[TenTec] RE: Omni V Fm'ing

[MW0CDO]

Hi Bob and the group.

Well, I've found out what the problem is.

The Molex PSU connector and the fuseholder were causing around 600mV drop @
20 amps.

I have now connected the radio directly to the PSU, using as short a length
as possible of 25 amp DC power cable ( approx 12 inches long ).
This is soldered to the radio side of the fuseholder and the ground
connection bolted to the rear of the radio.

The PSU being used is homebrew, consisting of a 723 > TIP41 > 3x BUV21 (
Icmax 40A Ptot 250Wc ) and has always worked faultlessly with all other
radios. It is RF hardened and incorporates current foldback beginning at 25A
and has a crowbar. The OMNI V has approx 100Hz freq shift on this supply
between min and max RF out in tune mode.

I still don't see why the OMNI V is so sensitive to 0.5-0.6v supply change,
especially as all the oscillators in it run off the 8.5v +REG supply which
doesn't change as the supply voltage varies..what about the owners who may
install the radio in a vehicle?

I also hooked up a car battery to see what happened, still get approx 100Hz
shift as RF out is varied from min to max.

Tried a Palstar 30 amp supply, approx 300Hz shift between min/max RF out.

I use digital; modes occasionally, eg PSK31 and even small TX frq shifts can
cause problems, especially if the shift is not constant but varying with TX
power out.

I do not have any problem with the physical location of the PSU relative to
the OMNI V.. it is on the right hand side of the radio, and the toroidal
transformer in the PSU is located in the top left hand area. On the left
hand side of the OMNI V, I have the old faithful Yaesu FT-102, complete with
it's massive built in PSU. This doesn't appear to cause any problems with
the OMNI V in RX or TX. or vice versa.

Any ideas on how to further improve on the situation are very welcome!

I would like someone else that owns an OMNI V to try this test for me:

Using another receiver on 14MHz SSB, monitor the OMNI V on 14MHz in tune
mode while varying the RF output power from min to max.
Do you notice any change in the beat note on your receiver?

This is all Walt K1QS's fault.. it was he who told me it was FM'ing a
little! :-)

Thanks for reading... Paul MW0CDO in sunny South Wales UK.

Happy holidays!


----- Original Message -----
From: "Robert & Linda McGraw K4TAX" <RMcGraw@Blomand.Net>
To: "MW0CDO" <gw7lhi@hotmail.com>; <VE1BN@aol.com>
Cc: "Ten-Tec List" <tentec@contesting.com>
Sent: Wednesday, March 27, 2002 11:53 PM
Subject: Re: [TenTec] RE: Omni V Fm'ing


> I still say it is still a connector problem which no one has seemed to
> explore.
>
> Regulation in a PSU is the result of an abundance of fast slew rate gain
in
> the regulator circuit.  In fact, a fast dynamic regulator (not a 723 type
> device either) does not need a filter capacitor at all, as it will follow
> the fluctuations of the AC ripple, much faster than a dynamic load of
speech
> or CW keying.
>
> There is no problem with the design of the Tentec 962 power supply.  It
> works up to 22 amps and does not cause a problem with the Omni or Paragon
> series radios.  Now, is there a fault in the PSU such as one of the series
> pass transistors, Q1 or Q2, open (not a typical failure mode), or no drive
> to the base or an emitter resistor (R3...R6) open and  etc. That's another
> problem.
>
> One problem that I discovered with my Omni VI+ was the fuse holder was
> broken at the threads on the inside of the radio.  The fuse had inadequate
> contact pressure and thus higher in-circuit resistance.  Replaced the fuse
> holder.........problem solved.
>
> 73
>
> Bob K4TAX
>