Types of Dummy Loads. (
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- čas přidán 30. 08. 2021
- Rod, VK4EZY, is setting up a dummy load that he has constructed but he doesn't know for sure how to cool it down, or dissipate the heat? Dave here to offer several options.
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as new ham... your videos are instructive and easy to understand. Thanks for all that you do!!!!
Dave mathed on camera like a boss. You don't have to get it exactly right the first go through, his math was right! I felt like an Elmer was explaining something
It should be stated that David says several times in series up to 5 minutes in, but he meant parallel.
Perhaps he should "proofwatch" prior to uploading?
My assistant and I are maintaining one video a day. To do more such a proofed scripts would take at least double the time.
@@davecasler So quantity is the goal? OK, Elmer Fudd...wascally wideo away!
Thanks Dave. You are my favorite ham channel. I love the way you explain practical and useful information. It's obvious you have a very strong background in electronics. Thanks, once again.
Ty Dave for your ever-thorough but understandable explanation. You put things in terms that us non-techie hams can understand.
These videos are great 👍 Thank you so much! This series takes a lot of load off me when elmering as I am able to forward the link to someone curious about certain things!
Glad you like them!
Very informative
Hi Dave,
Easy way to calculate the parallel resistance, if the resistors are all of equal value, is to take the value of the resistor and divide by number of resistors. MFJ caries the transformer oil in gallon quantities. Transformer oil does creep as I had it in my Cantenna, but the vent was the major culprit. Stay safe. 73 WJ3U
Don, Thanks for the tip on parallel resistance value divided quantity. That is something I can use having never heard it before. tnx agn es 73 de n4nrl
The transformer oil creeps just as the mineral oil. I had a similar dummy load in the 1980's with the transformer oil, and had to occasionally clean it as well.
Thank you so much I appreciate all that you do. From w30j
Dave, I enjoy your commentary on this and other videos. With the illustrations even if a misspeak I still get it as intended meaning which is part of the definition of learning. Thanks for all your work on the videos and no I have not seen them all. Illegitimi non carborundum de n4nrl
Oh, as a NOVICE I was told to put my Cantenna in a paint bucket which I did and never have had a problem. Recently made a smaller one for QRP testing.
We get mineral oil in gallon jugs at the farm store. It’s commonly used for horses and cattle.
Thanks I have one
RF resistors are the way to go. 200 watt resistor is around 5 dollars on eBay. Chinese. Mount it inside aluminum enclosure, and the enclosure itself is screwed to heatsink. The larger the better. Gives flat swr from HF to UHF and handles 100 watts easily with forced air cooling
Thank you, Dave. N0QFT
When Dave realized he was making a math mistake and said, "I'm so stupid." My first thought was, "Yeah... I'm not the only one!!"
I keep my Cantenna in a plastic tub so the oil does not get onto the floor.
1. You say it must be 50Ω, is there a tolerance of +/- XΩ?
2. How do I estimate the dissipation capacity of dry resistors before being immersed?
Let’s say I also use the ten 500Ω resistors in a 5w package, would this equal to 50watts or 10 watts if they were 1 watt resistors?
3. As to the creeping ability of mineral oil, is there a need for air to get in? If not I’m guessing you can use Permatex Silicone sealant No. 25228. This formulation cures in 90min and it’s made for sealing surfaces where oil is present, like oil pans or differential covers.
Paralel dummy load antena
If the resistors are inductive it will not work at higher frequencies.
When i see these for sale they are often rated with a frequency such as 6 ghz or other. Whats that about? Also pity the power cant be routed in such a way that heat can alternatively be dissipated via a 100w light bulb.
When heated, the resistance changes, so it is necessary to use resistors with the opposite value of the temperature coefficient. In addition, series-parallel wiring will reduce unwanted output capacitance.
capacitence rises by factor of2 when emerged in oil ;)
see patent from nicola tesla.
73!
Original transformer oil was made of PCBs (Polychlorinated biphenyls), which was highly toxic, carcinogenic, and far from being environmentally friendly. Many years ago, it was replaced by mineral oil, silicone oil, and, more recently, ester-based oil. Mineral oil had the lowest flashpoint of the three replacement oils, which made it highly problematic with high voltage transformers where arcing could be present, and fires could result. However, mineral oil is perfectly suitable for the comparatively lower voltages used in the dummy loads Dave talks about in this video.
