bit of an extreme design: co phased vertical with base load

[Nationalpatriot]

Alrighty, I'm working on another new design (yeah, sorta obsessed with having multiple radio antennas but hey, I have a lot of Coax at a good price).
I have been looking over a few different ideas and finally have sorta combined one that i think in theory might work. *ahem cue the National Patriot graphics department*

black is main antenna( say 9 feet or so vertical)
red is wrapped coil (let's say another 9 feet that then leads to the main verticle)
blue is guy wire
green is grass (please tell me you guessed this)

best distance I've been reading for cophased is about 18 feet (1/2 wave length and the harness between the two antenna is to be 75ohm not the 50 that the antenna is made out of. Any guidance/deter would be great appreciated!

(if you're wondering, the reason I want it base loaded or loaded at all is because of the height factor, I live in an area were I can't have a horizontal antenna mounted on my house, but I can have about a 9 foot antenna easily. If I have a chance of the antennas being half wave instead of 1/4 it'd be awesome)

National Patriot - Out

 

[mackmobile43]

How's a guy supposed to make grass grow on edge like that? and is that part of the required set up.

 

[Robb]

Well first of all, to co-phase two antennas you will need RG-59 coax. Which is 75 ohm coax; not 50 ohm coax.

Next, I don't see why you would need guy wires for a 9 foot antenna. Or even need a matching coil. You don't need either. You would need ground radials to improve the SWR and radiation pattern of the antenna.

Mounting it so low to the ground isn't what I would recommend either. Chances are - if you live in the suburbs you may well interfere with your neighbors TV, telephone, stereo, baby monitor and start a feud with someone that you used to call a friend. Antennas mounted at 36 ft height with an RF choke coil below the antenna feed point, a well grounded low-power radio, and non-conducting guy wire should keep the complaints from your neighbors to a minimum and still work quite well enough to be heard and to hear great distances.

In fact, for a base radio setup you can do a lot better than to run a three element horizontal beam and a cheap rotor. You will get more db gain out of an antenna rather than a fixed db gain in one direction only. you would have to spend almost the same amount of money - except a bit more because the cost of the rotor.

If that is too much, then running a single Maco ground plane or IMAX 2000 antenna will probably still yield more enjoyment than ground mounted 1/4 wave co-phased antennas. But that is up to you

 

[W5LZ]

It looks/sounds like you meant to post a graphic, I wish you had so what you described made more sense to me.
It sounds as if you plan to use some excess coax for the antenna? That can work, but it has disadvantages with it.
Ground mounted antennas also work. They usually require much more than just 3 or 4 radials, or just a ground rod or two. They can certainly be more practical for your situation, so it seems.
You're right about the phasing/timing coax being 75 ohms, or even high impedance if you can find it. While you're at it, you might as well double the amount of that 75 ohm coax and get an antenna switch to switch the direction of the radiation pattern. It's not that difficult, especially with ground mounted verticals. Beats only being 'pointed' in one direction.
Lots of possibilities.
- 'Doc

For clarification:
Coax vertical antennas are a problem cuz it's hard to make them stand up all by themselves. There's no real advantage to them unless you just have a lot more coax than you'll ever need. As long as it's conductive, you can make an antenna out of anything ... almost, wet noodles are a real PITA to make work.

Phased antennas are not beams, they are bi-directional, N to S for instance. If you switch that phasing 90 degrees, they become E to W. The radiation patterns for phased antennas are not 'razor' sharp by any means. More a 'wide angle lens' pointed in two directions forwards/backwards.

Ground mounted antennas work just dandy. Broadcast stations have been using them for a very long time.

 

[RickC.]

Ah, phased antennas. They can be fun (and frustrating).

You haven't mentioned radials, which you'll need in this installation. And there's no need for base loading or any other kind of loading with 1/4 verticals. If you were to use 1/2 wave radiators you'd have to be very careful to have the matching networks exactly the same or you'd be introducing phase difference you wouldn't want. 1/4 wave verticals would be much easier to deal with, both electrically and physically. I'm assuming you know you can switch the phasing on an array like this to go from broadside to endfire and have two bidirectional patterns (one or the other, not both at once).

