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Scanner / Receiver Antennas For discussion of any type of receiving antenna used by a scanner or receiver base, mobile or handheld.

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Old 01-10-2011, 11:43 AM
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Smile Homemade 850 MHz J Pole antenna?

Hello Everyone!

I'm looking at putting up a base antenna for my Pro-197 digital scanner.

I already have a Diamond D-130J discone antenna, but since the majority of the listening in my area is now digital in the 850MHz area, a dedicated antenna might be better.

Are these "copper pipe" J pole antennas worth trying to build. Specifically this one: Easy Jpole Building by dxzone.com (click on "Easy Jpole building")

It sure wouldn't be that big for 850 MHz. 9.9" for the longest section, and maybe 50' of rg-6 coax.

Should I bother with building one or just use my discone or just buy the Scantenna ST-2?

Thank you all for your thoughts and comments!
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Old 01-10-2011, 12:30 PM
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Discone might work better, the J-Pole isn't going to be much better than a 1/4w, though it can be built as a 1/2w too, but we aren't talking much for gain here.

The ST-2 while good on VHF seems to get a poor rating from everyone who tries them on 800. If your really concerned with getting as much as you can on 800 i would get an antenna dedicated to that band. All depends on what your looking to spend also. For around $80-$100 you could get a 5-6db gain antenna to cover those systems.

I got a used commercial antenna off ebay for this, its a commercial antenna that came off a tower for an upgrade, centered at 858 which is perfect. Your looking at 851-860 for the output frequency of these trunked systems.

One that has been recommended over and over is the Laird FG8246..

Antenex FG8246 824-896 MHz - 6dB, N Female connector.

It's the same one ScannerMaster sells, but its cheaper elsewhere.

Edit : Just realized your MN... Fellow ARMER scanner! That's why i needed an 800Mhz antenna also!
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Old 01-10-2011, 2:01 PM
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The scantenna ST-2 is terrabad at receiving 800MHz. A factory rubber duck picks up the 800 control channel near me (30+miles away) where my scantenna doesnt even register the CC noise. Its 30' up in the air even. Granted the duck is very scratchy, but the st-2 wont pick it up. It does a heck of a job on VHF and UHF tho. I use a old NEXTEL yagi antenna I salvaged off of a building that used it for a base antenna when NEXTEL was in its prime, as my 800 antenna of choice. I suggest if your just wanting to monitor a specific 800 system, grab a yagi off of eBay. Even the cell antennas from wilson are tuned for 806-900, and have a average gain of 12 dB
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Old 01-10-2011, 2:11 PM
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Your mileage may vary, I use the ST-2 and get excellent coverage. I had to ATT some to keep some 40 mile away stations out in the 700 Mhz system. I had a discone that did not perform half as well. I have not done a J-Pole at the high of a freq. before though. So can't say. But all in all, it is a fun project, and winter time is always a good time to work on stuff you can do indoors.
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Old 01-10-2011, 5:56 PM
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Hmmm, As has been said, you may not be super impressed with the J-pole performance. I think it would also be difficult to build to the small size with standard copper pipe. Maybe some brass brazing solid copper wire.

But, while it may be unimpressive in its performance, it would be cheap to play with and it would be a good project.

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Old 01-10-2011, 6:47 PM
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Thanks so much for all of your thoughts and comments everyone!

Maybe I'll just throw the old discone back up on the roof for a while then.

I agree that the Jpole would be fun to play around with. If I could fine 1/4" copper pipe that would be easier to work with. Maybe it would work fine using 1/2" pipe?
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Old 01-10-2011, 10:58 PM
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Quote:
Originally Posted by natiep View Post
If I could fine 1/4" copper pipe that would be easier to work with.
1/4" copper tubing is commonly used for supplying water to refrigerator icemakers. The typical installation kit has 15' or 20' of 1/4" tubing. Far more than you need.

The J-pole is just an end fed dipole, so it has essentially no gain (or something like 2.8dBi ... when the reference is an isotropic antenna).

At the higher frequencies, things like stacked arrays of dipoles and collinear arrays start to make sense.

Of course, if all you need to receive what you want is a simple 1/4 wave with groundplane or a J-pole, those are a lot easier to build.

Being lazy, my first antenna for 850MHz would be some #10 or #12 wire stripped out of romex cable and soldered to a SO 239 chassis mount connector. SO-239 Chassis-Mount Coaxial Socket - RadioShack.com Just solder on the vertical 1/4 wave, and 4 ground radials.

