THE SPARK GAP

A monthly publication of the Meridian Amateur Radio Club May 2019

 

 Bible Verse

John 6:37-40 / All those the Father gives me will come to me and whoever comes to me I will never drive away. For I have come down from heaven not to do my will but to do the will of him who sent me. And this is the will of him who sent me, that I shall lose none of all those he has given me, but raise them up at the last day. For my Father’s will is that everyone who looks to the Son and believes in him shall have eternal life, and I will raise them up at the last day.” (NIV)

 

coaxial

 

Happy Mothers Day

 

coaxial

President's Report

Hello all,

Well we made it to May and with the storms we had this month I would like to take a moment to thank everyone for checking in during the emergency nets on both repeaters. It was by the grace of GOD that we didn't have any real bad damage in the county. Thank you all for being there and being safe, but we are not out of the woods yet. More rain and flooding may be possible this month, so stay alert.

Field Day is coming up and we are preparing for that next. If you would like to be a part of it then let us know, either by the net or by coming to the meeting. You can get in on the fun this year, step up be a part.

73's Charles Grisham KB5SZJ

 

coaxial

*** Next MARC Business Meeting ***

IMPORTANT NOTE: Due to the Black Warrior Ham fest on the 1st Saturday, our business meeting has been moved to the second Saturday in May. The next business meeting will be held at the Checker Board Restaurant on Saturday, May 11th beginning at 10 A.M. Come join us for breakfast, coffee and fellowship.

 

coaxial

Black Warrior Hamfest (W4BWH)


Saturday, May 4, 2019
Echols Middle School
2701 Echols Ave
Northport, AL 35476
8:30AM until
Admission: $8.00, Online: $6.00
Tables: $10.00 Available Online
VE Exams, Card Checking, Live Auction, Silent Auction. Food Trucks Onsite, Tailgating, Forums
Talk-In: Tall Tower 145.350 Neg Offset and PL 91.5

 

coaxial

Vice President Report

We seem to be doing better on check ins on the Tuesday Night Nets. The first four weeks we have had 44 check ins. Sending cards as needed has blessed a few more folks within our reach. We rescheduled the Meeting for 5/11/19 @ Checker Board @ 10 A. M. Black Warrior Ham Fest 5/4/19.

Frank KF5ETN Keep On Praying

 

coaxial

Getting loaded (antenna-wise, anyway)

By Dan Romanchik, KB6NU


A couple of years ago, I homebrewed a "Cobra" antenna (https://www.kb6nu.com/yet-another-new-antenna-the-cobra/). It's a doublet antenna, meaning that it consists of two elements connected to a center insulator, where it connects to a feed line. The unique thing about the Cobra antenna is that each element consists of three parallel conductors connected in series.

My antenna uses a lightweight, three-conductor rotor cable that used to be available from Radio Shack. The feed line is 450 Ω ladder line that connects to an antenna tuner to give me multi-band operation.

Connecting the conductors in this way is is supposed to provide "linear loading." Somehow, running the conductors in parallel is supposed to increase the antenna's effective length. My antenna is only 73-ft. long, but it easily tunes up on 80m.

The ARRL Antenna Book has a short section on linear loading. It says that linear loading is a "little understood" alternative to inductive loading that can be applied to almost any type of antenna. Furthermore, "...it introduces very little loss, does not degrade directivity patterns, and has low enough Q to allow reasonably good bandwidths."

As I mentioned, I've been using this antenna with good results for a little more than two years now. When I first put it up, someone mentioned the concept of linear loading to me, but not being an antenna guru, I didn't 'give it much thought. About a week ago, though, I ran across a link to the page Short Ham Antennas for HF (https://www.hamradiosecrets.com/short-ham-antennas.html). That got me thinking about the topic again.



This page describes a way to build a linearly-loaded dipole antenna with a feed point impedance of approximately 35 Ω. This allows you to feed it with coax instead of the ladder line that I use. The author uses 390 Ω ladder line for the elements. He says it's commonly available, but I don't think I've ever seen 390 Ω ladder line. You could probably use 450 Ω ladder line by adjusting the element lengths a little.

At that point, I started Googling. The next linear-loaded antenna design that I ran across is a design from M0PZT (http://www.m0pzt.com/40m-linear-loaded-dipole/). He built his elements from some sturdy wire and homebrewed spacers made from PVC pipe. He's used this design for the 40m elements of a fan dipole covering the 40m, 20m, 15m, and 12m bands. Only the 40m elements are linear-loaded.

I also found a design for a linear loaded vertical antenna for 40m and 80m (https://www.qsl.net/pa3hbb/ll.htm). This antenna is only 7.736m, or 25.4 ft. tall. Of course, it requires a good radial system to work well, but it will work a lot better for DX than a low doublet or dipole.

Finally, there's an eHam discussion on linear loading...

(https://www.eham.net/ehamforum/smf/index.php?topic=84418.0).

Unlike a lot of eHam discussions, this one is quite civil. It's worth reading if you're interested in the topic.

So, if you're thinking of getting loaded, errrrr, I mean loading your antennas, here's a method for you to consider. It works!

 

coaxial

Quote of the Day

"To compel a man to subsidize with his taxes the propagation of ideas which he disbelieves and abhors is sinful and tyrannical." -- Thomas Jefferson

 

coaxial

Have a great month

 

IDrive Remote Backup

 

Last Month Next Month

Back to The Spark Gap