morse code versus VHF

[BOATKID]

excuse my ignorance but how come in olden days you could transmit for oodles of miles with Morse code type radio yet today you can only get 14 miles with your VHF set (exclude satellite)

/forums/images/graemlins/confused.gif

 

[Searush]

Morse code is effectively long wave, but VHF (Very High Frequency) is extremely short wave & therefore line of sight only. Simple physics of radio propagation.

 

[Major Catastrophe]

Morse code is transmitted on a long wave and can be skipped off the ionosphere, or summit similar, and bounced around the world. You can sometimes hear a skipped VHF message, if the conditions are correct, but nothing you can rely on.

Morse code, being just beeps, can cut through all sorts of interference that would drown out speech.

On long lonely night radio watches we could hear morse code, sometimes the reception was just a quite swoosh noise in the background, but our signallers could still read them.

 

[Beadle]

Not exactly

Morse can be transmitted on VHF and voice can be transmitted on low frequencies.

All else being equal Morse (more correctly CW) will be more effective than voice because it is only necessary to detect that a carrier exists enabling the receiver bandwidth to be very narrow. Foe voice you have to demodulate information (voice) from a carrier and require a much wider bandwidth.

The narrower bandwidth also means that the receiver picks up much less noise, This means that CW can communicate at much lower levels of signal to noise ratio than voice.

The signal to noise ratio is the limiting factor in any communications system.

 

[RogerRat]

Thanks, well put.

Must be a Ham, me thinks. /forums/images/graemlins/ooo.gif

 

[Poignard]

Ships used four frequency bands.

Medium frequencies used for Radio Telephony. Calling/distress frequency 2182 kcs. Using Single Sideband system [SSB]

Low frequencies for morse. Calling and distress frequency 500 kcs, then shift to a working channel. At these frequencies the"radio waves" follow the curvature of the earth so ranges in excess of line-of-sight were possible. This needs powerful transmitters and large aerials; you can see some of the aerials in a field near the M1 near Rugby.

High frequencies were used for morse. Several frequency bands were available and the best band for given conditions, and time of day, would be chosen by the Radio Officer so that the signal "skipped" or bounced between the earth and layers in the upper atmosphere. This enabled world-wide communication by low powered transmitters. This is what HAMs use.

Very High Frequency [VHF]. This is the short range, easy to use, sytem most of us have.

Morse code can be picked up in bad conditions when you could not make out speech because it is simply made up of short and long bleeps.

 

[nonitoo]

Sort of thread drift.

All this reminds me of the joys of using Consol (lots of dot and dashes) in endless North Atlantic bad weather and trying to find the English Channel from the depths of the Atlantic.

No radar, Decca or gyro compass - ship built in 1944

Tom