Multiband Homebrew

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br0adband

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Works just fine for me, I built one late last year from the SO-239 chassis mount and a few pieces of clothes hangers cut to fit, but then I went back and redid it a few months ago and did a better job. Honestly I have it mounted on a stand here inside my apartment but close to the window and it pulls in stuff my ducky antennas barely get signal on more often than not. I can't speak for it being great in terms of the 450/800/etc pickup, it gets the job done I suppose, but by design (per the actual specs) it'll provide awesome performance in the 150 MHz area on both sides of that center frequency.

It cost me basically $1.89 for the chassis mount and nothing for the coat hangers on my 1st version and it worked pretty damned well - it's not like they're expensive to make. ;)
 

Twister_2

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I'm glad! I was thinking about building one sometime in early May. I've used metal coat hangers before but they are super difficult to get perfectly straight so it makes me want to take shortcuts on other aspects of it, leading to a terrible looking antenna! I will probably get some good metal rods and do it the more aesthetically pleasing way. As for performance, back at my primary location, it is all 400-500MHz UHF. I would love to have a good preforming antenna at VHF frequencies too: ham, medical evac helicopters, etc. However, up here at school, the new system is a 800MHz P25 so I might want something for up here too.
 

fourthhorseman

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Built one,well a variant of one,when I lived in Philadelphia,,

Worked great.I used 1/2" copper pipe and 12G stripped Romex..Soldered all the radials to the pipe and used a panel mount F and an F terminator...Was nice,,I had all the parts in the shop..Cost was Zer0.!

Had to ditch it when I packed up,But Ill be making another very soon...

Recommended Project for all!
 

br0adband

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As far as the resonating elements being perfectly straight, it's not an absolute requirement obviously but that doesn't mean you can't do your best to get them as straight as possible. You can also make one of these from electrical wire, typically 10 or 12 gauge is best (that's what you'd find inside the walls of your home or apartment feeding all the AC sockets), 10 gauge being just a bit thicker overall and almost a perfect fit for the holes in the SO-239 chassis mount. My first homebrew multiband I built wasn't even soldered at all: I just put a tiny bend in the ends of the coat hangers (like about 3/16" of an inch from one end) and bent it back enough so that the element literally hung (hangers being hung, go figure) from the corners of the SO-239 mount, and then put the main element into the top of the mount with a tiny piece of aluminum foil wrapped on the end to make it a slightly "tighter" fit.

The PL-259 plug that I used was a screw on connector (meaning the RG-58u that I had laying around was attached to it just by stripping off the wrapping and then inserting it to the base of the PL-259 and screwing it into position on the cable - no solder required. The other end of the RG-58u was yet another screw on connector for the male BNC which then attached to the MCX-BNC pigtail going into the SDR stick.

Worked fine for months, and even when I "improved" my build with solder and screws and spade lugs, it worked pretty much exactly the same meaning that just because it was done "proper" the second time around didn't mean I suddenly got a +6 dB increase in signal strength or anything: the "proper" one worked and still works exactly the same as the un-soldered thrown together first attempt (which I still have here as well).

As far as specific 800 MHz coverage, that's the beauty of these oh-so-simple wonders: you can just get another SO-239 chassis mount and make one cut for 800 MHz specifically, it's not like you're going to have to spend a huge sum of money for these things, and if you do end up making one cut just to 800 MHz (I myself have one cut for 450 MHz and another one for 890 because I do monitor the traditional 850-860 MHz as well as 935-940 MHz so 890 sits smack in the middle for handling both ranges effectively) you're ahead of the game definitely.

I'll be making yet another one here this weekend cut to about 770 MHz since we'll be getting some more service in that area here in Las Vegas soon enough - our Metro PD will be starting up a new P25 Phase II system soon to replace the abomination they've had for 2+ years now known as OpenSky (what a failure that's been overall) and another system will be added as well, also P25 Phase II which is a big county-wide multi-system thing. Should prove interesting...

