Hi,
You misunderstood me. The 8 bit bus drivers would be used to drive a
transformer with a square wave LO in bridge mode to get 10 volts peak to peak.
TNX on k2 modifications. I am considering a homebrew first mixer module with a
pair of roofing filters in the future. Frank
Giancarlo <[EMAIL PROTECTED]> wrote:
Hi Francis
--- In [email protected], FRANCIS CARCIA <[EMAIL PROTECTED]> wrote:
>
> Hi,
> So the square vave drive to a bus switch must saturate better
than the SD5000. Racal drives the gates of the SD5000 through a 1:2
transformer with about 10 volts peak to peak drive.
Yes, you cannot really have analog input signals into FST switches
equal to Vcc(pp) as there will be distortion but in a RX
mixer ...you need a lot of power into the antenna...hi
> This means the gate pairs go about 10 volts peak to peak. I was
wondering if you took a AC bus driver one that is 8 bits and split
them in half in two pairs of 4 drivers. Then AC couple it to a
transformer in bridge mode to get 10 volts peak to peak drive.
No. Although I am a "complex mind".... I try to go KISS with
solutions, maybe starting from caos...hi
I have some 8 bits SWs I wanted to try in one of my designs. One idea
was to have switches in parallel to reduce the Ron but this may not
be a good solution as you have capacitance increase and although in
the same dice you may have the switches not switching on and off at
the same time, potentially ending in more problems than benefits.
> I'm considering converting the first mixer of my RA6830 from a ring
to H but presently the weak link appears the roofing filter not the
mixer so may have to do a homebrew module with a pair of roofing
filters. The Racal mixer can take a HP8640b at full bore and appears
to be just starting to saturate at full bore of plus 19 dBM.input.
OK. You should not be afraid of the H-Mode mixer. The suggestion is
to have a diplexer following at its output. The H-Mode mixer is not
so sensitive as diodes mixer to load changes. You may loose around 5
to 7 dBm in IP3. You will still have a mixer with an IP3 over
+30dBM !!!!
To give you an idea. The 1st mixer replacement in a K2 using an I7SWX
2T H-Mode followed by a simple 2 xtal roofing filter (10kHz BW), to
protect the IF amp and following stages, moved the K2 IP3 with SBL1-
TUF from +15dBm, with LO=+7dBm, to +27dBm (2 tones at 20kHz spacing)
with LO= 0dBm. Probably removing the roofing filter it may had
resulted in an IP3 = +33/35dBm. H-Mode Mixer hould be ok for input up
to +5dBm bedore starting to change 1:3 IP3 response.
> The bus switch sure works well in my SDR module I can get 96 dB
of dynamic range but it was limited by the sound card not my input
board. frank
You are right. The DR limit in a SDR is not much on the FST but the
low noise OPAs not in "line" with IP3 limiting around 80dB and sound
cards.
Please keep us informed on your Racal mods.
73
Gian
I7SWX
>
