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Author Topic: Dummy Load  (Read 2291 times)
KE4MNF
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Posts: 3




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« on: January 19, 2013, 07:35:21 PM »

I have a 100 Watt transmitter and I am interested in getting a dummy load. I have seen various units with different ratings: x amount of watts for a minute or 2 for example. What would you guys suggest I get.
thanks
Al Casanova
KE4MNF
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W6EM
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Posts: 710




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« Reply #1 on: January 19, 2013, 08:39:10 PM »

It really depends on how you want to use it.  Since most antennas are not purely 50 ohms resistance, it makes little sense to make adjustments to transmitter output impedance or via a tuner into a 50 ohm dummy load.

But, if you want to "see what it will do" then a dummy load wattmeter would be worth having as opposed to just a resistor.
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K8AC
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« Reply #2 on: January 20, 2013, 05:39:31 AM »

Hi Al. There are many possibilities.  One is to buy one of the MFJ dummy loads that are constructed in a one gallon paint can.  You buy the device minus the oil and then buy mineral oil locally to fill it.  Another possibility is to try one of the dummy loads available on eBay, most of which have seen duty in the cell phone industry.  They're dry loads with N connectors for which you'll need to purchase an adapter to accommodate your PL259.  All of the dummy loads have a duty cycle and you'll need to pay attention to that.  For example, a dry load rated at 100W won't handle that amount of power continuously.  The MFJ oil-filled load probably is rated for continuous duty at that power level.  MFJ also offers some dry dummy loads at various power levels.  Overheating any of the dummy loads by exceeding the duty cycle or maximum power rating will likely damage the 50 ohm resistor.

Another item to consider along with the dummy load is a peak-reading wattmeter.  That will allow you to measure your output without putting continuous power into the load and will measure SSB output power correctly.  With a peak-reading meter, just a few dits on CW will indicate your true power without having to hold the key down for an extended period. 

73, Floyd - K8AC
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G3RZP
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Posts: 4366




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« Reply #3 on: January 20, 2013, 08:45:35 AM »

If you think that you ever will consider getting a legal limit amplifier, have a look for a 1500 plus watt Bird load on fleabay. Very useful if troubleshooting.
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N6AJR
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« Reply #4 on: January 20, 2013, 11:31:18 AM »

there are dry loads and there are loads in a can of mineral or transformer oil. I have several of each.  most of the time you can turn down the power and test to a smaller load, or keep thhe time short . all stations need to have a dummy  load .
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N3JBH
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Posts: 2358




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« Reply #5 on: January 20, 2013, 01:45:53 PM »

Or you could buy one or more these and build your own dummy load. http://www.digikey.com/product-detail/en/CHF190104KBF500L/CHF190104KBF500L-ND/2174498
Put ten them together with a healthy blower cooled heat sink you have the mother of all dummy loads.
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WN2C
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« Reply #6 on: January 20, 2013, 04:25:25 PM »

Or you could buy one or more these and build your own dummy load. http://www.digikey.com/product-detail/en/CHF190104KBF500L/CHF190104KBF500L-ND/2174498
Put ten them together with a healthy blower cooled heat sink you have the mother of all dummy loads.


Let's see: MFJ Cantena for about $80 w/ oil or ten of these at $63 apiece...hmmhm???
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AC5UP
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« Reply #7 on: January 20, 2013, 04:28:36 PM »


.............a worker bee at the Pentagon would have never though of it that way.
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N3JBH
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« Reply #8 on: January 20, 2013, 04:37:02 PM »

WN2C  -Let's see: MFJ Cantena for about $80 w/ oil or ten of these at $63 apiece...hmmhm???


Well i agree ten of them a bit much. But then it take 10 of the MFJ dummy loads to equal the power they would handle.  hmmhm  Roll Eyes

So hence one these units would dissipate the same amount of power as the cantenna and could be mounted in a much smaller and easier to handle /store package yes ?
« Last Edit: January 20, 2013, 04:39:45 PM by N3JBH » Logged
KCJ9091
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« Reply #9 on: January 20, 2013, 05:06:54 PM »

Or you could buy one or more these and build your own dummy load. http://www.digikey.com/product-detail/en/CHF190104KBF500L/CHF190104KBF500L-ND/2174498
Put ten them together with a healthy blower cooled heat sink you have the mother of all dummy loads.

Series or parallel?
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KE3WD
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« Reply #10 on: January 20, 2013, 05:38:59 PM »

I think the OP, with a hunnert watt rig at the moment, could get a lot of learning and use out of a dummy load designed for that level of power or a bit above. 

The 2KW dummy load idea could certainly go on the back shelf of ideas unless and until such time as the OP desires to and is ready to go QRO. 


73
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K7KBN
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« Reply #11 on: January 20, 2013, 05:44:22 PM »

Or you could buy one or more these and build your own dummy load. http://www.digikey.com/product-detail/en/CHF190104KBF500L/CHF190104KBF500L-ND/2174498
Put ten them together with a healthy blower cooled heat sink you have the mother of all dummy loads.

Series or parallel?

Both.
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73
Pat K7KBN
CWO4 USNR Ret.
W9KDX
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« Reply #12 on: January 20, 2013, 06:13:09 PM »

I would avoid the oil type as I seem to read a lot of reports of leaking, to the point where a number of posters have strongly suggested getting a new can.  I would also suggest a 1500 watt load from a quality manufacturer.  The Palstar DL-1500 was my choice.  It is more than you need now, but I have always been glad I bought a bit more capacity and quality.  I can't count the number of times I was glad I did when I upgraded my power and did not have to change anything else.  If you want to add a linear and suddenly realize that you now have to upgrade the SWR meter, the dummy load, the tuner, and all the coax and any switches, the static arrestors, as well as the antenna and baluns, you will quickly see why this might be a good idea.
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Sam
W9KDX
G3RZP
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« Reply #13 on: January 21, 2013, 02:21:20 AM »

On many occasions, it seems the 'dummy' is the guy tuning the rig up on the air on top of a QSO!
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K5LXP
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« Reply #14 on: January 21, 2013, 06:01:37 AM »

Build your own dummy load from stuff you probably already have around the house:

http://www.qsl.net/k5lxp/projects/SaltLoad/SaltLoad.html


Mark K5LXP
Albuquerque, NM
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