Now if only DSD+ could do P25 Phase II I'd be getting somewhere. ;)

But that's the beauty of these homebrew antennas: they're simple and cheap and do offer damned good performance more often than not - and don't leave the homebrew OCFD out either, it's still relatively cheap to make from some copper pipe (or even plain old electrical wire if needed, for a rolled-up portable version) that may work well for you in your area.
 

LtDoc

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The antenna in question is a simple 1/4 wave on the bands of use. It should perform as well as any other 1/4 wave antenna. As for 'gain', it doesn't have any. And as for 'looks', that's a personal thing. Chrome plate it, paint it, whatever 'grabs' you.
- 'Doc
 

KE5MC

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I have used it with a 396T and now a 436HP. I am in a target rich environment. I am a few miles from DFW airport and easily pickup ground based side of comms. Good reception of Dallas 460Mhz PD comms. All from the indoor location as seen in the picture. Used a chassis mount BNC connector and 14ga Romex. 14ga is a little light weight, but with the indoor location works well. Easy to straighten. Cut a length longer than needed. Securely anchor one end and grab other end with vise-grips. Pull and stretch it a little.




Has anybody built this? I'm curious to hear how well it works. I'm thinking about building it but want to hear some opinions first! http://www.qsl.net/n4yek/scanner/antenna.pdf
 

br0adband

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Is it just me or are you missing 2 of the ground plane elements there? :D

I mean if you feel it's working great for you, fantastic, but... the plans are for 4 ground plane elements and damned if I see anything but two there, or was it just some quirk of the photo and lighting and I'm blind or whatever, who knows.
 

KE5MC

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You got it correctly. Only two ground plane elements present. I know its common that four are shown including the various illustrations in the ARRL Antenna Book 'a.k.a. The Bible' 22nd editions.

At some point in my reading/education on antenna I recall and could be wrong the first efforts at ground plane antenna only used two elements and now 4 are common. I was left with the impression from the reading that two was effective, but can not say why 4 is common now. EZNEC in this day and age is likely to establish the difference if effectively modeled/constructed. Not being an RF engineer and having limited space I stayed with two. It may have been for no other reason than the one sheet plan makes no reference to two additional elements which would not be easily seen in that single view. Ignorance can be a blessing. Just ask any respectable ostrich with his head in the sand.:cool:

The analyzer shows mine is a little long at the 150 and 450 frequencies. As a receive antenna it's getting the job done. :)

Mike
 

davenlr

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I would guess the reason is to make it more omnidirectional. I suspect using two would have an effect of slightly more signal in the direction of the radials, and slight decrease on the two directions there are no radials. If it works, why fix it. I wouldnt want a radial sticking out into the room, or through the wall either :)

FWIW, the Diamond 6M/2M/440cm antenna uses two radials for 2 and 440, and one for 6. Its pattern is also not quite omnidirectional on 6 meters, but is still effective.
 

Linneweh

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Is 1/4 wave the best?

I've been looking at building the multiband discussed here. Is there a reason it is build at 1/4 wave?
I was thinking of building it at 1/2 wave, tuned to the center of the bands used in the area.
36" for 156 MHz; 12" for 468 MHz; and 7' for 802.25 MHz.
If I can do the 1/2 wave, what would be the length of the ground plane radials need to be? Would they need to be 40", twice the original design?
Thanks in advance, Rich.
 

Linneweh

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I built this using a ground plan base from an old VHF scanner antenna. I used old antenna shafts, built with lengths of 18", 6" and 3.5". What a improvement, full bars on stations I only had a 2-3 bars. P25, DuPage County769-780 Mhz and Cook County, 850-855 Mhz, is much cleaner and stronger VHF, 154-158 MHz, [Chgo. FD, 15 miles off], is now full bars and clearer. Uhf-H, 470-480, [Chgo. PD], is now full bars and cleaner. We'll see how long it will last, 15' off roof, about 35' off ground. Well worth the effort.
 
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