pierpont@crboss.enet.dec.com (HOWARD PIERPONT) (01/22/91)
As part of a project at work I have been asked to configure a
van with the following hardware:
2 way radio [typical 2 way radio system]
Scanner
Cell Phone Computer System #1
Cell Phone Computer System #2
Cell Phone Voice System #1
Cell Phone Voice System #2
Cell Phone FAX System #1
Cell Phone Spare [FAX, Voice,Computer] System
OK that means eight antennas on the roof of a van [could be full size
or mini]. What should the placement be for the cell antennas? I
presume that I need six. I can mount anything anywhere on this
vehicle, so optimize.
Also, I'm looking for either a laptop with cellular modem or a good
source cellular modem.
Thanks,
Howard Pierpont Digital Equipment Corp.
77 Reed Road Hudson, MA 01749 508.568.6165mearle@pro-party.cts.com (Mark Earle) (01/26/91)
Howard Pierpont (pierpont@crboss.enet.dec.com asks in general about putting six phones in a van. While I cannot suggest much in the "correct" antenna placement or RF issues, I do have some advice. We use CMT's with external modems. The "magic" is a box from Telular (they have an 800 number). This box is called a "celljack". It connects in place of (or in paralell with, depending on cabling desired) the regular hanset/cradel. You then have a regular RJ-11 jack to plug in "whatever". The Celljack provides dial tone when the attached device goes off hook. It will interpret tone or pulse dialing, and send the correct data stream to the CMT transceiver. It will drive 5 REN-1 loads. So far, I've tried it on several Marata, Mitsubish, and Panasonic fax's. NO problem at all. We principally use it at remote sites, so we can modem in to a remote data collection computer. Again, no problems of significance. One thing you will notice, is that on calling TO a modem connected to the Celljack, it takes a bit longer. You may need to increase your terminal emulator's "time out" paramater. On OUTGOING calls through the Celljack, the same problem may occur, since it may take up to 5-10 seconds for the cell side of the call to set up. Most modems or software have a register or paramater to handle this, so it is generally NOT a practical problem. Audio quailty is good (a plain old black desk phone sounds better than the regular cmt handset). I have successfully used an HST 9600 bps modem, to another HST, and gotten 1600 cps; have also used a telebit; and have called to Compuserve's ports, both "regular" and MNP. Also to various Unix boxes and dos-based bbs's, all with no problems. This is both fixed, and while someone else was driving with the vehicle in motion. There is another distributor, Cellular Solutions, who sell the Celljack. It does not work with *all* CMT's but the included list is representative of the more popular units. The cost is about $450. Oh -- it has extensive on board diags you enable with a switch. For instance, ring attached instrument, decode touch tones, verify pulse make/break ratios, etc. For the $ it makes a good general purpose piece of test gear. It can also be set up for ground or loop start, etc. Another unusual use of this product (which is the size, about, of the CMT transceiver unit -- we just double-sticky tape the Celljack to the CMT!) is to connect to a port on a PBX. Dial '7' to get the "special" circuit. Turns out the CMT, with a directional antenna, could reach across an very expensive toll zone. The per minute airtime is about 1/3 of the rate to call direct -- and it gets cheaper at night. The celljack seems to provide all the DC signalling the PBX (small Panasonic) wanted-the pbx belived it has a standard line on that port. Hope this helps! mearle@pro-party.cts.com (Mark Earle) [WA2MCT/5] CIS 73117,351 MCI Mail to: MEARLE My BBS: (512)-855-7564 Opus 1:160/50.0 Blucher Institute, Corpus Christi State University