[NLRS] 222 ???

[John P. Toscano]

Gerald wrote:

>On Tue, 2005-09-13 at 22:24 -0500, christenson at charter.net wrote:
>  
>
>>Looking to add 222 to the operation. I have 2 rigs that can operate on the typical 10 meter inputs. Issue is that both of them the can only transmit a minimum of 5 watts. Every transverter I have seen out there wants a maximum of 100 mW. What do a ham do? The preferred rig is a TS-2000, currently the 6 M rig, or my faithful IC-706m2g. Don't want to put too much into it but then again don't want crap. Any ideas out there? Any info greatly appreciated.
>>
>>I may even drop the ic-910 and pick up a ft-736r with all the mods - 6 meters?
>>
>>KC0REO
>>
>>Kris
>>    
>>
>
>DEMI has a transverter interface that will take 5 or 10 watts.
>
>You can simply put in an attenuator, but the receive side may need some
>extra gain to overcome the attenuator if its in both the receive and
>transmit line. Or you may be able to drop the exciter power further by
>putting a DC bias on the external ALC line. Some rigs when turned down
>have a pulse of output before they go to low power.
>
>The transmit mixers tend to need only a milliwatt or just a bit less so
>there's already attenuation in the transverter.
>
>I have modified the 220 module in my FT-736R and it hears better there
>than on 2m. But its OK on 6m. With a couple FT-857D in the shack now, I
>should be selling that 6m module and 150 watt Mirage amplifier and keep
>looking for a 1296 module for the 736. Any trades out there?
>
>  
>
I use the DEMI transverter and an Icom IC-706MkII for the IF rig.  I am
using the TIB interface, which has a voltage inverter to drive the ALC
line of the radio, so that its transmit power is driven lower than you
can get by simply going into the radio menu and setting the transmit
power to "L" (low).

The IC-706 is one of the radios that has been noted to put out a high
power spike on transmit for a very brief time until the ALC wrenches
the power back down.  After using my system for several years, I am
happy to report that it does not hurt the transverter one little bit.

In fact, although I don't recommend you try this at home, when I was
first setting up my transverter, I was too anxious and got a little
careless.  I did two things wrong at once:  I had the output of the
transverter go through a short coax jumper to a power meter, then
another short jumper to a dummy load, so I could measure output]
power.  I put the IF radio into FM mode to get a full-duty carrier,
and started testing the power output.  It read zero.  I kept fiddling
and transmitting, still got zero.  Then my hand brushed against the
heat sink, and WOW it was hot!  So power was indeed being made.  It
turned out that the first coax jumper was bad (shorted), so the
transverter was transmitting into essentially zero ohms.  No harm was
done to it.  A little more fiddling, and POP, a puff of magic smoke
drifted out of the transverter and the smell of burning electronic
components filled my nostrils.  I then noticed that the ALC line
had come loose, and I had been transmitting the full 100 watts of
the IC-706 on ten meters into the transverter, and the 50 ohm resistor
in the input circuit had finally vaporized.  With much trepidation,
I replaced the resistor, and the transverter has never hiccuped again.
(I also re-designed the connections so that if the ALC line ever
becomes dislodged from the radio again, the TIB will automatically
drop into HF bypass mode and no RF will go to the transverter.
(Which goes to prove that mistakes are simply an opportunity to do
it better next time.)

In any case, my take on the matter is that the DEMI 222 transverter is
as rugged as you could possibly want, so don't worry about a 5-watt
spike for a few milliseconds.

P.S., if I was doing it all over again, I'd think twice about using
the TIB interface, because the ALC level adjustment is very fussy
and doesn't seem to hold steady from one month to another.  In fact,
I am seriously considering following KM0T's lead and setting up a
SDR-1000 Software-Defined Radio as the IF for 222, 902, 1296, and 2304
in the future, and with only about 1 watt of maximum output plus
easy setting of lower transmit levels, the problem should go away.
In your case, as Jerry points out, using one of the DEMI 10-watt
attenuator interface units is a good plan.  The transverter has
plenty of dynamic range on the Rx gain level, so even if you lose
some of the 10M signal back into the radio from the transverter due
to the attenuator, you can turn up the Rx gain (at the IF level) to
overcome it.  Note that since this is on the 10M side, not the 222
side, it will not harm your receive NF or receive sentitivity.

Good luck, and hope to work you on the band someday soon.

73 de W0JT