[hpsdr] CASMIR design v0.4 plus introducing COPERNICUS!

[pvharman at arach.net.au]

I think we should avoid relays if possible. The latest switches should have a 
high enough IP so as to not be the limiting factor on the receiver 
performance.   If we do have to use relays then bleed a little current through 
the contacts to help keep them clean over the long term. The CDG2000 does this 
along with a number of commercial designs.

In my SDR I use the bandpass filters from the Pic-A-Star design. Each is a ham 
band wide filter with good shape factor and low insertion loss on the high 
bands. The inductors were hard to find about 18 months ago so I expect we will 
need to find alternatives. There are also lots of 1% silver mica capacitors 
that I'm not sure have an SMD alternative. It was a lot of effort to hand 
build the board but the performance is excellent. 

I can provide a copy of the circuits and components that I used. I am 
currently using this in front of the LT2208, with a high performance pre-amp, 
to test the Mercury design. 

73's Phil....VK6APH 






Quoting Lyle Johnson <kk7p at wavecable.com>:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hello Alex!
> 
> > Personally it seems like a waste to use an ATLAS slot forducto
> > COPERNICUS, maybe an external card. There's lots of room 
> > in my ATX case to mount it!  : )  (hint, hint, hint)
> 
> Copernicus will need some sort of control logic to run it.  You could 
> reserve space at one edge for the ATLAS DIN connector and put another 
> connector in the same area. User than gets a choice of making it 
> Atlas-compatible or not.
> 
> It would also need space for the DS2431 1-wire ID chip.  If the control 
> is via SPI or I2C, then the lines are already predefined for the ATLAS 
> bus, making things pretty simple.
> 
> I suggest SPI, and use TI TPIC6C595, Allegro A6810 or similar ICs to 
> handle the control.  These can sink plenty of current for relay coils.
> 
> Alternately, I2C and use PC8574 (or similar) parts with some means to 
> strap the address.  Not sure if these can directly drive relays.
> 
> Almost as cheap, you could use a small PIC which can be set up as SPI 
> slave or I2C slave.  If you run the PIC from 6V, you may be able to 
> directly handle 5V coil relays.  Elecraft, for example,  has done this 
> for years in the various products.
> 
> Finally, please consider the use of latching relays.  They're not 
> expensive, the board then remembers its last state, and operating 
> current is nil.
> 
> 73,
> 
> Lyle KK7P
> 
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