[TenTec] Re: Split TX and RX feed Xvtrs.

Robert & Linda McGraw K4TAX RMcGraw@Blomand.Net
Sat, 07 Sep 2002 16:22:17 -0500

Wade: (and others as I've cc'd the Tentec list)

I understand your situation.  As to separate RX and TX lines to the
transverter, keep in mind that the SSB and DEM require about 100 to 200
milliwatts of RF drive on the transmit side.  To get this from a Omni VI+,
in my case, I have a 40 dB attenuator that I built (3 resistor, 3
connectors)  between the output of the Omni and the 28 MHz TX input of my
DEM.  This allows the Tentec to run about 15 watts out.  It is nice an clean
and very linear in this power range.  It also gives me very good power
control overall.  I use the 28 MHz  RX output from the DEM to the AUX ANT
jack and that is switched from the front panel of the Omni.  The N.O. relay
on the Omni is used to do the switching of the DEM, and the 150 watt brick

Keep in mind that I have a couple of configurations that I use.  One, is
legal limit 1500 watts TX and a mast mounted preamp.  For this mode I do
have a sequencer that really handles all the switching.  The sequencer is
actually controlled from the NO relay of the Omni and the sequencer does the
rest of the switching and control between TX and RX modes.  In this
configuration I must be sure that all relays have switched, stopped bouncing
and settled before RF is applied.  I think you understand why.  1500 watts
in to the back end of the MOSFET preamp at 60 ft leaves a black spot in the
preamp box.  That's about all that's left..... POOF!  No transistor, no
printed circuit board either.

In a basic station using a Omni, a DEM  (or SSB transverter), and a brick
amp, as I've done many times, I just let the N.O. jack handle the
transverter and the brick switching.  I do not trust RF switching.   I added
a 1N4001 diode in series with the DC switching line inside my DEM and inside
my brick amp to isolate the switching lines from the common N.O. relay on
the Omni.  Works slick and simple.

My 40 dB attenuator is a 50 ohm 15 watt dummy load for the input R that I
got at radio shack, a 2500 ohm 1/2 watt series resistor and a 51 ohm 1/2
watt resistor on the output side. This forms a PI network attenuator.  I use
a SO-239 for the 15 watt dummy to screw into, and a couple of BNC connectors
for the input and output.  While not suggested, this way, I can never run
too much RF into the transverter, even if I forget to turn the Omni down
from 100 watts.  (I do believe in and use a written check list when making
configuration changes.  Saves expensive RF parts.)

Also, another advantage of using 10M as the I/F as opposed to 20M  for the
IF frequency such as the Tentec uses, there's not much likely to have images
or feed through from strong signals on the IF band.  There's nothing worse
than digging a signal out of the noise only to find that it is coming in on
the IF frequency and not of the band of choice.

As I've said in my earlier post, using a single 10 ele yagi (home brew on a
16 ft boom), 75 ft of 1/2" hard-line, the DEM with no mast mounted preamp,
and the OMNI VI+ with a 500 Hz CW filter in the high IF and a 250 Hz CW
filter in the low IF, I frequently on activity weekends I hear signals off
of the moon at moon set.  These are of course the "big gun" stations, but
never the less, it speaks well for the DEM and the Omni.

Don't get me wrong, there's nothing wrong with the Tentec transverter. It
just does not provide the performance that a SSB or a DEM provided.  And of
course, it's about 1/3 to 1/2 the price of the DEM.

What else do you need?


----- Original Message -----
From: "Wade Anderson" <K5TN@att.net>
To: <RMcGraw@Blomand.Net>
Sent: Saturday, September 07, 2002 3:26 PM
Subject: Split TX and RX feed Xvtrs.

> Hi Bob----
>      I run a TT 1208 on 6M from an Omni V, into a TE Sys. amp and a 5 el.
> beam @ 58'.  I've worked 73 countries and 535 grids on 6 from Oklahoma, so
> no complaints, but I keep hearing about the DEM and SSB transverters and
> their superior noise figures as compared to the Ten-Tecs.
>      I picked the TT (besides being a TT fan) because it is fed with a
> single coax line, no separate TX and RX lines as with the DEM and SSB.  Is
> this a big change as far as switching, and it worth the effort to gain a
> little noise advantage??  All us curious Ten-Tekkies would like to
> know----ha.
>      Seriously, I would like to hear from someone who has experience with
> the split TX and RX operation.  Thanks for your time.
>                                 Wade   K5TN
>                                 EM15   Oklahoma