[amsat-bb] Re: Icom PCR-1000 PC controlled receiver

[Steve Fraser]

Hi All


> On Feb 10, 2007, at 11:05, Robert Bruninga wrote:
> 
>> Does anyone have a PCR-1000 ICOM remote controlled receiver?
>>
>> How long can the serial port cable be?  I heard it was operating
>> at something like 112,000 baud and could not be run the 200 feet
>> to our roof.  This makes it a deal breaker.
> 
> It powers up at 9600 baud.  If you use the Icom supplied Windows  
> software, the first thing it does is change to 38400 baud.
> 

I found this - partial quote follows:

http://www.lammertbies.nl/comm/info/RS-232_specs.html

The standard has a clear answer, the maximum cable length is 50 feet, or 
the cable length equal to a capacitance of 2500 pF. The latter rule is 
often forgotten. This means that using a cable with low capacitance 
allows you to span longer distances without going beyond the limitations 
of the standard. If for example UTP CAT-5 cable is used with a typical 
capacitance of 17 pF/ft, the maximum allowed cable length is 147 feet.

The cable length mentioned in the standard allows maximum communication 
speed to occur. If speed is reduced by a factor 2 or 4, the maximum 
length increases dramatically. Texas Instruments has done some practical 
experiments years ago at different baud rates to test the maximum 
allowed cable lengths. Keep in mind, that the RS232 standard was 
originally developed for 20 kbps. By halving the maximum communication 
speed, the allowed cable length increases a factor ten!

cheers

Steve