As for coax, you'd need to feed each antenna with 1/4 wave of 75 ohm and the rest can be 50 ohm-- though I did once put up a pair of phased ground planes using entirely RG59 because that's what I had on hand and the SWR was below 1.7:1 across the entire 20m band.

As for local coverage, you probably would do better with a single elevated antenna, but if that's not an option, it's not an option. For DX, a ground mounted array with a good radial system would work very well-- and I don't know of anyone who has done this at 27 MHz. It would be cheap enough to try, and you could make the verticals from EMT conduit, wire taped to crappie poles, just about anything. I like the idea and am always glad to see people interested in antenna building.

If you have the coax already and don't mind the work of laying down the radials, go for it!


Rick

 

[Nationalpatriot]

How's a guy supposed to make grass grow on edge like that? and is that part of the required set up.

Haha, It's Michigan, everything grows weird here....

Well first of all, to co-phase two antennas you will need RG-59 coax. Which is 75 ohm coax; not 50 ohm coax.

Next, I don't see why you would need guy wires for a 9 foot antenna. Or even need a matching coil. You don't need either. You would need ground radials to improve the SWR and radiation pattern of the antenna.

Mounting it so low to the ground isn't what I would recommend either. Chances are - if you live in the suburbs you may well interfere with your neighbors TV, telephone, stereo, baby monitor and start a feud with someone that you used to call a friend. Antennas mounted at 36 ft height with an RF choke coil below the antenna feed point, a well grounded low-power radio, and non-conducting guy wire should keep the complaints from your neighbors to a minimum and still work quite well enough to be heard and to hear great distances.

In fact, for a base radio setup you can do a lot better than to run a three element horizontal beam and a cheap rotor. You will get more db gain out of an antenna rather than a fixed db gain in one direction only. you would have to spend almost the same amount of money - except a bit more because the cost of the rotor.

If that is too much, then running a single Maco ground plane or IMAX 2000 antenna will probably still yield more enjoyment than ground mounted 1/4 wave co-phased antennas. But that is up to you

Thank you very much for your help, I guess I got mixed up with the pros of the cophasing. Still somewhat of an amateur when it comes to the Antenna building aspect. (as for the guy wires it was just a way to hold the antenna upright, I didn't feel like suing Paintbrush to make the 4 way stand like I did on my dipole antenna) but again, thanks for the help. Any idea on which kind of Beam antenna I should build? Yagi, Cubical Quad etc.

 

[RickC.]

Giving up already? Dang...

Looks like my post and Doc's crossed in the mail.

 

[Nationalpatriot]

How's a guy supposed to make grass grow on edge like that? and is that part of the required set up.

It looks/sounds like you meant to post a graphic, I wish you had so what you described made more sense to me.
It sounds as if you plan to use some excess coax for the antenna? That can work, but it has disadvantages with it.
Ground mounted antennas also work. They usually require much more than just 3 or 4 radials, or just a ground rod or two. They can certainly be more practical for your situation, so it seems.
You're right about the phasing/timing coax being 75 ohms, or even high impedance if you can find it. While you're at it, you might as well double the amount of that 75 ohm coax and get an antenna switch to switch the direction of the radiation pattern. It's not that difficult, especially with ground mounted verticals. Beats only being 'pointed' in one direction.
Lots of possibilities.
- 'Doc

For clarification:
Coax vertical antennas are a problem cuz it's hard to make them stand up all by themselves. There's no real advantage to them unless you just have a lot more coax than you'll ever need. As long as it's conductive, you can make an antenna out of anything ... almost, wet noodles are a real PITA to make work.

Phased antennas are not beams, they are bi-directional, N to S for instance. If you switch that phasing 90 degrees, they become E to W. The radiation patterns for phased antennas are not 'razor' sharp by any means. More a 'wide angle lens' pointed in two directions forwards/backwards.

Ground mounted antennas work just dandy. Broadcast stations have been using them for a very long time.

Ah, phased antennas. They can be fun (and frustrating).

