The Xiegu G90 Junkbox Manpack

Executive Summary 

Yep, still doing these summaries- your time is important, and you may decide to cut and run :)

1) The G90 needed an easy grab and go way to carry a battery, mount an antenna and operate easily in the field.

2) The G90 also needed a bit of protection from field abuse; so

3) A manpack configuration was designed that:

    a) uses two vented clamshell case halves and four clamps to secure the radio between eight Sorbothane shock absorbing pads;

    b) has a tray with hook and loop straps for securing a battery; and

    c) provides an antenna mount for a whip antenna.

Disclaimer: Calling this a "manpack" is a bit of a euphemism. I'll be the first to admit that a true manpack is portable, has rechargeable batteries, is relatively impervious to dust and water, and rugged enough to take a licking and keep on ticking.

This ain't that. It does provide some protection and impact resistance without compromising cooling as a sealed enclosure might, and handles an antenna and internal battery.  That's good enough to have a lot of fun.

The G90 Manpack

The first time I saw a G90, I knew that sooner or later I would buy one and try to make a self-contained portable grab and go rig with it.

20 watts is big, and like my favorite old FT-897.  But the G90 is much lighter, has a better display, is easily converted to HF general coverage, and is a pretty respectable radio for the price.  Like they say, IYKYK.

This is it.

The easiest way to unpack this is through pictures.  The first shows the radio with its two clamshell halves opened up.

On the left, the bottom clamshell half carries the radio and battery, and on the right, the top clamshell half carries the four buckles that secure the halves together, the antenna feed-through, and the antenna bracket. 

I'm not a big proponent of cases to protect radios. Radios should be free range, not caged.  Especially if the cases just bolt onto the radio, because a bolted-on cage just transfers any impact directly to the radio.

And I'm not a fan of camera cases that diminish airflow over heat sinks and other cooling surfaces.

But in a case like this, where the radio is isolated from any case impact by decent vibration damping pads, there is some serious benefit, as long as it can be done without compromising cooling.  So in this case, I'll take it.

The Battery Tray

For reasons I can't explain, it took me quite some time to develop this relatively simple battery tray.

Working down from the top, you see a right-angled piece of metal - the battery tray- that has two large holes.  These holes secure the tray to the bottom clamshell half, and secure the two hook and loop battery straps.

The battery tray was made to be removable, not to change the battery as much as to be able to change the tray to one that can hold larger or multiple batteries.  This set up uses a 5800 milliamp hour generic battery, which is fine for a few hours in the park.

The assembled tray and battery looks like this.  

If you look below, you can see how the bolts that secure the battery tray to the lower clamshell half also secure the ends of the hook and loop straps that overlap to secure the battery onto the tray.

One of the reasons it took a while to develop this tray was that I kept trying to use more complicated means to secure the battery.  In the end using a couple of straps with sewn hook and loop portions was easy.  Turns out that you can easily melt a mounting hole in a polymer strap by pushing a hot soldering iron through the strap.  This makes a hole and melts the periphery of the hole in effect forming a nice, plastic built-in washer for the bolt to pass through, like this.

The Clamshell Halfs

Both the upper and lower clamshell halves are made from identical discarded cabinet pieces.

In this case (no pun intended), the halves are tops of discarded Mirage VHF amplifiers. The tops are flexible enough that the top half can be spread over the bottom half with some overlap.

The lower half looks like this.

The two large cutouts in the sidewall of the bottom half are there so that the screws that hold the hinges to the upper half can slide over the lower half without the screw heads on the top inner wall pushing the bottom wall inward.  

This may make more sense if you look at a closeup of the clamps.  These are eBay specials, mounted with 4-40 by 3/8 inch screws, with the heads on the inside and the nuts on the outside of the clamshell wall.

You often see clamps of this style used to secure battery cases to the bottom of military manpacks.  

In this case, the clamps also serve to compress the clamshell halves together by squeezing the radio between shock-absorbing Sorbothane vibration damping pads.

Each clamshell half uses four one inch square Sorbothane pads for mounting and isolating the radio.  If you want to know more about how Sorbothane works, look at their website.  Basically, you need a calculated surface area for a given dimension and weight of radio, and the pads need to be in slight compression to work properly.

Sorbothane isolation pads are a bit pricey, so mine are cut from a sheet of 1/4 inch thick Sorbothane into one inch squares - much cheaper.  The pads are secured to the clamshell with carpet tape.  The Sorbothane can be purchased with adhesive on one side, but the carpet tape does a much better job of securing the pads than the manufacturer's adhesive IMHO.

So it's a happy coincidence that if the cabinet hinges are mounted properly, the pads (which are very grippy) will be properly compressed for vibration damping when the clamps are secured, and that compression traps the radio in the case without the use of further mechanical means.  If you're uncomfortable with that, you can add an L-shaped bracket to the lower clamshell that captures the G90 ground screw, but I've found that unnecessary.

Using the pads also ensures that there is airflow across the radio heatsink.  Look between the radio and the lower clamshell half in the picture below.  You can see the light shining through a large gap formed by the pads between the radio and the case.  This ensures that air can flow over the heatsink - something that would not happen if the radio was attached directly to the case.

