Category Archives: Antennas

APRS SATCOM base antennas

Years ago, Bob Bruninga, WB4APR, talked about a “good” antenna for APRS SATCOM applications.  It was a 19-inch vertical antenna that would function on both the 2m and 70cm bands, and had lobes that were up around the 30-degree mark.  Looking for information on that antenna last night I found a page Bob had written expanding on the idea.  This page provides designs for i-gate antennas on 2m and includes the 19-inch antenna as well as a new design, a 3/4-wave 2m antenna.

I’m seriously considering building one or both of these antennas this weekend to test out these antenna designs.

J-Pole antennas for SAR

Image of fibreglass mast with two VHF j-pole antennas affixed.

Fiberglass mast with two VHF j-pole antennas affixed.

I recently started working with Calvert K9 Search, a local SAR team that specializes in using dogs to search for people.  In an effort to improve communications between the command post (base) and teams in the field I embarked on a mission to find a simple solution to the problem of limited comms.

There were several requirements that prevented the use of a repeater (added complexity, weight, setup time), using a higher power base station (may damage dog collar transmitters and GPSr receivers1 and only amplifies one side of the communication), or a portable tower (see repeater above).

The solution was happened upon almost by accident and the improvements were immediately noticeable.  Digging through the back of my car I came up with a VHF j-pole and fiberglass expandable pole to put it up in the air.  A few adapters later and we were on the air!

The performance improvement was immediate!  Suddenly communications were possible at a much further distance and, when connected to the Garmin Astro 320, dog collars could be received from a much further distance away.

Anyone who has examined the efficiency of a “rubber duck” antenna will know that these stock antennas aren’t great and that almost anything is better.  Stepping up to a j-pole antenna is a significant improvement and then putting that antenna up in the air has a lot of wow-factor to a non-radio person.

Image of collapsed fibreglass pole, used as mast, straps, and two VHF j-pole antennas rolled up and ready for deployment.

Two VHF antennas, straps, and mast ready for activation.

With the tests complete I built two j-pole antennas: one centered on 155.160MHz, our primary operational frequency, and one centered on the average of all the MURS frequencies.  The latter is used as a receive-only antenna for the dog collars and hangs below the VHF “ops” antenna.  Both of these antennas are hung onto a fiberglass expandable pole that holds the antennas up in the air around 20 feet or so.  This pole can be attached to a fence post, command trailer, tent pole, or laid into a tree branch to keep it upright.

The most expensive part of the project was the LMR-240 feedline2 that we used.  The antennas were made out of 300-ohm ladderline with shrink wrap at each end to help keep the elements out.  The pole is actually made for pulling cable and wires and is made by PushPullRods.com.  It’s really strong but isn’t crush resistant so you have to be careful not to step on it when it’s laying on the ground.

For about the price of a good commercial antenna we were able to get a working antenna system that is completely portable/pack-able and lightweight and takes only a few minutes to setup and take down.  It also doesn’t take up much space for storage meaning it fits into the existing infrastructure without having to make changes.

We’ve deployed this antenna system several times this spring and summer and have noted improvements over a variety of terrain.  This project would have cost around $350 for parts if not for donations of parts and pieces along the way.

Footnotes

1. Calvert K9 Search uses the Garmin Astro 320 GPSr units that, when coupled with the dog collars, allow the user to track the location of the dogs on the screen.  These units are very sensitive to RF energy and the manufacturer recommends not using any more than 5 watts near these devices. (Although they don’t specify what frequency band they are most sensitive, the units use MURS for communicating between the dog collars and receiver units so I’m assuming VHF is the most sensitive.)
2. LMR-240 feedline was utilized as it was small, lightweight, and reasonably low-loss at VHF frequencies.

Now on medium wave!

160m on Kenwood TS-2000XYears ago I purchased a 40-80-160m dipole antenna in hopes of getting a good signal out on the lower bands.  Unfortunately the antenna ended up being too large for my yard and I didn’t use it.  Fast forward to now and I’ve got plenty of room for antennas.  When I put up this antenna the trap for 160m on one leg broke off.  I had most of the antenna up in the air so I just didn’t do anything with it.  Now that it’s winter and 160m is supposed to be useful now I wanted to get on the air and make some contacts there.

