the 2d^2/lambda when measuring gain on an antenna rangeSent via the Samsung Galaxy S24, an AT&T 5G smartphone
toggle quoted message
Show quoted text
-------- Original message --------From: "MARTIN HADFIELD via groups.io" <mdhadfield@...> Date: 11/15/24 4:45 PM (GMT-08:00) To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance Barging in here for a moment...In general antenna theory, the "far field" starts at 10x lambda.? That is where the E and H fields have become coherent.Regards,Marty Hadfield, CPBEWA/OR/ID FCC ABIP Inspector>>>On Nov 15, 2024, at 4:15?PM, Bill WA2WIO <sla@...> wrote:?Dave - W?LEV;I hadn't thought of near field issues. I have had instances of interaction between my body and other objects with VNA measures before.As I understand it, at 40m HF, using a 1/2 wave dipole antenna (66ft), far field starts at about 1/2 a wavelength from the antenna. Recommendations go so far as to recommend 2-3 wavelengths away to eliminate unwanted influences. This is not achievable as the rig is only about 30-40ft from the antenna.Would a few clamp-on ferrites correct for this? Perhaps I should make all these measurements from the rig side? Calibrating from the coax feed line connection point at the antenna in the attic? Leaving only the antenna as the DUT? A much greater pain in the butt, but doable. Moving 30-40 ft away from the antenna has to be better, but is it worth the effort?Thank you,Best,Bill WA2WIO-----Original Message-----From: [email protected] [mailto:[email protected]] On Behalf Of W0LEV via groups.ioSent: Friday, November 15, 2024 12:40 PMTo: nanovna-users@...: Re: [nanovna-users] Dipole antenna with Low Z0 feed point ImpedanceIn your measurement of the antenna only at the VNA end of your 6-footjumper, it would be a good idea to attach a couple of 43 material clamp-onferrites around the coax at the feedpoint to isolate you and the VNA/laptopfrom the measurement.? You will be in the near-field of the antenna andyour presence and the coax jumper will influence the measurement unlessisolated.Dave - W?LEVOn Fri, Nov 15, 2024 at 5:31?PM Bill WA2WIO via groups.io <sla@...> wrote:> Dave - W0LEV;> > Thank you for the insight. I will place the CMC choke as you suggest.> > I intend to calibrate in the attic using only a 6ft coax jumper to the> antenna feed point. I will calibrate out the jumper, etc leaving only the> antenna as the DUT.> > Once the antenna is trimmed, I was going to retest with the 1:2 BalUn in> place.> > Based on your suggestion, I would then add the CMC coax choke and test> again.> > I would finally recalibrate at the rig and retest the whole system.> > Does this all sound reasonable? Suggestions on process and procedure? What> am I missing?> > Thank you,> > Best,> > Bill WA2WIO> > > -----Original Message-----> From: [email protected] [mailto:[email protected]] On Behalf> Of W0LEV via groups.io> Sent: Friday, November 15, 2024 12:08 PM> To: [email protected]> Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point> Impedance> > Your coaxial CMC should be installed just after the matching transformer> between that and the coax.? This is to isolate the coax from being part of> the radiating structure.? If you use the outer surface of the coax as a> radiating element, yes, it should go 1/4-wavelength down the coax from the> matching transformer.> > Dave - W?LEV> > On Fri, Nov 15, 2024 at 1:57?AM Bill WA2WIO via groups.io <sla=> [email protected]> wrote:> >> Thank you all for your considered and detailed suggestions and teaching>> points.>> >> >> >> To summarize what I believe I have learned:>> >> ¡¤???????? I am running QRP <> 3 watts (uSDX+ HF), does not leave much>> power to loose.>> >> ¡¤???????? Serious attic structural? limitations do not allow for changing>> antenna leg angles or height.>> >> ¡¤???????? I am operating on 2 bands: 40m and 20m. I operate in both the> CW>> and SSB portions of the bands.