I couldn't the webpage showing the simple 1/4 wave version, but this dual band version shows pretty clearly how easy it is:
http://www.qsl.net/na4it/dbgp.html

Last edited by WA1ATA; 01-10-2011 at 11:01 PM.. Reason: add link
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Old 01-10-2011, 11:36 PM
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I built a j-pole to transmit on the ham 2 meter band and have used it with good success to scan our areas 860mhz law / ems freqs. I don't think you would have any problem if you built a bigger j-pole than the 800 would dictate when it comes to recieving, you have more leeway than TX. Now, is it ideal? No. But it works pretty good anyway
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Old 01-11-2011, 8:25 AM
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The only thing I'd add to the above is that someone mentioned using RG-6 for the feed line. The problem with using it is that it uses aluminum braid, which is difficult to solder to. Not a real biggy, but just be aware of it.
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Old 01-11-2011, 11:24 AM
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Thank you all so very much for your kind help and comments!

I think I will just look on ebay for a cellular omni-directional antenna that covers 800-900Mhz.

Plenty on ebay pretty cheap.
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Old 01-13-2011, 7:12 PM
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I just finished building my 154 MHZ J-Pole antenna out of copper pipe. I already have 1/2 water pipe, and have experience sweating copper, so I figured what the heck.
I used this online calculator to get my approximate dimensions. J Pole calculator by dxzone.com
My intension was to build the J-Pole to receive better reception of my local fire band. Because of the weather, I haven't been able to mount the antenna outside. Inside the reception is so so in the 154 MHZ range probably due to the fact that it is indoors. The antenna however works pretty good at receiving in the 851-854 MHZ range. So far, it has out performed my Watson W-881 Super Gainer at pulling in the 800 Trunking system.



I may try to build another J-Pole antenna to the specks of an 800 MHZ antenna.

Last edited by saleen49; 01-13-2011 at 7:16 PM..
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Old 01-14-2011, 2:17 AM
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how did you attach the so-239 to the copper pipe. Maybe a close up pic in order?

Frank
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Old 01-14-2011, 8:15 AM
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Quote:
Originally Posted by n3obl View Post
how did you attach the so-239 to the copper pipe. Maybe a close up pic in order?

Frank
A small dab of flux is applied to the mating surfaces. Apply a small amount of heat with a plumbers propane torch until the solder starts to melt.


Last edited by saleen49; 01-14-2011 at 8:27 AM..
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Old 01-14-2011, 12:22 PM
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How much, and what type, of feedline to you have on the ST-2?

It could be losses that are causing your poor performance.
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Old 01-17-2011, 9:36 AM
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The antenna on the right is the 154 MHZ J Pole I built. It works very well as a multiband antenna indoors. On the left is a mini 850 MHZ antenna i put together to test a distant 800 Trunked system for reception. The 154MHZ antenna out performs the 850 antenna in every band tested so far. I will wait until spring to try these antennas outside for reception.

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Old 01-17-2011, 12:00 PM
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Have you thought of using a smaller conductor for the 850 antenna? The diameter affects the Q, which makes me wonder if the antenna is too broadband.
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Old 01-17-2011, 3:18 PM
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Quote:
Originally Posted by krokus View Post
Have you thought of using a smaller conductor for the 850 antenna? The diameter affects the Q, which makes me wonder if the antenna is too broadband.
I did see some 800 antennas made of wire when I was searching for ideas. I have some 1/4" soft copper tubing used for ice makers I was thinking of using. I might mock up an antenna out of that to test. Thanks for the heads up.
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Old 01-17-2011, 7:56 PM
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I recently made my first J-pole out of 1/2" copper, and designed it for 155 Mhz. It cleans up all the static in and around that frequency, and also pulls in all the 850 area frequencies better than my 800 Mhz rubber duck. I'm using it inside right now, but come spring, i'm mounting it on the roof, which will put it about 35' off the ground. It's also pulling in a neighboring county that i cannot pull in with either of the portable antennas. The only thing i did different from the above photos is i used a tee and soldered the SO-239 to the bottom of the tuning stub. Hearing is believing. I don't think you can go wrong for the performance of these versus what they cost to build.
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Old 01-18-2011, 10:34 AM
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sparks40.......do you have a picture of your Jpole with the T?
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Old 01-18-2011, 7:45 PM
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Quote:
Originally Posted by natiep View Post
sparks40.......do you have a picture of your Jpole with the T?
It's not quite done yet. I got the idea from a webpage i found while researching these antennas (eham.net). I angled the wire to create a drip loop for water. The design i used also included a weep hole for water to escape from the pipe, but i did not install one on this antenna. I'm going to silicone where the wire exits the tuning stub, and use shrink tube to seal where it's soldered to the main pipe, as well as soldering on some caps. I'm going to clean it up and paint it after i take care of those two details. I've included two attachments. I hope they come out. Watch the heat on this design so you don't melt the plastic on the SO-239. I also used electrical rather than plumbing solder. I used the torch to heat the pipe, then removed the flame and the solder just sucked right in. MAPP gas is the way to go. I haven't decided what band i'm going to build the next one to, but i've decided to use 3/4 copper for a stronger antenna.
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Last edited by sparks40; 01-18-2011 at 7:59 PM..
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