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I installed a R1225 UHF repeater in a small building about 500 feet from a very large all metal building. I just need coverage inside and around the large metal building. I started with a Larsen BSA-450K (3dB) antenna. Antenna height is about 25 feet. I measured 30 watts forward and 0 reflected. Signals were very weak in the center of the building. I replaced the antenna with a Antenex FG4605 (5dB) hoping to get a little better penetration of the building. I measured 10 watts forward and 5 watts reflected. I did not try performance. I called Antenex and they said reflection of signal from large metal building was causing bad VSWR. I am not sure. I moved the antenna to another site (10 miles away) and got 18 watts forward and 4 reflected. A Bird load at end of same coax reads 34 watts forward and 0 reflected. What do you think about the Antenex and which antenna would you expect to work best?

The SWR should not be affected by a metal building that far away. The amount of SWR you are reading is excessive. Is the antenna designed for the frequency you are operating on? The higher gain antenna would have
a narrower bandwidth.

The additional 2 db of gain possible from that antenna would not be enough to make a significant improvement in the building even if the antenna was working properly.

If the metal building is that well shielded, and your coverage is to be inside and a small area around the building, you may need to use an antenna or "leaky coax" inside the building.

We have had a lot of SWR and very poor radiation problems with the Antennex FG series antennas. They are just a 18 ga wire inside the fiberglass tube. Not realy a good repeater antenna design. (infact a VERY poor antenna design)

Try a corner reflector antenna that puts all the transmitter signal at the building. Even then the metal building will zap the signal.

Antenna is 460 to 470 and repeater is 463.5

arlojanis wrote:Antenna is 460 to 470 and repeater is 463.5

It looks like the Antenex antenna is defective but it probably would not be a solution even if working properly. You would need about 10 db additional gain to see a significant improvement.

As Will mentioned, the additional gain of a corner reflector antenna aimed at the building may help.

If the building is really well shielded, the best solution may be to put the repeater inside the building as I suggested previously.

You may want to consider letting the RF into the building by adding a fibreglass skylight on the side (or a large plexiglass window).
You can run a test on some buildings by removing a sheetmetal panel if they are just bolted on.
Might be worth a try.

Or put the repeater inside the metal building. Hang a unity gain antenna from the roof rafters (inside) and a second one outside. Couple them with a power splitter.

The Antenex FG4605 appears to be defective when tested at either TX site but you have not provide what type of coaxial cable you’re using at your customer’s site. RG-8/U, 8214, LMR400 or ½” Heliax will all provide different Forward / Reverse Power Output characteristics when feeding the antennas. You stated that the Larsen antennas provides a perfect match but where are you measuring the Forward / Reverse RF Power … at the output of the Duplexers or at the base of the Antenna?

Another item to think about with your the so-called antenna’s perfect match is if you’re not using Andrew’s Heliax cable, but you could have an open at some multiple of the wave lenght frequency within the coaxial cable itself presenting what appears a perfect match and this does happen from time to time. The only way I know you can verify the center’s conductor is open or broken would be disconnect the feed line from the Duplexers and the Antenna. Then short the center conductor (using a jumper wire with alligator clips) to the shield at the antenna connector. Take your Ohmmeter and measure for a “Short.” Remove the Jumper wire with alligator clips and measure for an “Open.” This will verify if the feed line is ok or not.

The large metal building can produce up to 50 dB of attenuation path losses much like screen booth to the RF signal penetration level. You have a couple of alternatives to increase the signal strength within this building’s interior and the surrounding exterior. Relocate the /\/\ GR1225 UHF repeater to the metal building and centrally locate the repeater’s 3 dB Gain on the outside roof of the building.

Or purchase an antenna nothing more than a ¼ wave magnetic mount placing it on the interior of the metal building, a SCALA RF Antenna Power Divider PD2-55 (50%-50% Split) and moving the Larsen +3 dB Gain on to the exterior of the metal building. Then connecting the each antenna to the RF Output Ports and the Common Port to the feed line to the repeater. A little RF signal on the interior of the building goes much farther than none at all.

There’s a third method if you are unable to relocate the /\/\ GR1225 UHF Repeater to the metal building. In this case purchase a +10 dB Gain UHF Yagi Antenna mounting it on the top of the metal building pointed directly at the Larsen +3 dB Gain Repeater’s Antenna. Connect 25 to 30 Feet of ½” Heliax coaxial cable to the Yagi Antenna and route the cable through the metal wall to a ¼ wave or +3 dB Gain Antenna on a mobile magnetic mount. Mount the antenna vertically polarized, up side down on the interior of the building metal ceiling or horizontal “I” Beams. This is a Passive Repeater Antenna System. You can read more about this subject in the information listed below

Reference material:

System Infrastructure and Related Equipment

Posted: Thu Jul 14, 2005

Passive repeater signal calculator by Nand

http://www.kathrein-scala.com/ RF Power Dividers PD2 – 55

http://www.tessco.com/

Products >> Antennas and Base Stations Systems >>
UHF Yagi, Corner Reflector

Sucess! I installed a Maxrad 6 element yagi pointed towards the metal building. I measured 0 watts reflected VSWR. I added an Advanced Receiver Research preamp between duplexer and receiver. I used cables made by Advanced Receiver Research. Both preamp and duplexer are mounted inside R1225. Signals from deep inside the building are now repeated.

Arlo, you are probally going to need a RF radiation warning sign with that much ERP.

Antenex=POS

When I used to use them, I must have sent back every 1 out of 3 since it either didn't work, didn't tune or had a mechanical defect.

Looks like I will have a surplus Antenex for sale when I get it back. How long does it take to get one back from factory? The yagi is maybe 14 ft off the ground. I checked signal strength 5 miles away directly behind it and had a very strong repeater signal reflected of the building. At 7 miles in front of the yagi, with building between, signal is very weak. Ground elevation is a little above average.