You haven't mentioned radials, which you'll need in this installation. And there's no need for base loading or any other kind of loading with 1/4 verticals. If you were to use 1/2 wave radiators you'd have to be very careful to have the matching networks exactly the same or you'd be introducing phase difference you wouldn't want. 1/4 wave verticals would be much easier to deal with, both electrically and physically. I'm assuming you know you can switch the phasing on an array like this to go from broadside to endfire and have two bidirectional patterns (one or the other, not both at once).

As for coax, you'd need to feed each antenna with 1/4 wave of 75 ohm and the rest can be 50 ohm-- though I did once put up a pair of phased ground planes using entirely RG59 because that's what I had on hand and the SWR was below 1.7:1 across the entire 20m band.

As for local coverage, you probably would do better with a single elevated antenna, but if that's not an option, it's not an option. For DX, a ground mounted array with a good radial system would work very well-- and I don't know of anyone who has done this at 27 MHz. It would be cheap enough to try, and you could make the verticals from EMT conduit, wire taped to crappie poles, just about anything. I like the idea and am always glad to see people interested in antenna building.

If you have the coax already and don't mind the work of laying down the radials, go for it!


Rick

Alright thanks for your help everyone, I (just for the pure hell of it) think I'll try the 1/4 with radials in an array. It might work good, might be horrible, if so, I have extra PVC and coax to make into yet another project, I'll post updates when I get it done!
Haha no I'm not giving up, just perfecting my design from the above graphic.

 

[RickC.]

Good for you, and figure on a minimum of 20 radials per antenna to give your array a fighting chance. I won't repeat what's already out there on the net, but there are some very good links to radials and ground mounted verticals. I don't have any handy, but DX Engineering's website is a good one (it's not necessary to buy a big radial plate), and eham.net has one from a while back where a stainless sink strainer from Lowes was used as a radial connection point. I'd probably go that route or something similar for an experimental setup.

And (thinking ahead), if you ever got a ham ticket (assuming you don't have one now) that 1/2 wave spacing for CB is awfully close to 1/4 wave spacing on 20 meters and the radials could be used for a phased array there.

Just sayin'...


Rick

 

[Nationalpatriot]

Good for you, and figure on a minimum of 20 radials per antenna to give your array a fighting chance. I won't repeat what's already out there on the net, but there are some very good links to radials and ground mounted verticals. I don't have any handy, but DX Engineering's website is a good one (it's not necessary to buy a big radial plate), and eham.net has one from a while back where a stainless sink strainer from Lowes was used as a radial connection point. I'd probably go that route or something similar for an experimental setup.

And (thinking ahead), if you ever got a ham ticket (assuming you don't have one now) that 1/2 wave spacing for CB is awfully close to 1/4 wave spacing on 20 meters and the radials could be used for a phased array there.

Just sayin'...


Rick

Yeah I plan on getting my HAM ticket once I get out of college, as of right now I'm in for another 3 years for a law enforcement degree, a radio license wouldn't be too bad for my resume on top of that.

As for the radials, what would be a good material to use (yeah I know copper wire, but what gauge, shielded or not, and what length *exactly* should it be do you think?

 

[RickC.]

Good for you!

Well, I'll suggest you read up on radials for your own learning, but:

Radials don't need to be resonant, and they don't have to be buried. You can use insulated wire, aluminum or galvanized electric fence wire (OK for temporary use, it corrodes after being in contact with the ground after a while--and it's cheap). What's important is to have them distributed equally in all directions as best you can with the room you have, and 9-10 feet long each would be plenty at 27 MHz. What a lot of folks do is mow the grass short early in the season (as in NOW) and lay the radials out using staples from either wire that's been cut or the kind used for holding down landscape fabric. After a while the grass grows up over them and you don't see them.

The biggest consideration I see is how to get the coax to the antennas, which probably means digging a small trench and burying it. You'd probably want to use PVC to run it through unless you happen to have direct bury coax or you really don't care what happens to the coax you have.

You see, ground mounted verticals are very effective antennas when installed correctly with a good ground system, but it's pretty labor intensive. To get a better idea of what's involved, it might be a good idea to do a Google search on say, "5BTV" , or "BTV, vertical" for sites where guys have photos from their installations of the popular Hustler BTV series verticals. You would not have to go the heavy duty route many of them have for your purposes, but solving the problem of how to get the coax to the antennas would be the same and you could get some ideas on both that and radials. Of course you can just lay the coax on top of the ground if you think it'll be safe like that!

Good luck,

Rick

 

[BOOTY MONSTER]

heres a pic of the 1/4 wgp i made with speaker wire and pvc from lowes . it worked fine for the few months i needed it to . it was over the house though and had a elevated GP .
and heres a link to a home made 2 element quad you may find interesting .

2 Element Cubical Quad for 10 or 11 Meters by N1UUE

.

 

[Nationalpatriot]

Good for you!

Well, I'll suggest you read up on radials for your own learning, but:

Radials don't need to be resonant, and they don't have to be buried. You can use insulated wire, aluminum or galvanized electric fence wire (OK for temporary use, it corrodes after being in contact with the ground after a while--and it's cheap). What's important is to have them distributed equally in all directions as best you can with the room you have, and 9-10 feet long each would be plenty at 27 MHz. What a lot of folks do is mow the grass short early in the season (as in NOW) and lay the radials out using staples from either wire that's been cut or the kind used for holding down landscape fabric. After a while the grass grows up over them and you don't see them.

The biggest consideration I see is how to get the coax to the antennas, which probably means digging a small trench and burying it. You'd probably want to use PVC to run it through unless you happen to have direct bury coax or you really don't care what happens to the coax you have.

You see, ground mounted verticals are very effective antennas when installed correctly with a good ground system, but it's pretty labor intensive. To get a better idea of what's involved, it might be a good idea to do a Google search on say, "5BTV" , or "BTV, vertical" for sites where guys have photos from their installations of the popular Hustler BTV series verticals. You would not have to go the heavy duty route many of them have for your purposes, but solving the problem of how to get the coax to the antennas would be the same and you could get some ideas on both that and radials. Of course you can just lay the coax on top of the ground if you think it'll be safe like that!

Good luck,

Rick

Alright sounds good, I have some insulated wire that should do the job just fine, solid core and plenty of length. What I plan on doing is getting a small Project box from Radio shack (with rubber weatherproof seal) and feeding the radials ends into that, onto each radial ending I will put a copper Ring Eyelet and then attach all of them onto a copper plated bolt with wing nut. right now on my single vertical I have them just soldered into 1 but that doesn't seem to weather proof really. most of my antennas are portable so I will just lay them down in a safe area and "pack up" the lines when I need to mow. (the coax I have for the main antenna is actually housed in PVC pipe with fittings and a stand that allows it to stay up right in atleast 30mph winds.) the radials then lead out to skinny grounding rods about 2 feet long that I insert into the ground (do you know if Landscaping Fabric pins/stakes would work instead?) I'll work on making up a good visual (other than my Paintbrush image) to show you the "concept design". I am thinking of adding some Paracord inbetween the masts just to help support each other as well, we don't have terrible winds here but right now is tornado season and last I checked property insurance doesn't cover ameture/experimental antenna arrays....

 

[Nationalpatriot]

Alright, so it seems my CAD program is off of my Apple, but hey, here is yet another Paintbrush design.

Key:
Purple: support lines (just to help keep it up in high winds, I know it's short, but hey
Green: is the center of the coax
red: is the radials ( I know there are not 20 in each picture)[I know they aren't to proportion]
blue: is the junction box for the radials
pink: is the 75 ohm Coax that measures 18 feet
white is the OUTER PVC pipe that just keeps the coax straight and protects it from the weather
yellow: is the 50ohm coax leading to the CB radio itself.

Feel free to tell me if there is anything I am missing

 

[RickC.]

Question-- why use coax for the verticals? A piece of wire would do it-- cheaper, lighter, no capacitance or velocity factor (practically) to worry with. If you wanted self-supporting, I'd probably go with 1/2" EMT in this case.