A Funky Little Antenna Bracket for the IC-705

In the unlikely event you've read the last two blog entries you'll know that I'm preoccupied with brackets this month.

Because the KX2 and FT-817 handheld 3/8-24 stud mounting brackets in those entries worked better than I hoped, I had to try to do something similar for the IC-705.

But not even KA9P is crazy enough to try the IC-705 as a handheld.  Sure, you could make the bracket and use it for a bit, but the radio is heavy, and sideways. So it wouldn't get used much.

I decided the next best thing would be a bracket that let me set the IC-705 down on a flat surface, screw in an antenna, and operate.  

My hope was that the weight of the radio would counterbalance a halfway decent vertical antenna that did not require a tuner.  I rate this bracket a qualified success with the MFJ-1898 slider coil vertical, and better than that with the lightweight Buddistick shown below that uses a Featherweight whip and the small 10 - 20 meter coil.

Front and side views of the finished bracket in use with the MFJ-1898 are below.

Continuing the theme of easy fabrication, the bracket is made from a standard 4 by 10 inch piece of hardware store aluminum plate.

The plate should be at least 0.1 inches thick. I gave it a shot with 0.06 inch thick aluminum I already had on hand, but because of the cantilevered design of the bracket, the system oscillated like a bubblehead doll if provoked by stiff wind or collision with a klutzy operator.

The pictured bracket is formed from 0.125 inch thick aluminum and is pretty serviceable.  It still has a tendency to oscillate a bit. Depending on the antenna's mass and configuration, this might cause the radio to tip over under trying conditions, so like all homebrew projects, this is left to your discretion and good judgement, but I've had some serious fun with this version.

The pic above shows the 4 by 10 inch plate marked before bending.  The 4 small holes for mounting to the 705 were marked on the plate using the white paper template that was created by overlaying the cabinet and pushing a stylus through the mounting holes.

You'll want to mark both bending lines and the holes. 

Starting from the non-antenna end of the bracket, my bends are located 2 1/2 inches and 2 1/2 plus 3 3/4 = 6 1/4 inches from the end of the sheet. In other words, the bottom is 2 1/2 inches long, the back is 3 3/4 inches long, and the rest is the top, where the stud mounts.

As with the other brackets, the stud hole is 1/2 inch diameter, other holes are drilled as you think best to accommodate the mounting hardware and feedline jumper grounding lug.  Drill the 1/2 inch hole to center the stud over the center of gravity of the radio.

 

This is the drilled and bent bracket.  If you're not careful, you can bend this into a mirror image that looks right but isn't.  Ask me how I know.

I had a question about how to mount the antenna connector.  It is a 3/8-24 coupler like the one found on a standard mirror mount.  But instead of using the mirror mount's UHF connector with the 3/8-24 stud/UHF connector, you just use a 3/8-24 bolt on the bottom side. It mounts just like it would in standard mirror mounts for which it was designed with one exception. I use an insulating washer on both sides of the bracket.  

On thicker aluminum brackets, one washer might work, but if your metal is thinner, you'll want to use two. And the second washer will need to be mounted with the smaller part of the insulator directed up toward the coupler, as the bracket is not thick enough to accommodate the smaller diameter section of both insulators. 

It may help to study the bottom mount on the pic below from the FT-817 mount, that is an exploded view that shows how the components mount on the IC705 bracket.

The pic below is the MFJ-1898 as it arrives from DX Engineering. I was able to use this on the stud with a 13 foot drag wire on 10 - 40 meters.  I didn't try 60 meters.  I could reach an SWR of less than 2:1, often 1.5 to 1, on all bands.  The maximum packing length of the MFJ is about 11 1/2 inches, so it packs well.

These numbers are great for no tuner operation of the IC-705. But the antenna is a bit heavy, which can get you into the oscillation situation I described earlier.  So assess your operating situation when using the bracket.

If you want a lighter antenna, the Buddistick with small coil and featherweight whip mentioned above works well. It's lighter, and tunes up well. But tuning with the Buddistick can be annoying, and as we're talking portable operation here, predetermined band taps sometimes work and sometimes don't.

The variability of the coil taps is what led me to the MFJ-1898 in the first instance. The ability to QSY in a few seconds makes a big difference when all the high bands are open.

Ya pays your money and takes your chances, and the MFJ isn't cheap.  But it's nominally 5-6 dB better than a four foot antenna, and people are shelling out big bucks for those.

IMPROVEMENTS

I've added a handle and a couple of rubber feet to the prototype bracket.

The handle makes it easy to grab the 705 to move it around (including with the antenna installed.)

The rubber feet sit under cantilevered edge of the bracket top section, preventing oscillation in the downward direction, and damping the return from any oscillation in the upward direction.

I also think adding slightly taller rubber feet at the bottom corners of the 705 will make the system more stable - this will eliminate a propensity to rock caused by the uneven bottom surface of the 705 with the bracket attached. I haven't tried this yet but it's on the list.

I'll add a pic and some detail on these and other improvements after I paint the bracket and otherwise pretty things up a bit. 

I think the bottom line is this works in a lot of situations but not all- no tripod, quick set up, no need for a tuner, yadda yadda. The fabrication doesn't require anything hard or fancy.  

If stability worries you, add a brace. 

If you feel you need more viewing angle, use whatever you usually do to prop up the front of the radio, and then increase the bend angle of the top to make it horizontal when the radio is propped up.

This bracket's not for everyone or every situation, but if used sensibly, it's a nice arrow in the quiver of IC-705 portable ops tools.

The Fine Print  

As author Jean Shephard W9QWN once wrote, "You'll shoot your eye out!!!"

Probably not, but be careful.

This is a description of what I've done. You need to make your own decisions about suitability and safety.  Observe RF exposure guidelines, stay a safe distance from other people and pets, and objects, especially electrified ones. And watch out for yourself whether building or operating. Keep ham radio fun. 

72 Scott ka9p/zf2sc