Picking the right dummy load

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DanDXdare

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Hello there,

My question is not amateur radio specific but I couldn't find an exact sub forum for my question. I hope it fits in here anyway. (Suggestions?)
English is not my primary language, sorry about any English "drifting" of my part.

I'm very new to the RF world so (one of) my first task is to get to know what the signals looks like, how they vary under different circumstances etc... Besides general equipment the first piece of hardware I must get is a dummy load and there's where I'm stuck now.

I need a dummy load suitable for VHF and UHF bands. After researching about dummy loads I found this great document about the subject: http://www.birdrf.com/~/media/Bird/Files/PDF/Resources/app-notes/Dummy-Loads-and-Smart-Choices.ashx

I have the opportunity to buy this used dummy load in my city: http://www.emc-rflabs.com/Rflabs/me...rminations/Flange/1001025.pdf?ext=.pdf?v=9047

This dummy load specs states:

"1.1.3 FREQUENCY RANGE: DC - 2.0 GHZ.
1.1.4 VSWR: DC - 1.0 GHZ, 1.10 MAX.
1.0 - 2.0 GHZ, 1.25 MAX."

I'm confused about what "DC" means on this spec. It means "Any frequency" - 2.0 GHZ? I hope so because it will be acceptable VSWR for VHF/UHF in this case.
After all.... this is a good dummy load for VHF/UHF ?

Any input is appreciated!
Many thanks,
Rodrigo
 

AK9R

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This dummy load specs states:

"1.1.3 FREQUENCY RANGE: DC - 2.0 GHZ.
1.1.4 VSWR: DC - 1.0 GHZ, 1.10 MAX.
1.0 - 2.0 GHZ, 1.25 MAX."
Frequency range is 0 Hz to 2.0 GHz.
The VSWR that the dummy load will present to the transmitter will be no greater than 1.10:1 from 0 Hz to 1.0 GHz and no greater than 1.25:1 from 1.0 to 2.0 GHz. Ideally, a dummy load would present a pure 50 ohm resistive load (VSWR 1.0:1) to the transmitter, but that isn't always the case.

When it comes to dummy loads, also make sure it will handle the RF power that you plan to apply to it.
 

N9RMA

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Just looked at the specs. That unit is good for 150 watts. Be care if you are running lots of power. 1250 watts at 1us.That is 1 micro second..That is useless for a transmitter check
 

DanDXdare

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Thanks for the extra observations guys.

150W is quite well under my objectives. Like I said I'm interested in studying the signals and experimenting so this range is quite enough already. Also I can't go anywhere over 100W with my actual amateur license so, good deal.

Salute!
 

AK9R

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I sometimes find the dummy load is between the chair and the microphone...
More specifically, the sometimes empty space between the two sides of the headphones. ;)
 
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Not all dummy loads are equal as you can see from these return loss graphs.
The lower RL is better.
 

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majoco

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I certainly wouldn't put 100watts into it for too long - look at the derating when it gets over 100 degs C
 

zz0468

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In looking at the spec sheet, that dummy load looks like it's simply the load resistor. How is it packaged? What sort of heat sink is it mounted to? What sort of connector is it supplied with? Unless you are prepared to build the rest of the package, you're not ending up with a dummy load, you're ending up with the load resistor component to a dummy load. You'll need the rest of it.
 

majoco

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It looks like this....according to the manufacturer....

https://www.terapeak.com/worth/emc-...my-load-flange-dc-2ghz-125w-swr/282146735188/

....so to dissipate 100w perhaps it needs to be bolted onto something large.

IMHO you should be looking at something like a Bird thruline load with lots of fins on it. The whole idea of a dummy load is that it does not radiate an appreciable signal - this looks like it certainly would.
 

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AK9R

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Yep... That would be me.
Don't single yourself out. Any ham or electronics tech who hasn't made a bone-head move at some point in their career isn't doing anything. It's like the auto racing motto which goes something like: "If you don't spin out once in a while, you aren't going fast enough."

IMHO you should be looking at something like a Bird thruline load with lots of fins on it.
I agree. Bird loads are pretty universal in the U.S., but may be more rare in the OP's country. Still they are the "industry standard". I find them at hamfests (amateur radio fleamarkets for the OP) and usually don't have to pay anywhere near new price for them. At a recent hamfest, I found a Bird 30 dB attenuator rated for 150 watts that I got for $50. It's a little bulky and has lots of fins, but I'm pretty sure I can trust it.
 

majoco

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I found a Bird 30 dB attenuator rated for 150 watts that I got for $50.

Good skills! Don't forget it still needs a 50ohm load on the output end! It's only milliwatts but it does upset the impedance.
 

k6cpo

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Don't single yourself out. Any ham or electronics tech who hasn't made a bone-head move at some point in their career isn't doing anything. It's like the auto racing motto which goes something like: "If you don't spin out once in a while, you aren't going fast enough."

In motorcycling, we used to say "There were two kinds of riders. Those that had been down and those that were going to go down..."

Speaking of bone head moves... I just spent an hour looking for the wall wart charger for my FT-60 HT. It usually resides on the top shelf of my desk right next to the radio itself, but this afternoon it was nowhere to be found. I finally found it in the box containing my MFJ antenna analyzer. The analyzer just came back from being repaired and calibrated and I must not have been thinking when I unpacked it and thought the charger for the FT-60 was the one I used for the analyzer. Now I have to find what I did with the analyzer's wall wart and the spare connectors for it...
 

K4IHS

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Why not just purchase a Bird wattmeter? There are several 150 watt models like the Bird 8135 on eBay right now for less than $50 bucks shipped.
 

AK9R

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The 8135 is not a wattmeter. It's just a dummy load.

As mentioned before, the OP is not in the U.S. so his access to used equipment or his desire to have large, heavy objects shipped may be limited.
 

majoco

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I made one a long time ago from 80 4Kohm 2 watt carbon resistors - strange value and I don't remember where I got them from - all enclosed in a perforated brass case - good enough for HF and I can thread a bit of wire through the holes as a "sniffer"!
 

K4IHS

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The 8135 is not a wattmeter. It's just a dummy load.

As mentioned before, the OP is not in the U.S. so his access to used equipment or his desire to have large, heavy objects shipped may be limited.

I meant to type dummy load instead of wattmeter. And yes, I can see where postage to another country would be costly.
 
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