>> >> ¡¤???????? SWR without the ATU-10 tuner is =>6:1 at the rig, across all>> bands (MFJ-872)>> >> o?? The ATU-10 will bring it down to <2:1.>> >> o?? This will keep the rig happy, but actually waste >> significant> power.>> >> ¡¤???????? VNA at the rig end w/o ATU shows no resonance anywhere except> at>> 17mhz. (sweep 1-30Mhz).>> >> ¡¤???????? Antenna is certainly not actually balanced.>> >> o?? Antenna needs trimming, regardless.>> >> o?? My first step will be to go up into the attic, disconnect the feed>> line, and use my VNA to confirm just what the Z0 actually is.>> >> o?? I also need to verify the feed line from rig to antenna is viable.>> >> o?? Trim the antenna until resonant at 7.15Mhz (narrow sweep 7.0-7.4 MHz)>> >> o?? Assuming I am correct that Z0 is around 25 Ohms and complex, use a> 1:2>> BalUn to get closer to 50 Ohms.>> >> o?? Check 20m resonance (narrow sweep 14.0-14.5 MHz)>> >> ¡¤???????? If I get this far, I will add a CMC Coax Choke, 15T 4¡± on pvc>> form about 33ft (1/4 wave) from the antenna feed point.>> >> ¡¤???????? The goal is to get <> 2:1 across a reasonable portion of both>> bands without the ATU-10.>> >> ¡¤???????? Add in the ATU-10 ?>> >> >> >> Does this strategy make sense? Am I foolish to waste my time tuning and>> matching, as you say? I have made several contacts, but my RS(T) is way>> down in the mud. Noise level is >>S4-5 (a story for another day?). I do> not>> see any alternative.>> >> >> >> Thoughts?>> >> >> >> Thank You,>> >> >> >> Best,>> >> >> >> Bill WA2WIO>> >> >> >> -----Original Message----->> From: [email protected] [mailto:[email protected]] On Behalf>> Of Joe>> Sent: Thursday, November 14, 2024 6:03 PM>> To: [email protected]>> Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point>> Impedance>> >> >> >> WHAT??? All that power being lost????>> >> >> >> Seriously, a 2:1 SWR will only loose 11.1% of the power.? So a 100 watt>> >> station will give you 88.9 watts of ERP (Less cable loss and plus>> >> antenna gain).>> >> >> >> Really not worth loosing time on the air.>> >> >> >> 73, Joe, K1ike>> >> >> >> >> >> >> >> On 11/14/2024 4:23 PM, W0LEV via groups.io wrote:>> >>> My.....my........? For heaven's sake......!? What concerns about a> meager>> >>> 2:1 SWR!!? Just go with it, get on the air, and enjoy.>> >>> >> >>> Dave - W?LEV>> >>> >> >>> On Thu, Nov 14, 2024 at 7:15?PM DP via groups.io <dpoinsett=>> >>> [email protected]> wrote:>> >>> >> >>>> Hi Barry K3EUI>> >>>> >> >>>> You and others make an excellent point about the practical> acceptability>> >>>> of of a 2:1 SWR. I agree that for the casual ham using commonly>> available>> >>>> equipment, it's probably not a big deal especially on the lower HF>> >>>> frequencies.>> >>>> >> >>>> You are correct that by adding an inductor across the antenna> terminals>> >>>> and altering the antenna dimensions, the feedpoint impedance can be>> >>>> transformed to 50+j0 ohms, but the cut-and-try approach will be no>> easier>> >>>> than any of the other suggested methods. Also, just adding an inductor>> will>> >>>> not automatically increase the impedance. Depending in the initial>> antenna>> >>>> impedance, it may go up or down.>> >>>> >> >>>> If we stay with Bill's 25-ohm example, the antenna length and angle>> >>>> between each leg could be adjusted to get a 25-j25 feedpoint impedance>> at>> >>>> say 7.15 MHz. Adding a 1.1 uH inductor across the antenna terminals> will>> >>>> then get you to 50+j0 ohms. Other combinations could work, too. Of>> course>> >>>> whatever combination he comes up with will only work at the design>> >>>> frequency.>> >>>> >> >>>> Dave NU8A>> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> > > --> > *Dave - W?LEV*> > > --> Dave - W?LEV> > > > > > > > > > > --*Dave - W?LEV*--Dave - W?LEV
|
|
Re: Dipole antenna with Low Z0 feed point Impedance
?Hi, Bill - thanks for the welcome note.
