[TenTec] RF & Pegasus

[Greg Hodsdon]

After noting that my modified D-104 mic stand (with a preamp from recent QST
article) with PTT bar would not key the Pegasus but does fine with the Omni 6 plus,
I started wire checking the circuit.  The Pegasus measures 4.99vdc across pins 2
and 4 on the mic jack using a Fluke dvm. The other interesting item is that the mic
jack (threaded section on the panel) is not grounded and, in fact, is floating.
This is not the situation on the Omni 6 plus, where pin 2 is grounded and the mic
jack is grounded by virtue of its being mounted to the aluminum chassis. Also, my
recollection is that the voltage on pin 4 on the Omni is well over 8vdc. I called
TenTec on this issue and all was confirmed. My plan is to tie the Pegasus mic jack
to ground and raise the voltage on pin 4.

An interesting thought:  With the mic jack ungrounded, this means the mic cable
shield could be floating, depending upon how the connector is wired. Could this
possibly be a reason for some people experiencing RF in the audio with some
microphones?

Using the 705, I am getting good audio reports from the Pegasus.

73 de Greg, K7KJ
Portland, OR

Dale L. Martin wrote:

> My 705 schematic shows pin 4 and the + terminal of the battery each feeding
> through respective steering diodes (1n4148), then directly to pin 14 of the
> 14013 (a CMOS Dual D type Flip-Flop).  CMOS typically works across 3 to 15
> volts.  After the .7 volt hit through the steering diode, any 4.5v source would
> be very close to the hairy edge.  I'm betting it's better than 4.5 volts across
> pins 2 and 4 of the Pegasus mic jack--more along the lines of 9+ volts....the
> Omni VI derives it through a 470 ohm resistor from +REG (13.8v?).
>
> Someone, please, measure the Pegasus pin 2/pin4 voltage.  Settle this issue.
>
> 73,
> dale, kg5u
>
> -----Original Message-----
> From: JEFF S JOHNSON <aa8ve@juno.com>
> To: tentec@contesting.com <tentec@contesting.com>
> Date: Thursday, December 09, 1999 15:35 PM
> Subject: Re: [TenTec] RF & Pegasus
>
> >
> >I checked my Omni-V and the output for the mic is 8.6 volts.    I wonder
> >why they now supply only 4.5 volts?  Is anyone running a 705 off the
> >Pegasus with any problems? Perhaps 4.5 is enough to run the 705 from
> >anyway.  What is the voltage out in the mic jack on an Omni-VI anyway?
> >
> >73 Jeff aa8ve
> >
> >On Thu, 9 Dec 1999 13:22:19 -0400 (AST) David McClafferty
> ><at060@chebucto.ns.ca> writes:
> >>
> >>
> >>
> >> On Thu, 9 Dec 1999, JEFF S JOHNSON wrote:
> >>
> >> >
> >> > I should hope Pegasus has DC voltage out for the Mic. so a battery
> >> is not
> >> > needed.
> >> >
> >>
> >> I did not have a battery in my 705 when I used it with the Omni V.
> >> When I
> >> got the Pegasus the LED on the 705  base would only glow very dimly
> >> and
> >> the rig was obviously not being fully modulated, so I had to put a
> >> battery
> >> in. The manual says it provides 4.5 Volts for electret mics.
> >> Appearently
> >> that not enough for the 705. I hope that we will get schematics
> >> someday so
> >> one could look into modifying such things. I hate batteries, they
> >> leak and
> >> ruin a lot of good gear.
> >>
> >> 73, Dave, VE1ADH
> >
> >
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