Yet more antenna questions - Yagi-Uda and Gamma

[Pro-95]

Output from YagiMax

CENTER FREQUENCY = 865 MHz
GAIN = 17.4 dBi
DRIVE IMPEDANCE = 200 OHMS (APPROX), WITH FOLDED DIPOLE D.E.
BOOM LENGTH:
REFLECTOR TO
LAST DIRECTOR = 6.86 FT = 82.4 IN. = 209.2 CM
TOTAL NUMBER OF ELEMENTS = 20
ELEMENT DIAMETERS:
DRIVEN ANY DIAMETER
PARASITIC = 0.031 IN. = 0.08 CM

A non-metallic boom is used
---OR---
Elements are mounted on insulators above or below a metal boom
with metal-to-metal spacing greater than the boom radius.


CUMULATIVE ELEMENT
SPACING LENGTH
------------- --------------
CM IN. CM IN.
Ref Ref REFL ----------|---------- 16.53 6.51
7.49 2.95 D.E. =========|========= 16.36 6.44
10.31 4.06 D 1 --------|-------- 15.61 6.14
16.06 6.32 D 2 --------|-------- 15.48 6.09
23.52 9.26 D 3 --------|-------- 15.33 6.04
32.20 12.68 D 4 --------|-------- 15.19 5.98
41.81 16.46 D 5 --------|-------- 15.06 5.93
52.20 20.55 D 6 --------|-------- 14.95 5.89
63.23 24.89 D 7 --------|-------- 14.85 5.85
74.83 29.46 D 8 --------|-------- 14.76 5.81
86.93 34.22 D 9 --------|-------- 14.69 5.78
99.47 39.16 D 10 --------|-------- 14.62 5.75
112.41 44.26 D 11 --------|-------- 14.55 5.73
125.72 49.50 D 12 --------|-------- 14.50 5.71
139.37 54.87 D 13 --------|-------- 14.45 5.69
153.33 60.37 D 14 --------|-------- 14.40 5.67
167.29 65.86 D 15 --------|-------- 14.35 5.65
181.26 71.36 D 16 --------|-------- 14.31 5.63
195.22 76.86 D 17 --------|-------- 14.27 5.62
209.18 82.35 D 18 --------|-------- 14.23 5.60

17DBi! :shock:

Ok on the gamma correction ... I found a site where someone is matching without the gamma rod. http://www.clarc.org/Articles/uhf.htm

Pathetic photography but the picture does show a lack of gamma rod.

I find this interesting. Seems like a solid option for the lack of a gamma rod, even if it is at the cost of .5 DB. Not to mention that I don't have a gamma rod in the garage.

Is this similar to the J-pole and it's matching?

What do you think? Good idea/bad idea????

 

[Pro-95]

Output from gamma2002 indicates a capacitor value of 2.081. for gamma correction if you were to use a gamma correction connection via a variable capacitor.

2.081 what? mF, pF ?????

 

[loumaag]

I find this interesting. Seems like a solid option for the lack of a gamma rod, even if it is at the cost of .5 DB. Not to mention that I don't have a gamma rod in the garage.

Is this similar to the J-pole and it's matching?

What do you think? Good idea/bad idea????

First, all solutions to matching have their ups and downs. That being said, one of the main reasons that a gamma match is so popular is that it allows for all metal construction (in other words no wood/plastic/etc.) of yagi antennas and a pretty easy match to coax. The "J" type antenna is based on the end fed Zepp modified by using a 1/4 wave matching stub. It appears, (and I did not go to the site) that what is being done here is more along the lines of a off-center fed dipole and using the "U" shape as a matching device for getting close to 50 ohms.

As to no "gamma-rod" in the garage. What!?! :lol:

Build your own "gamm-rods" by using tubing where one piece of tubing with shrink-wrap tubing on it just fits inside the other piece of tubing (building your own capacitor). Trial and error is used here, but some "rules of thumb" will arrive with that antenna book you orderd. :wink:

 

[loumaag]

2.081 what? mF, pF ?????

Usually gamma matching capacitors are in the pico-farad range (pF).

 

[jpm]

for my mobile trunked scannersi just purchased a good ole fashion cell phone window mount antenna and it works great.

 

[Pro-95]

WOW!

I finished my temp/see if it works/experimintal Yagi-Uda.

Holy smokes batman. With the RS 800Mhz antenna I can barely pick up a control channel on Fox Mountain ~50 miles away. With my J-pole 865Mhz mounted on the roof I can get enough signal (+85%) and info to track the site with E-trunker. But the voice is too garbled to really understand well on a regular basis.

