Dummy Load

[undertaker]

Ok gents I just got a new dummy load from MFJ. Now can someone please explain to me how to use it. I want to check the dead key on some of my radios. Now I don't understand electronics like most do. My occupation does not require that...

So Please help
if you don't mind...…………...
Bobby

 

[Robb]

radio > jumper cable > watt meter > jumper cable > dummy load

OR

radio > jumper cable > amp > jumper cable > watt meter > jumper cable > dummy load

Dead key AM; no modulation
Amp on 'high'
Set radio dead key so that you see no more than 1/4 of rated amp output

 

[357magnum]

Bobby , Is this a trap again ? 73 and God Bless , Leo

 

[357magnum]

Someone has to come up with a way to explain it , in Embalming Lingo , just a thought .

 

[undertaker]

Thanks Robb Exellent idea leo!!!!

 

[El Kabong]

Has anyone else seen a dummy load that reads an SWR of 1.2:1? Mine does. It's an MFJ 1.5KW HF load.

 

[Robb]

Has anyone else seen a dummy load that reads an SWR of 1.2:1? Mine does. It's an MFJ 1.5KW HF load.

Did you check the resistance with a DVM yet?

 

[El Kabong]

57.5 Ohms. It looks intact inside. Nothing bent, burnt or broken. Next step is to take it ALL apart.

 

[Captain Kilowatt]

Has anyone else seen a dummy load that reads an SWR of 1.2:1? Mine does. It's an MFJ 1.5KW HF load.

What model number? Is it an MFJ-264? If it is it is hardly what one would call a 1.5Kw load. I have one. I know.

57.5 Ohms. It looks intact inside. Nothing bent, burnt or broken. Next step is to take it ALL apart.

You won't find anything. The resistor has changed value. If it was ever over heated, even just once, it will shift in value and go high. If you ar 100% it was never run too hot then the answer lies in the manufacturer's name.......MFJ. The are know for cutting corners and may have purchased some "close enough" resistors. In any event 1.2:1 is perfectly fine.

 

[sunbulls]

Did you check the resistance with a DVM yet?

I did a millisecond double take on that acronym when I realized my veterinarian is clueless about electronics.

 

[El Kabong]

Nope, I bought it used. It could have been run hot before. Crap, I needed a good reliable dummy load. Now I have a semi reliable dummy load, as long as I don't care about accurate SWR readings.

Yup it's a 264. I was hoping it was a series of resistors in the ceramic tube, then I could find the weak one and replace it. Guess not huh?

 

[El Kabong]

UPDATE: I just got this reply from MFJ. about my inaccurate Dummy Load. You're gonna love this one.

"there is a plus/minus tolerance of 10% on both sides for the dummy load resistor." Alice M.


So there it is. My load is not broken or even out of plumb. It's JUST FINE.

 

[nomadradio]

Assuming the meter is within 2 percent, that reading is probably within the limits of the 10% spec.

57.5 ohms would be 1.15 to 1 SWR.

No biggie.

73

 

[Captain Kilowatt]

Nope, I bought it used. It could have been run hot before. Crap, I needed a good reliable dummy load. Now I have a semi reliable dummy load, as long as I don't care about accurate SWR readings.

Yup it's a 264. I was hoping it was a series of resistors in the ceramic tube, then I could find the weak one and replace it. Guess not huh?

Nope. It is a single 50 I think.......or 100 watt ceramic resistor.

UPDATE: I just got this reply from MFJ. about my inaccurate Dummy Load. You're gonna love this one.

"there is a plus/minus tolerance of 10% on both sides for the dummy load resistor." Alice M.


So there it is. My load is not broken or even out of plumb. It's JUST FINE.

10% is a typical tolerance and the load should measure between 45 and 55 ohms and show 1.1:1. I have started looking at ceramic chip resistors on a LARGE heatsink and have bought a pair of 100 ohm 800 watt chip resistors. I mounted each of them on their own heatsink mounted back to back and wired in parallel. Makes a NICE kilowatt dry load. More if I put a fan on it. IIRC I got the resistors from Florida RF on Ebay.

 

[w9cll]

So there it is. My load is not broken or even out of plumb. It's JUST FINE.

Yep use is and stop being a slave to the SWR meter.