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Author Topic: dummy loads  (Read 3991 times)
KG6AF
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Posts: 357




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« Reply #15 on: August 18, 2013, 08:26:25 PM »

I see lots of questions on other areas of this forum that could be answered in part or in whole with the assistance of a dummy load.  For example:

Qu: I can't seem to put out a decent signal.  Is it the rig, the tuner, or the antenna?

Ans: The first step is to eliminate the rig as a trouble source by transmitting directly into a dummy load with the tuner off.  Do you get the expected power at a low SWR?  If so, move on to the tuner and antenna.

Qu: My transceiver seems to be behaving strangely when I transmit.  Is the problem due to RF getting back into the rig?

Ans: Does the problem persist if you're transmitting into a dummy load?

Qu: I'm hearing some signals that are always at the same place on the dial, day in and day out.  Are they coming from some external source, or is my rig generating birdies?

Ans:  Do the signals go away when you switch to a dummy load?  If so, they're external.  (You could do the same thing by detaching the coax going into the transceiver, but having a powered-up transceiver sitting there without a load is not my idea of protecting an expensive investment.  It's just too easy to hit the key or the PTT switch...)

Qu: I want to listen to my signal on a second rig, or perhaps monitor it on a 'scope.  How do I do that without subjecting other hams to 20 minutes of "Hellooooo, test"?

Ans: Transmit into a dummy load.  You'll get enough leakage to be heard on a (very) local receiver without disturbing others.

Let me turn the question around: how do you debug problems without even minimal test equipment?  I knew old timers who used to draw arcs off the antenna knife switch with a pencil, and I've used light bulbs for dummy loads in a pinch, but the rigs in question were tube rigs that could put up with more abuse and were easier to repair than today's solid-state, SMT wonders.
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VU2NAN
Member

Posts: 248




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« Reply #16 on: August 18, 2013, 09:10:23 PM »



And you can use it to heat up water for tea!


For sure, OM Eric!

73,

Nandu.
« Last Edit: August 18, 2013, 09:15:55 PM by VU2NAN » Logged
WN2C
Member

Posts: 466




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« Reply #17 on: August 19, 2013, 12:26:17 PM »

How many times have you heard someone tune up on top of a QSO in progress?  I just want to tell them why don't you tune up the amp into a dummy load, DUMMY.

Rick  WN2C
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G3RZP
Member

Posts: 4713




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« Reply #18 on: August 19, 2013, 01:19:55 PM »

Unless the antenna (via tuner) is the same as the dummy load, some on-air adjustment may well be necessary. If the antenna tuner needs to be tuned, there has to be a signal radiated. BUT, the good op chooses a clear channel and tunes up quickly......at the lowest possible power.
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N4JTE
Member

Posts: 1157




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« Reply #19 on: August 20, 2013, 02:49:50 PM »

KG6AF, thank you for the exact answer I was looking for and hopefully illustrated to others the reason I asked the question, somewhat tongue in cheek hi.
Tnx
Bob
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N4JTE
Member

Posts: 1157




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« Reply #20 on: August 20, 2013, 05:34:37 PM »

Oh by the way, just read a post about lids that tune up on the air, and this guy, and many others on the air, question why not use a dummy load?
Maybe because an antenna is connected ??
Lids are lids with or without dummy loads.
I can tune my various antennas, when needed, in 5 seconds or less at 5 watts, say a word or two on the air while identifying my call at 500 watts and voila, tnx to some arrows on the amp and tuner it's all done, if something ain't right it's time to check a problem with the antenna. So yes a dummy load is a great diagnostic tool while repairing things along with a vtvm and a double scope,  but in my experience it's not needed except for cutting phase lines, my story and sticking to it, hi.
Bob
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K6CPO
Member

Posts: 157




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« Reply #21 on: August 20, 2013, 07:00:23 PM »

Okay i will throw this on this forum, someone tell me what a dummy load is supposed to do; check a transmitter output into a 50 ohm load, okay but that seems silly, pretty obvious, should work.
I only use a dummy load to cut phase lines but what possible use beyond that can a dummy load be used for in this day of 50 ohm amps, tranceivers etc.
Tuning up with a dumb load has no meaning, the antenna is where the energy needs to be monitored and very easy to accomplish with 5 watts for 2 seconds on that thing in your backyard so what does a dummy load do these days?
Bob

Mostly, the dummy load is located between the chair and the microphone...
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WB0MCO
Member

Posts: 81




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« Reply #22 on: August 29, 2013, 11:42:00 AM »

"Mostly, the dummy load is located between the chair and the microphone..."

So True.....If you don't understand or use one ,the above statement says it all.

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K1DA
Member

Posts: 513




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« Reply #23 on: August 29, 2013, 01:02:34 PM »

   Good luck tuning a set of VHF or above cans with a field strength meter.  Many's the hack who tore up coax, connectors, and antennas looking for the reason why  something isn't reading right when a dummy load would have narrowed it way down. 
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