[hpsdr] ALEX - Call for comments

Mon Mar 5 20:40:32 PST 2007

Hello Graham,

Thank you for starting this project!

My first thoughts for Alex at this moment:

- Could you/anybody please provide links/references to or add
diagrams/info/core-specs here or to the WIKI of the original filter designs?

- About shielding:
In a "computer-signals infested environment" like the HPSDR/Atlas card cage
with al its processors, clocks, data/address lines etc., I would suggest
putting the individual filter sections in closed compartments, if possible,
avoiding noise pick-up by the RF-coils?
Be it at the cost of more space required. (see expandability)

- For this reason also no SMD components (of the filter sections at least
that is) outside on the back side of the board?

- top-side = ground-plane/shield?

- Would using relays lower the losses/noise and allow for more TX-power?

- What would be the estimated TX-power allowed?

- Max. Expected/targeted usable frequency?

- Expandability, using more daisy chained boards for more bands?

- Guidelines to change/make custom band pass-filter sections?

Maybe with the help of something similar like this I found on the net:

http://www.aade.com/filter.htm

It looks like a handy (and FREE!) tool to design custom (band pass-)filters,
gives you amongst other things the number of turns on a standard type
ferrite O-core (like I think used in the band pass-filters of the
SoftRocks). 
Not tested/used this though...

- There was a discussion on the SoftRock Yahoo group about some static over
voltage protection circuitry in front of the receiver which could be a good
thing to include here also.
Or maybe this should be part of a separate (sturdy) mounting bracket for the
antenna- (BNC socket('s) ) and earthing connections?

(I made the following suggestion there to call it Cyberus (Cerberus) .......
Defender of the gate that leads from RF-space to Cyberspace.........  ;-) )

Regards,

Henry.

- 

> -----Original Message-----
> From: hpsdr-bounces at hpsdr.org 
> [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of Graham Haddock
> Sent: dinsdag 6 maart 2007 3:31
> To: hpsdr at hpsdr.org
> Subject: [hpsdr] ALEX - Call for comments
> 
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> All:
> 
> Hello, I am Graham, KE9H, the project leader and PCB layout
> person for ALEX which is the RF preselector filter pack for use
> with Mercury or other receivers.    Phil, VK6APH, is the designer.
> 
> ALEX is a multi-band receiver preselector intended to
> reduce the level of out-of-band signals at the input of a
> receiver, but it can also be used as a low level transmitter
> filter.
> 
> ALEX is an Atlas bus compatible card.  The Atlas bus is used
> for power and control, and RF in and out will be on coax
> connectors on the card, separate from the Atlas bus.
> 
> The card is relatively "dumb" compared to the other HPSDR cards.
> It will set the switches as it is told, via an I2C command
> coming from the bus.
> 
> Switching will be via Hittite HMC226 RF switches, rather than
> relays.
> 
> If I try to stay with a 100mm by 120mm card, (same size as
> Janus) then I suspect that we will be limited to about ten
> filter sections.
> 
> I propose that these ten filter sections would be:
> 160 Meters
>  80 Meters
>  40 Meters
>  30 Meters
>  20 Meters
>  17/15 Meters
>  12/10 Meters
>   6 Meters
> User Defined #1
> User Defined #2
> 
> There is also a bypass feature, providing no
> filter or frequency selectivity.
> 
> Each "user defined" option would be an un-populated filter area,
> with circuit runners laid out to use the same family
> of inductors and capacitors as the others, and could be
> populated by the user to tune the 60 Meters ham band, Medium
> Wave, AM Broadcast, 160 KHz or whatever. A three section
> bandpass or lowpass could be placed in each "user defined" area.
> 
> A block diagram of Alex and other information is on the Wiki.  
> The current plan is to use an I2C I/O expander chip to control
> the RF switches, not the full CPLD bus interface as shown.
> 
> http://hpsdr.org/wiki/index.php?title=ALEXAIRES
> 
> 
> Specific questions for the group.
> 
> 1.) Is ten filter sections enough?  If more is needed, will
> there be any issues going to a longer card, such as the 160 mm
> length card proposed for Penelope?
> 
> 2.) Does anyone care if I put SMT chip components on the
> back side of the board, and perhaps a shield?
> 
> 3.) Any preference for SMA verus BNC connectors?  I propose
> to use BNC for "external" connections such as antenna(s), and
> SMA for "internal" or card to card connections.
> 
> 4.) Should we allow for multiple antenna inputs? - we could
> select each one on a Tx/Rx and band basis using a GUI on the PC.
>  
> 5.) Using Mercury as a base line, we have an MDS of -140dBm in
> 500Hz without Alex in circuit. Alex will degrade this by say
> 2.5dB on 6m due to the loss through the filter and RF
> switches.  Is an MDS of -137.5dBm acceptable on 6m or should we
> consider adding a low noise preamp after the 6m filter?
> 
> 6.) Any comments you want to make?
> 
> Best regards,
> --- Graham
> 
> ==
> 
> 
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