1. Nanovna-Users
  2. Теми

multiple resonances of a half wave end fed wire

 

*          OOOPS*

*What happens when an end-fed, one-halfwave wire is a bit too long?*

*
*

*I recently put up only half of my 80m (140 ft) end-fed MyAntenna wire (about 70 ft) and it shows*

*the typical RETURN LOSS (dB) indicating low SWR at multiples of the fundamental just below the 40m band.*

*This model uses a 49:1 UNUN and a 30 ft counterpoise.*

*Fed with 50 ft RG213 and 10 ft section of RG8X.
*

*
*

*I think if I shorten it about 3-4 ft the dips will land right where I want them - in the digi part of 40/20/10m.*

*It also has a very low SWR around 50 MHz  (the 7th harmonic of 7 MHz) -  super for 6 meter FT8.*

*
*

*But I plan to now stretch it out the complete 140 ft  to get 80m - that means crawling into the woods on a steep hill.
*

*de k3eui*

*
*

Jb04OTJ0ADcBdkz0.jpg

 

Divide the target 40-meter low SWR frequency by the just below the 40-meter
frequency. This will be a number a bit less than unity (one). Then
multiply the length of your EFHW for 40-meters by this number. The result
will be mighty close to the correct length of your 70-foot wire.

Dave - WØLEV

<http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
Virus-free.www.avg.com
<http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

On Sat, Jul 6, 2024 at 8:38 PM Barry K3EUI via groups.io <k3euibarry=
gmail.com@groups.io> wrote:


* OOOPS*

*What happens when an end-fed, one-halfwave wire is a bit too long?*

*
*

*I recently put up only half of my 80m (140 ft) end-fed MyAntenna wire
(about 70 ft) and it shows*

*the typical RETURN LOSS (dB) indicating low SWR at multiples of the
fundamental just below the 40m band.*

*This model uses a 49:1 UNUN and a 30 ft counterpoise.*

*Fed with 50 ft RG213 and 10 ft section of RG8X.
*

*
*

*I think if I shorten it about 3-4 ft the dips will land right where I
want them - in the digi part of 40/20/10m.*

*It also has a very low SWR around 50 MHz (the 7th harmonic of 7 MHz)
- super for 6 meter FT8.*

*
*

*But I plan to now stretch it out the complete 140 ft to get 80m - that
means crawling into the woods on a steep hill.
*

*de k3eui*

*
*





--

*Dave - WØLEV*


--
Dave - WØLEV
 

TU for the fine tuning advice Dave.

However, my goal is to now stretch out the wire to the full 140 feet, to get 80m digi band capability.
To do that I have to get into the weeds (steep hill) and find a tie-off point 150 ft distance.

The RETURN LOSS did show the multiple dips very nicely.

de barry k3eui EPA
 

SWR dips do NOT indicate resonance.

IF the wire is a resonant half wave and IF the transformer is a 49:1 impedance ratio, then you WILL have an SWR dip at the resonant frequency.

You will also have a dip at any frequency where the transformer loss is more than 2-3 dB and such dips are NOT an indication of resonance. They are actually exactly the opposite. They are indicators of frequencies where there is very high system loss.

The problem with this antenna is that there is a very good chance an SWR bridge at the radio will be lying to you.

When used with resonant half wave wires the EFHW is a very good antenna. When the wire is not a resonant half wave the EFHW is a reasonably good dummy load. And simply measuring SWR will not tell you which you have.

Warren Allgyer - WA8TOD
 

QUOTE: When used with resonant half wave wires the EFHW is a very good
antenna. When
the wire is not a resonant half wave the EFHW is a
reasonably good dummy load. And
simply measuring SWR will not tell you which you have.

Warren Allgyer - WA8TOD

Well stated, Warren.

Somewhere in the long lost past of amateur radio lore, maybe with the Wouff
Hong, the belief was launched that low SWR indicated a good antenna. This
could not be further from the truth!! SWR has nothing to do with a hunk of
conductor being a "good antenna". Once again: A dummy load exhibits a low
SWR across a wide range of frequencies. But it's a terrible antenna.

Maybe we should go back to the days when antenna current was measured.
Maximum current into the hunk of conductor indicated at least that the
generated RF was being sunk by the hunk of conductor. The hope was that
maximized current resulted in maximum radiation of the RF. Is this a
better indicator of a "good antenna" than SWR?

Let's all get on the bandwagon and shed this bogus belief that SWR
indicates a "good antenna".

Also, ask yourself specifically what constitutes a "good antenna".

Dave - WØLEV


On Tue, Jul 16, 2024 at 12:58 PM Warren Allgyer via groups.io <allgyer=
gmail.com@groups.io> wrote:

SWR dips do NOT indicate resonance.

IF the wire is a resonant half wave and IF the transformer is a 49:1
impedance ratio, then you WILL have an SWR dip at the resonant frequency.

You will also have a dip at any frequency where the transformer loss is
more than 2-3 dB and such dips are NOT an indication of resonance. They are
actually exactly the opposite. They are indicators of frequencies where
there is very high system loss.

