Antenna Upgrade: UHF Repeater System

[lardiop]

Hey all,

Long time lurker, one of my first posts on the forum.

We have a UHF repeater system (~450MHz, Commercially Licensed) running where I work. Unfortunately the people who originally setup our system did a really poor job with the equipment. (Pictures below) There is basically zero budget to redo things, but as an act of good faith I offered to try and improve our existing radio system. I'll even spend up to around $200 if need be to get this done.

We have a around 8 Motorola HT750 Mobiles out at any one time and an older Radius GR1225 for the base station.

The current antenna broke off the wall where it was originally mounted, but I'm looking to replace it with a much better one.

Questions:

1) How is the system wired? I've included pictures of all the wiring from the base station to the exterior antenna.

2) What (inexpensive, small, and preferably something I don't have to ground) antenna would you guys recommend to significantly improve the range and coverage of the system? If I do have to ground it, how would I go about it?

3) Is there any easy way to program the base station? I realize you need a cable and software, but I have no idea where to get a hold of that.

Pictures:

http://img120.imageshack.us/img120/8530/2tl0.jpg
- Back of the base station

http://img120.imageshack.us/img120/7390/1jx6.jpg
- After coming from the Base station, the original wire is converted into a larger format and sent outside to the antenna

http://img392.imageshack.us/img392/8918/3gu6.jpg
- Picture of the current antenna location (Don't laugh too hard... There is a roof directly above where the picture is cut off at the top. Current height is about 8 feet off the ground.

http://img241.imageshack.us/img241/747/4fv2.jpg
- Close-up of the antenna.

Much appreciated!

- Paul

 

[specman]

Hi Paul;

I suggest that simply getting that antenna up into some clear air will improve things drastically. From the pictures it looks like it's a mobile antenna that's had a ground plane added. Not sure if one of the radials is broken off... you might want to repair it if possible. There certainly would be better antennas for this kind of installation but I doubt your budget will allow it.

If you can manage it, try to get a mast (pole) mounted above the roof line. Get it as high as you can. That antenna looks like it has a decent mounting bracket on it; you should be able to use a couple U-bolts to attach it to the mast. Your Coax may not be long enough now; get some new stuff in the proper length (look for radio supply shops in your area if possible). It looks like they used RG-8 before; while not the best available it will work well enough and is economical. Replace that short thin section and run the new cable right to the radio.

For several reasons you should ensure the installation is grounded properly. You should seek the advice of an electrician in this regard so that there are no future insurance implications or other legal items.

They sure did do an amateur job before....

 

[N5TWB]

If your photo of the antenna is properly oriented (and I am assuming that it is based on the way the bricks run in the photo), then the antenna needs to rotated so it is vertical (perpendicular to the earth) with the ground plane elements parallel to the earth. Follow specman's instructions concerning a mast that gets the antenna up into clear space with no nearby objects to block the signal.

 

[popnokick]

Pic of UHF repeater antenna

I just finished putting up a UHF antenna, and it was pretty inexpensive and simple. I used:
- two 10 foot sections of heavy duty TV mast from Radio Shack (about $18 each)
- a wall mount kit from R.S. (about $13)
- This 6db gain colinear ground plane antenna for $55 http://www.antennawarehouse.com/VHF-UHF/AWH-450.htm
- LMR400 coaxial cable
- This RF surge protector http://www.k1cra.com/catalog/product.aspx?productID=911

As was noted in specman's post, simply getting the antenna up and in the clear away from the building will result in major increases in your received and transmitted signal strength. Also, you probably would do fine even if you only used one 10 foot section of mast, and it is simpler to put up 10 than 20.

 

[N_Jay]

What are you trying to cover?
On-Site or distance?

How is it working today (before any failure)?

How can anyone suggest a particular antenna system without knowing the answers to the above questions?
:roll:

 

[popnokick]

N_Jay is correct, and my suggestion was based on the ASSUMPTION that you are trying to cover a wider geographic area than the system pictured presently covered. If that is not the case, then what I described is likely overkill.

 

[traumacop]

I don't care what kind of area you are trying to cover, between the coax and the way the antenna is mounted your better off standing there with a handheld. At a minimum switch to LMR400 and mount the antenna vertically. You can order the coax with the proper connectors for about .50 cents a foot. If you want more coverage then consider a different antenna and changing the location.

You could most likely get free help from a local ham. Look up your local club or a member and introduce yourself. They love this stuff and you will be surprised how resourceful they are.

Good Luck,

 

[wesct]

I don't care what kind of area you are trying to cover, between the coax and the way the antenna is mounted your better off standing there with a handheld. At a minimum switch to LMR400 and mount the antenna vertically. You can order the coax with the proper connectors for about .50 cents a foot. If you want more coverage then consider a different antenna and changing the location.

You could most likely get free help from a local ham. Look up your local club or a member and introduce yourself. They love this stuff and you will be surprised how resourceful they are.

Good Luck,

area coverage is important.

if the antenna is above you, its not going to do well.

wesct

 

[N_Jay]

area coverage is important.

if the antenna is above you, its not going to do well.

wesct

If it is sideways that it "might" do fine above you. :lol: