[CQ-Contest] Band edges?
kw4t at state.net
Mon Dec 18 02:55:25 EST 2000
Now I'm getting just a little bit worried. There are a number of things
which should be cleared up I'll touch on just a few.
1. Your transmitter does not filter out one of the sidebands in CW.
The CW is a carrier keyed on and off. Some older rigs actually key
various stages of the transmitter directly with the key. Pure CW rigs
have no modulator section and thus no SSB filters. Most modern rigs use
the sidetone via the vox circuit to key the transmitter but in the CW
mode all other audio trains are disabled on transmit. The sidetone you
hear is to help you monitor your sending, not the transmitters
performance. The audio produced is nothing more than an audio
oscillator like the old CPO. You can usually adjust the frequency of
the note and audio level to your own liking. These adjustments DO NOT
affect the transmitted signal. If you can select an 6 KHz AM filter in
CW mode you will note that the CW signal appears to have a "note" on
either side of zero beat. (The zero beat is when the audio frequency
reaches zero and thusly produces no tone). The use if upper or lower
sideband filters in the reception of CW provides a means to eliminate
interference and properly align your transmitter with the other stations
receiver for transcieve operation. If this weren't true then we would
still call CW and tune for the answer like in the bad old days.
2. Bandwidth is defined in the regulations. As I recall it is the
transmitted signal's width within which the power is greater than 26 dB
below the mean power of the transmitter. At the receive end if you
receive a very strong signal at say -40 dBm,
the bandwidth would extend to those points on your dial where the signal
is only -66 dBm (still a whopper of a signal). The band width is
measured both above and below the center frequency.
3. ARRL in there product review always shows CW wave forms. Most
monitor scopes can also provide a look at your CW wave form. Sharp rise
and fall times produce an apparent increase in bandwidth and I find the
signals difficult to copy at any speed. On a fading path these sharp
rise and fall times tend to muddle the information being sent.
4. Failures in the linear amplifier adjustments or malfunctions
producing non-linearity such that would cause flat-topping in SSB
transmission can produce key clicks on CW. I find that the parasitic
chokes in the old SB-220 and SB-200 need to be checked from time to time
since these tend to fry rather easily. Other amps of similar design
should probably be looked at as well (BE CAREFUL OF THE HIGH VOLTAGE IN
THIS SECTION - REMOVE THE AMP FROM THE OPERATING POSITION and BLEED THE
B-PLUS to GROUND)
73 for now from a chilly Lake Moneysgone, Minnesota where I had to wear
mittens during the 10 meter test last week.
CQ-Contest on WWW: http://lists.contesting.com/_cq-contest/
Administrative requests: cq-contest-REQUEST at contesting.com
More information about the CQ-Contest