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TKR-750 Repeter setup...

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johndjmix

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Hey guys, im setting up a repeater here on a 40' tower we have. Frequency coordination is done and just waiting on FCC status to get out of pending. Picked up a tkr-750 v2 for $400 locally. Going to use a duplexer from china that has a good track record with others ive read about (same one that the msr2000 uses from what i understand). Running 75' of LMR-400 up the tower to a mast on the top section with a TRAM 1491 antenna on top of it.

Questions,

The TKR-750 can put out 50 watts at 50% duty cycle....a little confused by this. What time periods are we talking here? I can picture in a 12 hour period to have way less than 50% use, but during a event we may be using the repeater on a conversation for 30 minutes or so back and forth between mobile users hitting into it. Will the tkr-750 handle this safely? What happens if you exceed the "limit"?

If I want to run a amp to up the unit to 100 watts (and keep the tkr in the low 25-watt mode for a 100% duty cycle), where does that amp go...in line on the antenna feed or between the tkr transmit bnc and the duplexer? I would assume the later, but never ran a amp before so new to that!

Coming from the ham world so a little new to this, never setup a repeater before...
 
mikewazowski

mikewazowski

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First of all, I'm pretty sure the MSR2000 duplexor was a separate order itm and most likely it didn't come from China. I'm using a Sinclair unit on my 125w MSR2000 that was installed about 15 years ago.

A 50% duty cycle means that for your 30 minute conversation, you must have 30 minutes of non-transmitting time mixed in. If you continuously transmit for 30 minutes, you'll probably see reduced power and/or damaged output transistors.

Keep in mind that a 100w amplifier will probably overwhelm your Chinese made duplexor and your receive capabilities will suffer.
 
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johndjmix

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Mikeoxlong: actually only going to use the China duplexer if I go 50 watts, if I go more it would Definatly not do the job.

So that said, can anyone recommend a good amp/duplexer on the cheap, that I could possibly pickup used off ebay?

Thanks in advance.

--john
 
ramal121

ramal121

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There is no time limit stated in any of the specs and I can see where the confusion comes from. Does 50% duty cycle mean you can go key down for a hour and then let it rest for another hour? Hardly the case.

At 50 watts, the heat created by the transmit PA exceeds the heatsinks ability to dissipate it all safely. At what point does temperature rise to the point to where damage may occur? I don't know but after several minutes of transmit the thing gets a little too warm for my taste and I wouldn't exceed that. I guess if you could monitor the heatsink temperature at 25 watts for a while to see where it lands and then switch to 50 watts and time it to see how long it takes to reach the same would give you a benchmark.

If you need high power and a 100% duty cycle then yes an outboard PA rated for that is the only way to go. I prefer to get an appropriate PA and match it with a TKR-751 running say 3 to 5 watts. That way there is little chance of heat issues in the repeater.

For full duplex operations, yes the only place to insert a PA is between the repeater and the duplexer.
 
jeatock

jeatock

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1. Duty Cycle: The standard is pretty much per each minute (or two). I get nervous when public safety 100% duty cycle repeaters are up for fifteen minutes at a time. Amateurs may keep the machine in constant TX for hours. Ramal has it right- check the cooling fans for good flow, watch the temps at half power and adjust the output according. And yes, an external PA will give you 100% TX time.

2. If you give me a $2,000 budget I'm going to spend $2,000 on the antenna, coax and duplexer and whatever is left the radio. As I am fond of saying, a $50 radio on a $1,000 antenna will out perform a $5,000 radio on a coat hanger every time.

3. All duplexers work by throwing part of the baby out with the dirty bathwater. The higher quality duplexer you have the less baby goes down the drain. Also check the specs of the duplexer- they may say 50 watts, but only with a 5 MHz or more split. Two meter is normally a 600 KHz split and less expensive duplexers will smoke with anything more than a few watts input. There is a reason commercial or quality-brand duplexers cost more: they're worth it.

4. The TRAM 1491 is pretty much a bargain 6db antenna - but not bad for the price. If you can get 25 watts to the antenna and the antenna is tuned to your transmit frequency your ERP will be about 4x greater, or 100 watts. If you jump up to a 9db, like a DB-228, 25 input will give you a 200 watt ERP, and also deliver twice the uplink signal to the receiver.

5. LMR400 is for jumpers. At 1.5db loss per 100' a lot of the uplink signal will disappear before it even gets to the duplexer. Use real coax and ground it properly for both lightning and static bleed-off. LDF4 if you are dead broke. LDF4.5 is the minimum for VHF, LDF5 for UHF.
 
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BirkenVogt

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There is a rumor that has been prevalent for many years that LMR400 used in a duplex application can cause desense/noise. I don't believe it is as bad as "they" say but the possibility is there.
 
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nd5y

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It's not just LMR400. Any coax with dissimilar metal shielding (foil and braid of different metals) can make duplex noise.
 
