[Yaesu] FT890 strange behavior

[Joe Subich, W4TV]

Mike,

> the problem is definitely RF getting into the PS. It comes and goes
> depending on (1)where the PS is located relative to the radio and
> (2)which band I am operating on.

This is a textbook description of a common mode problem.  The shield
of your coax is becoming part of the antenna system - antenna currents
exist on the *outside* of the shield and the RF voltage at the power
supply changes based on frequency and placement (in other words the
electrical distance of the feedline and connecting cables from the
power supply to the feedpoint of the antenna.

> The antenna system is a short center-fed vertical without radials
> (for those who remember, it's a Mini-Products C-4, possibly the last
> one on the air anywhere!) fed with 50-ohm coax.

Verticals - particularly the soo called "ground independent" verticals
- have significantly unbalanced feeds and are very prone to "current
on the shield" or common mode problems.  You can probably fix your
issue by winding 8 to 10 turns of the rig's power cord through a
2" OD 31 mix toroid core but that would likely only move the issue
to a different part of your station (rig, computer, etc.) and another
set of frequencies.  Again, the best "fix" is to install a good RF
ground where the feedline enters the shack and install common mode
chokes at the antenna and between the shack and entry ground.  The
K9YC (Audio Systems Group) information is some of the best there is
for dealing with these issues.

I really do not believe the problem is your power supply - the Astron
supplies (particularly the old linear supplies) are some of the most
reliable there are once you understand the maintenance issues (keeping
connections tight, etc.).  $25 worth of ferrite is far less expensive
than a $250 replacement power supply that is likely to be impacted by
the same RF issues but in a different way.

73,

    ... Joe, W4TV


On 7/11/2013 1:50 PM, Michael Tortorella wrote:
> Thanks to everyone who offered help and suggestions. Here's what I
> have concluded so far. the problem is definitely RF getting into the
> PS. It comes and goes depending on (1)where the PS is located
> relative to the radio and (2)which band I am operating on. The
> antenna system is a short center-fed vertical without radials (for
> those who remember, it's a Mini-Products C-4, possibly the last one
> on the air anywhere!) fed with 50-ohm coax. Unfortunately, I am
> currently on vacation and my options are somewhat limited so I think
> for now I will just fool around with PS placement. When I get home I
> can take more serious steps along the lines suggested (probably ditch
> the PS first of all, folks on this list are not the only ones who are
> not fans of Astron).
>
> Not exactly a pileup-busting setup, but I have worked a couple new
> ones this week and I am having fun learning the computer
> control/automatic logging software which I had never used before
> (still a bunch of boatanchors at home). i do have to say the 890 and
> built-in antenna tuner has handled the short vertical very well, it
> even loads up OK on 40 meters which the antenna specs do not
> support.
>
> Thanks again to everyone, it's always a pleasure to be associated
> with a fine bunch of folks.
>
> 73 Mike
>