As temperatures recently poked above freezing for the first time in some days I heated up the soldering iron, bundled up, and made my way out to the antenna to make the repair.  Luckily it was a simple fix and in less than an hour I was back inside with the antenna up in the trees like it’s supposed to be.

I did some tests and I’m disappointed that there is only one real sweet spot on the antenna (around 1860kHz).  The little tuner in my radio doesn’t handle the band very well but I guess this is better than not having anything at all.

I’m glad to be concentrating towards the bottom of the band and I’m hoping to find some CW down there.  I’d love to get a signal report if you do hear me on the band.

Breaking the Arrow Antenna's diplexer

The Arrow Antenna for satellites has an optional diplexer that allows easy operation of 2m and 70cm from a single feedline.  I’ve used this configuration for over ten years with no problems.  I’m not sure, exactly, what happened but the diplexer failed.  After ordering a new one I started digging into the hardware to see if I could see anything that was the matter.

Arrow Antenna diplexerLooks like one of the surface mount parts got a little warm.  The picture does not show the hole that had melted through the shrink wrap but the bottom right component definitely got too hot.  The solder is completely gone from one side which was definitely affecting the circuit.  I’ll likely try to repair this even though I have a new one in service right now.

Parabolic antenna beamwidth calculations

Okay, I’m thinking about parabolic antennas right now.  I created a spreadsheet that would take care of all the formulas some years back but I can’t seem to find it now.  I’m trying to find all the formulas that I need to get the information I need to make my brain figure out the resolution at a distance based on dish size and frequency receiving.  So I don’t have to remember this, again, I’m writing it down here.

  1. The formula Ψ = 70λ/D creates an estimate for the beamwidth of half the power (to -3dB of the signal).
  2. A larger parabolic antenna will yield a smaller beamwidth which should result in a higher resolution.
  3. As frequency goes up the beamwidth goes down.

I’ll use a 1m [diameter] dish as a reference since that size isn’t too large for personal use.

This provides the basis of receiving a signal from a distance.  But the other question to look at is how big is that signal that you are looking for.  If you are trying to communicate with another terrestrial station, or even an orbiting station, then having equal footing is great as there is no waste.  This hardly happens and the antenna usually ends up trying to pull in a weak station and also gathering the surrounding noise.

But what if I’m not trying to communicate with another station but rather trying to hear a tiny “voice” in the middle of trillions of other voices?  I’d want a very tight beam to be able to not only pull out that tiny voice but also not collect the surrounding voices (and not overwhelming my receiver with a high noise floor).  The vocabulary escapes me at this point.  I’m sure there is a word for it but all I can come up with are words that describe optical reception (e.g. pixels and resolution).  When I can figure out the vocabulary and the formulas needed to put these two puzzle pieces together I’ll post it here.

Antenna maintenance

Harlan helping with antenna maintenance.

Harlan helping with antenna maintenance.

The weather was nice enough for me to get some of my antenna maintenance done that I couldn’t do during the cold winter months.  First on the list was to completely remove the 23cm (1.2GHz) antenna from the top of the tower.  While I’ve had good luck working stations up into New England from here on the band the antenna had lost the bolts holding it to the tower and was now fouling my two meter and seventy centimeter yagis. I also decided to remove the two meter yagi (13B2) from the tower and turn the seventy centimeter yagi vertical to accommodate better communications with the LPEN packet node.  I did place a two meter j-pole at the top to give me local coverage.

In addition to the tower work I was able to clean up a few projects in the back yard.  My four-element six meter yagi has now been disassembled and stored for future use.  A couple of expandable poles that were in the back yard have also been cleaned up and stored.  All that’s left is cleaning up the Butternut vertical antenna.  It was taken down for Hurricane Irene and wasn’t put back in service due to several problems I have had with it at this location (worked great in North Carolina).  I’m hoping my next location will yield a better location for this antenna.

While I got a lot accomplished I did have a little help.  Amanda fixed the j-pole I was installing (needed to be soldered in a couple of places) and Harlan came out, with wrench in hand, to work on the six meter antenna.  I’m certainly glad I have a supportive family!

