Homemade UHF Collinear?

[CalebATC]

I might be missing something here and please fill me in on what your making. If your building an exposed dipole array here are some basic starting numbers.

A 4-bay array set for an omni directional pattern will theoretically have at the most 6dBD gain when the dipoles are at the right spacing to combine in phase and the power splitter or phasing harness has no loss. Lining the dipoles up on the same side will make the antenna directional and add about 3dB more gain. Adding two more elements to make it a 6-bay would give a theoretical 7.78dBD gain if everything was perfect.

Every time you double the amount of elements you can get 3dB more gain. All dipoles would have to be made for the same frequency to reach these numbers and if you make the dipoles different sizes for different frequency ranges you will give up gain where the dipoles can't all overlap in frequency.

Then there is the power divider or phasing harness. A phasing harness made from 75ohm cable is common to use for matching and power dividing dipoles in multiples of two but the bandwidth will not be that great, maybe 10% at best. A coax phasing harness for 6 dipoles would need an odd impedance coax like 91 ohm or ??

You can use a 50 ohm power divider and equal lengths of 50ohm cable to each dipole and get some wider BW (assuming the dipoles are fat w/wide BW) but if you go too wide the spacing between dipoles is not ideal and your pattern suffers and you give up gain.

So, to achieve 15dBD omni gain you would need 32 dipoles spaced and fed correctly and it would be impressively tall. It would also have a very narrow main lobe on the order of 2 degrees or so. 16 elements all on one side of the mast would give roughly the same gain in a directional pattern.

Have you seen my fairly simple 4-bay VHF dipole array project on RR? It might give you some mechanical ideas to use on your project.
prcguy

It will be made from a combination on 1/2 wave parts, 1/4/1 wave coils. The guy who made it told me it should have around 15dbd of gain when done. Depending how much you repeat the cycle, the more gain (I'm sure you know that)

It is a J pole pretty much, has a 300 ohm matching section. That will be for 301 MHz. The elements and coils will start from 250 and goto 375 Mhz, so each will have to cover that. It will be for 50ohm coax, or whatever you decide to do with the matching section.

 

[captkel]

Collinears are a cool design but not usually associated with frequency bands. Normally you see the best gain resulting from tuning to one specific freq during construction and achieve a steep bell curve where gain falls off sharply above and below that point.

That being said, they are very functional omni antennas, within most folks capability and patience limits to construct, and they Work. The last part being the most important. When fed with good LMR coax (Shameless plug) they will give you a good amount of gain for the buck.

Just to make life interesting, have you thought about co-phasing two to give you a boost?

Oh no...help me Lord...I don't wanna mess with it, I'm done with it (at least for now-hehe) Yep it worked. I think like you said near the design frequency. True true I found I had the abailty to build it...Ok modify (change the innards) of an exsisting one. There is a problem as I'm sure you know with the aviation bands; there BIG especially the UHF spectrum for perfection with most antennas. What's a poor boy to do...compromise!
OR...I know that commercial "You can go with this or you can go with that, you can go with this or you can go with that" Are those mice or rats? Ok I'm just ramblin'...sorry
P.S. I recently purchased 100' of LMR600, the commission checks on the way.

KEL

 

[CalebATC]

Oooo, nice! Get your SDL yet?

 

[prcguy]

A colinear antenna usually requires about twice as many elements as an exposed dipole array for about the same amount of gain because you can't acheive the optimum spacing between elements.

This applies to the stacked 1/2 wave elements seperated by a phasing coil (usually 1/4 wave in coil) or the offset coax style colinear where you have 1/2 wavelength elements and alternate the center conductor and shield.

So if it takes about 32 elements of exposed dipoles at the optimum spacing to get 15dBd gain, you would need about 64 1/2 wave elements in a colinear fashion to get the same gain. At 300MHz that would be about 100ft tall. A 15dBD exposed dipole array for 300MHz would be about 40ft tall. If someone is advertising 15dBD gain and its smaller I would question how they estimated the gain.

And don't forget if you tune some of the elements for other frequencies very far away the whole thing will become a big noodle with a connector at the bottom.
prcguy

It will be made from a combination on 1/2 wave parts, 1/4/1 wave coils. The guy who made it told me it should have around 15dbd of gain when done. Depending how much you repeat the cycle, the more gain (I'm sure you know that)

It is a J pole pretty much, has a 300 ohm matching section. That will be for 301 MHz. The elements and coils will start from 250 and goto 375 Mhz, so each will have to cover that. It will be for 50ohm coax, or whatever you decide to do with the matching section.

 

[CalebATC]

And don't forget if you tune some of the elements for other frequencies very far away the whole thing will become a big noodle with a connector at the bottom.
prcguy

Hopefully that doesn't happen!

Just got done with the antenna, and a little testing while laying on the shed floor. Did get the trunking system inside shed, horizontally laying on the floor with a S-1 signal reading on the Yaesu FT-60R meter. About the same as the rubber ducky inside the shed. Hopefully off to a good start.

I will try to take down one of my dipoles or hang it from the tower tomorrow to see how it works. Wish me luck! So far, better than the Yaesu's rubber ducky.

 

[captkel]

Get your SDL yet?