Going along with Dave's recommendation of attaching a couple of proper ferrites around the 6-ft coax at the feedpoint, try adding a couple of ferrites at the distant end of your 6-ft coax jumper. The metallic cross-section of VNA won't present very much loading at 6-ft from the DUT input port. The VNA should be running on internal battery only. Find a 6-ft USB jumper cable to run between the VNA and your laptop (also running only on internal battery). Snap on a couple more of the ferrites to each end of the USB cable & you'll probably be at the best achievable distant from the DUT using a 6-ft coax. Have fun with it - try different lengths everywhere - keep track and share your findings! <smile> Cheers, Marty On Nov 15, 2024, at 5:00?PM, Bill WA2WIO <sla@...> wrote: ?Hello, Marty, Thank you for joining in! The question on the table is to formulate a viable VNA measuring strategy given all the previous discussion and specifics. Obviously, my measurements will have to be made in the near field. I can't see how it is practical for anyone to make any measurements in the true far field. ¡¤ What is common practical and reasonable ham level practice to get useable measurements with the 1/2 wave dipole antenna as the only DUT? o Would a few clamp-on ferrites correct for this? ¡¤ Perhaps I should make all these measurements from the rig side? o Calibrating from the coax feed line connection point at the antenna in the attic? o Leaving only the antenna as the DUT? o Moving 30-40 ft away from the antenna has to be better, but is it worth the effort? Thoughts? Thank you, Best, Bill WA2WIO -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of MARTIN HADFIELD via groups.io Sent: Friday, November 15, 2024 7:45 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance Barging in here for a moment... In general antenna theory, the "far field" starts at 10x lambda. That is where the E and H fields have become coherent. Regards, Marty Hadfield, CPBE WA/OR/ID FCC ABIP Inspector On Nov 15, 2024, at 4:15?PM, Bill WA2WIO <sla@...> wrote: ?Dave - W?LEV; I hadn't thought of near field issues. I have had instances of interaction between my body and other objects with VNA measures before. As I understand it, at 40m HF, using a 1/2 wave dipole antenna (66ft), far field starts at about 1/2 a wavelength from the antenna. Recommendations go so far as to recommend 2-3 wavelengths away to eliminate unwanted influences. This is not achievable as the rig is only about 30-40ft from the antenna. Would a few clamp-on ferrites correct for this? Perhaps I should make all these measurements from the rig side? Calibrating from the coax feed line connection point at the antenna in the attic? Leaving only the antenna as the DUT? A much greater pain in the butt, but doable. Moving 30-40 ft away from the antenna has to be better, but is it worth the effort? Thank you, Best, Bill WA2WIO -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of W0LEV via groups.io Sent: Friday, November 15, 2024 12:40 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance In your measurement of the antenna only at the VNA end of your 6-foot jumper, it would be a good idea to attach a couple of 43 material clamp-on ferrites around the coax at the feedpoint to isolate you and the VNA/laptop from the measurement. You will be in the near-field of the antenna and your presence and the coax jumper will influence the measurement unless isolated. Dave - W?LEV On Fri, Nov 15, 2024 at 5:31?PM Bill WA2WIO via groups.io <sla= [email protected]> wrote: Dave - W0LEV; Thank you for the insight. I will place the CMC choke as you suggest. I intend to calibrate in the attic using only a 6ft coax jumper to the antenna feed point. I will calibrate out the jumper, etc leaving only the antenna as the DUT. Once the antenna is trimmed, I was going to retest with the 1:2 BalUn in place. Based on your suggestion, I would then add the CMC coax choke and test again. I would finally recalibrate at the rig and retest the whole system. Does this all sound reasonable? Suggestions on process and procedure? What am I missing? Thank you, Best, Bill WA2WIO -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of W0LEV via groups.io Sent: Friday, November 15, 2024 12:08 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance Your coaxial CMC should be installed just after the matching