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Hello,
Once my antenna is up it will have a 50ft run of coax that enters my home. Do I measure the swr at the base of the antenna (before the 50ft of coax) or inside the house (at the end of the coax)?
Thanks in advacne,
Peter
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Peter,
It depends what you want.
Measuring at the antenna allows you to check the resonant frequency and the complex impedance of the antenna (to design a match to the coax impedance - often 50 ohms)
Measuring at the indoor end of the coax lets you see the complex impedance of the antenna plus coax system to determine whether a tuning unit is needed.
73
John
M0JBA
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On 7 Aug 2023, at 15:47, Peter N0PGM <pgmelton@...> wrote:
Hello,
Once my antenna is up it will have a 50ft run of coax that enters my home. Do I measure the swr at the base of the antenna (before the 50ft of coax) or inside the house (at the end of the coax)?
Thanks in advacne,
Peter
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I generally measure it at the end of the coax in the shack. That way I see
what the rig is going to see. I have had really long stretches of coax to
the antenna and the NanoVNA was unable to measure the SWR. I think it
required more power to overcome cable losses. In that case I had to check
it with a lot shorter length of coax.
73, Zack W9SZ
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On Mon, Aug 7, 2023 at 9:47?AM Peter N0PGM <pgmelton@...> wrote: Hello,
Once my antenna is up it will have a 50ft run of coax that enters my home.
Do I measure the swr at the base of the antenna (before the 50ft of coax)
or inside the house (at the end of the coax)?
Thanks in advacne,
Peter
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Measure it BOTH times.
First to make sure the antenna is properly tuned while it is still easy to work on.
Second on the tower to make sure the coax fittings and the coax line are good.Kent WA5VJB
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On Monday, August 7, 2023 at 09:47:24 AM CDT, Peter N0PGM <pgmelton@...> wrote:
Hello,
Once my antenna is up it will have a 50ft run of coax that enters my home. Do I measure the swr at the base of the antenna (before the 50ft of coax) or inside the house (at the end of the coax)?
Thanks in advacne,
Peter
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I'd propose the lack of ability to measure SWR is not due to the long coax,
but due to strong local sources of RF.
Dave - W?LEV
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On Mon, Aug 7, 2023 at 3:06?PM Zack Widup <w9sz.zack@...> wrote: I generally measure it at the end of the coax in the shack. That way I see
what the rig is going to see. I have had really long stretches of coax to
the antenna and the NanoVNA was unable to measure the SWR. I think it
required more power to overcome cable losses. In that case I had to check
it with a lot shorter length of coax.
73, Zack W9SZ
On Mon, Aug 7, 2023 at 9:47?AM Peter N0PGM <pgmelton@...> wrote:
Hello,
Once my antenna is up it will have a 50ft run of coax that enters my home.
Do I measure the swr at the base of the antenna (before the 50ft of coax)
or inside the house (at the end of the coax)?
Thanks in advacne,
Peter
-- *Dave - W?LEV*
--
Dave - W?LEV
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I really don't know. I just didn't seem to be getting a signal back through
the coax for some reason. My RigExpert AA-600 did OK in measuring the SWR
on the same coax and antennas, though. This was all on the HF ham bands -
3.5, 7, 14, 21 and 28 MHz. I don't know of any really strong signals on HF
that might cause that.
73, Zack W9SZ
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On Mon, Aug 7, 2023 at 12:17?PM W0LEV <davearea51a@...> wrote: I'd propose the lack of ability to measure SWR is not due to the long coax,
but due to strong local sources of RF.
Dave - W?LEV
On Mon, Aug 7, 2023 at 3:06?PM Zack Widup <w9sz.zack@...> wrote:
I generally measure it at the end of the coax in the shack. That way I see
what the rig is going to see. I have had really long stretches of coax to
the antenna and the NanoVNA was unable to measure the SWR. I think it
required more power to overcome cable losses. In that case I had to check
it with a lot shorter length of coax.
73, Zack W9SZ
On Mon, Aug 7, 2023 at 9:47?AM Peter N0PGM <pgmelton@...> wrote:
Hello,
Once my antenna is up it will have a 50ft run of coax that enters my home.
Do I measure the swr at the base of the antenna (before the 50ft of coax)
or inside the house (at the end of the coax)?
