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Maratrac continuous duty transmit power?

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Xnke
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Maratrac continuous duty transmit power?

Postby Xnke » Thu Aug 10, 2017 11:55 pm

So now that I have successfully managed to move one of the Maxtrac radios to the 6 meter amateur band (which is working beautifully, by the way) I got a low band Maratrac given to me from a local guy, who was going to build a repeater out of it and ran into the desense issue. He's given up on it as he never did read up on using a seperate reciever to get around that problem.

My question-what is a T81XTA7TA7BK (Maratrac, 110W, 42-50Mhz) actually going to be capable of in repeater duty? 50W, with a fan on it? I have read that the heatsink assembly is the same as a Mitrek, and I see Mitrek radios being used as the transmit side of repeaters occasionally.

Now, I have no knowledge of repeater ownership/coordination, but our local repeater guy has already offered space on his tower and in his shack if I were to get frequencies assigned and build/maintain the hardware. Not sure I really wanna get into that but I might as well find out.

Also, I assume I don't really *need* the control head to run the transmitter, assuming that the radio is programmed with 1 channel, it should always come up in that channel mode on a power cycle, correct?

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Bill_G
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Re: Maratrac continuous duty transmit power?

Postby Bill_G » Fri Aug 11, 2017 3:56 am

Any radio can be used in a repeater, but xmit duty cycle is always a consideration. The Maratrac is a Maxtrac mobile with a high power transmitter section bolted on, and a remote head. It is definitely NOT continuous duty. Don't expect more than fifty percent duty cycle. I'd put a strict TOT on it with a rekey delay, and a temp controlled fan.

I don't know if it will run without the head. You'll just have to find out. I imagine you could McGuiver it to run without a head. I'd get the service manual first.

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W3AXL
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Re: Maratrac continuous duty transmit power?

Postby W3AXL » Fri Aug 11, 2017 8:46 am

Maratracs will run headless just fine. We have two currently on the bench for a new 6M machine. We dialed power back to 50W and have two high-flow fans going across the radiator fins and haven't run in to issues with overheating. We're planning on adding a temp probe as well but for now it seems to be working fine.

I'd give you more info, but the project has unfortunately been on hold for almost a year now and I can't remember all the specifics. You can power up the radios by jumpering a few pins on the front connector, and I had custom PCBs made up for interfacing with the internal accessory connector for audio and PTT.

Now with you bringing this up I'm thinking I might want to get the project back off the ground. We had it working great for a small amount of time before something died on us, and that was the point at which everyone got busy with other things and the system was relegated to a corner of the shack.

If you've got any other questions, post them and I can try and answer as best as I can remember.

Xnke
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Re: Maratrac continuous duty transmit power?

Postby Xnke » Fri Aug 11, 2017 10:16 am

At this point, I'm just researching...considering welding more/bigger fins onto the stock heatsink assembly and adding fan-tabs, to bolt fans to. Wouldn't be hard to do at all, once the PA board is removed.

At any rate, if the local club decides to go ahead with this 6M repeater project I'll gladly build them the hardware but I don't have room for the thing at my house. (Nor a good tower site for a repeater...vandalism would be rampant!)

The configuration would be a Maxtrac reciever and the Maratrac (probably with bigger fins and fans) as a 50W transmitter. Still have to come up with a repeater controller and tower site, but I figure the club will have to work those things out.

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Re: Maratrac continuous duty transmit power?

Postby Satelite » Sat Aug 12, 2017 2:34 pm

Hello:
Just tossing this suggestion in for thoughts.
Think I recall this has maybe already been done in the past and even think I read about it here on batlabs years back during monty siscos time period.
Rest In Peace Monty.
But I recall the heat sink on maxtracs being too small and others wanting more fin cooling area.
So a Maxtrac 800 MHz long pa heat sink was added to a maxtrac VHF unit with the vhf pa components to get the larger cooling fins.
The lo bad maxtrac uses the larger pa fin assy just like the 800 MHz does soooo ????
Satelite

Xnke
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Re: Maratrac continuous duty transmit power?

Postby Xnke » Sat Aug 12, 2017 3:30 pm

The Maratrac radios use a Mitrek-sized heatsink, Satelite. From what I can read, using the 110W heatsink with the power down to about 50W, and running two fans on the heatsink, seems to get the allowable duty cycle high enough to work in repeater service-so I am thinking I'll strip the PA board assembly out of the heatsink to prevent damage-then weld on bigger fins, and then run fans. This should allow a more comfortable margin at 50W transmit power.

Like I said, until the club comes up with a tower and a shack to put the repeater in, it'll just sit and wait till then.

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kcbooboo
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Re: Maratrac continuous duty transmit power?

Postby kcbooboo » Sun Aug 13, 2017 4:55 am

The case is cast metal of some kind, probably aluminum or an alloy. Welding could be difficult. Easier to mill it flat and bolt on a decent-sized finned heat sink.

Interfacing the radio as a repeater transmitter is quite easy. I bet there's at least one article on the web that deals with it.

Bob M.

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Re: Maratrac continuous duty transmit power?

Postby Jim202 » Sun Aug 13, 2017 6:12 am

First of all let me state that I am not trying to hijack the thread here, but point out an important fact of life today with trying to put a 6 meter repeater on the air.

The heat sink issue is a major factor in getting a repeater package together. But an even more important issue is what the site your looking to use has to offer for 6 meter use. In this I am pointing out that over the years, many 6 meter repeaters have had to cease operation due to the noise floor at that site being so high. With the proliferation of computers, routers, hubs and Ethernet use, the usable noise floor has become so high, that many sites are not a good location any more. The 6 meter receivers are so deaf due to the high noise floor, they can't hear any usable signal.

So before you go to all the effort of building a repeater and installing it with the needed antenna system, it might be a good time to put a receiver at the site and see if it can hear anything usable on 6 meters.

I have been a long time supporter of 6 meters and the activity of 6 meter FM has been declining over the years at a rapid rate. I know of many of the active 6 meter repeaters that use to have good coverage and activity are no longer there. When I ask why, the answers are always the same. The noise at the tower site killed the repeater from hearing anything but a 100 watt signal from close by.

This is going on all across the country. Between leakage from cable TV systems, computers and the likes, 6 meters is becoming a dead FM segment. So do yourself a good move and check out the prospective tower site first. It might just save you from many long , frustrating hours of effort that won't pay off trying to reduce the noise floor at that site.


Jim

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Bill_G
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Re: Maratrac continuous duty transmit power?

Postby Bill_G » Sun Aug 13, 2017 7:15 am

+1
Unfortunately true in other bands as well.

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Re: Maratrac continuous duty transmit power?

Postby motorola_otaku » Thu Aug 17, 2017 8:18 am

I've built 2 and 6 meter repeaters using Maratracs as the TXers. I strongly recommend mounting them with the fins pointed upward, and you will definitely need hi-flow fans blowing across them continuously if the site/shelter doesn't have AC.

The one I built for 2 meters ran at 90W with no fans in a climate-controlled shelter, on a long-winded repeater pair. I mounted the radio "upside down" as described in a repurposed Micor cabinet and it ran for a year or two with no issues until we upgraded to a MSF.
When exposed to Rapid Fire Growth or Thermal Emergency, two things are lost:
1. Ability to use fine motor skills
2. Presence of mind


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