Radio Preppers

General Category => Antennas => Topic started by: gil on November 19, 2016, 05:24:57 PM

Title: Windom Antenna Analysis With The MR100.
Post by: gil on November 19, 2016, 05:24:57 PM
Hello,

This is the analysis of my 80m Windom antenna using the MR100 el cheapo Chinese antenna analyzer. Note that I am not quite sure the calibration was entirely successful... So take these results with a grain of salt, since some are somewhat puzzling... The length of the antenna is approximate since I made it a bit longer than calculated and later cut off about a foot... Coax length is 20m of RG-174. A bit thin but I needed something that would not pull down the radiating wire and go through a window.

The description of the antenna is somewhere in this thread: http://radiopreppers.com/index.php/topic,1096.0.html (http://radiopreppers.com/index.php/topic,1096.0.html)

(http://radiopreppers.com/images/W80m.png)

(http://radiopreppers.com/images/W40m.png)

(http://radiopreppers.com/images/W30m.png)

(http://radiopreppers.com/images/W20m.png)

(http://radiopreppers.com/images/W17m.png)

(http://radiopreppers.com/images/W15m.png)

(http://radiopreppers.com/images/W12m.png)

(http://radiopreppers.com/images/W10m.png)

(http://radiopreppers.com/images/W6m.png)

The 80m results aren't good but it seems a longer coax cable brings the SWR down, which suggests I still have some common mode currents on the cable even though I am using a dual-core Guanella BALUN.

The 40m graph suggests I might have shortened the antenna too much, though the SWR is still acceptable.

No surprise on 30m, it's not supposed to be resonant there.

The other graphs look weird. I think I need to do a proper calibration to verify these results. The plots look different depending on how the coax lays on the floor.

The graphs looked actually saner before I calibrated the gizmo. Anyway, It's fun to experiment.

Gil.
Title: Re: Windom Antenna Analysis With The MR100.
Post by: Lamewolf on December 01, 2016, 09:46:09 AM
Gil,

Looking at your 80 meter swr curve here and it looks like your antenna could benefit from adding the capacitor between the balun and longer wire, but if you do be sure and put the 1 meg 3 watt non inductive resistor across the cap to protect it from static damage.
Title: Re: Windom Antenna Analysis With The MR100.
Post by: gil on December 01, 2016, 01:04:59 PM
Well, in France 80m covers 3500 to 3800kHz. It seems only a longer coax lowers the SWR.. Do you think a capacitor would help? I won't take it down unless it falls, which could happen given the wind around here, but if it does I might try it!

Gil
Title: Re: Windom Antenna Analysis With The MR100.
Post by: Lamewolf on December 01, 2016, 01:30:20 PM
3.5 to 3.8 ?  I doubt it would help as it moves the resonant frequency up the band which would probably put it out of your privileges.  Didn't realize you could only cover the lower end of the band.
Title: Re: Windom Antenna Analysis With The MR100.
Post by: gil on December 02, 2016, 05:49:52 AM
Yep, same with 40m which only goes up to 7200kHz.

Gil
Title: Re: Windom Antenna Analysis With The MR100.
Post by: Lamewolf on January 10, 2017, 04:55:22 PM
Gil,

How do you interface the MR100 with a computer to get those nice looking graphs and what program do you use to do it with ?
Title: Re: Windom Antenna Analysis With The MR100.
Post by: gil on January 10, 2017, 05:13:22 PM
Hello. Connection is through a simple USB cable. I'll attach the software to this post.

I find myself using it all the time... Very useful piece of gear...

Gil
Title: Re: Windom Antenna Analysis With The MR100.
Post by: oz123colin on March 03, 2018, 08:50:27 PM
* WinPCC-Sark100.exe.7z  Downloaded this file but my Winrar is reporting the file is corrupt.:( Anybody having the same issue.???
Title: Re: Windom Antenna Analysis With The MR100.
Post by: Sparks on March 03, 2018, 09:29:28 PM
* WinPCC-Sark100.exe.7z  Downloaded this file but my Winrar is reporting the file is corrupt. :( Anybody having the same issue. ???

I am on a Mac and cannot really do much to help. The file downloaded OK, but cannot be opened on a Mac. Try removing the suffix ".7z" before opening, so your PC understands it's a .exe file may help.
Title: Re: Windom Antenna Analysis With The MR100.
Post by: Sparks on March 03, 2018, 09:40:12 PM
For what it's worth I found some links through Google:

http://www.sm6why.n.nu/sark-100 (http://www.sm6why.n.nu/sark-100)
http://www.die-jetzis.de/sark100.htm (http://www.die-jetzis.de/sark100.htm)
https://sark100-swr-analyzer.soft112.com/ (https://sark100-swr-analyzer.soft112.com/)
https://sourceforge.net/projects/sark100swranaly/files/ (https://sourceforge.net/projects/sark100swranaly/files/)
http://ok1rp.blogspot.no/2015/12/60-mr100-antenna-analyzer-pc-interface.html (http://ok1rp.blogspot.no/2015/12/60-mr100-antenna-analyzer-pc-interface.html)
http://www.jh4vaj.com/archives/2537 (http://www.jh4vaj.com/archives/2537)
Title: Re: Windom Antenna Analysis With The MR100.
Post by: C-ya on March 05, 2018, 07:14:23 PM
I just received my MR100 analyzer.  I found this site searching for it's use after I saw it on ebay.  I'm glad I did, as I have found some interesting topics on this forum.  You have even gotten me to download a CW app for learning and even going to the LCWO page.  I haven't signed up, but I plan to.

