110 watt Spectra as a repeater turned down to 60 watts?

[Bill Rogers]

I would like to use a 110 watt Spectra as the transmitter for a repeater. I read through the previous discussions and am still trying to learn what to do. Does anyone know if the radio will have problems if turned down in output to say 60 watts? Any ideas on what higher output level might be ok assuming the addition of some fans on the heat sink? I am thinking in termes of 100% duty cycle. Thanks for any help. Bill.

[Bill Rogers]

Also should have said that it is a UHF remote mount A7 type head.

[N9LLO]

That heatsink might be good for 30w max at 100% duty cycle.
I dont know how well behaved the Spectra 100w amp is when turned down that low (if it will even go) but I suspect if will not be too efficient leading to further derating.

Chris
N9LLO

[ricciticcitembo]

Water Cooled. 100% Operational At All Times.

[Bill Rogers]

Anyone else have experience with running one as a repeater? Only 30 watts sound right? Thanks, Bill.

[Bill Rogers]

WOW! Thanks for the advice guys. Bill.

[SlimBob]

Water Cooled. 100% Operational At All Times.

As silly as this sounds, it's certainly possible. You would have to find a way to cleanly interface with a large tank, but that could be as simple as putting the back part of the radio into water. Ideally, you'd want to be mounted at the bottom of a tank of some form with reasonably large capacity -- say a 55 gallon drum. Then fill the drum with oil or water and antifreeze, if you're certain you can keep the gunk out of the radio. Practical? Debateable, but a feasable idea nonetheless.

[DAL-COM]

FM is notoriously inefficient, I still think AC-SSB with pilot tone would have been better. (Especially for tactical or SAR use)
Anyway, is it possible on a Spectra to weld a bigger heatsink (more area) on to the existing heatsink? Then a few 110V fans would do the trick in a 25 deg C ambient.

[ricciticcitembo]

SlimBob-Well, That idea is certaintly unique, but not exactly what I have. I have more of a Standard Laboratory/NASA Type of setup with either a Neslab Chiller or Ninja Radiator Type Remote mount Cooling. Might be difficult to grasp the concept if you are not familiar with Water Cooling Hi-Power electronics But it's normal stuff in the AeroSpace world.

Anyhow, here is a link with Photos of the manifold with Three of my Spectras mounted to it. It only needs two tubes to work, as long as only one unit is Transmitting at a time because of the Genreally large Mass of Aluminum, so thats good. In fact it doesn't even need liquid cooling with the large heatsink, it will last longer though at 100% duty, which I don't run any Spectras that hard currently, but If I should feel the need, I got the cooling for it.

http://batboard.batlabs.com/viewtopic.php?t=9910

[Susan157]

Has No One Looked At The New Generation
Of Cooling With The Peliter-Effect PN Junction.

(P.S.)The 12 Volt Electric Cooler For Your
Beer?Bolt That To Any Heat Sink.
Turn On The 12 Volts And Cool It Down.

[SlimBob]

Has No One Looked At The New Generation
Of Cooling With The Peliter-Effect PN Junction.

(P.S.)The 12 Volt Electric Cooler For Your
Beer?Bolt That To Any Heat Sink.
Turn On The 12 Volts And Cool It Down.

Yes, but these have efficiencies at .33 at best -- your high-end Japanese air conditioners have an EER of 17, American -- 12. You're talking about wasting two watts to move one, requiring (3) watts to be dissipated at the heatsink. Any air conditioner with a compressor that half-way functions is more efficient.

[ricciticcitembo]

SlimBob is correct on that.

Thermoelectric coolers are inherently inefficient devices. Plus they melt sometimes.

A small 12Volt pump and a small radiator like a transmission cooler, one pint resivoir and your good to go. Pretty efficient, and not really all that elaborate, and gives excellent results. It's REAL easy to do it in a vehicle, It practically belongs there...

Fans work too. But Remote Cooling has some advantages also. It all depends on what your application is.

And I'm not suggesting everybody go out and start watercooling your Spectras. It is generally not necessary if you have a couple of 5 1/4 inch fans. It's just that I'm barely aquainted with thermodynamics, and sometimes use it when It's not totally necessary, but it might be cool.

On my original post in this thread, I was just sort of joking.
I probably shouldn't do that, but I can't help it sometimes.

[nc5p]

Thermoelectric cooling is only useful where you need to run the junction temperature below ambient. They create much more heat than they pump out. I use them for CCD cameras, the dark current goes way down when you chill the CCD down. Gets rid of the noise (looks like grain on film).

You might consider heat pipes, they are used all the time now on laptops. They use phase change of liquid to gas to liquid again. Usually they put wicks in the tubes so they are not totally dependent on gravity to return the condensate. You could build your own but need a vaccuum pump to get out the air. You could mount the finals on a "boiler", then run tubing up to a condenser with a fan on it.

For the water cooling, there are cold plates available ready made, I think McMaster-Carr carries them.

There is this stuff called pyrolytic graphite sheet, works wonders for getting rid of hot spots where you interface surfaces. It's very expensive but is worth it. Digikey sells it. I use it on the cameras.

Those HP Spectras do get hot, the one in my pickup gets real hot when I get long winded.

Doug