SGQ-450D Duplexer - Tune-up and Review

[LeoG]

Wasn't really talking about testing, but real world conditions.  The conditions between my house and repeater are sort of at the fringe even though it's only 1.9 miles as way of the crow.  And while walking around my neighborhood I can usually reach the repeater and transmit audio through my 5 watt HT.  There are times where I can hit the repeater and get nothing, just a blank receive from the repeater for the whole transmission and then the courtesy tone.  I  have a courtesy tone on my repeater so I know when I hit it with absolute certainty.  But I've never heard what I would consider an oscillation.  This theoretical oscillation would only happen as long as the HT is keyed up.

[marcspaz]

Maybe the word oscillation is whats got me. Oscillation is usually internal to the repeater due to a failure. Or if the separation and isolation are not good, you can end up with a transmit loop if the input and output tone are the same. You won't have any oscillation.

If you have a short tail, the repeater transmit may cut in and out as the receiver cuts in and out. I usually set mine to 2.5 seconds. You will hear the remote station drop out and come back in, but the transmit stays open for 2.5 seconds after the last drop.

[LeoG]

Yep, mine to.  But lots of sites run quick.  But that does answer the question about if there is a delay.  Yes, transmit stays on for predetermined time.  I guess my brain was off when I was thinking about that.  Not the first time, and I"m sure not the last.

[LeoG]

Looks like the duplexer is on the way and should get here late Wed if things go well.

[LeoG]

Did my walk around the block with to have a record of the 2nd original duplexer.  Since I do these things late at night I have a digital recorder I use to "listen" to me.  I do the test of the repeater and then switch to talk around to let me know where I am in case the repeater test doesn't go through.  There are a few spots on my walk that are iffy.  Like I've mentioned in other threads I have 1.6KM of dense forest in the way of my signal, 70' trees with my antenna at 40'.

After the new single channel tuned duplexer is installed I'll try to do the same test in the same spots.

[WRYZ926]

Trees are one of your worst enemy when it comes to UHF, especially cedar and pine trees. And it's not always possible to get an antenna above the local trees either. 

We look forward to updates.

[LeoG]

Of that I am very aware.  These are mostly leaf trees so there's that....

Always had issues from the house to the shop which holds the repeater.  50w vs 25w.  I could always come in mostly clear to the house, but from the house it was hit or miss.  Then I got a 50w radio for the house and the problem is mostly gone, certainly not R9 reception but easy to talk and understand.  Needed the extra wattage to punch through the leaves it seems.  On top of that what helped later on was swapping out to the Comet 712EFC.  Eventually the repeater will have that same antenna and upgrade from the Retevis 7.2dBi.

So sometimes a little more wattage works.  And since the 1st wideband duplexer was swapped out for the 2nd wideband duplexer I've been able to hit the repeater mostly successful with a 5w HT.  R7 at best, no communication at worst.

 

Duplexer is coming in today

[LeoG]

OK Boyz and Girlz, here we go.

I opened up the Btech RPT50 repeater to remove the original wideband duplexer

First thing I did was check the output wattage from the transmitter.  The power supply was set at 13.8 volts and it was putting out 71 watts into the duplexer.  Had 42 watts out of the duplexer.  And not the best SWR on my 50 ohm dummy load.  Right at the edge of spec.

I turned the voltage down to about 11.5 volts and it showed about 65 watts out.  Probably the lowest I can get it.

Then I swapped the original wideband duplexer for the one that Marc so graciously tune to a single frequency for me (600).  I relabeled it so some future person doesn't think it's wideband.  I should probably strip the other frequencies out of the channel selection also.

And I tested it and got about 48 watts from it.  I said what the heck and boosted the voltage a bit and got it to put out 50 watts.

I haven't put it back into service yet, soon.  And testing won't be done until it cools off from the 98ºF it currently is.  Says it's going to be low 70s tonight.  Probably be to excited to test things at midnight, so likely around 10 or so I walk my route.  Of course I'll key it up on the way home, at home on the base and try an HT from inside the air conditioned house.  LOL

Most of the duplexers I looked at said "40-80 watts (50 watts)" so hopefully I don't melt this one.  The replacement was accepting the 71 watts without blinking and the original had the power supply set for 12.5 volts which is about 67 watts into the duplexer.

 

 

[marcspaz]

I'm excited to hear how it goes. An additional 8w out was unexpected, but a plus, for sure.

[LeoG]

Well I was wondering about that but never asked the question.  Since the wideband was tuned flat(ish) I was wondering if it might restrict the power.  Just another compromise when doing this type of system I guess.  Was pretty shocked to see 70 watts out of the transmitter.  Thought maybe 60 at the most.  Hopefully the receive will give me the same boost as the transmit.

[marcspaz]

Its very possible that the wider configuration of the original notch was reducing power output more than the rated <‐1dB. 70w minus 1dB is about 55w.  -2dB would be 44w. Figure the meter probably isn't perfectly calibrated, you probably had -2dB of insertion loss with the wider notch, and -1dB with the more narrow notch. 

 

The receive side was/is probably the same. However, -2dB vs -1dB is not really noticeable to the user, even though its measurable.  It sounds like the second duplexer they sent you was tuned much, much better that the one that came inside the repeater. 

[LeoG]

Oh it absolutely was.  Noticeably so.  I wasn't able to contact the repeater from my area with the original duplexer and when they sent me the newer one I was able to connect somewhat reliably.  Still pretty iffy and right on the fringe.  But communication was acceptable.

[LeoG]

6 hours ago, marcspaz said:

I'm excited to hear how it goes. An additional 8w out was unexpected, but a plus, for sure.

Well the news is anything but exciting.  Reception is markedly worse.  I only had one spot in my loop that I was able to communicate through the repeater.  The rest of them either kerchunked it or didn't register.  Very disheartening.  I thought this would be much better than the other duplexer and right now it's looking like it is reacting like it was when I first got the repeater.  I can contact it with my 50 watt.  And I have a guy 2 towns up that I was communicating with before with good clarity, R7 and now he's barely an R5.  Lots of background noise and very low modulation.  Worked but you had to concentrate to hear what he was saying and even then it was hard.  Since tomorrow is a bust for things to do at work I'm going to swap out the duplexer tonight and make the rounds again.  It's always possible it's atmospheric and not the single channel duplexer.  Or maybe it just can't handle the 65 watts in like the 2nd one they sent me.  Either way it's getting swapped out for now.

Thank you very much for the effort Marc

[LeoG]

Swapped the wideband duplexer back in and did my test loop.  Pretty much back to normal.  I think yesterdays test was slightly better but not by much.  Had trouble in my usual spots.  But I had trouble in a reliable spot too.  Looks like for now this duplexer is staying put.