93 Ohm feed-thru terminators - Unobtanium? No, as it turns out.


 

Following this thread, I remembered that I had some odd BNC terminators in my accessory drawer. I just fished them out, and they are ELCOM FT-90, BNC (m-f) terminators and measure between 91.2 and 93 ohms each.  I have 5 of them, and no use for them. They are unused, and look good,, seem to be silver plated with gold BNC p[ins.

is $5 each reasonable/? please contact me off list if you want them. I think they are too heavy to go in a padded bag, so that means a small packet, which is around $20.  in any case, I have them if they will help anybody.

all the best,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.

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Walter Shawlee 2
Sphere Research Corp. 3394 Sunnyside Rd.
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IIRC 93 ohm is the impedance used by IBM 3270 terminals - could be wrong - it's a very long time.

David

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of walter shawlee
Sent: 14 February 2021 16:40
To: TekScopes@groups.io
Subject: [TekScopes] 93 Ohm feed-thru terminators - Unobtanium? No, as it turns out.

Following this thread, I remembered that I had some odd BNC terminators
in my accessory drawer. I just fished them out, and they are ELCOM
FT-90, BNC (m-f) terminators and measure between 91.2 and 93 ohms each.


Roger Evans
 

Yes, I can remember 93 ohm coax cables with BNC connectors being thrown out by the hundreds when the Lab went from 3270s to Ethernet connected IBM PCs in the 1980s. I seem to remember that you can mate the 93 ohm plugs with 50 ohm sockets if you are really determined, but it doesn't do the sockets any favours.

Roger


leonard scheepsma
 

Walter that would be perfect. Happy to have them.
I'll call you. I just remember we've been in touch before and you also shipped stuff to me earlier :-)
Fantastic!

Leonard


Michael A. Terrell
 

David C. Partridge wrote:
IIRC 93 ohm is the impedance used by IBM 3270 terminals - could be wrong - it's a very long time.
Yes. RG62. Prior to IBM, it was used for car radio antennas which act as a voltage probe rather than a tuned antenna.


leonard scheepsma
 

So I have 3 of them in the mail right now, an excellent result with many thanks to Walter. So still one failing in my double terminated set-up. Anyone with 1 or 2 in a drawer somewhere?

Thanks again, Leonard


Dave Wright
 

Yes, I have a number of RG-62 with BNC jumpers, about a meter or so long, in my pile. Wondered what they could have been for... As I recall the BNCs mated OK with my 50 ohm stuff, but now I am inclined to look closer and see if there are dimensional differences...

Dave KC6UPS


Glenn Little
 

In the 75 Ohm vs 50 Ohm world, the two are completely interchangeable as far as mating is concerned.
The 75 Ohm BNC connector is missing dielectric between the center pin and the shield.
Based on this I would suspect that this is the same with the 93 Ohm BNC connector.
But, I cannot guarantee this.
I have hear rumors that there was a difference in center pin as in the Type-N connector in early BNC connectors.
I have never seen this.
I have been working with radio for 50 plus years and am a retired TV chief engineer.
It was in the TV work that I saw the differences in connectors.
The clamp nut or crimp ferrule will be different in the different connectors.


Glenn

On 2/19/2021 9:35 AM, Dave Wright wrote:
Yes, I have a number of RG-62 with BNC jumpers, about a meter or so long, in my pile. Wondered what they could have been for... As I recall the BNCs mated OK with my 50 ohm stuff, but now I am inclined to look closer and see if there are dimensional differences...
Dave KC6UPS
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Milan Trcka
 

It is not recommended to plug 50 ohm N connector (central pin) into 75 ohm connector (central socket). The larger diameter 50 ohm pin will stretch the smaller diameter 75 ohm socket. This may (will) cause reliability of contact to degrade. This is important in precision test equipment such as network analyzers and similar. Opposite situation will not destroy the connector but may lead to reduced contact reliability all the same. HP manuals caution against mixing 50/75 ohm connectors.