With the Yagi-Uda I whipped together and using the dipole styled matching not a Gamma Rod, standing on the ground I can point the Yagi-Uda and not only hear the CC but the 95 will scan the bank and I can understand clearly the conversations!

I made my 84" Yagi-Uda based on info from a variety of websites and software I downloaded for free. I used a 87" hunk of 1" PVC I had laying around and I bought a 25' roll of #4 solid ground wire from Lowes for under $10 bucks. I used a spare Amphenol So-239 that is tucked into the PVC. I made a groove in the PVC for the elements with a small round file and attached the elements to the PVC using adhesive RTV. I cut the #4 to length witha baby set of bolt cutters. I currently don't have a mounting location or the rotor yet but the experiment proved to be a success. I am impressed. I am considering rebuilding the antenna with a little more sturdy design ie stapled to a 2"x4" stick. I have enough wire to make another antenna if I want or I can cannibalize from the PVC but I'd rather not as I am going to do some experiments with making my own Gamma Rod.

I love this experimentation stuff.

 

[loumaag]

WOW!
...

With the Yagi-Uda I whipped together and using the dipole styled matching not a Gamma Rod, ...

I love this experimentation stuff.

Great news. I am guessing, based on your description, you have cobbled together a "Delta" match to the element. Two things to consider, 1) since you are not transmitting, your concern should not be for an exact impedance match, but rather for what works well and 2) gamma match, although popular because of the ease of impedance matching to unbalanced lines (coax), does introduce distortion in the pattern of the yagi antenna not found when using Delta, T and other matching systems.

Good work!

 

[Pro-95]

Notice I had some difficulty keeping everything straight on the PVC pipe. Still had excellent performance.

PVC is actually 1-1/4 not 1".

 

[Pro-95]

Great news. I am guessing, based on your description, you have cobbled together a "Delta" match to the element.
<snip>

Good work!

Oh sure give me something else to go read about.

Thanks. I'm really enjoying this. Now to make it better/stronger/faster.... I one million dollar antenna, well at least the $20.00 antenna.

 

[kd4jxz]

Very impressive!

PM sent!

 

[Halfpint]

Impressive!

However... Why do all that filing? Wouldn't it make for just as good a performing and a lot sturdier antenna if one drilled through the tube for the elements? Even with a *cheap* drill press it wouldn't be all that hard even if you had to `offset' things to keep the `match' also drilled in place like you've done.

Just an `Olde Fart's' 2¢ worth. {GRIN!}

 

[Voyager]

Notice I had some difficulty keeping everything straight on the PVC pipe. Still had excellent performance.

Note for future reference: To help keep the elements straight, after you have them sealexed (is that a word?) to the mast, lay a 2x4 on top of them to keep everything lined up. Balance it on top of the elements as shown, or just lay everything on the 2x4, sealed the 'top' of the elements, then lay your mast on top of that (assemble it upside-down). You can add more sealex later if needed for more support once the first layer is down holding the elements straight.

As was suggested, you could drill through the mast. This would be better if you have a drill press, of course, to keep all the holes straight.

Really nice job, BTW.

Joe M.

 

[Pro-95]

Even with a *cheap* drill press

Yep. There is the operative. My sortof neighbor but good friend has offered me the use of his drill press. When I finish my plans for a really long boom Yagi-Uda with elements going through and soldered to, the copper boom I will do just that, drill through the center of the boom.

For this test (PVC Boom) I considered hand drilling through the boom because of non-conductive boom material made the boom itself not a factor but my days of drilling straight by eyeball are over. I have made another antenna using a 2x4x10 that seems to work quite well by adjusting the element positions using simple math. I am(was) working on modifiying the back end to acheive a match through distance, then my ARRL Book arrived yesterday so now the project will have to wait until I can read some more and maybe find out what I'm doing!

Course I will probably finish my helical antenna this morning just because.

-Because I like the "different-ness" of the shape and if gain to gain between Yagi-Uda and Helical, I'd much rather have the Helical shape on the roof if for nothing else to make the neighbors wonder what the heck is that. :lol:

 

[Pro-95]

I was asked about the versions of Yagi-Max I was using so here is the files for anyone interested.

 

[Voyager]

I was asked about the versions of Yagi-Max I was using so here is the files for anyone interested.

I'm getting the error on both files that they are corrupted.

Joe M.

 

[Pro-95]

Hmm

 

[Voyager]

Hmm

Same thing that time, too. Can you post the site where you DLed them from?

Joe M.

 

[Pro-95]

Or:
Yagi Max 3.11
Yagi NEC files

 

[Voyager]

Or:
Yagi Max 3.11
Yagi NEC files

Same thing. Must be a problem with the XP unzip program.

Joe M.

 

[Pro-95]

Same thing that time, too. Can you post the site where you DLed them from?

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