Onto many dummy loads it is written 3GHz. Are good for testing power in 136-500 MHz range ? (radios within VHF and UHF bands)
Just put in an order for an MFJ oil can heat sink. They claim that they are sending actual transformer oil with the can, not just mineral oil. I'll be interested in seeing if they follow through.
When you drilled the holes and mounted contact and skrews, put on some varnish on the inside of the lid. That will reduce the leak. The films will be shorter if you check the facts before you start recording. Write down a script before you start is a good thing. You should always think before you speak. In Sweden we have a cartoon named Arne Anka (Arne Duck). His favorite expression is "To think before you speak is like dry your ass before you shit." Have a good day /SM6RDD
This was very informative, thanks! I have a couple of questions. I’ve seen some dummy loads manufactured that say they’re good for a specific range of frequencies. What resistors would I need for CB band?
Where is a reputable place to find decent quality components? When I search on my computer I get MANY results. Too many actually. I’ve never purchased individual components so I’m not sure where to steer.
I’ve disassembled a few compressors from refrigerators. They contained oil. Does anyone know if that oil would work in this application? It’s been sealed in the compressor it’s whole life so it’s quite clean.
Ok last question lol. Can I measure the impedance of my creation just by touching the center pin and the nut on the connector with a voltmeter (set to Ohms of course)?
A reactive dummy load gives the impedance curve of a cab-mounted speaker via an RLC series/parallel network.
I have a Xiegu X-6100 that I can dial down to as little as 0.1 W. Is there any need to using the dummy load at 10W or can I just do all the testing I need at 0.1W?
I'm backpacking, so want to keep my gear tiny. The little brass SMA shorting "standards" that come with a NanoVNA for calibration are rated for 1W. Is there any disadvantage to just using one of those at the end of a BNC->SMA coupler, if I dial down to 0.1 W?
If you are using dummy loads at UHF/VHF frequencies you will find that all dummy loads are not equal. I have some dummy loads that start to give higher SWRs at 10m while others are good to at least 1Ghz.
Yes, agreed.
I’m a total newbie… can anyone recommend suitable dummy loads for the front/rear antenna connectors on a Yaesu FT-818ND..? Rated 6W. Thank you in advance.
Dave you kept referring to puting the 10 resistors on series
You really need to correct that!
Did I? My bad! Definitely in parallel.
At 5:49 you said that you can put 5 resistors in series and you can get what you are looking for. It should be parallel.
Greetings from England,
Thank you for a nice video, you got us worriesd when you started to drink from that blue bottle... I thought that was mineral oil!!!
Also, would I need specific solder wire to withstand immersion in oil?
Cheers, stay safe.
73 de Manny-2E0HJN
Maybe it's BOMBAY Gin? When I made my DL (years ago) I used some scrap #14 bare copper (Cu) wire, still works fine.
Any wire ought to hold up to mineral oil
I agree with the other comments. Mineral oil, or for that matter transformer oil, is pretty benign. By using the havey-duty Nalgeen blue bottle I've saved countless thousand plastic one-time-use water bottles.
5:23 In Parallel?
Same at 5:48
Yeah, I screwed up.
What about deionized water?
The unfortunate issue with deionized water is that water is the universal solvent. It won't stay deionized, even if it's hermetically sealed.
Mineral oil is mostly inert and gets the job done just fine.
Water doesn't have the heat-carrying capacity of the mineral oil. If a resistor gets hot, the water might boil.
@@michaellin4553 Deionized water can be a bit acidic from absorption of carbon dioxide . That forms carbonic acid.
If you use nanowire water, that can dissolve stainless steel.
Stay with the mineral oil or transformer oil. N0QFT, a retired laboratory chemist
Dave,, I like your subject matter,, Videos are too long and rambling.. That said ,, your channel is thriving so do what you gotta do,, from KK5VN
I try. I'm trying to figure out a way to develop scripts for each video and use a teleprompter. The problem is time.
You really need to do your research before you make your videos.
Ok, so what did I mess up?
what a vague, unhelpful, information-free post