[Milsurplus] Reduced EVEN MORE: 4 Ham TVI Filters

[Bill Cromwell]

On Fri, 2013-04-12 at 09:44 -0400, Ray Fantini wrote:
> The old EF Johnson tubular low pass filters are great to have around
>  and use on vacuum tube military surplus equipment. I have several and
>  know from personal use that they block all spurious products above 30
>  MHz down at least 40 to 50 Db. Also running one on my RCA BTA 1MX
>  transmitter on 160 at 375 watts with no issues from the filter, no
>  added VSWR or heat from the filter and clean output above 30 MHz, so
>  now when I see them always buy them at ham fest so have a couple
>  spares around the house but am saying this just in case anyone else
>  wants to avoid VHF spurious running an old rig. The only issue is that
>  it is a 50 ohm device only so may be a problem with transmitters not
>  designed for 50 Z. RF

Hi Ray,

I contacted Bry about the Johnson filter and offered to buy it at his
asking price. I intend to use it in the shack with my Ranger, Match box,
T-R switch - all from EF Johnson. The newer filters that replaced them
are easy enough and cheap enough to make. The ones with pi-l format
using toroidal inductors that are popular on the output of solid state
transmitters are also 50 ohm filters. So we tune the pi network in our
transmitter to 50 ohms (using a 50 ohm dummy load), match the antenna to
that 50 ohm transmitter (SWR bridge) and "tuner" and we're good to go.
Some of the mil radios weren't designed for 50 ohms but that can be
changed externally according to Dave Stinson and some others. So it's
the same process of touching up everything to match the 50 ohms and it
all works.

That other filter that Bry is offering is probably a good deal for
somebody, too.

73,

Bill  KU8H