Newsgroups: comp.robotics
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From: up729@freenet.Victoria.BC.CA (Wayne Chin)
Subject: Re: 19.2K RF spread spectrum modem - $99!
Message-ID: <1994Oct6.153638.11632@freenet.victoria.bc.ca>
Sender: news@freenet.victoria.bc.ca (News Manager)
Reply-To: up729@freenet.Victoria.BC.CA (Wayne Chin)
Organization: The Victoria Freenet Association (VIFA), Victoria, B.C., Canada
References: <STEVE.94Oct4011135@susie.vigra.com> <sasrer.780723957@sas.com> <Cx0EsH.8sw@csn.org>
Date: Thu, 6 Oct 1994 15:36:38 GMT
Lines: 86


Since the author (Steve Haehnuchen) is well on his way on getting the
RDA-100 to work, I'll only add info from my experience with the RDA-500
units, which are mechanically identical. The RDA-500 is spec'd for 800',
and we've had no problems at over 500' outdoors.

In a previous article, steve@vigra.com (Steve Haehnichen) says:

>-=> On Sat, 1 Oct 1994 19:43:28 GMT, dvukovic@csn.org (Donald VuKovic) said:

<STUFF DELETED>

>- The antenna connector on the modem is wacky.  I haven't found anyone
>who has ever seen it before, much less sells the mating connector.
>The good news is that there are four well-placed holes around the
>micro connector.  This is so that you can install a standard
>right-angle SMA connector instead of theirs.  I did it, and it works
>great, but it took some careful work.

The antenna connector is a real OEM one, due to FCC regulations that
discourage antenna "upgrades" that will push the power output above the
1/2W level (hence, will require a radio bradcast license). Proxim says
that you can get the BFA antenna connector pigtail directly from Murata (part
#MXYH63XX152) at 814-237-1431, with a 12-week lead time. If you're lucky,
Proxim will even sell them to you, but they're not cheap at $9 a piece.

>- The pin header on the modem is not right-angle like the OEM manual
>says.  It's a straight pin SIP row coming out the bottom, which makes
>it odd to work with.  It's also 2.0mm pitch instead of the standard
>DIP spacing.  I just shrugged and soldered right to the pins.  If I
>could have found a female header, I'd rather use that.

Proxim uses JST connectors for the power/data lines, but these appear to
be OEM ones as well (very hard to find).

I used HRS A4B series 2mm connectors, since I needed to have the connectors
removable. I got mine from Digikey. I had to shoehorn two of the
single row crimp socket connectors side-by-side to reach all 16 pins, and
crimping the pins with a pair of pliers takes a bit of patience.

>I'll post more details when I get the two of them talking.  If anyone
>knows a good source for cheap 900Mhz antennas (directional would be
>nice), please post or mail!  Right now, it looks like cellphone
>antennas will have to do.

I used cellular phone antennas (both vehicle and base-station types), and
they work well. However, the RDA-500s worked well inside our building even
without antennas attached (although it may not be good for the RF
amplifier to do this). Virtually any 3dB to 6dB antenna will work.

>
>-Steve
>
>Steve Haehnichen                 Vigra, Inc.  San Diego, CA
>steve@vigra.com                  (619) 597-7080 x116   Fax: (619) 597-7094
>                                 Serial #: 14358
>
>Serial Port
>-----------
>          Operating Mode: Pass-Through             Delimiters: 13,10
>               Echo Mode: Simple                   Max Length: 256
>               Baud Rate: 9600                 Input Time-Out: Off
>
>     XON/XOFF Generation: Disabled       XON/XOFF Recognition: Disabled
>          CTS Generation: Enabled              DSR Generation: Enabled
>

The delimiters are used as flow control characters-the current packet in
the buffer gets sent when it detects a delimiter character. Max Length is
the length of the buffer; the current packet is sent when any of the
following conditions occur: 1) a delimiter character is detected 2)the Max
Length is reached 3)a Time-Out oc 4) XON/XOFF characters are detected

If you have the luxury of using hardware flow control (which I didn't),
CTS will save you from the hassles of the above.

Although the modem can communicate at 19K2 on the serial link, there is a
latency time involved every time a packet is sent. We were transmitting
binary data at 9600, but the effective data rate was about half that.

Have fun!

-WaC

-- 
Wayne Chin
