50 MHz/ 6 meter SWR


Charlie T, k3ICH
 

Yes, you are absolutely correct.

 

The wrong Z even if off my a small amount, and/or length of coax can REALLY screw up SWR measurements.

 

Want proof?  Add a ¼ λ piece of RG-59 or RG-62  in series with your good-working antenna and observe the results.

 

73, Charlie k3ICH

 

 

 

 

 

 

From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of Dan Roberts
Sent: Sunday, May 08, 2022 12:16 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] 50 mhz/ 6 meter SWR

 

Is your coax really 50 Ohms?  I’m not joking.  Just because it says RG8/U on the jacket, doesn’t mean it is.  I found this out the hard way, a few months ago, when trying to tweak the tuning on a new 6 meter beam.  After several days of ladder climbing and strange results, I put a precision load at the end of the off-brand coax and measured a VSWR of about 1.6 on all frequencies!  Clearly not a 50 Ohm cable.  Replaced with cable from well known  U.S. manufacturer and saw zero reflected.  Antenna tuned right up. 

 

I then went through my collection of old cables and found most to be good, but two off-brand cables were not. 

 

Until that experience, I’d always assumed that RG-8/U meant 50 Ohms and never questioned it.  Now, before I start any antenna project, I check the cable with a precision load and my antenna analyzer.  Absolutely worth the few minutes it takes.

 

Dan-K9DR

 

 


Wes Stewart
 

Wait a minute Charlie.

First you say a small amount/length difference can screw up a measurement and then offer a 1.5 to 2 difference in Z and the worst possible length to bolster your claim. I say change the length to 1/2 wavelength and get back to us :-)

Wes  N7WS


On Sun, May 8, 2022 at 11:12 AM, Charlie T, k3ICH wrote:

Yes, you are absolutely correct.

 

The wrong Z even if off my a small amount, and/or length of coax can REALLY screw up SWR measurements.

 

Want proof?  Add a ¼ λ piece of RG-59 or RG-62  in series with your good-working antenna and observe the results.

 

73, Charlie k3ICH

 


Charlie T, k3ICH
 

Correction….”a small length of the WRONG impedance can screw up……

The ¼λ was to illustrate the worst case.

Reality is somewhere in between…

 

Diddle dee dah didah., C

 

 

From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of Wes Stewart via groups.io
Sent: Sunday, May 08, 2022 3:15 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] 50 MHz/ 6 meter SWR

 

Wait a minute Charlie.

First you say a small amount/length difference can screw up a measurement and then offer a 1.5 to 2 difference in Z and the worst possible length to bolster your claim. I say change the length to 1/2 wavelength and get back to us :-)

Wes  N7WS


On Sun, May 8, 2022 at 11:12 AM, Charlie T, k3ICH wrote:

Yes, you are absolutely correct.

 

The wrong Z even if off my a small amount, and/or length of coax can REALLY screw up SWR measurements.

 

Want proof?  Add a ¼ λ piece of RG-59 or RG-62  in series with your good-working antenna and observe the results.

 

73, Charlie k3ICH

 


Ray Maxfield
 

Especially at 6 meters !

 

Ray WA6VAB  K3

 

 

From: Charlie T, k3ICH
Sent: Sunday, May 8, 2022 1:28 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] 50 MHz/ 6 meter SWR

 

Correction….”a small length of the WRONG impedance can screw up……

The ¼λ was to illustrate the worst case.

Reality is somewhere in between…

 

Diddle dee dah didah., C

 

 

From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of Wes Stewart via groups.io
Sent: Sunday, May 08, 2022 3:15 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] 50 MHz/ 6 meter SWR

 

Wait a minute Charlie.

First you say a small amount/length difference can screw up a measurement and then offer a 1.5 to 2 difference in Z and the worst possible length to bolster your claim. I say change the length to 1/2 wavelength and get back to us :-)

Wes  N7WS


On Sun, May 8, 2022 at 11:12 AM, Charlie T, k3ICH wrote:

Yes, you are absolutely correct.

 

The wrong Z even if off my a small amount, and/or length of coax can REALLY screw up SWR measurements.

 

Want proof?  Add a ¼ λ piece of RG-59 or RG-62  in series with your good-working antenna and observe the results.

 

73, Charlie k3ICH