transformer between that and the coax. This is to isolate the coax from being part of the radiating structure. If you use the outer surface of the coax as a radiating element, yes, it should go 1/4-wavelength down the coax from the matching transformer. Dave - W?LEV On Fri, Nov 15, 2024 at 1:57?AM Bill WA2WIO via groups.io <sla= [email protected]> wrote: Thank you all for your considered and detailed suggestions and teaching points. To summarize what I believe I have learned: ¡¤ I am running QRP <> 3 watts (uSDX+ HF), does not leave much power to loose. ¡¤ Serious attic structural limitations do not allow for changing antenna leg angles or height. ¡¤ I am operating on 2 bands: 40m and 20m. I operate in both the CW and SSB portions of the bands. ¡¤ SWR without the ATU-10 tuner is =>6:1 at the rig, across all bands (MFJ-872) o The ATU-10 will bring it down to <2:1. o This will keep the rig happy, but actually waste >> significant power. ¡¤ VNA at the rig end w/o ATU shows no resonance anywhere except at 17mhz. (sweep 1-30Mhz). ¡¤ Antenna is certainly not actually balanced. o Antenna needs trimming, regardless. o My first step will be to go up into the attic, disconnect the feed line, and use my VNA to confirm just what the Z0 actually is. o I also need to verify the feed line from rig to antenna is viable. o Trim the antenna until resonant at 7.15Mhz (narrow sweep 7.0-7.4 MHz) o Assuming I am correct that Z0 is around 25 Ohms and complex, use a 1:2 BalUn to get closer to 50 Ohms. o Check 20m resonance (narrow sweep 14.0-14.5 MHz) ¡¤ If I get this far, I will add a CMC Coax Choke, 15T 4¡± on pvc form about 33ft (1/4 wave) from the antenna feed point. ¡¤ The goal is to get <> 2:1 across a reasonable portion of both bands without the ATU-10. ¡¤ Add in the ATU-10 ? Does this strategy make sense? Am I foolish to waste my time tuning and matching, as you say? I have made several contacts, but my RS(T) is way down in the mud. Noise level is >>S4-5 (a story for another day?). I do not see any alternative. Thoughts? Thank You, Best, Bill WA2WIO -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Joe Sent: Thursday, November 14, 2024 6:03 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance WHAT?? All that power being lost???? Seriously, a 2:1 SWR will only loose 11.1% of the power. So a 100 watt station will give you 88.9 watts of ERP (Less cable loss and plus antenna gain). Really not worth loosing time on the air. 73, Joe, K1ike On 11/14/2024 4:23 PM, W0LEV via groups.io wrote: My.....my........ For heaven's sake......! What concerns about a meager 2:1 SWR!! Just go with it, get on the air, and enjoy. Dave - W?LEV On Thu, Nov 14, 2024 at 7:15?PM DP via groups.io <dpoinsett= [email protected]> wrote: Hi Barry K3EUI You and others make an excellent point about the practical acceptability of of a 2:1 SWR. I agree that for the casual ham using commonly available equipment, it's probably not a big deal especially on the lower HF frequencies. You are correct that by adding an inductor across the antenna terminals and altering the antenna dimensions, the feedpoint impedance can be transformed to 50+j0 ohms, but the cut-and-try approach will be no easier than any of the other suggested methods. Also, just adding an inductor will not automatically increase the impedance. Depending in the initial antenna impedance, it may go up or down. If we stay with Bill's 25-ohm example, the antenna length and angle between each leg could be adjusted to get a 25-j25 feedpoint impedance at say 7.15 MHz. Adding a 1.1 uH inductor across the antenna terminals will then get you to 50+j0 ohms. Other combinations could work, too. Of course whatever combination he comes up with will only work at the design frequency. Dave NU8A -- *Dave - W?LEV* -- Dave - W?LEV -- *Dave - W?LEV* -- Dave - W?LEV |
|
Re: Dipole antenna with Low Z0 feed point Impedance
On Fri, Nov 15, 2024 at 04:34 PM, Bill WA2WIO wrote:
The antenna should approx. a full wave on 20m. What am I missing here?Best for you to read up on antenna design. But think of a drawing of a half-sine-wave along the length of your antenna. The voltage is maximum in the middle, dropping to zero at the ends. We drive it with the voltage from the center pin of our coax in the center. Now do the same with a full-sine-wave. Now the voltage is at zero on the ends, and is also zero in the center: you can't easily drive a 0 voltage there - it is a current max/voltage min, with a very low impedance. That's why people do off-center fed or end-fed dipoles: to move where they can drive a meaningful impedance for multiple bands. Note that making an end-fed-halfwave or end-fed-random-wire antenna is very easy, at least as easy as matching a dipole - just need to buy or build an inexpensive 49:1 or 9:1 transformer, and use it with the wire you have. " Fan Dipole" vertical height to spread out the fan at the far ends. Ideas?You don't need vertical spread, you can do the spread horizontally - it will work just as well. "trapped dipole" DXE has a compact one only 38ft long.That would be a good option my VNA test strategy, dealing with the near field issues, regardless of design strategy.Don't overthink this. The interference is minimal. Just go measure the antenna - at the low levels the nanovna uses, the near-field issues won't make more than a tiny difference - I do it all of the time. Your nanovna will show you the SWR dip accurately for you to tune the antenna, and see where the natural resonance is. Stan KC7XE |
|
Re: Dipole antenna with Low Z0 feed point Impedance
Hello, Marty,
toggle quoted message
Show quoted text
Thank you for joining in! The question on the table is to formulate a viable VNA measuring strategy given all the previous discussion and specifics. Obviously, my measurements will have to be made in the near field. I can't see how it is practical for anyone to make any measurements in the true far field. ¡¤ What is common practical and reasonable ham level practice to get useable measurements with the 1/2 wave dipole antenna as the only DUT? o Would a few clamp-on ferrites correct for this? ¡¤ Perhaps I should make all these measurements from the rig side? o Calibrating from the coax feed line connection point at the antenna in the attic? o Leaving only the antenna as the DUT? o Moving 30-40 ft away from the antenna has to be better, but is it worth the effort? Thoughts? Thank you, Best, Bill WA2WIO -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of MARTIN HADFIELD via groups.io Sent: Friday, November 15, 2024 7:45 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance Barging in here for a moment... In general antenna theory, the "far field" starts at 10x lambda. That is where the E and H fields have become coherent. Regards, Marty Hadfield, CPBE WA/OR/ID FCC ABIP Inspector On Nov 15, 2024, at 4:15?PM, Bill WA2WIO <sla@...> wrote: ?Dave - W?LEV; I hadn't thought of near field issues. I have had instances of interaction between my body and other objects with VNA measures before. As I understand it, at 40m HF, using a 1/2 wave dipole antenna (66ft), far field starts at about 1/2 a wavelength from the antenna. Recommendations go so far as to recommend 2-3 wavelengths away to eliminate unwanted influences. This is not achievable as the rig is only about 30-40ft from the antenna. Would a few clamp-on ferrites correct for this? Perhaps I should make all these measurements from the rig side? Calibrating from the coax feed line connection point at the antenna in the attic? Leaving only the antenna as the DUT? A much greater pain in the butt, but doable. Moving 30-40 ft away from the antenna has to be better, but is it worth the effort? Thank you, Best, Bill WA2WIO -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of W0LEV via groups.io Sent: Friday, November 15, 2024 12:40 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance In your measurement of the antenna only at the VNA end of your 6-foot jumper, it would be a good idea to attach a couple of 43 material clamp-on ferrites around the coax at the feedpoint to isolate you and the VNA/laptop from the measurement. You will be in the near-field of the antenna and your presence and the coax jumper will influence the measurement unless isolated. Dave - W?LEV On Fri, Nov 15, 2024 at 5:31?PM Bill WA2WIO via groups.io <sla= [email protected]> wrote: Dave - W0LEV; Thank you for the insight. I will place the CMC choke as you suggest. I intend to calibrate in the attic using only a 6ft coax jumper to the antenna feed point. I will calibrate out the jumper, etc leaving only the antenna as the DUT. Once the antenna is trimmed, I was going to retest with the 1:2 BalUn in place. Based on your suggestion, I would then add