All antennas up in the air.


All antennas are up. I now have 11 elements on 2m, 22 elements on 70cm, and 25 elements on 23 cm. I was able to trim a couple of branches out of the nearby tree and now my antennas swing nearly free through space.

I’ve also noted that the only clear shot that isn’t through the trees is towards the south-east. That should make it interesting during today’s UHF Contest. But it also is encouraging for checking into the 70cm East Coast Net.

New antennas up in the air.

It was hot this afternoon but I was able to get two of the three planned antennas up. Tomorrow is the ARRL UHF Contest so hopefully I’ll be ready (still have to trim a limb or two out of a tree).

Top antenna is 23cm (1278MHz) and the lower one is 70cm (432MHz). There will be a 2m (144MHz) antenna added later (tomorrow?).

VHF/UHF Update

Well, things took a slight turn for the worst last night. After receiving the UT-10 and the coax, N-connectors, and rotator control wire I realized that the pole I have stuck up in the air isn’t wide enough to support the rotator. Apparently the pole is 1″ in diameter and I need at least a quarter inch more for the rotator to grab on to. Of course not knowing this I went down to Lowe’s last night and purchased a 1″x10′ pipe to mount all the antennas on which will no longer be of use. Not sure about what to do with the lower portion (under the rotator) but I’m pretty sure I can just return the pipe I bought and buy a larger one.

I also sat down with a pencil and paper last night and figured out how I was going to mount the three antennas on the pole. Since the 1.2GHz antenna is a loop antenna and can’t tolerate anything metal in the middle of the field that antenna will be at the top of the pole. 14″ lower will be the 70cm antenna and then 79″ below that will be the two meter antenna. This will leave enough room for the h-plane of each antenna to be unobstructed by the other antennas for a better performance.

Now if I can only figure out how to get them up in the air.

New toys…

I haven’t posted anything lately but that doesn’t mean that nothing has been happening.

First, a couple of weeks ago I found a Kenwood UT-10 1.2GHz module for my TS-790A. I’ve been looking for one of these for going on two years. Finally my eBay alert came through and I was able to pick it up within my budget. Of course that also means that I need a new antenna, low-loss coax, and some N connectors. Never fear, the Internet is here!

The Antenna
So I talked to a few people and was sent to Directive Systems in Maine. I called them up and talked to the guy that was busy building antennas but had enough time to answer some of my questions. After about a half-hour of microwave antenna theory I decided on the 2325LY which is a 1.2GHz (23cm) beam that uses loops for elements instead of dipoles. The antenna is 6-feet long and has approximately 17 dBi of gain. Not too shabby. With 10-watts in and around 1 dB of loss in the coax and connectors I should be seeing nearly 400 watts EIRP.

The Coax
Okay, so I have a transceiver and an antenna coming. I must missing something, right? Yeah, something to hook them together. I’m lucky. At the house I have a relatively short run to the radios (around thirty to forty feet) so it won’t cost me an arm and a leg to connect everything together. Even so, The Wireman has just shipped me 17 pounds of wire. Yep, LMR-400, rotator wire, and a couple of N connectors. I bought enough LMR-400 to get my 432MHz beam on the air as well (23-elements). See what happens with the wife leaves me at home… alone?

The End Result
Well, I can’t really talk about the end result because I’m still waiting for everything to get in. But I’ve been doing my prep work. I pulled the rotator out of storage and I’m going to get it prepared for installation. The 432MHz (70cm) antenna has been brought out from storage and is on the deck partially assembled (still need a couple of screws and four U-bolts). Today I swapped out a 2m/70cm J-pole for a 6m J-pole at the top of my “tower” (I worked quite a few VEs (using CW) on that J-pole just minutes after it was in the air. Amazing how it outperforms the dipole (not really amazing)). Unfortunately I have to figure out something else to do with the J-pole as the 23cm antenna has to go at the very top without anything running through the antenna. Looks like I’ll be putting up another pole soon.

So that’s what’s been going on. As soon as I start getting stuff in the mail I’ll try to remember to take pictures and post them here.

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