Thanks in advacne,
Peter
--
*Dave - W?LEV*
--
Dave - W?LEV
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Coaxial cables have loss. With long cables it is best to match the antenna to 50 ohms before connecting it to the cable. If this is not done, a mismatch between the cable impedance and the antenna reflects some power back to the transmitter. The cable loss dissipates some of the reflected power and less of it is reaches the transmitter than was actually pushed back by the antenna. If the cable is mismatched at both the antenna and transmitter ends, then part of the power reflected by the antenna travels back and forth between mismatches creating further losses in the cable. Power lost in the cable does not get radiated and does not show up as bad VSWR at the transmitter end giving the false impression of a better match than is actually present. __Joe VE6JSL On Mon, Aug 7, 2023 at 09:06 Zack Widup <w9sz.zack@...> wrote: I generally measure it at the end of the coax in the shack. That way I see
what the rig is going to see. I have had really long stretches of coax to
the antenna and the NanoVNA was unable to measure the SWR. I think it
required more power to overcome cable losses. In that case I had to check
it with a lot shorter length of coax.
73, Zack W9SZ
On Mon, Aug 7, 2023 at 9:47?AM Peter N0PGM <pgmelton@...> wrote:
Hello,
Once my antenna is up it will have a 50ft run of coax that enters my home.
Do I measure the swr at the base of the antenna (before the 50ft of coax)
or inside the house (at the end of the coax)?
Thanks in advacne,
Peter
-- __Joe Leizerowicz 6424 34 Avenue NW, Calgary, AB T3B 1N1 403-604-7791
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On Mon, Aug 7, 2023 at 07:47 AM, Peter N0PGM wrote: Once my antenna is up it will have a 50ft run of coax that enters my home. Do
I measure the swr at the base of the antenna (before the 50ft of coax) or
inside the house (at the end of the coax)?
The SWR at the transmitter will be higher at the antenna than at the receiver. The more attenuation in the transmission line the greater the difference. See attached graph below. Roger
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/The SWR at the transmitter will be higher at the antenna than at the receiver.///
Shouldn't the SWR be lower, because at the transmitter, power reflected from the antenna will be attenuated by losses in the transmission line?
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On 8/7/23 11:35, Roger Need via groups.io wrote: On Mon, Aug 7, 2023 at 07:47 AM, Peter N0PGM wrote:
Once my antenna is up it will have a 50ft run of coax that enters my home. Do
I measure the swr at the base of the antenna (before the 50ft of coax) or
inside the house (at the end of the coax)?
The SWR at the transmitter will be higher at the antenna than at the receiver. The more attenuation in the transmission line the greater the difference. See attached graph below.
Roger
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NOPE!? ? Due to coax losses, the analyzer doesn't see the reflected power.
SWR is LOWER with a long coax.
Assuming the coax is not damaged of course.
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On Monday, August 7, 2023 at 02:34:59 PM CDT, Dave via groups.io <dvfuller@...> wrote:
I think that's what Roger was trying to say. The SWR at the antenna will be higher because of losses to the return signal back at the receiver.
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Cable loss to antenna will reduce the forward, then return reflected power.
It can be calibrated out but the round trip loss reduces the dynamic range of network analyzer by the round trip dB loss. If you are looking to get impedance at the antenna you must calibrate out the cable because you also need the phase information correct for network analyzer to figure terminal impedance at end of cable.
Also on NanoVNA, when measuring antennas you have to be careful of strong nearby radio transmitters, like AM or FM broadcast stations. The input mixer chip of NanoVNA can be overloaded by strong RF signals.
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I would think you would want to know exactly where the antenna stood before complicating matters by assuming the antenna is ok and your not knowing where your hi swr readings are coming from. Fred N4CLA On Mon, Aug 7, 2023 at 10:58?AM John Baines via groups.io <jbaines= [email protected]> wrote: Peter,
It depends what you want.
Measuring at the antenna allows you to check the resonant frequency and
the complex impedance of the antenna (to design a match to the coax
impedance - often 50 ohms)
Measuring at the indoor end of the coax lets you see the complex impedance
of the antenna plus coax system to determine whether a tuning unit is
needed.
73
John
M0JBA
On 7 Aug 2023, at 15:47, Peter N0PGM <pgmelton@...> wrote:
Hello,
Once my antenna is up it will have a 50ft run of coax that enters my home. Do I measure the swr at the base of the antenna (before the 50ft of
coax) or inside the house (at the end of the coax)?
Thanks in advacne,
Peter
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Here's an EFHW I measured at the antenna and in the shack.
First I calibrated the NanoVNA at the far end of the feeder (18 metres long and about 0.5dB loss) and measured the VSWR there. Then I calibrated again on a short cable and measured inside the shack.
Here's the result.
--
Mike G8GYW
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Second time lucky ...
--
Mike G8GYW
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The minimums are almost the same. . . thanks for the measurement.
Vy 73, Roger DL2YDP
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You can do both. If you calibrate with the SOLT loads at the cable end you will get the antenna impedance. If you calibrate at the nano-vna end you will get the line plus antenna.
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Mike,
Tell us more about your antenna.
What length is your EFHW?
Did your EFHW have a reflector stub of some length connected to the shield side or is it fed straight to coax?
Any choke in the line at some point?
I wonder how common mode currents would contribute to the measurement.
73, Bryan, n0lif
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On Fri, Aug 11, 2023 at 12:36 PM, Bryan Curl wrote:
Mike,
Tell us more about your antenna.
What length is your EFHW?
Did your EFHW have a reflector stub of some length connected to the shield
side or is it fed straight to coax?
Any choke in the line at some point?
I wonder how common mode currents would contribute to the measurement.
73, Bryan, n0lif
Bryan The attached drawings should answer your questions. The wire was bent to fit my garden. Performance is very good, with 100W SSB QSOs from my QTH near London to the US midwest, South America and Indonesia. -- Mike G8GYW
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Hello Mike,
Very nice setup. Everything looks great.
I see the wire is 16 SWG (14AWG) enameled copper wire. Since you installed it, have you noticed any stretching of the wire? (Does it droop more?) ===> Stretching of the wire will cause your plots to shift more because your wire length is now longer and not the same tuning length as when you first installed it. Using a copper clad steel wire will lessen the stretching or maybe even a kevlar based wire will help.
For the overall SWR presented to RADIO measure at end of coax in shack. Since you are in a PERMANENT setup and not changing locations, heights, ground effects, etc, this is the SWR setting that your use to TUNE your antenna (if needed). Since you are possibly stretching your length you MIGHT need to trim the "C location" end a little bit to move your plots to the right and back into perfect tune for your needs. Watch this over time because your wire WILL stretch and de-tune. But it is a simple measurement in your shack. Save your plots and compare them over time.
Optional:
Disconnect the coax from the CMC choke and do a quick scan down (or up) the coax to make sure it is all clean (you can find youtube vids on that) (obviously the coax is not in radio for this test, just an open coax).
Move the next measurement to the bottom of choke. Test the swr. The result should be close to the coax measurement results if you have a good quality coax in good working order). This will not be your overall SWR tuning measurement. You will want the reading that your SHACK measures of the ANTENNA system for a permanent antenna tuning.
It is nice to know your measurement at the 49:1 just for future reference, but it will only tell your if your WIRE has changed characteristics OR if your 49:1 has changed (but at 100W, it is probably not going to cook the wires, if it is well made). If you do not change the choke or the connectors or coax, you can already see this result from the shack measurement alone (and that is the only measurement that matters) but each piece of the puzzle is good to know if you have issue and want to find out what changed (over time).
Overall, Very nice setup and documentation. And GREAT results on the contacts...
Hope this makes sense and if I am mistaken with anything, please chime in everyone.
73,
Mark
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Just an additional note, that I did not mention in this type of scenario...
If you do need to do tuning, make sure you are making that decision AFTER examining the plots across ALL your workable bands. Since you are using this antenna for multiple HF bands, you will want to look at the plots where you USE the bands. You do not just want to look at 40m and then start trimming like crazy and shift all the other bands into unworkable frequencies. So just a SAFETY note. Make your trimming decisions using all the information and with your goals in mind and know when to stop tuning as to hurt other bands.
ALSO, since you are using enameled wire your can fold back your wire after using some sandpaper to strip the enamel off and wrap the wire around. This is the same as shorting (cutting). If you mess up to much just unwrap and shorten your fold back and wrap again, test, and continue. Your do not really need to cut at all then.....
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Peter N0PGM #3460
Roger Need
Paul - AI7JR
Roger DL2YDP
F4WCV
