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Best upgrade for two repeater system

Joined
Sep 20, 2008
Messages
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In the 'patch
#21
We're limited to 50' by the tower. We have one of these Telescoping Fiberglass Push-Up Masts - Max-Gain Systems Inc and like it a lot better than our old metal tower that was really really hard to put up and take down by hand with a bunch of volunteers.

We're at 13MHz difference between the two repeaters (I have a third frequency pair assigned that is only 50kHz off another pair that I don't use).

And yes, I've considered a transmitter combiner, but the cost of that + the cost of the amplifiers needed to overcome the 3dB insertion loss are a bit out of my price range.
3dB of insertion loss is SFA, I would guess you are using portables? 4w to the system, and you likely are transmitting 25w+ before system losses? Take the 3dB hit. Transmit power is not everything. Dump the LMR feedline, and get a higher gain antenna to overcome feed line losses.


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Joined
Feb 1, 2010
Messages
548
Location
Tampa, FL
#23
I concur with many of the previous posters: duplexers, deadline, antenna separation. However, I would recommend not more than 3-5dB gain. A simple test to determine relative level of self interference would be to deploy the system and get a user at max range of the system. Then, cut you power to 1/4 of its current level (50w to 12w). If you coverage improves then you are significantly interfering with your self. Keep in mind there is repeater interfering with itself AND repeaters interfering with each other. How far does this trailer travel around the area (city, county, state, region)? And how are the frequencies licensed? TT
 
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Messages
2,581
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New York North Carolina and all points in between
#25
I agree that the losses for a CCR duplexer can be a problem, but I think the problem is more related to the fact of noise. CCR duplxers are reject type, and still allow for all the rest of the frequencies around those being rejected to pass. That's a lot of power going out as noise and if you are running TRBO the noise I believe is even more so. If you are going for good branded new duplexer, expect to pay up to several thousands. I recommend used DB Products, Phelps Dodge/RF, Motorola's newer type T1500 series, Bird, Telewave. Here are a few examples listed below, and some sellers may actually be able to tune to your frequencies, but make sure they are tuned with actual test equipment (sweep generator) not a pair of radios. While I am not against dealing with a local vendor, deal with the service department and not sales, (where did you buy your present equipment?) and if they wont do the work find another vendor, as a lot of current radio shops and especially on line dealers only sell, and are not interested in working on products they didn't sell, and are not plug and play if at all.

Telewave UHF pass-reject duplexer TPRD-4544 {400-470 MHz} | eBay

Decibel Products DB4076W-B UHF Repeater Duplexer, for Commercial or Ham Bands | eBay

SINCLAIR Q301GC UHF 6 CAVITH DUPLEXER 440-470MHZ- 125 DB NOTCH/2.0 DB LOSS | eBay
 
Joined
Feb 1, 2010
Messages
548
Location
Tampa, FL
#26
Yes and it is due to being tired..... I have been on a new refinery radio system cutover that includes several weeks of 16-18hr days. It is a decent size system with 900 radios and 6 RF sites of MOTOTRBO LCP. After cutting over they asked why a (previously unknown to us) 12 channel Telex dispatch system wasn't working. We solved that issue and asked if they had any other equipment that they didn't tell us about. They said no. A few hours ago, their Safety department complained that the new system was making it to the (previously unknown to us) NICE recording system. So it will be another very long day....... TT

Tampa, your keyboard is as bad as mine. I think you mean hardline, not deadline.
 
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#29
I want to mention EMR as a filter / duplexer source, great guys. They let me hang out in the shop and show me tips on tuning duplexers and filters with 2 port VNAs.
Duplexers | EMR Corp

They lend me stuff to use in class and never complain when I take extra Hershey kisses from the candy jar at their booth at trade shows.
They make good kit. They would be my second choice.


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alcahuete

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Jul 24, 2015
Messages
426
Location
Antelope Acres, California
#30
Something is definitely wrong here. If you are getting a mile with an antenna up 50 feet, there are major problems. You could tape a handheld radio to the top of a 50' mast and get way better than that.
 

buddrousa

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Joined
Jan 5, 2003
Messages
5,161
Location
NW Tenn
#33
While reading the OP it looks like this is a portable system that is moved from place to place and if that is the case the cheap duplexers being moved around in a trailer not using the same jumpers and or antennas will not help the OP's system. Many times I have tuned duplexers in the shop moved them to the tower site installed them and touched them up with the service monitor after hooking them up to the antenna.
 