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johndjmix

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Decided to give the LMR-400 a shot, since i had it here allready, and since my frequency's were almost 7mhz apart.

Seems to work extremely well. Drove about 20 miles away, hit into the repeater crystal clear. We will see if the LMR causes an eventual issue.

I do want to get a 50 or 100 watt amp so i dont have any duty cycle worries, but really dont want to spend more than a few hundred on it. Any recommendations?

Thanks again guys...

--John
 
n5ims

n5ims

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johndjmix said:
Decided to give the LMR-400 a shot, since i had it here allready, and since my frequency's were almost 7mhz apart.

Seems to work extremely well. Drove about 20 miles away, hit into the repeater crystal clear. We will see if the LMR causes an eventual issue.

I do want to get a 50 or 100 watt amp so i dont have any duty cycle worries, but really dont want to spend more than a few hundred on it. Any recommendations?

Thanks again guys...

--John
Click to expand...

Give it some time. Once those dissimilar metals do their dirty work, you'll have various other signals in your area mixing with yours and start having random noise and other intermod effects on your signals. Times Microwave (the maker of the real LMR-400) has a line of "Low-PIM" cable to address the passive intermodulation issues of their regular LMR line, so it isn't just a few of us that understand this issue.
 
jsikora

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I agree. I tried the LMR400 for a VHF repeater I had. Only had 18' from the bulkhead to the antenna (4000' hill helps) and the first month was fine. As soon as winter set in I had all sorts of issues. Noticable on portables first then by spring a mobile had issues. Swapped to a chunk of 1/2 LDF and not only increased portable ranger but has been like this for 3 years with no issues.
 
ramal121

ramal121

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Fresh LMR will work great, but as soon as a little moisture works its way up the braid the frizzle will raise its ugly head. You can seal the connections all you want but coax will "breathe" as it heats and cools and suck in surrounding air. Now if you want to go to the trouble of pressurizing it with nitrogen....

As a side note, the last roll of LMR-400 we ordered came with the braid flooded with icky-pick. Don't know if it was ordered wrong, but I'm wondering if the gack would hold off the interaction between the braid and foil???
 
ramal121

ramal121

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FKimble said:
Ramal, could you explain icky-pick and gack? Tks
Click to expand...

Well gack is my own personal adjective. From the wiki:

Icky-pick or icky-pic is a name for a gelatinous substance or filler contained within outdoor-rated communications cables, including both twisted pair copper cabling and fiber optic cabling.

PIC is the abbreviation for Plastic Insulated Cable. The cable is filled with an icky substance. The filled cable itself, therefore, is called an "Icky PIC".

Icky-pick has two primary functions:

Deter animals from biting and damaging the cable due to the smell and taste of the gel
Seal any nick or gash in the outer jacket if they do bite it, preventing water from entering the cable and damaging it by corrosion and freeze expansion
The actual icky-pick compound is a very thick petroleum-based substance with very high flammability, and consequently is only rated for outdoor use, frequently direct-buried in the ground. An outdoor cable spliced onto an indoor terminal block is prone to leak the gelatin which is a fire hazard, hence in many situations the icky-pic cable is spliced (usually outside the building) to a short run of normal cable which is run in a protective conduit into the building and then terminated. The thick gelatin stains clothing and hands and is very difficult to remove.

When fiber-optic cables are to be spliced, the gelatin must be removed with solvents and swabs to prevent fouling of the splice. Paint thinner or charcoal starter is a frequently used and commonly available remover and clean-up agent.
 
J

johndjmix

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Will change cable comes summer if the problems start! Too cold to clib the tower now.

Hey, any way to make my TKR-750 make the cool tail "Courtsey" beep 2-tone? I have it doing the normal beep, but really want the cool dual tone beep i hear when using the ham repeaters. Is there a cheap board i can pick up that does this?

--John
 
cmdrwill

cmdrwill

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johndjmix,

How do you have the 'TKR-750' interfaced? Where/what makes your 'normal beep'.

50% duty cycle in Land Mobile Radio is one minute onTX and one minute OFF.

These mobile radios made into a repeater do not have very good heat transfer from the final PA.
I have seen the stock heatsink milled off and a big copper slab added to help transfer the heat away from the final stage.

The /\/\ Quantar has a copper heat spreader between the final transistors and the heatsink.

An idea, Akasa 80mm x 25mm Auto Thermal Fans with the built in temp sense/speed control work well to help cool the TKR heatsink. I have two of these on my GM300 repeater.

http://www.frozencpu.com/products/1..._26C_-_45C_-_AK-181BKT-C.html?tl=c15s1167b181
 
J

johndjmix

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cmdrwill: Im using the "Courtesy tone" built into the TKR-750. Thats what makes the beep, you program it in the kenwood software. In a way its cool that its not the standard dual tone beep, since i can easily know im on our company repeater and not the ham repeater if i key up the mic and not realize im on the wrong one...

copy on the fans, will be adding them soon

--John
 
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