Made In the USA - SigmaIV ;)

[HomerBB]

I decided to use the materials I had at hand to make another antenna to replace the Qv4k I had traded away for a radio I wanted. I knew I could always make another antenna, and lacked the skills to build a radio.

So I did. Here is the Made in the USA SigmaIV
This antenna is built virtually identically to the production SigmaIV, at least in terms of its dimensions .

The only significant difference is the ring is slightly smaller in diameter because it is preformed and served to get the project kicked off.



It's very windy today!

More later. Time to go to the Home Depot and earn a living.

More adjusting to do later, But here is SWR bandwidth with MFJ-209 at the shack end of the coax.

2.1:1 ---------------------- 28.155
1.5:1 ---------------------- 27.840
1.0:1 ---------------------- 27.565
1.0:1 ---------------------- 27.555
1.0:1 ---------------------- 27.445
1.5:1 ---------------------- 27.085
2.1:1 ---------------------- 26.600

Initially, it appears to be less widebanded than the Qv4k, but I will have to look that up and do some more adjusting. It is 4 feet above the roof ridge for now - 23' from the ground.

[HomerBB]

More Photos:

[HomerBB]

As a matter of interest to those looking for a stout way to mount a gamma:

As for the bottom of the gamma, what you see there comes from making the mobile antennas.
For a person without a true fabrication facility getting a mobile antenna together was not too much
a problem, but finding a way to securely attach it to the mounting bracket was challenging. I tried
various things until I eventually landed on a combination of a brass compression fitting and the brass
reducing bushing. The pipe threads in the brass reducer are the same as those on a standard 3/8" fine
thread stud used with antennas except pipe thread tapers slightly. I use a 3/8" thread tap for bolts to
chase the threads straight. once done, I merely thread a bolt from the top side of the reducer bushing
into a standard mount, as you see it done in the photo. I migrated the same process over to the gamma
for use here, and that will likely be the manner of mounting all my gammas for all types antennas in the future.

Notice the bottom of the homebrew mobile. the bottom tube of one of these is what the gamma is (of proper length, of course).

[HomerBB]

Should anyone get inspired to try this, the materials are simple.

Tubing: start with minimum diameter of 1-1/4" for bottom section and have a finished total length of 28' 7" when all are joined together from largest at bottom to smallest at top.

Radials: three or four tubes/rods that are each 7' 6.5" long - you can use fiberglass rods, cane poles, (wrapped with aluminum duct tape) aluminum tube etc.

Ring: 29.5" to 30" diameter - you can make this of PEX tubing wrapped with aluminum tape, or even flat aluminum stock.

Angle for feedpoint where coax connector is mounted - this can be a pre-made mobile antenna bracket, or fabricate one from metal.

Antenna coax connector from mobile antenna.

Gamma Match - 1/2" ID x 17.5" tube. 3/16" x 34" rod. 1/4" ID x 3/8" OD rubber tube for gamma rod insulator.

Gamma connector - brass compression connector and brass 1/2" PT x 3/8" brass bushing for gamma connection to coax connector. (Read how-to in above post.)

Aluminum mechanical lug* for top of gamma rod and aluminum strap for gamma tap.

Various screws and clamps for joints.

You're ready to go.

*


Make the bottom of the radials 12" up from the bottom end of the vertical.

[HomerBB]

I had reported to some that there seemed to be excessive white noise on the SigmaIV when pre-amp was on.

I need to make a correction here. In spite of how embarrassing it can be, I was hearing this whote noise increase on the loop in the attic. I had switched the coaxes on the antenna switch and forgotten. back tracking the wires through the attic confirmed this for me.

On the other hand, another discovery is that I had put a bad coax in line with the SigmaIV. I can not get it down until this wind stops. I have tried in high winds only to have the wind stand the tower back upright. I need to put a good coax in line. In the meantime, I am on the loop in the attic. The AP is on the ground, and the 4el beam is tied to the fence sitting on the reflector with the beam pointed straight at the sky.

Weather permitting, I will fix it Monday and get back on target.

I'm very put out with myself . . .

[HomerBB]

Here's the exploded view of the bottom connector setup for the gamma match:

[Pioneer621]

Hey Homer, was browsing the forum & seen your post & figured I would comment, I’m not on this for as much as I use to be.

But your antenna looks great as always man, very nice; I always enjoy seeing your home built antennas. I wish materials were not so expensive or I would try to build some myself.

Again, very cool my friend, keep it up!

[HomerBB]

I appreciate the interest. materials do cost,
but the key is to slowly accumulate pieces from junk yards,
yard sales, etc until you have it all together at low cost.

You take care, too.

[HomerBB]

From the beginning I have planned to use a 102" steel whip as the top section of the antenna. I hadn't prepared it yet, so I went with a tube and solid aluminum rod for the upper most section. In these photos you'll see the 102" whip mounted to a fluted 1/2" tube picked up for 50¢ from a junk sale. I used the pipe threader on the job on the aluminum tube so I could mount the brass coupler. Into that I put a 1/2" x 1/8" pipe thread bushing that I reamed for the 3/8" x 24 antenna threads. The final photos show it in the air on the SigmaIV just as the cloudy skies darken to sundown.

[The Defpom]

This is a great post, thanks for sharing it.

[HomerBB]

You're welcome, Scott.

The forum offers invaluable information for the hobby in a lot of ways. I count it a privilege to be here.

Charles/Homer

[Animal]

Great job HomerBB

I had an Avanti Sigma IV back in the day (circa 1980) & worked the world on 12w ssb

Last home-brew for me was a four-element loop driven array - I'll post some pictures when I get time.

Keep up the good work

[HomerBB]

Thanks, Animal.
I love this part of the hobby most, and will surely enjoy your photos when you get them up.

[Animal]

Bit late with the reply but I found some pics of a four element quad mid build and some of the four element loop driven yagi hoisted aloft!









The loop fed array worked really well - cut down massively on rain static and noise from my neigbours broadband over powerline (BPL)

[HomerBB]

They look great! Thanks for sharing them.