Returned Power / SWR

[krazybob]

Recently while we had our repeater off-site for lengthy work our site vendor pulled our hard line for routing in cable trays on the tower. Previously our SWR was nearly flat as viewed on a Bird 43. Now we have 5 watts returning of 100 watts. 5%. Is this really significant?

[nukedude]

That's about 1.6:1, or about 5% loss of that 100 watts. So it isn't too bad, depending one cable length, connectors/adapters and all. With that Bird 43 you may be using more adapters than will be in the hardline normally, so you may actually be better than that anyway. Not really significant.

Before the hard line was placed into cable trays, it may not have had the bends in it, which may have helped your SWR be "nearly flat". It would be interesting to know what that number was before.

[Bill_G]

He may have done you a favor. Sounds like you are getting a truer reading. It depends on how long the total run is, and how many jumpers are in place. 5w over 100w is usable. That's a return loss of 13db. I would prefer 15db or greater (2w reflected). Move your wattmeter down line to the next connector (if possible), and measure again. This is where an Anritsu really pays off.

[Will]

I would be inspecting the cable for kinks and other deformations.

[krazybob]

Thank you all for your replies. I suspect we might have water in the hardline. When first installed we sealed it well with sealing tape/putty. But this morning receive was terrible. Nothing but popcorn. I'm grasping at straws.

[desperado]

First question I would have is how long is the line and second what kind of line. Here's the thing with just going by what the watt meter reads at the bottom of the line. Each connector junction has a .5 DB loss. So figuring there is a polyphaser or other lightning suppressor in the line you have 2 db of loss before cable loss is calculated. Now, if the line is 250 foot and 1/2 inch hardline, the line is just over 1 db of loss. So that's 3 db total system loss. Bear in mind that the antenna gain has nothing to do with this, we need to know loss so we can figure SWR. If there is a missmatch at the top of the line (10 watts reflect figuring the 3 db of calculated loss) and the fact that you are loosing 50% of the signal going up as well (3 db of loss applied to a 100 watt signal is 50 watts). You actually could have a serious issue, because you are getting 10 watts reflect on a 50 watt signal.

[krazybob]

Thank you for an excellent answer.

We are using new Andrews LDF4-50 @ 100 feet. Coming out of our Sinclair duplexer we have a measured loss of 1.5dB. We are using a Polyphaser and new POS connectors. POS should stand for something else. I really prefer the solder type N connectors but Tessco no longer sells them. A source anyone? I don't know what we did differently. I tested using a 100 watt slug reversed and got 5 watts reflected. That's 5% and livable. A couple of days later my associate was at the site and tested the line and got 1 watt reflected. That's 1%. He used a 250 watt slug reversed.

The only variable is that our site vendor pulled all of the lines on the tower without any notice to us in advance. The repeater was at our backup site (my home an an 85 foot tower and a dDB224 fed with 1/2" as well. My home is at 6,300 feet ). 0 reflected with the DB224. Once we had done a major tune-up after parts replacement we returned it to the commercial site right around the corner from my home. How cool is that? Coffee. Toilet... We questioned whether pr not the vendor removed our hard line from the antenna when he installed new cable stays. We got no reply. We had some wind and precipitation but not poor performance. Our receive with the MSF 5000 remained rock solid.

So why such a difference in readings? Could it be that the accuracy of the slug is -/- 5%?

[desperado]

Ok, Bird meters are great, if you know how to use them and understand their limitations.
First limitation. A Bird 43 is either 5 or 10% can't remember which, of FULL SCALE. S a 100 watt slug at 100 watts can be 90, 110 or anything in between.
Second, Where are you placing the meter? It's either between the duplexer and transmitter (probably since you are seeing 100 watts, and between the duplexer and the antenna system (proper location) but then you will NOT see 100 watts unless you are putting out able 120 from the radio. Now if you are reading it between the radio and the duplexer, the reading is the reflected power from the duplexer back to the radio and doesn't give an accurate reading of the antenna at all. If you are reading it there, move it to between the antenna and the duplexer. Now, that being said. A 5 watt reading on a 100 watt slug is meaningless. Get a 5 watt slug and make the reading with that. Using a bigger slug screws up the reading at that low level. As far as readings, so you are aware. I have a DB-222 on 300 foot of line with a 500 watt transmitter driving it. I get 2 watts reflected from the antenna with 500 watts going up. The total system loss is 3 db. The antenna gain is 3 db so the antenna system has unity gain from the TX. Since it's licensed for 500 ERP (effective radiated power) it's all legit. If I was to have used lower loss cable, I would have needed to decrease power to stay under the license limit. That part was just informational, back to your situation. You still have 3 db of system loss with LDF4-50 at 100 foot line length with the connecters and polyphaser. So your meter reading is still half what it is at the antenna feed point. Now, you never commented about the antenna from what I saw. If it's a DB-22X then it's got a flying lead with an N-male or possibly a PL-259 on the flying lead input. If the tower company pulled all the line loose and let the 100 foot of cable hang from the flying lead, there is a real good chance they broke it. It's a common issue with those antenna. I would be finding a TDR or a good professional antenna system sweeping unit and sweeping the antenna line and antenna to see if there are issues. Beyond that, yank the crap down and replace it all. I know that it's a pain, but I personally pay 2000 per climb to the tower crew. It's cheaper to buy new, have them install it than have them climb up, find it broke, order a replacement whatever, and have them climb again another day.

[tvsjr]

You need to find someone with a SiteMaster, NetTek, or equivalent... and they need to know how to use it properly. Have them come sweep the antenna. You can also do this old-school with a dual directional coupler and a network analyzer. Otherwise, you're just guessing.

[raneeya]

Are the subscriber units a commercial unit like Kenwood, Motorola, etc. or are they ham rigs? I have noticed also on some other repeaters when you get the squelch set tight that it also causes squelch tails on some units versus when it is set a little loose it doesn't. If the subscribers are ham radios they drop the PL when the carrier drops. They do not turn the PL off before the carrier drop unlike commercial radios. If they are ham rigs, or if the loosening of the squelch doesn't work an audio delay board might help. I have heard those can help eliminate squelch tails but I haven't tried one myself.