Deployment ICOM radio project - Page 2

allester666 · 04-07-2011, 11:47

Once again, thanks to all that have given input on this topic. I have done a ton of research on this subject, and based on the environment/cost/availability of raw materials I have constructed the 5/8 collinear J-pole antenna. I was able to easily tune the antenna to 1.1:1 SWR at the frequency i wanted using galvanized wire, pvc pipe, hose clamps and some coax cable. I chose galvanized wire for the environment, and based off of the past success of a HAM enthusiast.

The links previously provided had easy to follow instructions for constructing a 2M (146mhZ) antenna. Provided in the comment section was a design made by an enthusiast who decided to used steel over copper...what a great and unexpected result. I used hose clamps over circuit breaker connections, and achieved the same awesome 1.1:1 results with a slight bit of tuning. Great antenna, great comments, thank you all so much.

Please PM me with any requests regarding this subject.

allester666 · 05-02-2011, 15:41

I built the antennas, which are Double Stacked collinear J-poles. They tuned up GREAT, easy to do with parts from the city (all but the transmission lines that is). I was able to finally get MBITR/ICOM/repeater coms, with a ton of different guesses in the programming settings. Now if I could only tie in the older Motorola radios used by the police here....

A quick question for the SME's out there...can the repeater be set as the "base" and still function as a repeater? If not, then the local Comms Center will just have to operate off of an individual radio. Thanks for the help, wish I could get my QP status straight so i could post pictures...pm if you have any questions, and thanks for all the help!

Paragrouper · 05-02-2011, 20:42

Quote:

Originally Posted by allester666

can the repeater be set as the "base" and still function as a repeater? If not, then the local Comms Center will just have to operate off of an individual radio.

I do not believe that is possible. The repeater operation will be full-duplex and the Base station operation would be simplex. I will make a call tomorrow to see what your options are.

Paragrouper · 05-04-2011, 12:17

Quote:

Originally Posted by Paragrouper

I do not believe that is possible. The repeater operation will be full-duplex and the Base station operation would be simplex. I will make a call tomorrow to see what your options are.

Contrary to my previous message, it seems that you should be able to to both.

I contacted ICOM America technical support, ( 425) 450-6087, and they left me a message stating that it should be as simple as hooking up the microphone. He further stated that when you transmit it will interrupt the repeater function until you finish transmitting.

I hope this helps.

allester666 · 05-15-2011, 06:20

Both antenna's are now bolted up in the 50ft tower. The antennas are 10 ft long...so i had them mounted so that the second antenna is 5 ft below the top of the other one. That means that they are on the same level for about five feet (bottom half of top one, and upper half of second one). I have conducted some radio checks from within the city, with mixed results. The base station reported that my transmissions came in very clear most of my check points except for at the police station (didn't hear me at all). I had another unit being monitored by a friend on duty indoors, and he was not able to hear my traffic about 2 km away from town.

I am wondering if I should try Yagi antennas? I figured a repeater pushing 50 watts of RF would have no problems!

SF_BHT · 05-15-2011, 06:46

Quote:

Originally Posted by allester666

Both antenna's are now bolted up in the 50ft tower. The antennas are 10 ft long...so i had them mounted so that the second antenna is 5 ft below the top of the other one. That means that they are on the same level for about five feet (bottom half of top one, and upper half of second one). I have conducted some radio checks from within the city, with mixed results. The base station reported that my transmissions came in very clear most of my check points except for at the police station (didn't hear me at all). I had another unit being monitored by a friend on duty indoors, and he was not able to hear my traffic about 2 km away from town.

I am wondering if I should try Yagi antennas? I figured a repeater pushing 50 watts of RF would have no problems!

It may be the orientation of the antenna. We use antennas that are down looking for sites on mountains/hills. We have 90 deg side radiating antennas and then Yagi's to shoot up to interconnected repeaters. You need to put a antenna analyzer on your transmission line and check for loss at your connectors, Heliax cable and then check you antenna. All points are problems when you are using factory or home made systems.

Paragrouper · 05-15-2011, 06:55

The distance between your antennas is likely an issue.

Because of their proximity, you are likely inserting noise into your receive path, which will reduce the range that your repeater can effectively receive incoming signals. this will also impact transmitted signals from the repeater, as the quality of the retransmitted signal may be degraded.

I suggest you try increasing the the vertical spacing between your antennas, which will increase the isolation between the receive and transmit paths. Also verify that your cables and connectors are correct, as shielding issues will exacerbate the problem.

Changing to a directional antenna array would help, but only if your desired coverage area lies within the effective beamwidth of the directional antenna.

allester666 · 05-15-2011, 08:15

I was kind of afraid of that answer, but knew it was coming

Guess I need to get a lineman's belt, and get up their and raise one of the antenna's. Do you think it would be sufficient to have the bottom of the top antenna level with the top of the lower one? I would like to keep the antenna's up as high as possible, but a previous post talked about keeping a few feet in vertical distance apart. Thanks again for the help...I wish i could post pictures of this project, I think you guys would like to see what I'm working with here!

no-hertz · 05-15-2011, 12:52

Going with a Yagi setup would not be wise unless all of your operations were taking place in a specific, and somewhat narrow band away from your transmission location.

You are likely receiving well at the base station because of the height of the antenna, and are likely having problems with your re-transmit due to coupling of the antenna's in the near field. The antenna could also be coupling with the tower as well.

Getting the antenna's some physical separation is going to help a bit, and also as a thought if you have a tower, You could consider two different types of antenna's, like a dipole or inverted V using the top of the tower as a center support, and your folded antenna used to transmit mounted 10 feet down the tower, or even the inverse.

Hard to armchair quarterback your antenna setup without seeing it, and hell you probably don't need any armchair QB advice anyways. Sounds like you are getting a good setup built, just to iron out the damn kinks as always.

Paragrouper · 05-15-2011, 12:57

Quote:

Originally Posted by allester666

Do you think it would be sufficient to have the bottom of the top antenna level with the top of the lower one? I would like to keep the antenna's up as high as possible, but a previous post talked about keeping a few feet in vertical distance apart.

My previous post, (3-6') was actually a somewhat of a compromise, given the importance of maintaining good height for the antennas. Try to keep some physical separation, as this vertical "stacking" makes the best use of the nulls in the radiation pattern to improve your isolation.

allester666 · 05-20-2011, 10:44

I was blessed with the availability of a communications testing team being available, and know the right guy to knudge them in our direction. The out come was amazing; to senior enlist NCO for them Marine Corp and Airforce that could speak to the locals, and were very knowledgabe about older systems and HAM/VHF systems. The gave me some critical guidance in getting the city covered, just one more week till we see the final results!

Learning what i did today, i know i will have to bring my RX antenna down to a resonable VSWR, and hoist it up higher in length.

Paragrouper · 05-22-2011, 08:16

Quote:

Originally Posted by allester666

Learning what i did today, i know i will have to bring my RX antenna down to a resonable VSWR, and hoist it up higher in length.

It's good to hear you got some onsite assistance. Hopefully you will get things worked out this time. Perhaps when all is said and done you can post your lessons-learned, along with a good description of the final soluition to help others with a similar problem.

I am curious, your previous posts suggested that you had the antenna VSWR in order. What is it now?