the CMC coax choke and test again. I would finally recalibrate at the rig and retest the whole system. Does this all sound reasonable? Suggestions on process and procedure? What am I missing? Thank you, Best, Bill WA2WIO -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of W0LEV via groups.io Sent: Friday, November 15, 2024 12:08 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance Your coaxial CMC should be installed just after the matching transformer between that and the coax. This is to isolate the coax from being part of the radiating structure. If you use the outer surface of the coax as a radiating element, yes, it should go 1/4-wavelength down the coax from the matching transformer. Dave - W?LEV On Fri, Nov 15, 2024 at 1:57?AM Bill WA2WIO via groups.io <sla= [email protected]> wrote: Thank you all for your considered and detailed suggestions and teaching points. To summarize what I believe I have learned: ¡¤ I am running QRP <> 3 watts (uSDX+ HF), does not leave much power to loose. ¡¤ Serious attic structural limitations do not allow for changing antenna leg angles or height. ¡¤ I am operating on 2 bands: 40m and 20m. I operate in both the CW and SSB portions of the bands. ¡¤ SWR without the ATU-10 tuner is =>6:1 at the rig, across all bands (MFJ-872) o The ATU-10 will bring it down to <2:1. o This will keep the rig happy, but actually waste >> significant power. ¡¤ VNA at the rig end w/o ATU shows no resonance anywhere except at 17mhz. (sweep 1-30Mhz). ¡¤ Antenna is certainly not actually balanced. o Antenna needs trimming, regardless. o My first step will be to go up into the attic, disconnect the feed line, and use my VNA to confirm just what the Z0 actually is. o I also need to verify the feed line from rig to antenna is viable. o Trim the antenna until resonant at 7.15Mhz (narrow sweep 7.0-7.4 MHz) o Assuming I am correct that Z0 is around 25 Ohms and complex, use a 1:2 BalUn to get closer to 50 Ohms. o Check 20m resonance (narrow sweep 14.0-14.5 MHz) ¡¤ If I get this far, I will add a CMC Coax Choke, 15T 4¡± on pvc form about 33ft (1/4 wave) from the antenna feed point. ¡¤ The goal is to get <> 2:1 across a reasonable portion of both bands without the ATU-10. ¡¤ Add in the ATU-10 ? Does this strategy make sense? Am I foolish to waste my time tuning and matching, as you say? I have made several contacts, but my RS(T) is way down in the mud. Noise level is >>S4-5 (a story for another day?). I do not see any alternative. Thoughts? Thank You, Best, Bill WA2WIO -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Joe Sent: Thursday, November 14, 2024 6:03 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance WHAT?? All that power being lost???? Seriously, a 2:1 SWR will only loose 11.1% of the power. So a 100 watt station will give you 88.9 watts of ERP (Less cable loss and plus antenna gain). Really not worth loosing time on the air. 73, Joe, K1ike On 11/14/2024 4:23 PM, W0LEV via groups.io wrote: My.....my........ For heaven's sake......! What concerns about a meager 2:1 SWR!! Just go with it, get on the air, and enjoy. Dave - W?LEV On Thu, Nov 14, 2024 at 7:15?PM DP via groups.io <dpoinsett= [email protected]> wrote: Hi Barry K3EUI You and others make an excellent point about the practical acceptability of of a 2:1 SWR. I agree that for the casual ham using commonly available equipment, it's probably not a big deal especially on the lower HF frequencies. You are correct that by adding an inductor across the antenna terminals and altering the antenna dimensions, the feedpoint impedance can be transformed to 50+j0 ohms, but the cut-and-try approach will be no easier than any of the other suggested methods. Also, just adding an inductor will not automatically increase the impedance. Depending in the initial antenna impedance, it may go up or down. If we stay with Bill's 25-ohm example, the antenna length and angle between each leg could be adjusted to get a 25-j25 feedpoint impedance at say 7.15 MHz. Adding a 1.1 uH inductor across the antenna terminals will then get you to 50+j0 ohms. Other combinations could work, too. Of course whatever combination he comes up with will only work at the design frequency. Dave NU8A -- *Dave - W?LEV* -- Dave - W?LEV -- *Dave - W?LEV* -- Dave - W?LEV |
|
Re: Dipole antenna with Low Z0 feed point Impedance
Barging in here for a moment...
