GR1225 UHF System

johnny1225 · Post by **johnny1225** » Thu Apr 24, 2008 4:09 am

I have a GR1225 UHF Repeater down at one of our local hospitals. Freq is 453.7000/458.7000 with a TPL code of 91.5. This system is approx. 5-7 years old. We have just put in 3 other GR1225 Repeaters for the other groups within the Hospital and they are all working amazingly. This is the senero. The hospital is about 10 floors with one sub basement. The Repeater is on the 3rd floor. We have one antenna going up to the roof, which is a SRL301 Antenna. We also have a antenna that is going down to the 2nd floor which is a mag antenna. My question is this setup is working great for the other 3 groups but for this one it is not. Brought repeater back to the shop and everything with the repeater is completely on spec. My question is with a wattmeter i am getting 34 watts out of the repeater to the cable going to the top and 3 watts of reflected power. My antenna going down i am getting about 34 watts and about 1 watt of reflected power. With about 4 watts of reflected power in the system what would you do to resolve this issue. My problem is with the coverage going down it seem i can't get it to the sub basement, but like i said the other 3 systems are working fine and i can get the sub basement perfectly, does anyone have any recommendations for this problem.

Regards,

John

Bat2way · Post by **Bat2way** » Thu Apr 24, 2008 4:56 am

Are you saying you're splitting the transmit out into two separate runs, or just using the tx power out as a reference check of each line's condition? If so then, are you simply running separate tx-rx antennas with no duplexer?

If using the tx power test method, you need to measure the power at the antennas to actually figure what's happening. Did this repeater work fine before the addition of the other three units? Just need to check what's changed.

Bigred · Post by **Bigred** » Thu Apr 24, 2008 7:02 am

Since the repeater checks out at the shop, we really need more info about your antenna scheme.
A normal combining system would have two antennas, TX & RX, and then that could be split into
the roof and 2nd floor, for a total of four antennas. Not sure how you're getting 4 repeaters into
two antennas.

johnny1225 · Post by **johnny1225** » Thu Apr 24, 2008 9:50 am

I am using a Duplexer on this system that is split one antenna SRL301 Sinclair and one Mag Antenna Split to the 2nd floor. The other 3 Repeaters are done the same way (1) Repeater 1 antenna Split up to the roof and the other Antenna Split to the second floor. They all have there own Antenna's and Duplexers. The other 3 Repeaters that are working great are new repeaters complete with new antenna's and new Cabling both top to botom. The only one that has the problem is one that has been there for many years. Expect for a new antenna SLR301 Sinclair that we provided on the roof at the same location.

Bigred · Post by **Bigred** » Fri Apr 25, 2008 6:49 am

Gotcha. Same antenna scheme times four. So I agree. Wattmeter check at the repeater may not be
telling you the whole story. Can you swap antennas on repeaters to see which way the problem goes?
Also, what freqs are you using for all?

Post by **wavetar** » Fri May 02, 2008 3:47 pm

I agree with bat2way. You need to check the forward/reflected power right at the end of the cable runs, where they connect to the antennas. You may have degraded cabling which won't show much reflected right at the repeater simply because the RF is getting attenuated through the cable & registers almost nil by the time it gets back. Also, 3 watts reflected on an SRL301 with 34 watts is way too high as it is...those antennas generally give 1.5:1 or better matching, which barely registers on a wattmeter, if at all. Cable or connector problem, I'd wager.

Todd

Will · Post by **Will** » Fri May 02, 2008 10:31 pm

Is the antenna you are using on the rooftop?
http://www.sinclairtechnologies.com/cat ... spx?id=408

chartofmaryland · Post by **chartofmaryland** » Wed May 07, 2008 12:38 pm

What kind of line are you using? RG-58? or FSJ1? or LDF5, If its a braid jacketed anything, figure on 7 years of now inefficent cable. If your lines are close do the swap and recheck performance. If you have done a visual and have found nothing major out of place, you may only find a mismatch by means of a line sweep.

CoM