The problem with this antenna is that there is a very good chance an SWR
bridge at the radio will be lying to you.

When used with resonant half wave wires the EFHW is a very good antenna.
When the wire is not a resonant half wave the EFHW is a reasonably good
dummy load. And simply measuring SWR will not tell you which you have.

Warren Allgyer - WA8TOD





--

*Dave - WØLEV*


--
Dave - WØLEV
 

I think that is overstating the case a bit Dave. If a low SWR exists then the return loss is by definition low, so that means that the power is going somewhere other than back to the Tx. It may be that losses in the system have increased for some reason, but more than likely a fair amount the power is actually getting to the antenna. If you are running any sort of power it will become clear if things are getting hot!!

73
Jeff G8HUL

-----Original Message-----
From: nanovna-users@groups.io <nanovna-users@groups.io> On Behalf Of W0LEV
Sent: 16 July 2024 14:51
To: nanovna-users@groups.io
Subject: Re: [nanovna-users] multiple resonances of a half wave end fed wire

QUOTE: When used with resonant half wave wires the EFHW is a very good antenna. When
the wire is not a resonant half wave the EFHW is a reasonably good dummy load. And
simply measuring SWR will not tell you which you have.

Warren Allgyer - WA8TOD

Well stated, Warren.

Somewhere in the long lost past of amateur radio lore, maybe with the Wouff Hong, the belief was launched that low SWR indicated a good antenna. This could not be further from the truth!! SWR has nothing to do with a hunk of conductor being a "good antenna". Once again: A dummy load exhibits a low SWR across a wide range of frequencies. But it's a terrible antenna.

Maybe we should go back to the days when antenna current was measured.
Maximum current into the hunk of conductor indicated at least that the generated RF was being sunk by the hunk of conductor. The hope was that maximized current resulted in maximum radiation of the RF. Is this a better indicator of a "good antenna" than SWR?

Let's all get on the bandwagon and shed this bogus belief that SWR indicates a "good antenna".

Also, ask yourself specifically what constitutes a "good antenna".

Dave - WØLEV


On Tue, Jul 16, 2024 at 12:58 PM Warren Allgyer via groups.io <allgyer= gmail.com@groups.io> wrote:

SWR dips do NOT indicate resonance.

IF the wire is a resonant half wave and IF the transformer is a 49:1
impedance ratio, then you WILL have an SWR dip at the resonant frequency.

You will also have a dip at any frequency where the transformer loss
is more than 2-3 dB and such dips are NOT an indication of resonance.
They are actually exactly the opposite. They are indicators of
frequencies where there is very high system loss.

The problem with this antenna is that there is a very good chance an
SWR bridge at the radio will be lying to you.

When used with resonant half wave wires the EFHW is a very good antenna.
When the wire is not a resonant half wave the EFHW is a reasonably
good dummy load. And simply measuring SWR will not tell you which you have.

Warren Allgyer - WA8TOD





--

*Dave - WØLEV*


--
Dave - WØLEV
 

As lower the SWR is as higher the return loss is.

https://www.amphenolrf.com/vswr-conversion-chart

73
Peter, DJ7WW

-----Original-Nachricht-----
Betreff: Re: [nanovna-users] multiple resonances of a half wave end fed wire
Datum: 2024-07-17T09:52:07+0200
Von: "G8HUL" <g8hul@...>
An: "nanovna-users@groups.io" <nanovna-users@groups.io>

I think that is overstating the case a bit Dave. If a low SWR exists then the return loss is by definition low,
 

VSWR and Return Loss are different expressions of precisely the same parameter. Just a different calculation.

Low VSWR is the same as high Return Loss is the same as "the power is going somewhere other than back to the Tx. And the parameter tells nothing about where the power is going.

The ONLY way to know how much power is getting to the wire is to:
1) MEASURE the impedance of the wire
2) MEASURE the current in the wire.
3) Use the two results to determine the power in the wire.

This is the method required by the FCC for commercial broadcasters.

Warren Allgyer - WA8TOD
 

This is true when Zo is real, which is true almost all of the time for most of us. If, though, you venture into lower frequencies where Zo is complex, and the high frequency approximations are not valid,then VSWR is not equivalent to return loss. Be careful with anything below about 300 kHz.

This is why telephone engineers working at voice frequencies and analog carrier telephone frequencies use reflection loss and return loss to characterize transmission lines, almost never SWR and reflection coefficient.

73,

Maynard
W6PAP

On 7/17/24 05:44, Warren Allgyer wrote:
VSWR and Return Loss are different expressions of precisely the same parameter. Just a different calculation.
Low VSWR is the same as high Return Loss is the same as "the power is going somewhere other than back to the Tx. And the parameter tells nothing about where the power is going.
The ONLY way to know how much power is getting to the wire is to:
1) MEASURE the impedance of the wire
2) MEASURE the current in the wire.
3) Use the two results to determine the power in the wire.
This is the method required by the FCC for commercial broadcasters.
Warren Allgyer - WA8TOD

1 - 9 з 9