Geof Wheelwright enjoys the flexibility of the Sendata/Tandy modem

Built-in modems are the big difference between North American portables and the versions of them that reach our shores. Consequently, the effectiveness of portable machines 'in the field' is considerably reduced and the great advantages of portable computing cannot be exploited to their full. There are any number of reasons why UK editions of portable computers don't come with the built-in modems - not least of which is an allegedly slow modem approval system by British Telecom that would unduly delay the introduction of new machines in this country.

The long and short of it is that if you want a portable with a modem in the UK you'll have to buy a modem yourself. And if you want to maintain the idea of total portability in your choice of modem, you'll probably consider either the Tandy TRS-80 or Sendata 700B acoustic coupler.

These two modems are battery-operated by built-in rechargeable nickel cadmium batteries and can run up to ten hours on one charge. They are similar enough to be treated as one modem because they are manufactured by the same company - Tandy buys them from Sendata and puts on its own 'badge'.

The modem comes in a two-piece styrofoam box and is wrapped in plastic. It consists of two 'cups' bridged by an accordian-like bit of flexible plastic and features two lights and an answer/originate switch at one end. As the batteries are rechargeable, they don't need to be removed from the machine - just plug the modem into the mains overnight and it'll be fully charged in the morning.

The modem is only slightly larger than a telephone handset and will fit over any business phone and most home sets - although slimline phones could prove difficult to use with the machine.

If you know how to use your communications package (you do need one to make the most of this modem), you shouldn't have any problem hooking up the modem and getting it going. This being the case, little documentation is needed, which is lucky as little is provided.

This boils down to the following, which covers the main problems you're likely to come up against:

• Remembering to leave the modem on Originate when you're dialling up a bulletin board or machine;
• Putting the mouthpiece in the hole that says 'mouthpiece';
• Plugging the RS232 cable into the computer the right way up.

Flexibility is provided by the articulated section between the cups that allows you to get a snug fit between phone and modem. The portable nature of the modem means that you can even download information over the phone at a callbox (although the pip-pip-pip sound every 5p may cause problems with data transmission).

I tested the modem with a wide variety of computers and mailboxes, and found it to be reliable and effective with all of them. The cups cut out the kind of sound interference that often garbles signals through acoustic couplers.

I used the modem most with the NEC 8201A portable computer and found that it really did give the machine that one measure of portability that was missing from it. I called from Coventry and Birmingham to London and from London to Manchester, Sweden and even Australia with no problems, and obtained consistent performance from both these modems.

I also tried using both the Tandy and Sendata modems together to allow communications cost more than £200) for this form of portable acoustic modem than you do for their cheaper 'mains-bound' counterparts.

I thoroughly enjoyed these and would recommend them to anyone who wants a reliable and portable 300/300 baud modem. The only hesitation I might have is on price - but the superior design, inclusion of the built-in nicad batteries and portability scotches that hesitation with the assurance that, as always, you get what you pay for.

The Tandy modem is more expensive than the Sendata - but it's more easily available as Tandy has stores all over the country and Sendata is a smaller London-based company.