For me these have been a very good few months on 6 meters. FT8 is obviously the big story due to its universal popularity and, more importantly, it delivered results. Big time. The difference is obvious by comparing this article with the one I wrote after last year's sporadic E season.
In two months using FT8 I made almost 500 contacts and worked 56 DXCC countries. On August 4 alone I put 40 European stations in my log. That was a phenomenal opening that lasted several hours. Many others on both sides of the Atlantic have been similar successful. I haven't seen DX activity like that since my last F-layer openings in 1990, and never via sporadic E.
Now I'll dive into the details. The past 2-½ months have been very educational to me and I've learned a lot about just how far one can push marginal propagation with the help of technology. These paths must have always been there but missed without the assistance of FT8.
Discovery
Some say CW can do as well as FT8 under weak signal conditions using good narrow filters. This may be true, give or take a few decibels. That means little when the opening to any particular station is fleeting because on CW you likely will not find the station since you must spin, spin, spin the dial hunting for them.
When they're spotted it gets easier since you can park on their frequency and wait, perhaps flipping among several spotted stations. It quickly becomes a tedious chore. Yet it can work and has worked for me in the past. FT8 is very different since you are in essence copying the entire band without lifting a finger. When a station is workable on FT8 you'll know immediately.
Discovery is perhaps the greatest advantage of FT8 on 6 meter sporadic E. You need no beacons, no spotting network and no arduous tuning around. When the station is workable you know it. Some DX stations -- CT1HZE in particular come to mind -- CQ continuously when conditions are favourable, essentially becoming beacons themselves, so you may not even need to check for actual beacons at the low end of the band.
Time is of the essence
Of course you must still work the station. This is a challenge since the typical FT8 QSO takes more than 1 minute. If your experience with FT8 is on HF this may seem inconsequential. On 6 meter sporadic E it is often critical since many of the longer DX paths last only this long if not shorter before rapidly fading out.
I have many partial QSOs, including perhaps another 10 DXCC countries, because signals faded, often never to return. I gave examples in my earlier FT8 article.
Despite this duration difficulty FT8 is still superior to CW since with FT8 you have more of a chance to make the contact because of the discovery challenge I described. In particular, you decode the desired station when the path opens so you can take advantage of its full length. Even so you'll need to get used to regular disappointment as you watch a signal gradually fade to nothing in 30 seconds, and there's nothing you can do about it. You can't speed up FT8 transmissions.
To ameliorate this difficulty more callers omit the grid square and jump straight to the signal report on the initial transmission, thereby reducing the time to complete a QSO. They are not being rude by omitting this information. Similarly they'll use RR73 rather than the slower RRR sequence, even if conditions are not truly good enough for RR73 to be a reliable concluding message.
WSJT-X supports these methods for shortening QSOs and they do come in handy when DX openings are breathtakingly short. Give it a try yourself.
Agony of the single decode
Often you never get a chance to attempt a QSO since there is only one decode of the DX signal. In these cases of marginal propagation a signal may peak above the noise for just one 15-second window. This behaviour is normal on the shoulders of an opening, while other times it really is just a single decode. Waiting for the opening to progress may be fruitless.Examples of single decodes can be seen in the accompanying activity monitor from a few weeks back. There are two of them. Notice that the signal strength is very low. This is typical in the case of single decodes in these types of fleeting openings.
There are other peculiar single decodes that I've experienced. One was a CQ from a YO station with a SNR of -8 db. There were no other decodes and no other signals from Europe, although others in eastern North America were seeing a few marginally copied Europeans. I copied several stations from VE3 down to W4 reply to the YO. No one got through and there were no other decodes.
Unusual propagation must have been present for this to happen. Perhaps a bolide over the North Atlantic briefly provided a bridge between E-layer clouds. Intense meteor trails can support propagation on 6 meters long enough for a 15-second FT8 message. That's just speculation since I have no idea what happened. FT8 is providing us with new insights into propagation.
Signal reciprocity
When I first got on 6 meter FT8 I was surprised at the asymmetry of signal reports I sent and received; the reports I received were mostly worse than the ones I sent. I attributed it to the several decibels of loss in the 40 meters of ancient RG213 coax feeding the yagi. Now I'm not so sure.