I'll try to post a few plots of my 80-40-20 OCF.  I'm having issues tuning it since I went from twin lead feed to coax and balun due to space restrictions at my current QTH.  With 100 feet of 300 ohm twin lead, it was pretty much "no tune".  With the balun and 50 feet of coax, 80 is tough for the LDG tuner, 40 is great, and 20 is not perfect.

Thanks for the forum and hopefully I can contribute a bit as well as learn a lot.  I have been lurker for about a month but I registered tonight to post in this thread and a Slim Jim thread.
Title: Re: Windom Antenna Analysis With The MR100.
Post by: gil on March 06, 2018, 05:45:15 PM
Awesome. I'll tell you, I came back from anything not fed at the center or at the end. Too much trouble with stray currents...
Gil



Sent from my SM-G928F using Tapatalk

Title: Re: Windom Antenna Analysis With The MR100.
Post by: C-ya on March 21, 2018, 07:43:10 PM
OK, I finally got some readings with the MR100.  My antenna is right on at 80 - imagine that!  40 and 20 are very high and require a tuner.  I haven't hooked it up yet and gotten scans with it but I'll try to do that soon.

I used two different programs.  Slightly different measurements but they tell me the same thing.  I only scanned the voice portion of the band for my privilege.

WinPCC plots

(https://i.imgur.com/0rzosxD.jpg)

(https://i.imgur.com/1hMuM0R.jpg)

(https://i.imgur.com/SAsjOrG.jpg)

SM6WHY program

(https://i.imgur.com/pTBjhmE.jpg)

(https://i.imgur.com/cKJAFBT.jpg)

(https://i.imgur.com/cxDE2Rt.jpg)
Title: Re: Windom Antenna Analysis With The MR100.
Post by: gil on March 22, 2018, 09:38:36 AM
Interesting...

I have almost given up on the Windom. The asymmetry creates a lot of stray current problems... I also had trouble with my MR100 after I calibrated it. I should have left it as it came. I plan on making a box with resistors and switches to calibrate again...

Gil.
Title: Re: Windom Antenna Analysis With The MR100.
Post by: C-ya on March 22, 2018, 10:37:22 AM
I have a "decade box" of sorts to use when I attempt calibration, should I actually do it.  We have a club event coming up on the 21st of April that I can compare it to better quality analyzers at the location we are doing the event.  There are 8-10 antennas on site, so I can compare the MR100 back to back with another analyzer on the same antenna.  If it looks similar, I won't calibrate it.

(https://i.imgur.com/esS9kUsl.jpg)
Title: Windom, or OCFD?
Post by: KQ4BX on November 03, 2018, 08:52:35 PM
A Windom is another name for the Off Center fed dipole. I have been using one for years, and they are fairly simple to make. My OCFD  gives amazing performance, but that was no accident. I did a lot of research before making an OCFD that worked so well, that many of my friends made one after trying mine.

Some things to know about the OCFED are that the height of the feed point  determines the BALUN needed. The most common BALUN would be a 4:1 current BALUN. The 4:1 works best if the height of the feed point is 35 to 45 feet, or even 50 feet. If you go any higher, the BALUN may need to be adjusted.

The second thing to know, is that ground radials below the antenna, will help tremendously, or i would say they are essential for a well working OCFD.

The ground radials can be place in the ground, just cut a V in the dirt, and place the radial into it and cover it up. The radials should be grounded to your station ground  point. In my case, that is several ground steaks around my tower, and a short connection to the well pipe that is  very close to the tower leg. 

You MUST also connect your home ground to the station ground , if you don't, you will create a dangerous situation for lightening strikes that will hot one ground point, then run through your home toward the next ground point, blowing out everything in between.


Lastly, the 4:1 BALUN I originally made did not work so  well. I was not an expert at making BALUNS, but I followed  directions very well. After a lot of testing and not getting what I considered good performance, I called  BALUN DESIGNS by getting their number off of their website.  I spoke to Bob, and Bob explained a few things to me, and suggested that i try on of his 4:1 BALUNS that was made specifically for an OCFD.   It was rated for 5KW, and had a duel core. Mine was not anything like that.   That BALUN Designs BALUN was the first step in getting an OCFD that worked pretty well. The next improvements came later. one was the height of the feed point went higher, and the next was the ground radials   My OCFD is now amazing, and tunes from 10 to 40m, only skipping 30M. It has flat SWR across 12m, and gives me nice working spots on each band that do not need a tuner. I do use a tuner to widen some of the bigger bands, like 40m. I also can tune to a small section of 75M.  Low low you can go, is alls about the total length of wire you are working with. I work with roughly 45'x90' , but if you have more room, you can double those lengths, and  do much better. My property is not that big.
Title: Re: Windom Antenna Analysis With The MR100.
Post by: Wingfoot on November 10, 2018, 05:37:06 AM
I have been given an ocfd to try by a friend, it one made by M0CVO it's the HW-40HP model, I've not tried it yet but finding this thread has been helpful & I'll use some of the tips here when installing it, I'll let you know how it goes.

73
Wf