Pics of the 865Mhz Ray Gun

[Pro-95]

Well ok Debbie calls it the ray gun.

It was fun building this antenna. I started out twice as long as it is in the pictures just to see if there was gain beyond. There wasn't. So I've trimmed it down a bit and is to the point where I can finish it up. I've been using this antenna for some experimentation with tuning and think I have it good enough to finish and put on a rotator on the roof. This antenna is very directional so it will help me in id'ing sites as they pop-up. So far this antenna on the ground can lock onto (read tg's) a distant control channel that my 800Mhz ducky will only hear the noise.

Yes, I still need to cut the support down some.

Temporary tuning clip.

Some expanded metal used for support + SO-239 mount.

Front side of SO-239

The ray gun. I'm thinking of painting it like a barbers pole.

j/k

 

[K5MAR]

Looks really good, nice job! Where'd ya get the plans? One suggestion though. Ditch the SO-239 and put an "N" connector on it.

Mark S.

 

[crayon]

wow. You have been busy. It looks great!

What type of gain do you estimate with this rig?

 

[KT4HX]

Nice job Michael. Btw, what length of wire did you settle on, and what is the spacing? Also, what is the diameter of the form you wrapped on? Curious if you got plans elsewhere or just brainstorming? Thanks and I'm sure others would be interested in details.

 

[Pro-95]

From an eariler thread I started about "something rattling in my brain". I guess it could have easily started with "in the morning and fell and hit my head against the toilet and then drew this".

From the thread:
Hmm intersting info I've found regarding this type of antenna. Anywhere from wi-fi antennas to listening in on the Mars Explorer! This antenna is small and compact on high frequencies and when used in an array can make for a powerful receptor as in the case of listening to the Mars Explorer. The gain is directly related to turns as Yagi-Uda gain is related to ladder length, I mean directors.

Building on should be relativly easy. Let's see if I can describe the construction with out pictures.

The ground plane is the diameter of the wavelength. This is the reflector in the back of the spiral. For 865Mhz the wavelength = 13.65 inches so the reflector will measure 13.65 inches across. You can easily see where lower frequencies will make for a very large object.

The diameter of the spiral is 1wl / pi or 13.65 / 3.14159265=4.344931 inches.

The spacing or Gap in turns is 1wl / 4 or 13.65 / 4 = 3.4125 inches.

For approx tuning, start the spiral at Gap / 2 or 3.4125 / 2 = 1.70625 inches.

The length of the assembly is an even number * gap + start(tuning) + cap if any. So for 8 turns = 8 * 3.4125 + 1.70625 + cap = 29.00625 inches.

Assuming that turns = gain in DBci is constant then the antenna above should yeild approximately 9.5DBci or 7Dbi gain.
:end thread

The differnences I did over this plan was minimal. In the ARRL antenna book it discussed locating the connector to the outside at the start of the heliax as opposed to in the middle of the reflector. The ARRL book also indictated a diminishing returns with twists and 8-10 being best bang for the buck or in this case length for gain. I started out with 20+ twists and worked my way down to this 8 twists which had roughly the same gain as the 20 but the 20 posed some significant engineering challenges.

It is also fairly interesting that the ARRL book goes into some detail of the design of this type of antenna and short of some particulars like keeping the pitch of the twist at Xdegrees the math I assumed/deduced from a variety of sources before hand appears to be fairly accurate and consistant with what the ARRL book describes. This includes my "tuning point". With all the playing I've been doing with this my un-scientific math seems to be working.

I used #4 copper and made the twists over 4" pvc. The size of the copper plus the 4" gets me real close to 4.3449" and with the relaxing of the copper after I spun it puts it dang close.

I quess I need to read up some more on what an "N" connector is.

So is it a brainstorm or a plan....... Yes.

 

[nmfire10]

Are your neighbors starting to worry yet? I would if I saw my neighbor mounting a ray gun on their roof.

 

[N_Jay]

From an eariler thread I started about "something rattling in my brain". . . . . . .

I quess I need to read up some more on what an "N" connector is.

So is it a brainstorm or a plan....... Yes.

Wow, quite an acomplishment!

I think you need to do a bit more reading first and building second (not to dimminish what you built).

Not knowing what an "N" connector is in the antenna world, is like not knowing what a torque wrench is when rebuilding an engine.

You are "likely" to get it right, but are just as likely not to.

I would have to check the equasions, but I think that gain is proportional to the ratio of length (or turns). So to get the next 3 dB requires doubling the turns.
As gain goes up, beamwidth goes down.
As gain goes up, the criticallity of tuning goes up, so hand built anttenas become further from their theoretical specifications as you try to push the gain.

With all your energy and enthosiasm, you seriously NEED to get your Ham license and get active in the experimentation side of the hobby!

 

[KT4HX]

Thanks for the info Michael. N Jay is correct that the PL-259 will be lossy at that high of a frequency. I know the ham transceivers I have dealt with use the PL-259 only up through the 2 meter (144-148 MHz) range. Above that they go to the N-type. Below is a link for a place with specifications on the various types. Keep plugging away at it, and you should indeed get your license, as you seem to have the experimenter's gene in you!


http://rf-components.globalspec.com...F_Microwave_Wireless_Components/RF_Connectors

 

[nmfire10]

I have never seen a ham radio with N connectors on them in any band. Where have you seen that??

 

[K5MAR]

They're older radios (what I can afford), but the Alinco DR-600 dualband mobile has seperate VHF amd UHF antenna pigtails, the UHF pigtail is terminated in a N female. And the 430-440 module on my Yaesu FT-726R has a female N connector. But the rigs with the built-in antenna duplexer (like my Alinco DR-610s) use PL connectors.

Mark S.

 

[KT4HX]

Yes I agree that I overstated myself for the majority of equipment. What I should have said was the Icom 910H I own is configured that way, and that my personal opinion is that they should all be using the N connector for 430 and above. Though I realize that is more the rareity than the norm. Sorry for the confusing comment.

 

[fourwd1]

Painting the copper wire will detune the antenna slightly.

 

[BANDIT]

The Icom R8500 receiver also has the N conn for Vhf and above.

 

[Pro-95]

So today on a lark I bought another 25' of #4 and another section of PVC as I've cut down the one I originally bought. I made ~22 turns of the 25' of copper and put it over the new section of PVC pipe and placed it over my ray gun. This effectively extended my antenna ~2.5 times.

And gain probably as much.

Thanks to some new found knowledge of reading and some perseverance I have an antenna that scans (yes I can understand the conversation) EDACS on sites I can't even hear the control channel on with the 800Mhz +6db ducky.

I am currently listening to the control channel in Homewood California. That's over the hill and across the lake from me. The hill is about 5000' tall and the lake is Tahoe so several miles and significant obstruction.

Hmm I may just have to make this version work in a permanent application.

 

[Radiorick]

Have you had anyother sudden brain storms?