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75ohm stub position


Will Grocott, M0LGW
 

A Question for the group:
is the position of the 75ohm matching stub critical for a low VSWR on 20m?

I’ve heard some people coil up the stub, some bury it, some have it running around a fence corner and some have it in a straight line from the antenna base back towards the shack. How critical is the position of the stub to the performance of the 20m band?

Thanks
Will, M7APJ 


Lon Kinley
 

It makes no difference whatsoever. Whatever is convenient for your location is fine

Lon W3LK

On Jul 1, 2020, at 6:59 AM, Will Grocott, M7APJ <wjcgrocott@...> wrote:

A Question for the group:
is the position of the 75ohm matching stub critical for a low VSWR on 20m?

I’ve heard some people coil up the stub, some bury it, some have it running around a fence corner and some have it in a straight line from the antenna base back towards the shack. How critical is the position of the stub to the performance of the 20m band?

Thanks
Will, M7APJ 



 

When I first installed the antenna, I had it laid straight out.  That got in the way so I made a loop around a tree and that had no effect.  A later mod to the installation, had me make a 1' diameter loop and that still did nothing that I could see.  The landscapers move it around while weeding and that does nothing other than to weaken the center conductor at the antenna.
Al
WB9UVJ


Dave KD7LRS
 

Hi from the new guy

It just so happens I asked this very question of DX Engineering this morning.  They said if you make a loop around the base to keep the connector off the ground as we do then make it a large loop. Also to not put the cable through the bulkhead fitting cut out on the Radial plate.
Thanks for the add to the group.
73's
Dave
KD7LRS


Virus-free. www.avg.com


On Wed, Jul 1, 2020 at 9:36 AM Al WB9UVJ <markaren1@...> wrote:
When I first installed the antenna, I had it laid straight out.  That got in the way so I made a loop around a tree and that had no effect.  A later mod to the installation, had me make a 1' diameter loop and that still did nothing that I could see.  The landscapers move it around while weeding and that does nothing other than to weaken the center conductor at the antenna.
Al
WB9UVJ


Scott AC8DE
 

While it isn't very important what you do with the matching section, you certainly don't want to have it lying tight up against the antenna base, due to the higher currents that will be induced at the antenna base.  That is what DX means.  Best to run it away from the antenna.  That said, I've seen them loosely coiled up against antenna bases with no problems, but still, not recommended.

 

The method I always suggest is to run the feedline and matching section is to bury 1" PVC conduit just below your radials all the way back to the shack and put "candy canes" on each end.  Then pull the matching section and feed line into conduit, after taping the connection.  This then protects the matching section as well as the feed line from any damage from rocks or anything else.  It also facilitates a quick change of feed line and matching section if it were to go bad.  Since 1" conduit costs a whopping $4 for 10' section, it is a very inexpensive solution.  It also takes no longer to bury than direct burial coax, as it doesn't have to be deep, even in areas where it freezes in the winter.  Make sure the PVC bells are cleaned and glued like you would do for PVC water pipe so it stays dry.

 

The DX radial plate is a "multi use" plate.  It was originally designed with Hustler BTV's and monopoles in mind, which do not use a matching section.  In the case of those antennas, having a bulkhead connector on the plate is convenient for grounding the shield to the radials.  It does nothing for the Butternut HF6/9V series, since this antenna requires the 75 ohm matching section.

 

73,

Scott AC8DE

 

From: Butternut@groups.io On Behalf Of Dave KD7LRS
Sent: Wednesday, July 01, 2020 11:53 PM
To: Butternut@groups.io Group Moderators <Butternut@groups.io>
Subject: Re: [butternut] 75ohm stub position

 

Hi from the new guy

 

It just so happens I asked this very question of DX Engineering this morning.  They said if you make a loop around the base to keep the connector off the ground as we do then make it a large loop. Also to not put the cable through the bulkhead fitting cut out on the Radial plate.

Thanks for the add to the group.

73's

Dave

KD7LRS

 

 

Virus-free. www.avg.com

 

On Wed, Jul 1, 2020 at 9:36 AM Al WB9UVJ <markaren1@...> wrote:

When I first installed the antenna, I had it laid straight out.  That got in the way so I made a loop around a tree and that had no effect.  A later mod to the installation, had me make a 1' diameter loop and that still did nothing that I could see.  The landscapers move it around while weeding and that does nothing other than to weaken the center conductor at the antenna.
Al
WB9UVJ


Chuck N0NC
 

I have used mine with the matching section coiled around the base (about ten inch diameter), and stretched out flat with a dozen ferrite cores on it. I notice no differance in tuning or operation. Not buried (we live in a rental duplex) just laying ontop of the ground, and have to coil it up to mow the yard. Hope to some day get a house of my own, them it will be buried as Scott suggests
73, Chuck
N0NC


Scott AC8DE
 

Are you running an amp or barefoot?

 

Scott AC8DE

 

From: Butternut@groups.io On Behalf Of Chuck N0NC
Sent: Saturday, July 04, 2020 12:50 PM
To: Butternut@groups.io
Subject: Re: [butternut] 75ohm stub position

 

I have used mine with the matching section coiled around the base (about ten inch diameter), and stretched out flat with a dozen ferrite cores on it. I notice no differance in tuning or operation. Not buried (we live in a rental duplex) just laying ontop of the ground, and have to coil it up to mow the yard. Hope to some day get a house of my own, them it will be buried as Scott suggests
73, Chuck
N0NC


Will Grocott, M0LGW
 

Thank you everyone for your replies. Very helpful. As a newbie this group has been awesome with such a lot of smart hams happy to share their ideas and experience. Fabulous 👍🏻

Scott
Currently I am running barefoot, no amp. I am only running low power <10w as that is all my license will allow (I’ve only been on the air 3m). As I move up the license classes I will be able to use 50w then 400w.

As a QRP station I am learning a lot and I realise optimising what I have to get it ultra efficient is my challenge. So far I am doing ok, I’ve had 1000+ QSOs and worked 61 countries, so I’m happy. But if I can optimise further and improve my efficiency then that would be great 

Thanks again all
Will, M7APJ