In general antenna theory, the "far field" starts at 10x lambda. That is where the E and H fields have become coherent. Regards, Marty Hadfield, CPBE WA/OR/ID FCC ABIP Inspector On Nov 15, 2024, at 4:15?PM, Bill WA2WIO <sla@...> wrote: ?Dave - W?LEV; I hadn't thought of near field issues. I have had instances of interaction between my body and other objects with VNA measures before. As I understand it, at 40m HF, using a 1/2 wave dipole antenna (66ft), far field starts at about 1/2 a wavelength from the antenna. Recommendations go so far as to recommend 2-3 wavelengths away to eliminate unwanted influences. This is not achievable as the rig is only about 30-40ft from the antenna. Would a few clamp-on ferrites correct for this? Perhaps I should make all these measurements from the rig side? Calibrating from the coax feed line connection point at the antenna in the attic? Leaving only the antenna as the DUT? A much greater pain in the butt, but doable. Moving 30-40 ft away from the antenna has to be better, but is it worth the effort? Thank you, Best, Bill WA2WIO -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of W0LEV via groups.io Sent: Friday, November 15, 2024 12:40 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance In your measurement of the antenna only at the VNA end of your 6-foot jumper, it would be a good idea to attach a couple of 43 material clamp-on ferrites around the coax at the feedpoint to isolate you and the VNA/laptop from the measurement. You will be in the near-field of the antenna and your presence and the coax jumper will influence the measurement unless isolated. Dave - W?LEV On Fri, Nov 15, 2024 at 5:31?PM Bill WA2WIO via groups.io <sla= [email protected]> wrote: Dave - W0LEV;-- *Dave - W?LEV* -- Dave - W?LEV |
|
Re: Dipole antenna with Low Z0 feed point Impedance
Stan KC7XE,
toggle quoted message
Show quoted text
Thank you for the comments. ". . . A 40m dipole just won't match or radiate well on 20m. . . ." 20m is the first harmonic of 40m. The antenna should approx. a full wave on 20m. What am I missing here? " . . you need to either feed it at the end (EFHW or EFRW) or off-center (OCFD), and use the proper transformer at the antenna feed point. . ." If need be, I will start from scratch and build one as you suggest. " Fan Dipole" I considered this, and chose not to go this route, because I do not have the vertical height to spread out the fan at the far ends. Ideas? "trapped dipole" This is in fact my fallback position. DXE has a compact one only 38ft long. In any case, I need to refine my VNA test strategy, dealing with the near field issues, regardless of design strategy. Thought? Thank you, Best, Bill WA2WIO -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Stan Dye via groups.io Sent: Friday, November 15, 2024 12:37 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance Just one comment from me on basic antenna design/performance that you can check with your nanovna. It seems that you have installed a dipole in your attic, properly center-fed. And it seems that you are expecting to use that dipole on both 40m and 20m, and perhaps other bands with use of a tuner. This will not work well. When you trim your dipole for a low-swr and resonance on 40m, you will see in your nanovna measurements that it will have a very high swr on 20m. A 40m dipole just won't match or radiate well on 20m. It will likely work fine on 15m (its 3rd harmonic), which you will see on your nanovna measurement, but may require a tuner to lower the swr a bit. A good tuner may indeed tune this antenna to a low swr on 20m, but it will not radiate well at all. If you want a single wire antenna to radiate well on multiple bands, you need to either feed it at the end (EFHW or EFRW) or off-center (OCFD), and use the proper transformer at the antenna feedpoint. There is tons of info on such antennas. A 40m EFHW or OCFD will work best (about as good as a dipole) on 40m, but will also work quite well on some of the higher bands. Another way to get