50 Ohm Dummy Load

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James:
hi,

perhaps the RS load was damaged by excessive power ?

73 james

Steve Katz:
Can you say "defective?"  

Which would apply to a lot of stuff from Radio Shack!

Best 50 Ohm dummy load for VHF, unless you have a Bird Termaline or equivalent, is about 1000' of RG58/U, whether anything's connected to the far end, or not.

;-)

Dale Hunt:
Was it a dummy load designed for CB?  The kind built into
a PL-259?  They are rated at 5W max and can easily be
smoked by the full output of a transceiver.

If the problem is that the tuner can't match it, the
dummy load must be WAY off from 50 ohms - I'd suspect that
if you check it with an ohmmeter you'd see that something
was wrong.  This isn't the sort of thing that would be
caused by the difference between HF and VHF dummy loads.
(Unless the dummy load was intentionally built to have
a limited operating range.

leland pechacek:
i was once told a 150 watt lightbuld makes a great dummy load    how true is this?





dummyload= grab the antenna while i key up   hihi

Mike Yetsko:
USUALLY a dummy load will fall out of 'compliance' as the frequency goes up, not down.  A dummy load for HF will start acting flakey as the frequency goes up and all kinds of parasitics and internal 'leakages' come in to play.  

In the other direction, there's nothing to prevent a VHF or higher dummy load from working at lower frequencies, other than power ratings.  And that should be fairly obvious.

On the other hand, it could be something built so bad that it DEPENDS on stray leakage and coupling to work (especially if it's a load built 'in' to a meter or other piece of test gear for VHF) and when you try to operate it out of it's normal frequency area, you lose the interaction to the 'stuff' around it and now it appears to be bad.

Most of your 'CB' type dummy loads are actually a 2W resistor inside a PL-259 plug with a plastic pipe cap on the end.  They depend on the user not cooking the thing for extended periods to keep from popping the resistor.

Radio Shack actually sold a really great VHF 25W dummy load (contrary to the no-nothings that think that all RS stuff is junk.  But then, consider the source!)  but it was only sold for a short time and wasn't in all stores.  Now I think they don't even carry a CB dummy load any more.

You can make your own fairly easily.  Just get a 50ohm NON-INDUCTIVE resistor of at least 2W rating and solder it into a PL259.  For intermittant duty, it should be good for 4 or 5 watt, and probably up through VHF.

I've made my own for years.  But I also make a 75ohm (gives me a known 1.5:1 SWR) and a 100 ohm (a known 2:1) for when I'm testing.  (In the CB craze days, you could also use the 100ohm load to help you tune up any of the 'co-phased' antennas truckers used to love.)

Avoid using any of the BNC or F type dummy loads.  They are for small signal work, and generally have power ratings in the fractions of a watt.

Use a light bulb?  Well, I know a lot of hams that used to do that years ago.  In fact, I used to do that in college.  But it's more of a 'sorta work' kind of thing than what you would really want to do.  However...  some habits just won't die.  There are groups that now run 'light bulb' contest to make contacts from your 'dummy load light bulb'.  Some of the rules limit feed line length and position (gotta be 14/2 if I remember) and you gotta use a ceramic screw type base like you find in old basement ceilings.  Kinda fun, but not too many of the transistor rig type guys like it.  I think for best performance, the wattage of your bulb should match your output, or be a little higher.  But then, I don't really know.  Just realize when your bulb is off and cold, it's gonna look like close to a short to your rig!

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