What is this? A 5 kw Dummy Load or what?

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fjstuden
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Re: What is this? A 5 kw Dummy Load or what?

Post by fjstuden » Mon Jan 08, 2018 2:14 pm

I had some elements like that in a turkey rotisserie, one time. Maybe this did double duty for on-site BBQs. Outside, near the table for eating, too.

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Dale H. Cook
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Re: What is this? A 5 kw Dummy Load or what?

Post by Dale H. Cook » Tue Jan 09, 2018 9:15 am

COMMENG wrote:
Mon Jan 08, 2018 10:51 am
The "resistive" strip appears to have come from an older Gates BC-1T or similar vintage vacuum tube transmitter.
I agree - I have a BC-1T load here and it appears identical. Bear in mind that a BC-1T load is not a 50 ohm load - it is a 51.5 ohm load.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

COMMENG
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Re: What is this? A 5 kw Dummy Load or what?

Post by COMMENG » Tue Jan 09, 2018 10:38 am

Dale H. Cook wrote:
Tue Jan 09, 2018 9:15 am
COMMENG wrote:
Mon Jan 08, 2018 10:51 am
The "resistive" strip appears to have come from an older Gates BC-1T or similar vintage vacuum tube transmitter.
I agree - I have a BC-1T load here and it appears identical. Bear in mind that a BC-1T load is not a 50 ohm load - it is a 51.5 ohm load.

It's still a 50 ohm dummy load, in the vernacular.

My complete statement was:
The "resistive" strip appears to have come from an older Gates BC-1T or similar vintage vacuum tube transmitter.

Each resistor is most likely rated at 412 ohms, 150 Watts or so.

The other other stuff appears to be added on to get to J0.
Obviously, 412 ohms/8 resistors = 51.5 ohms.

COMMENG

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Shane
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Re: What is this? A 5 kw Dummy Load or what?

Post by Shane » Wed Jan 10, 2018 12:39 pm

Wasn’t 52 ohms once a common impedance for coaxial cable? We have at least one AM site that uses 52 ohm coax. That the BC-1T designers chose 412 ohm resistors instead of 400 indicates perhaps they were trying to get closer to 52.

Not too much different but enough that a solid state final might mildly object.
Mike Shane, CBRE
---Omaha---

ncradioeng
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Re: What is this? A 5 kw Dummy Load or what?

Post by ncradioeng » Wed Jan 10, 2018 1:43 pm

I was told the the 51.5 ohm value came from early RCA rigid coax line that was made from standard copper water pipe sizes.

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Dale H. Cook
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Re: What is this? A 5 kw Dummy Load or what?

Post by Dale H. Cook » Wed Jan 10, 2018 2:56 pm

ncradioeng wrote:
Wed Jan 10, 2018 1:43 pm
I was told the the 51.5 ohm value came from early RCA rigid coax line that was made from standard copper water pipe sizes.
That is correct, and all of my oldest broadcast catalogs show 51.5 Ohms as the standard antenna, line and termination value.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
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TPT
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Re: What is this? A 5 kw Dummy Load or what?

Post by TPT » Wed Jan 10, 2018 4:01 pm

Some of the early hard line designs were 51.5 ohms. I can remember pulling up what looked like copper water pipe --with little ceramic insulators holding the center conductor--that was part of the late 30's installation at WSPD Toledo.

Steve Brown
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Re: What is this? A 5 kw Dummy Load or what?

Post by Steve Brown » Wed Jan 10, 2018 7:28 pm

An old TV engineer once showed me a 'whiskey cup', which was an adapter for the center conductor of 51.5 ohm line to make the transition to the 'new' standard of 50 ohm line.

Steve Brown

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