multiple bands is to use a fan dipole - meaning just hook more sets of dipole wires on the same feedpoint, each trimmed to resonate on their own band. The wires need to be separated by several inches to make this work well, and they interact, so you have to tune them with the nanovna as a set - but the performance is great on each of the bands. Yet another way is to use a trapped dipole - but this may be a little difficult to set up and tune in a crazy attic configuration. So the main note here is to not expect good performance on 20m from a 40m center-fed dipole, regardless of how you match or tune it. Stan KC7XE |
|
Re: Dipole antenna with Low Z0 feed point Impedance
Dave - W?LEV;
toggle quoted message
Show quoted text
I hadn't thought of near field issues. I have had instances of interaction between my body and other objects with VNA measures before. As I understand it, at 40m HF, using a 1/2 wave dipole antenna (66ft), far field starts at about 1/2 a wavelength from the antenna. Recommendations go so far as to recommend 2-3 wavelengths away to eliminate unwanted influences. This is not achievable as the rig is only about 30-40ft from the antenna. Would a few clamp-on ferrites correct for this? Perhaps I should make all these measurements from the rig side? Calibrating from the coax feed line connection point at the antenna in the attic? Leaving only the antenna as the DUT? A much greater pain in the butt, but doable. Moving 30-40 ft away from the antenna has to be better, but is it worth the effort? Thank you, Best, Bill WA2WIO -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of W0LEV via groups.io Sent: Friday, November 15, 2024 12:40 PM To: [email protected] Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance In your measurement of the antenna only at the VNA end of your 6-foot jumper, it would be a good idea to attach a couple of 43 material clamp-on ferrites around the coax at the feedpoint to isolate you and the VNA/laptop from the measurement. You will be in the near-field of the antenna and your presence and the coax jumper will influence the measurement unless isolated. Dave - W?LEV On Fri, Nov 15, 2024 at 5:31?PM Bill WA2WIO via groups.io <sla= [email protected]> wrote: Dave - W0LEV;-- *Dave - W?LEV* -- Dave - W?LEV |
|
Re: Dipole antenna with Low Z0 feed point Impedance
Even though most readers will understand what Joe intended to say,
toggle quoted message
Show quoted text
his usage of the term ERP is fundamentally incorrect and could lead to further incorrect use of the term by others. I'm sure Joe intended to say 88.9 watts at the feed point of the antenna 73 Frank W3LPL ----- Original Message -----
From: "Joe" <k1ike_mail@...> To: [email protected] Sent: Friday, November 15, 2024 8:58:49 AM Subject: Re: [nanovna-users] Dipole antenna with Low Z0 feed point Impedance Warren, I think I stated that. "So a 100 watt station will give you 88.9 watts of ERP (Less cable loss and plus antenna gain)." So, I accounted for the fact that there would be cable loss and it would have to be subtracted from the calculated loss of the antenna.? Also, antenna gain or loss would come into play for calculating ERP. I didn't really mean it to be a scientific statement, just a common sense statement why 2:1 SWR is not a really big thing to worry about. 73, Joe, K1ike On 11/15/2024 9:42 AM, Warren Allgyer via groups.io wrote: Joe |
|
Re: Dipole antenna with Low Z0 feed point Impedance
In your measurement of the antenna only at the VNA end of your 6-foot
jumper, it would be a good idea to attach a couple of 43 material clamp-on ferrites around the coax at the feedpoint to isolate you and the VNA/laptop from the measurement. You will be in the near-field of the antenna and your presence and the coax jumper will influence the measurement unless isolated. Dave - W?LEV On Fri, Nov 15, 2024 at 5:31?PM Bill WA2WIO via groups.io <sla= [email protected]> wrote: Dave - W0LEV;-- *Dave - W?LEV* -- Dave - W?LEV |
Roger Need
Warren Allgyer
to navigate to use esc to dismiss