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Short-haul Modem Summary

Short-haul Modem Summary

If phone service is not available, Short-Haul Modems (SHM) can be very useful for extending RS-232 distances from the limit of the 50 foot RS-232 cable up to 4 miles. (Please see manufacturer specifications for connections and actual distances).

There are two SHMs which the UNAVCO facility has in use at permanent stations, and which transmit asynchronous data up to 4 miles depending upon wire specifications and data speed.

A short-haul modem might be required if the base computer is located at a distance greater than the practical limit of 50 feet for standard serial RS-232 cables. However, the requirement for a physical wire connecting the computer and receiver limits the usefulness of using a short-haul modem to distances usually shorter than their intended limit of approximately 4 miles. A reason for this is that the transmission rate is a function of distance with maximum data rates of 19200 bps being achieved over distances of 1 mile or less.

RAD modems

Black Box Corporation

There are two SHMs which the UNAVCO facility has in use at permanent stations, and which transmit asynchronous data up to 4 miles depending upon wire specifications and data speed.


Send questions or comments to Support (supportunavco.org).

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Comments (1)
Comment by Dazy on Sat, Mar 17th, 2018 at 9:34 AM
modems are work properly when we need a high-speed internet connection where especially when we need to access a big amount of data over the data. Short-Haul Modems work well. https://babasupport.org/routers/dell-routers-customer-service/624
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Last modified: Monday, 12-May-2014 00:18:29 UTC