Kanthal-Globar or Cesiwid sells such professional water(-stream) cooled
rf-loads...
73 de Andy DH5AK
----- Original Nachricht ----
Von: Paul Christensen <w9ac@arrl.net>
An: amps@contesting.com
Datum: 29.11.2011 16:05
Betreff: Re: [Amps] Can distilled water be used for a dummy load ??
> Jim,
>
> Tap water has long been used as a coolant in high-power loads, like the
> Altronic Omegaline models. In college, I used a 25KW Omegaline water-cooled
>
> load with a Harris FM-25K FM broadcast transmitter. These loads are very
> compact in relation to their ability to dissipate heat through running
> water. With 25KW being dissipated, you can hold the load in your hand and
> it stays cool. However, touch the water on the output and of course it's
> very hot but nowhere near boiling. All one needs is a household faucet,
> garden hose, and a water drain. For shacks in a basement with a utility
> sink, it's ideal.
>
> Flow sensor switches are commonly available that open the transmitter's
> interlock in the event water flow stops or become impeded below a
> pre-determined cubic volume per unit of time. The Omegaline loads can be
> found on the used market although it takes a hawk to find one at a
> reasonably inexpensive price - but they're out there. These loads offer
> incredibly good return-loss specs. Typically one can expect -30 dB
> return-loss up to near 1 GHz.
>
> So, I see no reason why water cannot be used, but I would sweep the load in
>
> water with a VNA and plot return-loss as a function of frequency. You may
> find that the Z changes substantially as it's immersed in water. Z may also
>
> change with temperature, and that's something that may be part of the
> commercial designs. It may be helpful to call the folks at Altronic for
> their input. They're the world's experts with H2O-cooled loads.
>
> Paul, W9AC
>
> ----- Original Message -----
> From: "Jim Thomson" <jim.thom@telus.net>
> To: <amps@contesting.com>
> Sent: Tuesday, November 29, 2011 9:05 AM
> Subject: [Amps] Can distilled water be used for a dummy load ??
>
>
> > My hb 50 ohm dummy load consists of 4 x 200 ohm globars in parallel
> > [type SP, glass bodied
> > and suitable for oil immersion]. Each resistor is 1" diam x 12" long.
> > [275 W CCS in air]
> > Each resistor resides inside it's own 2.875" OD x sched 40 Aluminum
> > tube.
> > All 4 x thick walled AL tubes are heliarc welded.
> >
> > I heard some place that instead of xfmr oil, that distilled water can be
>
> > used instead?
> > The same glass bodied type SP resistors, [50 ohm, high wattage] are used
>
> > in water cooled loads,
> > the type that has the garden hose on one end, etc.
> >
> > Seems to me that distilled water will conduct heat a lot better than xfmr
>
> > oil. The question is,
> > will the use of distilled water in a 7 gallon metal container, with
> > resistors immersed present any
> > swr problems ? If I remember correctly, swr was high on heath cantenna
>
> > loads if no oil used at all,
> > and dropped to dead flat once the oil was poured in. There was also a
> > similar 50 ohm load in the
> > old arrl books, same resistor as I'm using but it was a single 50 ohm
> > unit, and not 4 x 200 ohms in parallel.
> >
> > I would prefer not to use xfmr oil if at all possible. It's a little
> > tougher to get a hold of these days..and not cheap.
> > My main concern however is something leaks. Water on the concrete floor in
>
> > the shop is one thing, but 7 x
> > gals of xfmr oil is a disaster. Can you add rust inhibitor's or glycol
>
> > to the distilled water ??
> > Do I even have to use distilled water, or will clean tap water work ?
> >
> > A 50/50 mix of water/glycol will result in a 265 deg F boiling
> > point..BUT the heat transfer is no
> > where as good. I'm using a new 7 x gal paint can for this project, the 4
>
> > x resistors and the welded AL
> > tube assy, hang from the top lid.
> >
> > Thanks... Jim VE7RF
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>
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