4-bay VHF dipole array project

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prcguy

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I'll send you enough solderable RG-59 (Belden 1505A) for free to make the harness and you can get two PL-259s and a T adapter at any R/S and that will mate with 50 ohm coax. Or I'll make a harness using F connectors and an F type T adapter for 75 ohm connection for $5 + shipping. Send me your address off line and let me know which one you want.
prcguy
I'm sorry for the misunderstanding. I looked at RS website and they don't even have RG59 that is solderable. So i'm not sure if it's easy to come by locally. Then i've have to order online and then order connectors and all that. I don't even know what F T connector to use as RS site only shows splitter and diplexers. I didn't realize you were going to test it. we can do it your way if you still want.
 
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I was wondering if anyone tested this antenna, single dipole or multiple dipoles, against other antennas such as the ST-2? How does it do on upper bands. I know just a single dipole works well. I'm thinking maybe even 2-3 db gain. Works good for UHF. don't have much 800mhz to really test with without going digital.

I'm going for two phased together so we'll see how that does against my ST-2 when i get the harness ready. 4 gets pretty tall and heavy and hard to work with without help. I haven't decided it i'm going to arrange them for omni or directional yet. probably try both for kicks.
 

mancow

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I'm not sure you are understanding what the antenna is or does. It's not a multi-band antenna like an ST-2. It's a fairly broadband single band antenna optimized for gain in a specific block of spectrum.

Then again, maybe I misunderstood your question.
 
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I'm not sure you are understanding what the antenna is or does. It's not a multi-band antenna like an ST-2. It's a fairly broadband single band antenna optimized for gain in a specific block of spectrum.

Then again, maybe I misunderstood your question.
I know what this antenna is. i've been studying dipoles for a long time. I just want to know how single or multiple dipoles compares to other scanner antennas.
 

Skypilot007

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Anyone ever try making a UHF version?

Dimensions for that model?

73s,
AJ, K6LOR
YES ! I'm in the finishing stages of building one for the GMRS band (462-467MHz). I'm hoping it will tune up on 440 too. I changed a few monor things to compensate for the frequency change but basically mimicked this design. I have two of the arrays setup in my attic right now as a directional antenna and it is working very good. Stand by for more details and photos when I get it completed.
 

breadtrk

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The metal mast is a reflector and part of the antenna. Each dipole becomes a 2-element beam in this case and that's why its directional when all elements are arranged on one side. If you don't use a metal mast the coax will interact with the pattern and that would require a lengthy study to see the effects.


Can I infer that this same concept would work with a 3 or 4 lelemnt yagi if the same basic rules about wavelength distance from the tower were applied? Would you wind up with a more directional or higher gain if all placed on one side? How about 90 degrees apart, would that give more coverage? At 450 and 850 these things are very easy to work with so the actual mounting would not be much.

Even better yet, quad phased LPDA's ...............................
 

prcguy

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Yes and no. Spacing from the mast will not interact the same becauae a yagi has a reflector and the dipoles are working against the mast as a reflector.

If you place four identical yagi's facing the same direction with the proper spacing between you will have about 6dB more gain than a single yagi + or - combining losses.

If you aim four yagi's different directions each one will receive 25% of the power due to the power divider or phasing harness and depending on the pattern overlap you can add back the gain of one yagi and probably more. The dipoles have a very broad pattern and several add in phase at any given direction but there will be holes using yagi's depending on beamwidth. It gets complicated and would have to be modeled or tested to get a realistic answer.
prcguy



Can I infer that this same concept would work with a 3 or 4 lelemnt yagi if the same basic rules about wavelength distance from the tower were applied? Would you wind up with a more directional or higher gain if all placed on one side? How about 90 degrees apart, would that give more coverage? At 450 and 850 these things are very easy to work with so the actual mounting would not be much.

Even better yet, quad phased LPDA's ...............................
 

breadtrk

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I was thinking of letting the mast be the reflector, the dipole the driver and then adding one or 2 directors. My location is almost in the center of the 4 agencies I want to monitor and they are all about the same distance apart. I'll try the dipole first, then decide if I need more, might not.

