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Made In the USA - SigmaIV ;)
- Thread starter HomerBB
- Start date
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).
The antenna has a propensity for being noisier than both the Astroplane and the 4el beam. It is very quiet without the preamp on, whereas the other two antennas handle preamp without added white noise. However, it seems to do well so far. Today's conditions are not very good into NW Arkansas, so I am still out with a verdict.
In spite of poor conditions I've managed a few contacts with unsolicited good comments on the other end not using a preamp. I will keep monitoring under various conditions, but the homebrew AP is tougher competition than many folks will admit.
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).
The antenna has a propensity for being noisier than both the Astroplane and the 4el beam. It is very quiet without the preamp on, whereas the other two antennas handle preamp without added white noise. However, it seems to do well so far. Today's conditions are not very good into NW Arkansas, so I am still out with a verdict.
In spite of poor conditions I've managed a few contacts with unsolicited good comments on the other end not using a preamp. I will keep monitoring under various conditions, but the homebrew AP is tougher competition than many folks will admit.
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B
BOOTY MONSTER
Guest
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).
The antenna has a propensity for being noisier than both the Astroplane and the 4el beam. It is very quiet without the preamp on, whereas the other two antennas handle preamp without added white noise. However, it seems to do well so far. Today's conditions are not very good into NW Arkansas, so I am still out with a verdict.
In spite of poor conditions I've managed a few contacts with unsolicited good comments on the other end not using a preamp. I will keep monitoring under various conditions, but the homebrew AP is tougher competition than many folks will admit.
that looks nice and clean
as long as where the rod goes in the tube is %100 sealed from moisture getting in it should work perfectly . i like your mobile stud idea , i use it and i like it better than trying to solder or attach to a so-239 . BTW , you weren't concerned about , making a weak point at the verticals feed-point with the 6 bolts/screws going into it for the bottom basket elements ? also , what is the washer looking part behind the 259 for ?
I gave it some thought, but decided others I used this method on survived extremely high winds. They are self-drilling screws - #8
I do hope to get time to do something more like you've done.
Remember that I use what is at hand. It is a washer. It holds the coax connector "L" bracket on. The hole in the bracket is large, and my washer supply lacking. I'll change that out.
B
BOOTY MONSTER
Guest
so since the stud is on a L bracket i'm guessing you just bent that slightly to get the angle for the gamma rather than bending the bottom of the gamma tube ? at some point when im bored id like to change my gamma to a tube sealed/siliconed closed on the top going down to a smaller diameter tube at the bottom that goes inside and use your compression idea so that there's %100 no way rain/moisture can get inside it to effect it . hopefully there's no polarity issue that would be caused by that . i think the bug type caps have a + and - side and reversing them will cause issues , but i could be wrong .
nice idea , thanks for sharing it
nice idea , thanks for sharing it
Once your match is set, use heat shrink on the upper end and you're sealed off nicely.
I used 1/2 OD tubing for the Gamma tube, so a properly sized compression fitting was a standard in plumbing supplies. There was no need to swage down the tube to fit.
I used 1/2 OD tubing for the Gamma tube, so a properly sized compression fitting was a standard in plumbing supplies. There was no need to swage down the tube to fit.
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.
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.
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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 . . .
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 . . .
B
BOOTY MONSTER
Guest
good to hear the noise issue isn't caused by the antenna .
BTW , do you use a choke under the feed-point ?
BTW , do you use a choke under the feed-point ?
Normally, yes. The coax I put in line had several coax ferrite beads on it, so I did not. When it was on an alternate mast for setting SWR I had the choke under it.
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.
