LA6LCA high level 2m ssb receiver (IP3=40dBm)
Have been
curious about the unusual 2m project by LA6LCA.
He uses very sharp front-end selectivity and it is possible to
use 4-5MHz IF.
This was designed for earlier 2m bandplan, but the beacons
are now moved below 144.5 and we need not to
cover more than 500kHz, so
the tuned 1st IF bandpassfilter requirement and
tracking problems would be easier to solve.
The idea was created when he got at high level 70MHz xtal
filter, he uses a Philips BLU99 doubler
to 140MHz.
The 2nd mixer is SAY1 type with +24dBm VFO drive level..
If you can't make a local oscillator with 180dBC/Hz purity
at 1MHz distance - and it is quite flat towards the carrier
frequency,
it is no point in using this concept.
You'll find data for BLU99 at http://www.semiconductors.philips.com/pip/BLU99_99-SL_CNV_2.html
Will try to update information as soon as possible
Believe the reason for building this high
level transceiver was some local problem with other local
amateurs who used mediocre rigs,
claiming that LA6LCA was the person causing trouble, so he wanted
to build a rig with documented specifications - far batter than
any
of the mediocre rigs found in the neighbourhood - so it should be
no reason for complaining about his bad equipment. For further
improvement
he uses remote control and gain some more distance to the
complaining parts. He also built a portable 2x 4CX250B
power amplifier with
ALC to compare the RF input envelope with the output and correct
the envelope to improve IMD.
Next version of transceiver is supposed to use 1.4MHz IF
xtal filter instead of 455kHz. He is also building a receiver
using 4-gang tuning capacitor
from an American WWII surplus receiver
2m RX pre-amp using MRF134. The device needs 100-150mA for low
noise figure, maximum voltage +28V. Suggest to use a constant
current circuit as shown, but only a simple circuit is shown,
some optimization of input impedances is neccessary for optimum
noise factor (LA6LCA).
Just wonder if the Zwischenbasis-amplifier would
be an improvement at some of the stages where LA6LCA uses BLU99
or MRF134,
see /la8ak/c19.htm
more comments are shown on page d14
d91. SCA
VHF meeting June 2003
n16 LA7MI highlevel mixer notes
c19 mixer
termination amplifiers
2004.10.24