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.

[marcspaz]

Hmmm...  I can't help but wonder if it is an over-power issue with the duplexer.  It's rated for 50w, I tested with about 45w after tuning it, and you're using 70w, which exceeds it's power rating by 30%.  Exceeding the rating can cause overheating that can warp/melt internal parts and even cause internal arcing.  That will definitely cause detuning and poor isolation, 

 

If I was a gambling man, I would say that it was off frequency when I got it, because parts were partially damaged inside (plating damaged, parts warped).  I was keeping the power within spec, so I was able to tune and use it with the parts warped to the position that they were in.  Now that it's being over-driven by 30% again, you are likely warping parts further, possibly causing plating to peel with excessive heat, which is causing arcing and detuning the duplexer.

[Lscott]

31 minutes ago, marcspaz said:

Hmmm...  I can't help but wonder if it is an over-power issue with the duplexer.  It's rated for 50w, I tested with about 45w after tuning it, and you're using 70w, which exceeds it's power rating by 30%.  Exceeding the rating can cause overheating that can warp/melt internal parts and even cause internal arcing.  That will definitely cause detuning and poor isolation, 

 

If I was a gambling man, I would say that it was off frequency when I got it, because parts were partially damaged inside (platting damaged, parts warped).  I was keeping the power within spec, so I was able to tune and use it with the parts warped to the position that they were in.  Now that it's being over-driven by 30% again, you are likely warping parts further, possibly causing plating to peel with excessive heat, which is causing arcing and detuning the duplexer.

Everyone should review this old thread.

 

[LeoG]

This was the duplexer that came with the repeater originally.  It was suppose to work with the transmitter power they had but obviously they were mistaken because they had to replace them.  The duplexer they replaced it with seems to have the same power rating but has been working well since I replaced it.  Most of the ratings I've seen on duplexers have a range rating and then a listed rating like this 40w-80w (50w).

Before I toss it I'm going to pull it apart to see if there's any scorching of the internals.  I don't expect anything to be wrong on the high (receive) side but on the low side there might be issues.

[marcspaz]

56 minutes ago, Lscott said:

Everyone should review this old thread.

 

 

 

Whoa... that is the same issue Leo is having and on the same duplexer....  I may need to withdraw my endorsement.  

[SteveShannon]

The excessive RF power will take a toll on the circuitry of the transmitter as well as being non-compliant with GMRS regulations.  I would suggest adjusting the RF output down to 50 watts at the transmitter output, before the input to the low side of the duplexer.  Many times repeaters are run at reduced power levels to prevent early failure.

[LeoG]

So far my wideband duplexer is working fine.  Maybe the out of tune lets you throw more power at it.  IDK. 

Looks like Btech will let me purchase another one of the newer Duplexers.  It's the one I'm currently running and has been able to take the 70 watts in so far for about a year with no degradation.

Not sure if they'll send it tuned to my spec or just send me another wideband.  In which case I'll get it tuned.  I have to go to their link they made specifically for me because the duplexers aren't in their catalog to sell.

[LeoG]

8 minutes ago, SteveShannon said:

The excessive RF power will take a toll on the circuitry of the transmitter as well as being non-compliant with GMRS regulations.  I would suggest adjusting the RF output down to 50 watts at the transmitter output, before the input to the low side of the duplexer.  Many times repeaters are run at reduced power levels to prevent early failure.

This is compliant with part 95.  Because it is sold as an all in one unit the output at the antenna connector is limited to 50 watts max.  It has nothing to do with the internal components.  But if you had this same transmitter and hooked it up to an external duplexer it would be against regulation.  It's just like buying a 50 watt mobile radio.  The output of the radio is 50 watts (or less) at the antenna output which falls within part 95.

The duplexer needs to be inside the system and specifically designed to be an all in one system to comply.

I think it's a 65 watt transmitter.  I can't get it to go below 60 watts with the voltage on the power supply dialed down to 11.5 volts and I think it went up to about 71 when it was dialed up to 13.8v.  I've never had it higher than that.

This is what I bought, not something I made.

[SteveShannon]

3 minutes ago, LeoG said:

This is compliant with part 95.  Because it is sold as an all in one unit the output at the antenna connector is limited to 50 watts max.  It has nothing to do with the internal components.  But if you had this same transmitter and hooked it up to an external duplexer it would be against regulation.  It's just like buying a 50 watt mobile radio.  The output of the radio is 50 watts (or less) at the antenna output which falls within part 95.

The duplexer needs to be inside the system and specifically designed to be an all in one system to comply.

I’m not sure why you think regulations are different if the transmitter and duplexer are packed into an enclosure.  The regulations very clearly state that the transmitter output power must be limited to 50 watts, not that the all-in-one box output power must be limited to 50 watts. You obviously understand the difference because you clearly distinguished between the transmitter output power and the duplexer output in your earlier post.

But that was really the least of my concerns.  The fact is that the transmitter is putting out 71 watts, which is harder on the circuits.  That’s 40% higher power than designed. 

[marcspaz]

14 minutes ago, SteveShannon said:

I’m not sure why you think regulations are different if the transmitter and duplexer are packed into an enclosure.  The regulations very clearly state that the transmitter output power must be limited to 50 watts, not that the all-in-one box output power must be limited to 50 watts. You obviously understand the difference because you clearly distinguished between the transmitter output power and the duplexer output in your earlier post.

But that was really the least of my concerns.  The fact is that the transmitter is putting out 71 watts, which is harder on the circuits.  That’s 40% higher power than designed. 

 

Steve, the FCC gave the repeater type certification based on the output of the duplexer because the duplexer is inside the chassis and considered and internal part of the radio... part of the design.

 

https://fcc.report/FCC-ID/2AGNDGMRSRPT50

 

I am trying to find the official FCC cert, but that is the reference I found so far.

[marcspaz]

I can find this stuff... but nothing I can open.  Not sure where the actual letter and artifacts are.

 

https://apps.fcc.gov/oetcf/eas/reports/ViewExhibitReport.cfm?mode=Sum&calledFromFrame=N&RequestTimeout=500&application_id=MjZkkijyA8IfBeMCZsYVMw%3D%3D&fcc_id=2AGNDGMRSRPT50

[SteveShannon]

Thanks, Marc. The test report (not performed by the FCC) doesn’t even mention the existence of a duplexer.  Although the test setup photos do show that the repeater output is what’s being tested, I wonder if the FCC even realized that there’s an internal duplexer.