Category Archives: Antennas

Assembling Glen Martin Rt-424 Roof Tower

The RT-424 is a 4.5 foot tall roof-mounted tower for rotatable antennas.

As I have heard, this looks like a nice product but the instructions leave something to be desired – something HUGE. Here are a few notes and warnings from my assembly process.

Things you MUST know:

  1. There are 28 bolts, and eight of them are shorter than the others. You must use the 8 shorter bolts in the top section to secure the thrust-bearing plate. otherwise (if you use the longer ones), it will not be possible to assemble it.
  2. If you tighten everything as you build the tower from the ground-upwards, you will not be able to align the holes to attache the thrust-bearing plate (unless you are very lucky).

Some General Observations

The pieces came well packaged, with the hardware in one of those multi-section shrinkwrap bags.

The machining appears to be well done but they did not deburr the holes on my parts. Be careful, you could get a nice cut from the sharp edges.

Some Assembly Photos and Suggestions

When assembling the tower, leave all hardware loose enough that you can move around the parts, until you are ready to put on the top thrust-bearing plate. I suggest starting by attaching two-each of the cross-braces to each of the legs using the top bolt for each brace, as shown below.


Two legs with the braces attached at the top


Next attach one of the rotor plates between each pair of legs, and then attache the lower portion of the cross-braces between the two legs.


One side lower assembly with two legs, braces, and cross-plate attached


Here is a closeup showing the attachment of the braces and the rotor plates.


Completed Corner, Outside View

Next, attach the cross-braces between the two pairs of legs Now you have the entire tower together. If you tried tightening all the hardware as you built the tower, you might now have a situation like mine shown below, where you can not possibly align the holes to attach the thrust-bearing plate.


Top Plate holes do not align with the top of the four legs.

Once everything is loose enough, install the thrust bearing plates, then tighten all the hardware starting from the top. The top plate should align nicely like this:


Now attach the feet on the bottom and your tower is ready to mount on the roof. Here is a shot of the completed 4.5 foot RT-424 tower. Good luck.



Roof Tower RT-424

I have been looking at a way to get a Yagi on my roof. No room for a big tower at my QTH, but something on the roof is within reason. I have been looking at the Glen Martin Roof Towers, particularly the smaller Glen Martin RT-424 Roof Tower. It is a 4.5 foot tall, four-legged “quad pod.” The prices on these have suddenly been reduced substantially, so I finally placed an order.

I received the package a couple days ago. Today I decided to put it together. It is a lousy day here anyway, so I will build it in the garage. The box was surprisingly small. They did a good packaging job. Just a bunch of pieces of machined aluminum, a shrink-wrapped container of hardware and a 4-page manual.

Looking at reviews on eHam, it appears to be a good quality item, with not-so-great instructions. With a couple pictures in the manual, it looks like is should be fairly easy to build.

I will post some of my findings as I put it together. Hopefully everything I need is there. I still need to find a rotor for the rooftop setup. The antenna will be a used C3S 10/15/20 meter yagi that I bought a few months ago. This will be the first yagi I have had in a station for many years, so it should be fun.

It Really is all About Antennas

As I try to continually improve my Station, I keep coming back to the antennas. I have a couple very nice Radios, but I am still not very competitive in Contests, especially DX contests. I have always used mainly wire antennas and generally if I can hear them, I can work them. Now I know the problem is that I can not hear enough of them!

I had an opportunity to work a Contest from a world-class Contest station (NR4M) recently. The contest was the ARRL International DX CW. I won’t go into the details of the antenna system there (you can search on NR4M), but let’s  just say they have about 65 acres worth of antennas like I will probably never see anywhere else.

I had access to all kinds of antennas on all the HF Bands. One antenna group that really impressed me was on 80 meters. I heard all kinds of DX during the weekend and I even managed to work China on 80 meters. That will not be happening at my Home QTH any time soon. I was using two antennas at the time, in Diversity Mode on a K3. This was quite a new experience. The diversity did just enough to bring the China station’s signal out of the noise enough for me to work him.

So the lesson learned here is that if I really want to improve my station and get to the next level, I have to do something about the antennas. First project is going to be getting a yagi on the roof. I will always use wire antennas, and I will be trying to improve them as well. I  recently installed a Beverage antenna for the first time. At a length of about 300′, it is not very long, but I am hoping it will improve my hearing ability on the Low Bands.

