[NLRS] 222 ???

[Gerald]

On Wed, 2005-09-14 at 09:44 -0500, John P. Toscano wrote:
> 
> Gerald wrote:
> 
<SNIP>
> 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.

The ALC input is part of a control feedback look which doesn't need loop
gain stability. That can let it be variable. One could use an ALC
detector at the input of the transverter to probably control the last
20% of the voltage going to the exciter. One could detect the input
signal and use a variable attenuator on the input of the transverter, as
in some of the transverters in G3SEK's book.

>   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 sensitivity.
> 
With lots of strong and weak signals about, receiver gain in front of
the IF rig is very important.

Its a good feeling to hear lots of noise when you turn on the
transverter, but that easily kills dynamic range so the assembly is
easily overloaded by strong in band and out of band signals (154 MHz
pagers are the most common problem after in band repeaters on 2m or
channel 13 TV at 222).

Receive converter gain needs to only be just that which lets the
converter RF stage set the system noise figure. Adjusting takes the old
fashioned diode noise generator and the audio VTVM. Some front ends like
the FT-736R have poor gain distributions so the NF is defined after then
RF stage, but that can be fixed. My 220 module works much better than my
2m module.

Long ago, about 1965, I was in Texas and using a 75S-3B and a home brew
converter for 2m. Once I got the converter giving a decent NF, I had
lots of problems with one strong signal leading to spurious responses
all over the first 200 KHz of the band. The CW segment hadn't yet been
legislated. W5WXV running 650 watts to a quad of Telrex yagis about 20
miles from me was the problem station. I heard him something like 18 or
20 times in that 200 KHz with our beams facing each other. He was on
144.085 running very narrow FM that was beautiful copy with the receiver
on SSB mode. I worked over the 75S-3B to improve its dynamic range, then
put an attenuator between the nuvistor converter and the receiver and
adjusted that attenuator for the least signal from the converter that
didn't increase the system NF. Then I heard W5WXV only three places in
that 200 KHz. Once at full scale where he was supposed to be and the
other two very close to the system noise level. Every receiver converter
needs that same adjustment. A relatively narrow band IF filter between
converter and receiver can help a weak IF receiver, a narrow band RF
filter can help too though its hard to get really narrow (200 KHz)
without excessive insertion loss.

> Good luck, and hope to work you on the band someday soon.
> 
> 73 de W0JT
> _______________________________________________

-- 
73, Jerry, K0CQ
Dr. Gerald N. Johnson, electrical engineer
All content copyright, Dr. Gerald N. Johnson