A few weeks ago, I wrote about building some ARDF gear. We've got the boards transmitting, with about 0.7 Watts out, and we're eager to try them out. We're planning to set a small ARDF course this Sunday.

Our current 2m gear is built into military surplus ammunition boxes, or "ammo cans". They're rectangular steel boxes with a rubber gasket and a solid latch. They work really well, and they protect the radio gear, but they have one problem---They're heavy. I can carry three if I really have to, but two is the limit for long treks. Dick Arnett (WB4SUV) has a backpack frame that can hold three of these ammo cans, and then you can carry one in each hand, but it's still heavy and inconvenient.

I was hoping we could package these TRO-2 transmitters so it would be easy to carry all five of them in a small backpack. During the tune-up session I wrote about a few weeks ago, we brainstormed some packaging ideas. This is what we came up with.

All of these photos are for Bob Frey's (WA6EZV's) TRO-2. Bob did a great job building this:

This is a PVC pipe cap with a turnstile antenna built into it. 

 Turnstile Details---The clear goop that is not coax dielectric is probably hot glue. {Update: RG179 is 75 ohm and .1 inch in diameter.  Dick Arnett was wondering if he could build the antenna using RG179 for the phasing line and RG174 for the feed line. I certainly don't know for sure, but for these short lengths I think the losses would be insignificant.  Does anyone know how to size the phasing harness based on velocity factor?  G3ZOI has a little table on his turnstile page, but his numbers differ from our directions.  Bob recommended starting with a 19 inch piece of coax (RG-59) and then stripping it from there, rather than using solder tabs like G3ZOI. Also, here are Jay Hennigan's construction directions, which include an RG-179 harness.}

 This is Bob's TRO-2 board with round plastic end plates.

 Okay. Here's the good stuff. This is how it all fits together. The turnstile end cap is on the top. Below it is the battery pack, then the radio. The pipe fits over that, and another end cap goes on the bottom.

The pipe is a 3 inch (about 75mm) drain pipe---It has a label that says, "Not For Pressure". It is not Schedule 40. Schedule 40 pipe has much thicker walls, and is much heavier. We chose this nonstandard pipe because it's much lighter, and because it's cheaper. The end cap fitting costs US$1.09, while a Schedule 40 end cap costs over $3.

We're still working out the details of whether or not the controls stick out the bottom end cap. 

Below is the assembled package. Bob made the turnstile antenna elements long, and then used an antenna analyzer to cut them to the proper length. The SWR is about 1.2:1 at 144.5 MHz.

{Update: Dick writes: Bob trimmed the element lengths for best SWR.  The article at http://www.cebik.com/wire/turns.html says not to do that. It says to trim the first dipole to resonance and then make the second the same length.}

Here's another view of the assembled package.

I'm going to maintain the same general arrangement, but I'm going to do it differently. Although I like the removable antenna elements, I might take the cheap route and use four threaded studs out the end of the end cap, and attach copper wire elements to the studs. That way they can be bent down for storage and up for use. If they break, you can just replace the element. I'm considering it an experiment.

My transmitter works, but I haven't even started to package it.

Right now I've got about 2 days to duplicate this. If I don't get it built before bed Saturday, I'll have to kludge together a battery and a plastic bag or something so we can use it at Mt. Airy Forest on Sunday. Wish me luck!