Of course another thing I could do is raise my Power to the KW level. I do not plan to do that, mainly due to the small lot I am on and the close proximity of my antennas to the Shack. I think going QRO would result in an RFI nightmare.


CW Contest Made my F-150 Truck Crazy

After a weekend-long CW contest at my Home, I jumped into my Ford F-150 to head out, and it was acting very strange. It seemed like the automatic transmission was dead or dying. I knew it was a little touchy going into 2nd gear at times, but it had been working just fine when I parked it for the weekend. I thought my week was ruined and I would have to call for a tow of my truck for an expensive transmission repair.

As I headed out of the driveway, shifting was still awkward. Then I noticed that as it changed gears, the dash display still said I was in 3rd gear. Once I saw that I knew something was fishy. So I went back to the house. I went through a couple power on-off cycles and things started to change. The dash display went nuts briefly, but then it started to come back to normal.

Seeing this change in behavior made me finally realize what had happened. I had parked the truck with its HF rig and screwdriver antenna right under one of my wire antennas, a ZS6BKW. The tip of the truck’s HF whip was directly under the antenna and only about 20 feet away. My guess is that there was RF coupling between the Home antenna and the wiring in the truck. As a result of the RF, some computer memory in the truck got corrupted. Eventually the vehicle must have loaded some historical or factory settings. After that, all was well again.

So now, when I park near the Home HF antennas, I remove the whip from the truck. I plan to do some more RFI mitigation soon, but for now this seems to have solved the problem.

ARRL Sweepstakes CW (SSCW) 2014

Here we go again. Time for ARRL Sweepstakes CW (SSCW) 2014. Same plan as always – main objective is to get a personal high score. Secondary objective is to get that elusive “clean sweep” – all US and Canada Sections in one weekend. I have been within 1 or 2 sections the last several years, with Nebraska being the holdout last year. Never even heard it! Yes, really, NEBRASKA. Oh well..

I always like to try a new antenna or 2 for SS. This year I may  need them as the forecast is for high winds nearly all weekend. Got 4 antennas and two radios for the hunt this year.

  1. 80m dipole, ladder line fed, usable on all other HF Bands as a doublet
  2. ZS6BKW oriented E-W
  3. ZS6BKW offset 45 degrees from antenna #2
  4. 6BTV Vertical on a pier over the Chesapeake Bay

The radios are an ICOM IC-7600 and an Elecraft K2

I have no idea how I will do in terms of score, but I know I will have fun. Hopefully one or two of the antennas will still be standing when Sunday night gets here.

Mobile Antenna Testing

I was doing some testing of mobile antennas on my F-150 this weekend. I had a mag mount on the roof, and a door-edge mount on the rear door. Both had NMO mounts, so I could easily move antennas between the mounts. Here is what I found:

I had an HT (Kenwood TH-F6A) connected to an antenna switch, connected to the two antennas. I tuned to a weak repeater. I found that I could hear it with the roof-mounted antenna, but not with the door-mounted antenna. I could switch the antennas between the 2 mounts with the same result, so it was the mount or the mount location making the difference.

When I opened the door with the antenna on it (moving the antenna and mount away from the chassis), I suddenly could copy the repeater with either antenna. I had the bottom of the door-mounted antenna about 4 inches below the roof line. moving it up about 2.5 inches made a huge difference in reception.

So if you are using one of the door-edge mounts, you may want to experiment with the placement.

Sweepstakes Results for 2012

Well I kept up the time-honored tradition of missing 1 or 2 Sections in the CW SS contest this year. Had about 575 QSOs (a personal best) and all but 2 Sections – MB and NNY. I never had trouble with a New York section before. I guess the monster storm Sandy may have been the reason, as they were all trying to get their lives back together and probably had little time for playing with radios.

I did not make any further adjustments of my ZS6BKW (ref: earlier posts on this subject). The SWR was well within usable range for the CW Band segments and I did not want to jeopardize that just before the Contest. Now that CWSS is over, I may get back to some final tweaking of this antenna to see if I can get 80m Phone in the 3:1 range needed by the IC-7600’s internal tuner.