This gets to the real point. You can pop the radio in and out of the case by releasing or securing the four clamps, and you don't need any extra fixtures added to the radio to do that.

BUT fitting the clamps and pads to get the right tension to keep the radio in place and have the clamps operate properly can be a PITA. At the very least, it requires careful experimentation, even more careful placement and drilling, and lots of testing to make sure the clamps remain closed and the radio remains secure.

The top clamshell half carries the antenna hardware - the BNC pass-thru, the antenna bracket, and the feedline connecting the feed-thru to the antenna mount secured to the antenna mounting bracket.  This half also includes four Sorbothane pads, all visible in the picture below.

As with the lower clamshell half, the pads are located approximately at the edges of the radio on a line with the hinges, to maximize the compressive effect of the hinges on the pads.

 

If you look closely at the picture above of the top half, you can see the mounting hole for the BNC feed-thru on the right, and a line of 5 holes for securing the antenna bracket just to the left of center.

The Antenna Hardware

The antenna bracket looks like this.

The bracket was bent in a vise and then trimmed to size with a hack saw.  It's easier if you drill all the holes while the bracket is flat, but you have to be careful bending near the large hole.

The large hole is 1/2 inch diameter.  This fits standard mirror mount 3/8-24 feedthrough hardware.

The antenna mounting hardware is pictured below.  The beauty in using a half inch hole is that it can be fitted with the hardware for UHF, BNC or 3/8-24 studs.

The hardware configurations are pretty much self-explanatory from the pic, with the possible exception of the UHF mount.  

If you have a UHF mount whip, like on a Outbacker Joey or some of the Yaesu portable antennas, you reverse the standard mirror mount, leaving the SO-239 end up for the antenna, and then secure the feedline to the 3/8-24 stud using a 3/8-24 bolt and ring terminal.  Pretty handy if you switch antennas often.

The Assembled Manpack

When the two halves are clamped together, the outside of the manpack, on the antenna side, looks like this.  

That extraneous connector at the bottom is a dongle for plugging in a keyer paddle.  It really should be routed through the gap inside the case formed by the Sorbothane pads, but my only dongle was too short.  A longer one is on its way. I hope.

I've had a comment that there are a lot of connectors in the antenna line. This is true. 

It's a tradeoff I made so that the antenna mount can remain in place, while allowing the feedline to be disconnected at the feed-thru to connect other antennas, or a two wire BNC adapter for wire antennas.  

If you will always use a whip, it's much simpler to just route the feedline from the back of the radio to the antenna mounting bracket.

False Starts

No project note would be complete without listing a false start or two.

This is Bertha, a classic example of trying to do too much the first time out.

You'll see some similarities to the Rev.0 manpack.

There is a bottom half clamshell tray for mounting the radio and battery and antenna.

There is a bolt-on battery tray at the back, but it's sized to fit at least a 9 aH battery.

And because this was going to have everything including the kitchen heat sink, it even had a cooling fan inspired by the Xiegu cooling fan stand.

It all got to be too much.  I don't have a machine shop, and there's only so much you can do with a scrap metal, a drill, saw, file, and a cheap Harbor freight sheet metal press.  Everything was made from scrap and cut, drilled, screwed, and sometime hand bent.

In the end there were too many things to accomplish with primitive tools and screws, so I moved on.

But now that I've solved many of the problems one way or another, it may be easier to go back and finish up Bertha. Especially if more cooling and battery life are needed.  Stay tuned for that.

In closing.....

This is Rev. 0, there's lots to refine.  A few of the things I need to deal with are:

1) The hinges aren't spring-loaded.  On eBay you find identical looking hinges, some spring-loaded, some not.  The spring-loaded ones tend to stay out of the way when the hinges are open.  These aren't and they are sometimes flopping in the way when trying to fasten the hinges.

2) The hinges and antenna bracket need to be relocated, because the feedline interferes with opening and closing the latches on the antenna side of the case.  It's not unworkable, I just add the feedline after the case is fastened, but it would be better to eliminate the interference between the feedline and the hinges.

3) If digital modes are run, there needs to be more clearance between the back of the radio and the battery so that the extra cables can be plugged in. This means making the case longer, or the battery tray longer and with a lid. No problem for now, but just a head's up.

I'm sure more issues will arise, but so far it's fun.  The G90 tuner seems to load up a military 9 foot AT-271 whip just fine up through 40 meters, and I can just grab the radio, and sit on the deck with the radio on my lap and operate comfortably.

If you decide to try one, have fun. Collect all your parts first, and fit things up, before you drill any holes. Fit it all up after you drill the holes before you paint.  Ask me how I know..... 

But always, be careful, and use good judgment. 

 

Watch out for people, pets and electrified objects. Follow the RF safety rules. Remember, these are my experiences, not recommendations, you're own your own here to keep it safe. 

Also, remember that if you don't have the right tension on the clamps, the radio may come loose or the case may open, so make certain that's working to your satisfaction, and add that clamp for the ground screw if you can.

And of course, please shoot me a note with your improvements, happy to add anything you send, with credit of course, as I think the G90 is a great radio deserving of a decent grab and go kit.

72/73 Scott ka9p/zf2sc