[hpsdr] ALEX - Call for Comments - III

[Eric Ellison]

Folks

Gess I'll throw in my 2 Cents.

I like all of Phil_C's justifications for CPLD control in an earlier
message.

I don't see this Monster Alex on the Atlas buss for the few minor
connections, but an external board mounted in the inside world, shielded,
and RF connectors through the rear/front panel for all RF inputs and
outputs. The board could probably even be supported by it's heavier duty UHF
or other Antenna connectors through the rear/front panel. Small smx jumper
cable from the output of Merc/Pen (or some QSD/QSE combo) to input of Alex. 

Inside world connections for clock, I2C, Reset coming off Ozy HDR2, for
command and control of whatever 'smarts' go on Alex who is perhaps equipped
with a RJ45 for TP connections from Ozy. 

>From the Alex diagram it looks like every filter section has one input and
one output going to the 'relays' This would make an Alex motherboard a great
candidate for little 'daughter' filter cards on a 'plug in' basis. Tunable
in place. Small 'filter cards' could probably be 2 sided 10 or more to a PCB
sheet, since the configuration is about the same. Alternate circuit configs
could be accommodated. This would satisfy the myriad of filter combo's which
have been requested and 10 could be accommodated. Mounted so they are
accessible by removing the shielded side panel on my Aria enclosure. (smile)

Make the board the same size as the Amplifier board and go in a TenTec 9??
Enclosure!

Carry on! Great brainstorming!

Thanks
Eric - AA4SW




 






-----Original Message-----
From: hpsdr-bounces at hpsdr.org [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of
Graham Haddock
Sent: Wednesday, March 07, 2007 8:03 PM
To: 'High Performance Software Defined Radio Discussion List'
Subject: [hpsdr] ALEX - Call for Comments - III

***** High Performance Software Defined Radio Discussion List *****

All:

Thanks to all for good continuing input and discussion.


General:
Interesting reading suggested by other emails earlier today:
"G3SBI H-Mode Mixer as tested by PA3AKE"
Specifically - preselector comments/measurements on Page 9.
Best I can tell, we are using the improved topology he refers to.



1.) Name...
I'll take offline with Don.



2.) Control...
Lyle's KK7P comments on control lines allowing coupling to the
input and output of the filters and allowing "filter bypass"
are noted.

A question for Lyle or Phil C or someone familiar with the CPLD parts...
If I don't care about output rise and fall time, what is the
largest capacitor (I am thinking 0.01 uF or 0.1 uF, .01 ohm ESR)
that I can throw on the output line of a CPLD?  Will it current
limit and protect itself until the capacitor charges, or will
it trigger life issues after repetitive cycling?

Phil C. - I will research the EPM240 CPLD.  

Also, I am thinking about inverted signals from the decoder, versus
distributed inverters for the RF switches, versus a distributed
SPI decoder and respective impacts on PCB layout and
potential RF coupling.



3.) Filter Design and selection...
I posted the individual filter performance plots on the bottom of the ALEX
page on the Wiki, for those of you that wanted to look at them.

These look like a "contest" or "field day" grade set of preselectors
appropriate for use in "Overload Alley".

Read Phil H's comments on the robustness of the native
Mercury receiver (yesterday).  It does not sound like a preselector
is always necessary on a Mercury.  The story may be different
on other receivers.

I also played around a bit with opening this filter topology out
to about 40 percent bandwidth, (you have to relax the ripple
spec from 0.01 dB to 0.1 dB) and posted a sample of that to the
Wiki, too.

It looks reasonable, which means that a ten section overlapping
filter continuous coverage preselector is also possible, with just
L and C value substitution.  I assume that MW and down would
be a single low pass filter, and 1.7 to 30 MHz would be 9 overlapping filter
sections of about 40 percent bandwidth each.



4.) Physical design...
Nothing to report



5.) Preamp...
The preamp guys came alive last night.  I need a recommendation
for a 6M preamp of known performance/layout to add to the board.



6.) Transient Protection
I don't think that the neon light will work in this application.
The weak link is the Hittite RF switches.  Their spec
sheet does not say, but I can't imagine a GaAs FET
in this part surviving anything over 30 volts.
I think we need to consider biased diodes or something.
Does someone have a circuit of known performance/layout to
add to the board?


--- Graham / KE9H

==


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