Sunday, January 24, 2010
Recently I blogged about amateur radio's culture of exclusion; a post which generated a large amount of interest, new readers, and surprisingly little if any hate mail. Based on the blog post I doubt I'll be invited to join CWops or FOC, but the SOC has welcomed me with open arms and they're a fun bunch of folks.
One of the areas I touched on was how some modes such as RTTY tend to stay away from subbands used by older modes such as CW during contests. WW2PT pointed out a post by W2LJ which indicates that RTTY contester's self-enforced deference to CW may be ending.
It's clear that there is a schism within amateur radio's digital mode world between RTTY and basically everything else. Amateur radio's so-called digimodes (PSK31, Olivia MFSK, etc) are almost always run at 50 watts or less. Some modes such as JT65 and WSPR (developed by K1JT ) are run around 20 watts. And CW (which is technically a digimode) has a large following of QRP operators who run CW using 5 watts or less.
Reason for these low power levels is that modulating/demodulating a radio signal using a digital signal processor allows the use of error-correcting techniques which results in what's termed "Coding Gain". Coding gain usually adds (depending on the code used) about 2 - 6 dB to the system gain. This means that a signal which is transmitted 50 watts into a vertical antenna (unity gain) is seen effectively as 75 - 200 watts by the receiver. Coding gains higher than 6 dB are possible. So digimode practitioners don't run "big power" because in digimodes you don't need much power to work the world.
Stack this up against RTTY where "big gun" stations running kilowatt amps into high-gain antennas are not unusual. While it's true that RTTY doesn't offer any coding gain I think that a kilowatt of power is a bit overkill. If all RTTY operators remained within the usual subbands there wouldn't be many issues. But the problem comes up during contests where the contesters spread out across the band and the other digimodes simply get wiped out; this includes QRP CW ops.
Lately there has been a resurgence of interest in WSJT modes; probably due in part to the excellent work done by W6CQZ in providing a reverse-beacon system, chat/sked system, and building upon K1JT's original software to create a new and improved application. Yet with this new interest there have been a disturbing trend of late where people have been applying an RTTY approach to WSJT modes and wiping everyone out in the process. For example; there's one guy who's just across the valley from me that's creating all sorts of havoc by (1) running big power (his QRZ vanity photo clearly shows his amps), and (2) driving his system into ALC which heavily distorts his signal. And it's not just one guy; the other night I was getting overloaded by a guy in Colorado. How much power must he have been running to overload the front-end of my receiver from 1,000 miles away?
So why is this happening? Because many operators have forgotten a cardinal rule of amateur radio; use only as much power as you need to complete the contact. I've completed three JT65a QSOs to South Africa using 50 watts of power with no sunspots on a vertical antenna that most people consider mediocre at best. Big power in digimodes is simply not necessary. Running JT65a with a linear and a gain antenna is like shooting a mosquito with a bazooka.