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Author Topic: Help choosing a High Power dummy load  (Read 2656 times)
AE7UT
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Posts: 60




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« on: November 06, 2012, 03:28:35 PM »

I've recently burnt something up in my shack.
I'm trying to diagnose the problem and I'm FINALLY
to the point I have to have a good dummy load.
I'm running a K3, KPA500, Palstar AT2K into an OCFD.
I also run a K2, AL-811H into a vertical.

I was thinking of getting the Palstar DL2K.
I'm open for any other suggestions.
Thanks for any help.

Stan
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AC5UP
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Posts: 3825




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« Reply #1 on: November 06, 2012, 03:46:32 PM »

If a dummy load has a good quality connector and presents the rated impedance to the load with a minimum of stray reactance... That's about all you can ask. Anything beyond that is marketing.

As for power rating, unless you're looking at commercial quality goods with a price that makes you want to whistle, the dummy load will be rated for intermittent duty. Check the specs for a duty cycle and continuous dead key rating. If none listed, keep your power ON testing time to a minimum as it is very common for a resistor to change value when heated. This means if you're relying on an accurate load impedance to calculate power against voltage....... Don't push the load into toaster oven territory.

You could get some fuzzy numbers.    Embarrassed
« Last Edit: November 06, 2012, 03:51:09 PM by AC5UP » Logged

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K6AER
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Posts: 3489




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« Reply #2 on: November 06, 2012, 03:49:14 PM »

You can build you own with a block of metal (5 ibs) and a 50 ohm flange resistor from

 http://www.rfcom.co.uk/products/Resistor%20Products/PMS-PPR-PPT.pdf

this flange resistor is rated for 800 watts continous and twice that in intermittent duty. I have used a pair of 100 ohm units in parrellel for up to 2500 watts at 30 seconds.
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K0IZ
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Posts: 737




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« Reply #3 on: November 07, 2012, 12:27:25 AM »

I am a big fan of Bird dummy loads.  New, very expensive, but frequently available on eBay for quite reasonable prices.

Here is a current eBay listing:

http://www.ebay.com/itm/DA-515-U-dummy-load-W-N-Connector-Bird-Termaline-8402N-Type-1KW-/170936994880?pt=LH_DefaultDomain_0&hash=item27cca38c40

My Bird dummy load is good up to 2.5GHz.  Rated for 500 watts.  I have pumped 3KW into it for several minutes with only slight warming. 
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AD5X
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Posts: 1426




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« Reply #4 on: November 07, 2012, 04:50:17 AM »

I have the Ameritron ADL-2500 dummy load.  Works great.
Phil - AD5X
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NR4C
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Posts: 306




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« Reply #5 on: November 07, 2012, 06:04:33 AM »

And, there is always the good ole "CanTenna", originally from Heathkit I think, but now sold by MFJ.  It's a gallon paint can, with a big 50 ohm resistor immersed in vegetable oil to keep it cool.  Simple but works....

...bill nr4c
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W5FYI
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« Reply #6 on: November 07, 2012, 07:21:03 AM »

Mineral oil is better, transformer oil is best....
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AE7UT
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Posts: 60




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« Reply #7 on: November 07, 2012, 07:34:28 AM »

Thanks for the input guys.
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K8AXW
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Posts: 3688




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« Reply #8 on: November 07, 2012, 10:14:54 AM »

Like 4C I support the Heath Cantenna (Now replicated by MFJ) It's the cheapest dummy load available that will handle that much power for comparatively long periods of time.  I've used the Cantenna for 35-40 years now. 
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WB2WIK
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Posts: 20547




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« Reply #9 on: November 07, 2012, 02:20:11 PM »

I am a big fan of Bird dummy loads.  New, very expensive, but frequently available on eBay for quite reasonable prices.

Here is a current eBay listing:

http://www.ebay.com/itm/DA-515-U-dummy-load-W-N-Connector-Bird-Termaline-8402N-Type-1KW-/170936994880?pt=LH_DefaultDomain_0&hash=item27cca38c40

My Bird dummy load is good up to 2.5GHz.  Rated for 500 watts.  I have pumped 3KW into it for several minutes with only slight warming. 

+1.  These are a great deal, if you don't mind something rather heavy.  I have a few of these, including one rated 5000W (it's very large and heavy and has a 7/16 DIN connector), and didn't pay much for any of them.

Advantage of the Bird loads, if you don't mind the weight, is they are not only great on HF but most are rated to at least 1000 MHz, where they work just as well with a nearly perfect 1:1 SWR.  Most of the "amateur" loads can't do that.  So, I can use the same load on 160m and also on 1296 MHz, or anywhere in between. Wink
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NA0AA
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Posts: 1043




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« Reply #10 on: November 08, 2012, 07:37:40 AM »

The cantenna is a good deal for power and time, it's got a fair amount of thermal mass and takes a while to heat up.

But it's not very portable.  I also have a small dry ome for portable or field use.
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KA5IPF
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Posts: 980


WWW

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« Reply #11 on: November 08, 2012, 07:17:09 PM »

I am a big fan of Bird dummy loads.  New, very expensive, but frequently available on eBay for quite reasonable prices.

Here is a current eBay listing:

http://www.ebay.com/itm/DA-515-U-dummy-load-W-N-Connector-Bird-Termaline-8402N-Type-1KW-/170936994880?pt=LH_DefaultDomain_0&hash=item27cca38c40

My Bird dummy load is good up to 2.5GHz.  Rated for 500 watts.  I have pumped 3KW into it for several minutes with only slight warming. 

That's fine for the oil filled loads, just don't try it on the dry ones. I fried a beautiful Bird 8431 with about 1kw. That little resistor won't take it, arc's over. I wound up throwing it away. No resistor replacement available.

Clif
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K0IZ
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Posts: 737




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« Reply #12 on: November 09, 2012, 05:30:27 AM »

Yes, my Bird is oil filled.  I agree that dry type (any brand) has much less thermo mass and can be destroyed by substantial overload.  Most all of the bigger Bird's I have seen (250W rated and up) are oil filled.

I also have a couple of non-Bird dummy loads, the type that have large finned heat sinks.  Mine are 50 and 100 watts, and rated up to 1Ghz or so.  Frequently on ebay as well, for example:

http://www.ebay.com/itm/Celwave-75-Watt-Dummy-Load-100-TESTED-USA-Seller-CB-Ham-VHF-UHF-Police-Fire-/121013725966?pt=US_Radio_Comm_Antennas&hash=item1c2cfaeb0e

http://www.ebay.com/itm/RF-Delta-Dummy-Load-N-Type-100w-4Ghz-Antenna-RELM-T44004-50-Ohm-58B83464R01-/140881704066?pt=LH_DefaultDomain_0&hash=item20cd343482
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