I did try the 20m 4-element colinear antenna this year. I can’t say I was real impressed. I guess a fixed antenna with higher gain is not really what I want. Next year I may go to something rotatable. I did pickup a couple sections with the colinear that I could not get with my other wire antennas, but overall I am not sure it was worth the trouble.

ARRL CWSS 2012 – Preparation

Well, hurricane Sandy did no damage to my Chesapeake Bayside QTH. I am thankful for that and I wish a quick recovery to those that were ravaged by this nasty storm. The winds did leave one of my antennas needing attention. The winds pulled my anchor for the center of my ZS6BKW antenna out of  the ground and it is now hanging in mid air. This should not be difficult to fix.

I see from last year that we also had high winds just before SS in 2011. Guess I should expect more of that in the future. It is calm now but they are expecting fairly high winds all weekend. I will need to clean up my two existing antennas and I hope to hang the 4 element 20m colinear array on my Penninger Tilt-up mast.

Inside, my station is all ready to go for the contest. I have an SO2R setup using the Icom IC-7600 and an Elecraft K2. This year I will also be using some ICE Bandpass filters to try and reduce the Band-to-Band interference I had in past years. I tested the station, including the DX Doubler, last weekend when I operated a couple hours in the CQWWDX SSB contest. I got about 48 Contacts and added a good number of new Countries in the Log.

I really like the SO2R setup with the DX Doubler and N1MM software. I think I have all the technology pieces in place now. Hopefully I can ramp-up the Sweepstakes operation this year. I will be looking once again for that elusive (for me anyway) Clean Sweep. 83 Sections are needed this year for the Broom.

ZS6BKW Antenna

The ZS6BKW Antenna is one of many HF multi-band wire antennas. It is similar to the famous G5RV antenna, which can cover multiple HF Bands but requires an antenna tuner on most bands. The ZS6BKW follows the design of the G5RV, but makes improvements. These improvements allow it to be used on more bands, and to exhibit better SWR on several Bands. There is an excellent article that compares these two antennas, and it shows me that this is a better bet for my station than the G5RV.

I built the ZS6BKW and am now starting the tuning process for my location. I have many trees, so any wire antenna I build needs some pruning, no matter how I model it. I used standard household 14 gauge wire for my antenna and fed it with 450 ohm ladder line. I used the “fat” 450 ohm ladder-line (about 1.5 inches wide), because that is what I have available. My ladder-line uses solid number 14 conductors. That makes it a bit hard to work with, but it holds up very well to the elements at my Bayside QTH.

The one thing I dislike about this antenna is that it is not expected to work on 15 meters, where it has a very high SWR. I can use my 135′ dipole on all bands with my antenna tuner, so I am wondering if this antenna gives me any advantage over that. It is shorter, but I have room for the 135′ wire, so maybe this is a compromise I do not need.

I will be trying it and tweaking the dimensions. I’ll post my results for anyone that may be interested in the ZS6BKW.

Antenna Design: 20 meter 4-element Colinear

After looking at articles in the ARRL Antenna Book and on L.B. Cebick’s web site, I thought a 4-element colinear wire antenna might be useful for my station. I currently use only wire antennas which work fine on 40 and 80 meters, but on the higher Bands, I need some gain. My main goal is to be able to improve my ability to reach Stations in the Northwestern US and Canada. Since this is a bi-directional antenna, it will also help with my DX contacts.

This is a classic antenna design that has been used by many people. I am not claiming to be doing anything unique here. I am just keeping some notes to track my attempts to make this antenna work at my QTH. There is an excellent description of HF Colinear antennas in the ARRL Antenna Book.

Here is the basic design of the antenna


The picture of the antenna above is a little hard to see. It consists of 4 half-wave elements in a line, with two quarter-wave stubs between the pairs of elements. Each stub is a piece of ladder line, with the end shorted. This provides the necessary phase shifting to align the half-wave sections to provide gain. The antenna is fed at the center and the feedpoint impedence is near 450 ohms.

In case anyone is interested in experimenting with the EZNEC model, here is the listing of the wires for this antenna.


Note – this is just one trial set of element lengths. It may not be ideal for any particular location, and may not even be the actual dimensions I use in the final antenna. But if you have EZNEC, you can take it from here and see what works for you.