Sunday, January 24, 2010

Power Struggle


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.

2 comments:

John said...

It's ignorant and rude at best. You also, sadly, find this "Go Big Or Go Home" attitude in the satellite world as well. The mindser goes like this: I bought the amp...the law SAYS I can run 1500 maximum watts, therefore I WILL!". These hams are not only selfish, but also in direct disagreement with the law. Part 97 has a section that states that the MINIMUM power be used to complete desired communications. 1500 to a gain antenna might help in trying to contact the moon, but with JT65 and the such, it is simply inappropriate.

Great article.

John KB2HSH

Paul said...

I can't speak directly to your complaint about RTTY intrusions into the JT65 and WSPR band segments, but know from my satellite days how pissed we all used to get when a couple of guys would pop up on FM simplex smack in the middle of the 145 MHz Oscar 13 downlink band. Some would get belligerent when you asked them to QSY. So I feel your pain. Unfortunately there's no legal basis for claiming a band segment as "RTTY" or "JT65" or SSTV" or "DX Window" -- it's a gentlemen's agreement... and as we know there are so few gentlemen left these days. People are a-holes, and hams are people. 'Nuff said.

I love RTTY, been using the mode since I started out in the 80's, but I'm growing tired of it. It's at the point where I only bothered to make 65 contacts in last weekend's BARTG Sprint. It is an outdated mode which offers no advantage to a modern mode like PSK which in a just society would have replaced RTTY years ago. Speed? Nope. Fewer errors? Nope. More efficient in any way? Nope. Even those who say CW is outdated can't argue that it doesn't have big advantages in weak signal usage. But RTTY? There is NO advantage that I see over the new digimodes.

From a little-pistol contester's perspective, I enjoyed the few PSK-only contests I've worked recently far more than any RTTY test I've ever played in. I can run 50 watts yet not feel I'm at a disadvantage to the "big guns" running at the 100 watt maximum. I'm able to work just about any station I can copy (unlike RTTY where I can hear the kilowatt kowboys at 20 over S9 off the backs of their beams, while they can't hear me at all). The lower signal strengths mean I can cozy up between two other stations who are 100 Hz apart without causing or receiving undue amounts of QRM.

On the downside, PSK seems to attract the, shall I say, less experienced ham, so a fast and efficient contest QSO is more likely to be dragged out with "My station..." macros and weather reports than they should be. This is probably a big reason PSK isn't more universally adopted as a contest mode.

One of these days we need to talk about WSPR and WSJT, I need to try this stuff out.

Paul WW2PT