How hard?

[Telecolor 3007]

How hard was in 1946-49 to intercept police communications? How big it was an radio that could intercept police communications on diferet states (for eg. like an radio that you could turn from M.W. to L.W.); it needed a big antena?

[wa2ise]

LIkely that radio would be a little bigger than the size of an ordinary shortwave radio. Possibly a double conversion superhetrodyne. The police would have had such radio sets mounted in their police cars, probably most of the set in the trunk, and a small control head on the dashboard. Maybe they used VHF FM radios, sinilar size. American police and fire depts used General Electric "Progress Line" FM transcievers back in the 1950's. These radios used about 20 tubes, and were about 40cm by 30cm by 10cm big.

The antennas would be small enough to mount on a vehicle.

A radio that could intercept local transmissions would be essentially the same as an AM radio or an FM radio.

[blue_lateral]

I dont know if you mean in the U.S.A, but if you do, It wasnt hard at all. The federal communications act of 1934 guranteed the right of any citizen to recieve any signal, so it was legal, too.

In the 1930's, most if not all police agencies that were using radio were using "one way" radio. This just means they had a radio station, and all the cars had recievers. The cars could not talk back to the station. Have you heard the expression in old movies "Calling all cars"?

These police stations were just above the broadcast band at about 1700kc and were AM. Any home radio that could tune up that high could recieve it, and a lot of older american radios are marked "police" up at that end of the band.

By the mid 1950's I think most agencies were probably using FM two-way radios just like today. In the period you ask about, 1946-48, I would guess the system in use probably varied wildly among different agencies, with some still using one-way AM, some using the old AM but adding FM transmitters so the cars could talk back to the station, and some using FM two way as today.

Heres how the California Highway Patrol did it.

http://www.mbay.net/~wb6nvh/chpradio.htm
http://www.mbay.net/~wb6nvh/CHPcycle.htm

And a little about Motorola from the same guy

http://www.mbay.net/~wb6nvh/Motadata.htm

I think in Canada, before world war two, you had to have a license for a radio reciever. I think right afterward you didn't, but I don't know for sure. Maybe some Canadians will jump in here and tell us.

John

[blue_lateral]

Listening to different states probably wasnt easy. It was probably not really tough in the one-way AM days, but FM isnt good for long distance, and most of the early FM two way stuff was on what we now call "Lowband VHF", about 30-50mc.

There's an exception. These frequencies are subject to "skip" like a CB radio. You might hear someone from another agency a long way away. Up here in Washington, lowband VHF isnt used much anymore, but those agencies (and businesses) that do use it hear others a long way away, usually in the deep south. There is no way to predict exactly what area you will be hearing.

[Telecolor 3007]

So a criminal, beeign folowed by the police could found out if the cops chased him?

[blue_lateral]

Yes, Anyone who was interested could listen. The police of course knew this and would probably say only what was really necessary. I doubt this was a big advantage to the criminal being chased. The radio was more of an advantage to police.

There was a saying in the old days, "You can't outrun the Motorola" (Motorola was a major manufacturer of police radios). Someone running in a car for instance would have had to deal with traffic, and so on. If every police car in the area knew where he was and what direction he was going there wouldn't have been much chance of getting away.