antenna question for you hams

[dime196604]

I just got my tech license a week ago. So I am gonna start using some of the ham frequencies. My question is this. My brother in law works for the city, the public safety building just upgraded all of their stuff so now I have 2 151mhz collinear antennas, they are about eight feet tall. I have opened them up and the innards are easy to get to and I have easy access to all the solder points.

Can I convert them to 2m? I know I would have to add length to them but I do not know what section to lengthen, if is even possible.

[North Texas Mudduck]

im no ham yet
what kind of antennas are they ?
name model?

[dime196604]

im no ham yet
what kind of antennas are they ?
name model?

They are antennx, a four element colinear array, it like four lengths of coax inside a PVC pipe, each peace of coax attaches to the next from the center to shield

['Doc]

Can it be done? Yes, with a lot of effort. I think the biggest hang-up would be squeezing the 'extra lengths' into the casing. You would also have to be able to 'measure' things to see how 'close' you are, so start looking for a good way of doing that (no, I don't mean a ruler/yardstick or an SWR meter).
One common way of doing that sort of thingy, using a commercially made antenna not made for the ham bands, is to just put-up with the mismatch and use it. Depending on the 'gain' of the antenna the mismatch losses are sort of 'canceled out'...
Good luck.
- 'Doc

[Island_0860]

Much easier being in the cut mode than the add on mode...so get a cup of coffee ,sharp cutters and your MFJ 259 ........use it for the 440 mhz band

[Savoirfaire]

First see what the SWR is on 2 meters.

Second try and find a 2 meter antenna tuner.

73, Frank 10 X-Ray 47 (SSB)
N4SLR (Amateur)

[Flapjack]

First try and find a 2 meter antenna. A modification like this will result in marginal results, unless you are a EE or really tight friends with one. DNJ has a really good two meter antenna. Good front to back selectivity. I listened to a mobile unit over 40 miles away and they were crystal clear and they were not on the repeater.(We were both hill toppers) I know doing modifications are fun, but it is wiser to pick your projects that have solutions. The spacing between the elements would have to change as well. Save your time and money and get a functional antenna that is inexpensive and works well.

[ch17Critter]

Or go for it.....what's to lose?

They were free and the worst that can happen is they dont work but you LEARN something in process.

Critter

[North Texas Mudduck]

Start here a good beam on 2meter is always best
http://search.yahoo.com/searc ... 20antennas

[721HACKSAW]

Antenna building or modifying is always trial and error, it all depends on how much time and effort you're willing to put into it and what kind of result is intended.
As 860 posted, having an analyzer such as the MFJ 259 can help tremendously.

[Flapjack]

Or go for it.....what's to lose? They were free and the worst that can happen is they dont work but you LEARN something in process.

Yep, like how to replace the finals in your transmitter, and how much time and money you could have saved just buying a good beam antenna.

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Sun Apr 21, 2013 4:43 pm

I just got my tech license a week ago. So I am gonna start using some of the ham frequencies. My question is this. My brother in law works for the city, the public safety building just upgraded all of their stuff so now I have 2 151mhz collinear antennas, they are about eight feet tall. I have opened them up and the innards are easy to get to and I have easy access to all the solder points.

Can I convert them to 2m? I know I would have to add length to them but I do not know what section to lengthen, if is even possible.

You would have to lengthen all of them. The radiating element is the second longest element. The longest would be the reflector. All of the others would be directors, and they would all require lengthening. Good luck on your project if you choose to go that way.

[dime196604]

You would have to lengthen all of them. The radiating element is the second longest element. The longest would be the reflector. All of the others would be directors, and they would all require lengthening. Good luck on your project if you choose to go that way.

It a omni, vertical not a beam. Its got four elements hook end to end. Its a four element colinear

[Flapjack]

You would have to lengthen all of them. The radiating element is the second longest element. The longest would be the reflector. All of the others would be directors, and they would all require lengthening. Good luck on your project if you choose to go that way.

It a omni, vertical not a beam. Its got four elements hook end to end. Its a four element colinear

Whoops my bad I thought a four element co-linear was dual or stacked Yagis. google.com/search?q=collinear+antenna

hamuniverse.com/w7lpnCollinear002.pdf

It could be very do able. Very precise measurement are required.

[dirtyjob]

if you must Finangle something out of what you have then go for it but where 2 meter antenna's are prolly the cheapest antenna's out there , i'de simply buy one.

[ch17Critter]

Or go for it.....what's to lose? They were free and the worst that can happen is they dont work but you LEARN something in process.

Yep, like how to replace the finals in your transmitter, and how much time and money you could have saved just buying a good beam antenna.

---

Sun Apr 21, 2013 4:43 pm

Ever hear of an analyzer? Guess trying something is just out of the question. Huh....who knew?

Critter

[dime196604]

if you must Finangle something out of what you have then go for it but where 2 meter antenna's are prolly the cheapest antenna's out there , i'de simply buy one.

its very cheap and easy to make a beam for 2m as well. I just wanted to know if it was possible since i have 2 and they are well maid and free, and i was reading that vertical colinears have a decent about of gain

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Sun Apr 21, 2013 8:16 pm

I am thinking of making the tape measure beam since i have everything needed to make it

[ch17Critter]

Again....what have you got to lose? Except a chance to learn a little bit about antennas and antenna construction. They were free.

Will it be easy? Depends on the person I guess but in no way do you need to be an EE to do this if you can get the thing apart as easy as you say. There are many places online for calculations and tips on building antennas.....just not as easy to find as posts saying it's next to impossible.

Have fun...learn something.....win win

Critter

[dirtyjob]

if you must Finangle something out of what you have then go for it but where 2 meter antenna's are prolly the cheapest antenna's out there , i'de simply buy one.

its very cheap and easy to make a beam for 2m as well. I just wanted to know if it was possible since i have 2 and they are well maid and free, and i was reading that vertical colinears have a decent about of gain

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Sun Apr 21, 2013 8:16 pm

I am thinking of making the tape measure beam since i have everything needed to make it

sure thing, there are many many inexpensive plans to be had making antennas and 2 meter antennas are very dirt cheap to make, i run a jpole made from copper pipe, cost 20 bucks to make, hits repeaters 60 miles away and only 20 feet off the ground.

[231]

There are a ton of good and easy to build 2m designs out there. If it were me, I'd throw together a simple omni for 2m and start enjoying local repeater action right away...along with some simplex. I wouldn't lay my eggs in the co-linear basket until you've had time to go through it and test it out. Like mentioned, you'll likely need to lengthen the elements a tad (doesn't take much) to get them to dip where you want. Honestly, a good simple to build 1/4 wave ground plane will do a great job for most of the repeaters and even simplex. Heck, even a 2m dipole or J-Pole will do great!

Enjoy and let us know how it goes.

231

[Flapjack]

Ever hear of an analyzer? Guess trying something is just out of the question. Huh....who knew?

Critter

Analyzers are great if you can afford them. I have several. I have a HP spectrum analyzer cost over $7000.00 new. I also have multiple Antenna analyzers One for the 160 through 6 meter range and one for 2 meters and up. Field strength meters are a good way to tune them up as well and you can also map out your radiation patterns of the antennas. I was just sayin many people are not that technically inclined or have so much money invested in test equipment as I/we do. Some times it is just better to buy one instead of modifying an item made for something else.

[MDYoungblood]

Naturally most of us can't afford extravagant equipment but settle for a plain old SWR or if you can afford one an antenna analyzer. If they were in the 151mhz range they will be a little short. Made out of PVC makes lengthening them easy, the local Home Depot has the parts. If they are a beam design they will also be short in spacing. Search around for an antenna calculator to get things going and to figure out what you will need. So far the only thing you spent is your time. I enjoy experimenting and have built several antennas over the years, I even remember going to the library to get reference material, thank god for computers and the internet.

3's

Greg

[ch17Critter]

Ever hear of an analyzer? Guess trying something is just out of the question. Huh....who knew?

Critter

Analyzers are great if you can afford them. I have several. I have a HP spectrum analyzer cost over $7000.00 new. I also have multiple Antenna analyzers One for the 160 through 6 meter range and one for 2 meters and up. Field strength meters are a good way to tune them up as well and you can also map out your radiation patterns of the antennas. I was just sayin many people are not that technically inclined or have so much money invested in test equipment as I/we do. Some times it is just better to buy one instead of modifying an item made for something else.

Noted.

My point is....why discourage a chance to learn something? The job of converting that antenna he has is, I admit, a more challenging project for a first timer but far from something needing to be an EE. Nor would it have to an expensive project....whats the most he could lose here? 10 bucks?
Any chance to learn something is well worth the effort.

Critter

[Flapjack]

My point is....why discourage a chance to learn something? The job of converting that antenna he has is, I admit, a more challenging project for a first timer but far from something needing to be an EE. Nor would it have to an expensive project....whats the most he could lose here? 10 bucks?
Any chance to learn something is well worth the effort.

Critter

If you don't have a real solid grasp of how radio frequencies act and react the project could be too technical for some people. The absolute last thing I would ever do is discourage a person from learning something new. But I also would caution them about getting in over their heads technically. The finals in good quality ham equipment can be expensive. I know EE's that could not handle that project. I had several working for me that could not do that project. They were competent in the projects that I hired them for but not much else. All I can do is put my opinion out there and they can choose to take my advice or not. Can we still be buddies?

[ghz24]

A collinear is that hard to make? Really? The hardest part is the sleeve balun the calculations for the proper lengths of coax segments are 8th grade math. There are plans/directions on the web to make coax collinear antennas for 2.4 GHZ do a little research, calculate the lengths needed to make the one you have then check if the calculations match your antennas dimensions (you'll need the velocity factor of the coax used in the antenna) if the dimensions match your calc. then you are on the right track. redo the calculations for 2 meters and what ever coax you'll be using . you'll need to replace each segment of coax with a correct size one.
good luck.
If you can't find directions PM me I'm sure I can find one.

[dime196604]

Well Doc got me thinking about the small amount of extra room inside the PVC casing and there is only about one inch on top and one on the bottom so I don't think that would be enough room to lengthen all four element, also I would have no idea how to tune it, every colinear antenna design I look at has a different way to tune it, I will keep it and maybe someday mess with it.