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 Post subject: Ohmite D-101?
PostPosted: Mar Mon 18, 2019 3:22 am 
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Location: Charlotte 28211
I've run up on an Ohmite D-101 100 watt dummy antenna 600 ohms, because I need something to work on my Knightkit T-60 transmitter. But if the dummy load is 600 ohms, what good is it? For what purpose would a 600 ohm dummy antenna be made?


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 Post subject: Re: Ohmite D-101?
PostPosted: Mar Mon 18, 2019 4:01 am 
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How old does it appear to be? In the 1930s 600 ohm open-air transmission lines were pretty common for radio amateurs, so they could use a 600 ohm dummy for transmitter tune-up and testing.

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 Post subject: Re: Ohmite D-101?
PostPosted: Mar Mon 18, 2019 4:27 am 
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Thanks. You answered my question and it's all I need to know. I can't use it. It's on ebay right now for 4 or 5 dollars.


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 Post subject: Re: Ohmite D-101?
PostPosted: Mar Mon 18, 2019 6:50 am 
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Is it in a can?

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 Post subject: Re: Ohmite D-101?
PostPosted: Mar Mon 18, 2019 8:25 am 
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henry finley wrote:
For what purpose would a 600 ohm dummy antenna be made?
600 ohms is standard impedance for audio systems.

Your item is a dummy load, but not a dummy "antenna".

- Leigh

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 Post subject: Re: Ohmite D-101?
PostPosted: Mar Mon 18, 2019 9:09 am 
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Location: Cedar Rapids, Iowa, USA
I have found pictures of D-100 clearly marked DUMMY ANTENNA RESISTOR at 73 and 146 ohms. I have not seen one for 600 ohms.


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 Post subject: Re: Ohmite D-101?
PostPosted: Mar Mon 18, 2019 1:26 pm 
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Larry

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 Post subject: Re: Ohmite D-101?
PostPosted: Mar Mon 18, 2019 2:21 pm 
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Leigh wrote:
henry finley wrote:
F600 ohms is standard impedance for audio systems.

Your item is a dummy load, but not a dummy "antenna".

Leigh - After almost 50 years of working with 600 ohm audio lines I have never seen one that would need a 100 watt dummy. Whether they be studio audio lines or telephone lines their power is measured in milliwatts, unlike 70 volt or 100 volt speaker lines. I would note also, after nearly 50 years of working in broadcasting, that a number of transmission line standards were used in the decades preceding the development of coaxial lines.

Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA

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 Post subject: Re: Ohmite D-101?
PostPosted: Sep Fri 10, 2021 3:43 pm 
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I'm two years late to this party but I just saw one on eBay and had to have it. But mine is the earlier D-100 model in the lovely glass globe. They are real dummy antenna loads intended for HF transmitter work. They are non-inductively wound and the envelope is gas filled although I have seen no reference to what gas(es) were used. The 1945 Radio's Master Catalog had this entry:

Attachment:
D-100_Dummy_Antenna.jpg
D-100_Dummy_Antenna.jpg [ 416.4 KiB | Viewed 396 times ]


And they were mentioned in the MIT Radiation Lab Series, Vol 17, Components Handbook:

Attachment:
D-100_Dummy_Antenna_2.jpg
D-100_Dummy_Antenna_2.jpg [ 517.19 KiB | Viewed 396 times ]


I have seen a screenshot of a section index for the Ohmite Catalog #40 that says they are listed there but I have not found one online so I don't know if any more details are given.

So, more than most will want to know but if there are others who stumble onto this thread in the future all the information we have currently is now in this one spot!


Last edited by khutch on Sep Tue 14, 2021 2:17 pm, edited 1 time in total.

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 Post subject: Re: Ohmite D-101?
PostPosted: Sep Fri 10, 2021 6:16 pm 
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The T-60 will probably match a 600 ohm load. Give it a try. If it doesn’t work, use a 40 watt incandescent light bulb.

Darrell


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 Post subject: Re: Ohmite D-101?
PostPosted: Sep Tue 14, 2021 1:33 pm 
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Joined: Jan Thu 16, 2014 10:38 am
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Location: Near Newcastle NSW. Australia.
G'day everyone.

Would make a good terminator for the far end of a rhombic antenna.
Terminator resistor power rating should be about half of the transmitter continuous power.
600 Ohm 100 Watts. Hmmmm, Nice!
200 Watts continuous TX power.
Whatever you do, don't throw it in the bin!!
Non-inductive resistors of that value are not common.
Someone will want it.

Cheers,
Robert, VK2BNM.

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 Post subject: Re: Ohmite D-101?
PostPosted: Sep Tue 14, 2021 4:06 pm 
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Location: Montreal, Quebec
Australians and their rhombics. Nothing like having so much space.

In the sixties Ray Naughton, VK3ATN, did moonbounce from Australia. Lots of room, little money, he hung rhombics for multiple bands off surplus telephone poles. Big enough to get enough gain, even with Australia's 200W power limit.

Since he coukdn't aim them, he was limited to a few days a month, when the moon was in.line with his antennas. Actually, he had a level of adjustment, role and pulleys, for a tiny bit of adjustment.


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