[R-390] Balanced input on higher bands correction

[Dave Merrill]

IBM used twinax on their System 34 token ring network and at least some of
the twinax to BNC adapters you'll find are from those networks. They
contain a balun which may or may not be responsive at HF frequencies.

A safer bet is a UG-971/U and a UG-636A/U C to BNC adapter. Both of these
are found in the MK-288 Maintenance Kit.

NOS UG-971/U adapters are available very reasonably here: eBay item
312574496229.

The UG-636A/U can be found on eBay for about $20.

73 & Happy Holidays,

Dave N9ZC

On Thu, Dec 23, 2021, 11:11 PM Jim Whartenby via R-390 <
r-390 at mailman.qth.net> wrote:

> Jordan There are Twinax to coaxial adaptors available so you don't really
> need to jury-rig the connection.  I believe that you have a choice of
> Twinax to N, BNC or UHF.
> There is one on eBay, Item # 401412862478 which adapts Twinax to BNC.
> Another is Item # 132072997494 which is Twinax to UHF.  If you are patient,
> the perfect adapter for you application will eventually show up, at a
> decent price.
> Not my auctions, don't know the sellers, etc.  <grin>
> Jim
>
> Too much agreement kills a chat.  E. Cleaver
>
> -----Original Message-----
> From: Jordan Arndt <Outposter30 at shaw.ca>
> To: R-390 Forum <r-390 at mailman.qth.net>
> Sent: Thu, Dec 23, 2021 12:38 pm
> Subject: [R-390] Balanced input on higher bands correction
>
>
> Hi group and Happy Holidays...
>
> Sometime back I responded to a post stating that my 390As all had an issue
> above 15-16Mhz when connected to my ~90 foot wire via the balanced antenna
> input...
>
> The problem was not the antenna or the balanced input. The real problem
> was
> that I was temporarily using an 18" jumper to ground one side of the
> balanced input connector to the chassis.
>
> Once I replaced the 18" jumper with a 2 inch wire grounded to the mounting
> screw just below the balanced input connector, the sensitivity was
> restored
> from 15 to 32 Mhz. In fact, I'm surprised at how much of a difference the
> length of that connection made...
>
> Live and learn...!
>
> 73...Jordan VE6ZT
>
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