[AMRadio] 7160 tonight: Suggestion


D. Chester k4kyv at charter.net
Fri Apr 3 13:51:50 EDT 2009


> From: "Todd, KA1KAQ" <ka1kaq at gmail.com>

> On Thu, Apr 2, 2009 at 1:45 PM, D. Chester <k4kyv at charter.net> wrote:
>> One suggestion. We need to be more careful about zero beating each other
> on
>> the 40m frequency. At times in the QSO, stations are so scattered out 
>> over
>> a 1-2 kHz range, that my sync detector won't stay locked when one station
>> turns it over to another. But the real problem is that this frequency
>> scattering is bound to be generating unnecessary hostility from the SSB
>> DX'ers, and will likely to result in deliberate QRM and other hostile
>> actions against the AM'ers

> When has that ever bothered you before, Don? To borrow your own words
> on such matters, 'strap and ignore', 'turn up the wick' etc. I'd agree
> with you if folks were scattered out over 4-5 kcs or more, but 1-2
> seems m ore related to sync detectors not locking up than to offending
> any SSB ops. After all, it's been one of the ways to discourage
> anti-AM SSB types from crowding in close to a QSO in progress.

I have ALWAYS, ever since the early 60's, advocated operating zero-beat with 
the other station whenever possible.  One exception might be when two or 
more stations are xtal controlled, and some of the older VFOs do drift.  But 
failure to zero-beat when it is easily possible and convenient is just plain 
sloppy operating.

This is an example of the difference between necessary bandwidth and 
occupied bandwidth.  If you are running audio out to 5 kHz, 10 kHz is the 
NECESSARY bandwidth of the signal.  But if two stations in the QSO are 3 kHz 
apart, then the OCCUPIED bandwidth of the QSO becomes 13 kHz.  There is no 
rule that says all stations in a QSO have to be on the same frequency. 
Hell, DX'ers routinely take up two whole SSB communications channels for one 
QSO by working split frequency (and these are often the very same 
self-righteous kilocycle kops who gripe the loudest about all that 
"bandwidth" that AM and ESSB signals take up).  Nevertheless, conspicuous 
sloppiness about zero-beating just unnecessarily gives the slopbucketeer 
lunatic fringe more ammunition to use against AM.

Another often-overlooked advantage of carefully zero-beating (whenever 
practicable) is that a "breaking" station attempting to enter into the QSO 
is less disruptive.  If you can hear his audio underneath the transmitting 
station, and at most, the puttering sound of a nearly zero-beat carrier, 
this is far less disruptive to the conversation, than a loud 1-2 kHz squeal 
of an off-frequency carrier, which garbles up the sidebands of both signals. 
You often miss what the transmitting station was saying, while at the same 
time, missing the callsign of the breaking station. It is not unusual that 
"breakers" into a QSO are ignored for this very reason.

But older transmitters with drifty VFO's are not the only problem.  Some of 
the worst offenders are using modern transceivers on AM.  Even if the audio 
level and carrier level are adjusted properly, so that a good, undistorted, 
plate-modulated quality AM signal is generated, many transceivers lack any 
kind of frequency spotting function.  In AM mode the received signal is 
clearly audible as long as it lies within the transceiver's passband. So it 
is easy to tune in the signal on the receiver and then transmit, and end up 
with a carrier 1.5 kHz or more off frequency.  If everyone is using a wide 
bandpass at the receiver and there is little congestion on nearby 
frequencies, this is  no big deal and no-one may even notice.  But if the 
band is crowded and many stations in the QSO are operating with the receiver 
in narrow bandpass, with heavy QRM off to both sides, some people in the QSO 
may miss the call entirely.

I have seen modifications to transceivers that allow a spotting function for 
zero-beating purposes.  Depending on the circuit design, this may be very 
easy with minimal alteration of the circuitry, while on others it simply 
isn't practical.  Lacking a spotting function, the easiest method would be 
to put the rig in SSB/CW mode and zero-beat the AM carrier, then switch back 
to AM.  But on some rigs, this automatically produces a frequency error, 
because there is a built-in frequency offset when switching between modes. 
In that case, you have to note the digital display frequency, and retune 
back to that frequency in AM mode.  Even then, there may also be an offset 
in the digital display reading that  must be taken into account.  It is a 
matter of figuring out exactly what works with a particular ricebox and 
getting into the habit of using it.

One factor that hinders proper zero-beating with any receiver is 
space-shuttle quality, so-called "communications grade" audio, that cuts off 
everything below about 500 Hz.  That makes it nearly impossible to hear two 
carriers approach zero-beat, if the audio drops out once they are within 
300-500 Hz of each other.  One more reason to have good low frequency 
response at the receiver, working into a decent speaker or headphones.

While it may be poor operating practice to intentionally operate on 
scattered frequencies just to discourage SSB stations, that doesn't mean you 
should hesitate to go into the "SBE" mode when SSB stations intentionally 
zero in and try to piggy-back ride the AM carrier.  Then, to use a Timtron 
expression, it may be time to "exit stage left" and move about 1.5 kHz down 
into the LSB passband, and for each station in the QSO to operate a  little 
off frequency to make it necessary for the offending  parasites to keep 
changing frequency to keep up with you.  But this should be used only as a 
defensive tactic in the presence of deliberate QRM, not as a preventive 
measure. When the QRM finally goes away, then everyone should re-zero beat.

Something that I have experienced many many times, is for the offending 
slopbucketeers to zero-beat, so I exit stage left.  The other AM station in 
QSO zero-beats me. Then the SSB'ers re-zero beat to ride the  carrier.  So 
we exit stage left once again.  This continues for several more 
transmissions, until we are 5-6 kHz down from the original frequency. Then, 
without fanfare, we move back up to the original frequency.  Sometimes the 
SSB QSO stays down below, and we all co-exist peacefully.  At other times 
the slopbucketeers move back up to zero-beat us.  When that  happens, they 
have clearly demonstrated that the interference is intentional.  Once, 
someone from an FCC monitoring station (remember those?) explained that if 
one amateur station merely transmits on top of another, it is not considered 
deliberate and no "pink slip" will be issued, because amateur radio operates 
on an interference-expected basis.  But if the operators in the original QSO 
move frequency, and the interfering station follows them to the new 
frequency to continue causing interference, the FCC considers that to be 
deliberate.

But rather than getting into a pissing  contest with jammers, it is 
sometimes better to just pretend they don't exist and ignore them.  "Strap 
softly and turn up the wick."

All said, careful zero-beating is even more essential in the 7125-7200 
segment during prime time after-work hours, which just happens to 
simultaneously be prime time for cross-country propagation AND for European 
grey-line DX propagation.  Because of the outmoded subband restrictions that 
presently exist on 40m in continental US,  the overlap between the new 
privileges enjoyed by European and other DX stations, and US phone 
privileges, is only 75 kHz.  One AM QSO occupying 7.5 kHz, about the minimum 
actual bandwidth occupied by a real-world AM signal, is fully 10% of the 
entire segment, while ZILLIONS of the "Hello-g'bye, ur five-nine, pse QSL, 
73, QRZ?" DX'er types are just getting home from work to play a little radio 
before dinner, or are getting in some last minute DX before bedtime in 
Europe.  Sloppily operating in a manner such that we occupy 15-20% of the 
segment for one round-table will do nothing but attract the massive 
wholesale wrath of this element, which will eventually generate unwanted 
anti-AM sentiment within the greater amateur community, and possible 
lobbying efforts and FCC petitions to restrict or downright outlaw AM.

To repeat a cliché, we need to keep our ducks in a row while using the 7160 
frequency.

Don k4kyv

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