No not yet. I finally was able to get through to AR2. I ordered a couple of pre amps from them, they'll be here at the beginning of next week, I'll order cables, etc. tomorrow from somewhere else. If it comes tomorrow I'll hook it up to the existing pre amp, etc. and see what happens. Also all the rain your getting now will be here tomorrow night so there may be a rain delay.

 

[CalebATC]

LOL on the picture.

How much did they cost? Were the specifically for air/milair band?

 

[captkel]

to get 15dBd gain, you would need about 64 1/2 wave elements in a colinear fashion to get the same gain. At 300MHz that would be about 100ft tall

COOL it would look something like this

KEL

 

[zguy1243]

KEL,

Just tracked it and it shows to deliver to you on Friday. Will send you over the number so you can keep a eye on it.

No not yet. I finally was able to get through to AR2. I ordered a couple of pre amps from them, they'll be here at the beginning of next week, I'll order cables, etc. tomorrow from somewhere else. If it comes tomorrow I'll hook it up to the existing pre amp, etc. and see what happens. Also all the rain your getting now will be here tomorrow night so there may be a rain delay.

 

[captkel]

LOL on the picture.

How much did they cost? Were the specifically for air/milair band?

$129.95 each + shipping They don't have ONE that covers the entire UHF band, remember it's huge. VHF is no probIemo. I think from them you would need 2 or 3 different UHF ones to cover the whole band. I checked out another company that claims theres will cover it all, still waiting for the quote...I can't WAIT...ahhhhhh. I chose one that covers 300-330 Mhz, it has a 30 Mhz bandwidth above and below those freqs. I think I'll be ok???
Also $44.95 I think for the DC injector to get power up to it without running a separate line. They have some broadband ones but they have higher noise figures.

KEL

 

[captkel]

KEL,

Just tracked it and it shows to deliver to you on Friday. Will send you over the number so you can keep a eye on it.

OK Thanks

 

[captkel]

I will try to take down one of my dipoles or hang it from the tower tomorrow to see how it works. Wish me luck! So far, better than the Yaesu's rubber ducky.

Any luck with your homebrew ? I finally got a quote from the other pre amp company that claims there amp can do the entire UHF band....$450 and they can ship tomorrow. So maybe I'll order one, or how about ten and have them send you the bill...hehe.
Cables and fittings are now on order and should also be in next week.
Also-How do you get the smilies in your post?

LATER

KEL

 

[captkel]

this is a test (a smilie) test http://forums.radioreference.com/images/icons/icon7.gif
http://forums.radioreference.com/images/icons/icon10.gif

 

[captkel]

that didn't work

 

[zguy1243]

Any luck with your homebrew ? I finally got a quote from the other pre amp company that claims there amp can do the entire UHF band....$450 and they can ship tomorrow. So maybe I'll order one, or how about ten and have them send you the bill...hehe.
Cables and fittings are now on order and should also be in next week.
Also-How do you get the smilies in your post?

LATER

KEL

wow man, 450 is way too high. Chip sells the 225-400Mhz tuned Phempt model with a .2 thats point two db noise figure and around 20 db gain for $190.00. What did Chip say the wait time was?

 

[CalebATC]

wow man, 450 is way too high. Chip sells the 225-400Mhz tuned Phempt model with a .2 thats point two db noise figure and around 20 db gain for $190.00. What did Chip say the wait time was?

Amen to that, get a Angle Linear!!!

Waiting to put it up until Saturday, just got home and have homework to do. And the fact it is sleeting outside!!

 

[captkel]

wow man, 450 is way too high. Chip sells the 225-400Mhz tuned Phempt model with a .2 thats point two db noise figure and around 20 db gain for $190.00. What did Chip say the wait time was?

I did not call Chip this time, I ordered from Advanced Receiver, The one that's coming has a 1 db noise figure and 19 db gain with N connectors $129.95. After you told me you have been waiting for over 2 months I decided to go elsewhere. I will have it next week. How's the bandwidth on Chips pre amps? Also do you do anything special about protecting your pre amps from being damaged by electrical static?

KEL

 

[CalebATC]

Let us know the comarison over the Radio Shack preamp. I like these Scientific Atlanta preamps, good with a cheap price. I'm sure Jody will chime in and say the same thing, obviously they don't Angle Linear preformance, but they are great to get started. I'm thinking of getting another and putting it in series. More noise but more amplification (of noise too, doesn't the world suck? ) and then I will have the FM trap before the amps and after the amp to get every little bit of it out.

Hopefully I will be able to get the collinear up tomorrow.

 

[Napalm]

RF Bay Inc: LNA-300

0.8dB noise figure, and 225-400MHz with a modest 20dB gain.

It's a very good price too (look on eBay, he sells some on there regularly).

7-12V, SMA connectors, built into a nice milled metal case, with a feed-thru cap for power. You just need to build it into a weatherproof box and bob's your mother's brother.

 

[prcguy]

I would recommend a filter in front of the RF Bay and most preamps.

I'm a big fan of Angle Linear and have several of Chip's high level models that have been tuned fairly broad. The 225-400MHz unit shown is the original model used in a NASA upgrade for the space shuttle program.
prcguy

RF Bay Inc: LNA-300

0.8dB noise figure, and 225-400MHz with a modest 20dB gain.

It's a very good price too (look on eBay, he sells some on there regularly).

7-12V, SMA connectors, built into a nice milled metal case, with a feed-thru cap for power. You just need to build it into a weatherproof box and bob's your mother's brother.