Thank you for your input.
 

ratboy

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I had the Cushcraft UHF version, and it was an awsome antenna. I lost it when my antenna rotor above it broke (the case shattered) and the beam and mast came down and broke the insulators on a couple of the dipoles. I had it aimed due north and Detroit PD was full quieting most days. I could hear all kinds of traffic. It wasn't bad on VHF either, equal to my discone for sure.
 

IdaScan

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Dimensions we're looking at for a future build once the weather cools down:

Center frequency 147.0800 MHz

Starting copper pipe length 20.50" (1/4 wave=20.07")

Dipole to Tee cable length (Commscope TriShield RG6/85% VF) 51.18"

Tee to Tee cable length 85.30"

Hopefully we'll get a spare weekend to throw one of these together... Might consider throwing one of these up on the test VHF repeater over the winter to check performance and ruggedness. UHF would be the next build on our 444 pair.

Thanks PRCGuy for a great project!

Anyone else build this?
 

Rman1968

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prcguy - antenna plans

Ok, hopefully this will work since I hacked a bunch of stuff out of the article. If not I'll have to find another place to host it.
prcguy
Hi prcguy,

Thank you very much for the plans. I am going to try making this antenna tomorrow for my new (used) Pro-162. It was missing the antenna from ebay and I will buy a cheap portable one and make this for home in hopes of good reception at a great price.

If you ever need to host anything large or small, just let me know. I have dozens of servers and tons of unused space and bandwidth available.

Well obviously I am brand new to this hobby, I hope that it works out for me. I got hooked by listening to feeds on my iPhone. Someone is selling an app that uses all the existing feeds on the web, I hope you guys are getting paid a royalty. lol.

I'll be scanning the Seminole County police, fire. And some Orange count police fire, police, ems. Orlando city proper has digital but the city is pretty far anyway.

Regards,
Rich
 

prcguy

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You would combine two 4-bay dipole arrays using a T connector and the critical length cables used at the input of the original 4-bay dipole project. An 8-bay array should have up to 9dBD omni gain and 12dBD offset gain and would need at least 40ft of mast.
prcguy


prcguy - what would be involved in an 8 bay array as far as a phasing harness?
 
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Exactly what im looking for! I am going to build this as a omnidirectional antenna for 444.500MHz

Do I attach all of the cables from each of the 4 parts together at the bottem and solder to a connecter, also can i use 50 ohm cable on this?
the duplexer and radios are 50

Great design....!!!
 
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prcguy

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I don't completely understand the question, try again on the 4 parts part.

The phasing harness should be 75ohm and you don't want to use 50ohm between elements. The common connection to your radio will match well to 50ohms.
prcguy
 
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I don't completely understand the question, try again on the 4 parts part.

The phasing harness should be 75ohm and you don't want to use 50ohm between elements. The common connection to your radio will match well to 50ohms.
prcguy
ok, i mean to ask... there are the 4 parts, how do i connect the cables comming from each part together?

and do you mean to say that using 75 ohm cable on the antenna to the 50 ohm feedline will be ok with the mismach?
 

kayn1n32008

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Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9780; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/6.0.0.600 Mobile Safari/534.8+)

The 75ohm cabling is used to phase the 4 antennea together so that the combined array is 50ohms. You should, as many of us have suggested, buy the ARRL antenna book, phasing antennea together is covered in detail in the book. It will also teach you why you use 75ohm coax to phase them together.
 
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Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9780; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/6.0.0.600 Mobile Safari/534.8+)

The 75ohm cabling is used to phase the 4 antennea together so that the combined array is 50ohms. You should, as many of us have suggested, buy the ARRL antenna book, phasing antennea together is covered in detail in the book. It will also teach you why you use 75ohm coax to phase them together.
Oh... I get it now. Understand... and yes i am going to look into getting the handbook
 
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