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New York North Carolina and all points in between
#34
Quote"
Many times I have tuned duplexers in the shop moved them to the tower site installed them and touched them up with the service monitor after hooking them up to the antenna.

Not casting dispersions on you tuning capability, but any duplexer that hasn't been subjected to a physical shock should not require a touchup to match to the antenna when moved from shop to site. I found in order to eliminate coax length variations and antenna mismatches you have to tune them up with at least a 20db pad in line, 30db if you monitor/sweep generator can put out the signal.

The OP's number 1 problem is the CCR duplexer.
 

buddrousa

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NW Tenn
#35
True but ruff riding trailers or in the bed of a pickup truck is enough vibration or shock. On top of the antenna system line and antenna may noy be the same load as a dummy load. Antenna connectors on all items exposed to air (may lead to corroded connectors.
 
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#37
I think most of "whats wrong" has been listed, CCR duplexer, poor coax, and low gain antenna.
Plus both repeaters are likely blasting out at Max power.

If this was my set up this is what I would likely do

-Tx combine both repeaters using the pairs that are 50KHz apart (ASSuming they are 5MHz pairs).

-Rx combine the receivers.

-use a good 6 cavity BpBr duplexer(Sinclair ResLoc or the one listed further up this thread) tunes to pass both pairs.

-knock down the transmit power to have 5-10w exiting the duplexer.

-use a single 3-6dB gain antenna fed with 1/2” hard line.

He should be able to easily get 5 to 10km of decent coverage with an antenna at 50’ depending on terrain.



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#38
Yes, it is mostly serving portables, so I guess I can see your point that loosing 25W and still having ~25W of output power isn't the end of the world in that case.

Assuming I went that route, we're looking at:
1 multicoupler for the RX antenna (something like a Stridsberg MCA204M I guess?)
2 filters to prevent in-band feeding back to the receivers? Or would the ~55dB from 10 feet of vertical separation between rx and tx antennas be enough there?
1 TX combiner (something like a Sinclair TJ3 series?)

So somewhere in the $7000 range? Or am I mis-specing something?
If you are serving portable radios, you should only really need 5-10w at the output of your duplexer/combining system. Use low loss feedline and make up losses at the antenna(3-6dB gain)

Receiver combiners(Sinclair at least) usually have a low gain preamp after the preselected to zero out the combiner losses.

Having 50w transmitters is going to cause you all kinds of grief(as you are seeing with your serious range issues) even with 3-6dB of loss in a transmit combining system will still leave you with 25-12.5w headed up the feedline, more than enough RF for a system primarily using portables.


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#40
There are a lot of good used repeater parts available in my town and I got a Telewave 2-ch UHF hybrid combiner with isolators for about $150 and band pass cavities run about $75 each used in perfect condition. I also got a 4 cavity band pass preselector for about $100 and an Angle Linear UHF preamp for a fair price. Those parts would build what you need to have a filtered and amplified master receive antenna with about a 2MHz wide receive window and combine two transmitters cleanly. This would work best using your two frequencies that are only 50KHz apart.

Your vertical antenna separation will add a little isolation but maybe only in the 10dB range or a little more. You want the TX/RX filtering to give you a big isolation number, maybe 90dB would be a goal, then a little vertical antenna separation will add to that.

Using your 13MHz separated frequencies you would be better off using good pass/reject type duplexers with isolators on the transmitters and a separate antenna for each repeater. With 13Mhz separation you probably have a transmitter and receiver freq that are about 8MHz apart without the ideal transmitter notching for that split.
In this situation I would avoid separate TX and Rx antennas entirely.

Use the two channels 50KHz apart.

I had the opportunity to look at a 4 channel NXDN trunk system. It uses a single antenna, with a 6 cavity ResLoc. All 4 transmitters we’re combined to a single feedline, to the low pass side of the duplexer, all the receivers were combined with a receive multicoupler fed from the High pass side of the duplexer.

Crecend amplifiers, Sinclair transmit combiner, Sinclair dual circulators , Sinclair receive multicoupler, Sinclair Duplexer.


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