As I said in my earlier article FT8 is no more a low power mode than any other. Many 6 meter operators have long used high power and they continue to do so on FT8 since it pays dividends in teasing QSOs out of marginal propagation, which is typical for long DX paths on sporadic E and other transitory propagation modes. I have become accustomed to signal report differences of 10 db or more, and often not being decoded by stations received well here.
There may be other reasons for the difference. For example, noise. Because WSJT-X signal reports are the calculated SNR (signal-to-noise ratio) each station's noise floor is a factor. Although external noise (QRN) is usually lower at VHF than HF there is still the receiver noise to be considered. I live in a low noise environment where I am able to turn up the receiver's pre-amp to improve SNR, a common requirement on VHF and higher where atmospheric and man-made noise is below the receiver's thermal noise level.
When is a QSO complete?
I was pleased to see this issue mentioned in the recently arrived September QST. There has been some confusion on the air, including those I try to work. For transitory 6 meter openings one's view of the matter becomes important.
The issue is exemplified by a QSO that proceeds as follows:
QQ8ABC VE3VN FN24The other station insists on receiving a "73" message to complete the QSO. It isn't necessary since both stations have exchanged and confirmed call signs and signal reports. When conditions fade -- as they frequently do for marginal DX paths -- the "73" is never received. Should I log the QSO?
VE3VN QQ8ABC -10
QQ8ABC VE3VN R-08
VE3VN Q8ABC RR73
Q8ABC VE3VN 73
VE3VN Q8ABC RR73
Q8ABC VE3VN 73
My concern is whether the other station logged the QSO, not whether the QSO is valid. It is valid. My choice then is to log the QSO or not. In almost every case I do. Whether he logged it may only be known when it is confirmed in LoTW or via some other system. In one instance the questionable QSO was a new country, which I logged but did not include in my DXCC worked list.
Quirks
In my previous FT8 article I mentioned a few quirks of the software and its users. Here are a few more.
I call CQ, someone answers on my transmit frequency and we complete the QSO. They then proceed to call CQ on frequency. This happens more often than you might imagine. I suspect carelessness rather than malice. Most likely they forgot to QSY back to their previous transmit frequency after we've worked. All I can do is QSY, which is a minor inconvenience on FT8 compared to CW or SSB.
WSJT-X occasionally decodes noise as a valid message. The frequency of these occurrences increases with how aggressive you set the decoding options. This is no surprise to FT8 operators. What does surprise me is that some of these messages are addressed to me! If it occurs while I'm CQing with "Call 1st" selected the software will happily reply to the noise. I've seen numerous instances of others answering what are obviously nonsense call signs magicked into existence by WSJT-X. There is something in WSJT-X that causes it to try to preferentially interpret noise as your call sign.
WSJT-X occasionally loses track of its transmit state when a transmission is manually halted within the first second. You press the appropriate button and it goes on transmitting, while also receiving. With the rig's monitor feature enabled (which is usually the case here) the transmission is received and decoded. It is highlighted since my call sign appears in the message. It takes a couple of clicks of the "Tune" or "Enable TX" button to fix the problem.
In a good opening the full 3,000 Hz is densely occupied. Stations overlap since, due to the spotlight nature of sporadic E propagation, I can hear both stations but they can't hear each other. This is less of a problem that it might be because WSJT-X is astonishingly capable of decoding each of the overlapping signals, even when they differ in strength by 10 db. That's impressive, and useful. It's a skill even the best DXpedition operators would envy.
Contests
After observing FT8 activity on 6 meters during ARRL Field Day and the CQ WW VHF contest I've chosen to not contest with FT8. I like DXing and I'm happy to periodically work US and Canada on FT8 (especially west coast), but for contests it's just too slow for my taste.
There are other difficulties with FT8 use in contests that may be corrected when WSJT-X 2.0 arrives in several months. If you're already using FT8 on VHF the following should be familiar.
First, there is inconsistent use of NA VHF contest mode in WSJT-X. When selected the messages change such that stations decoding your transmissions will see messages that are seemingly incomprehensible. Unless both stations select (or deselect) this option QSOs aren't possible. Endless repeats between incompatible stations were often heard both weekends. Selecting the option midstream or between QSOs does not retroactively translate messages already received. I was puzzled by what I saw during Field Day since I hadn't yet learned about NA VHF contest mode. The manual enlightened me. Others remained confused.
Many NA stations incorrectly selected this option during the CQ WW contest. It is not intended for worldwide contests and none of the European and other DX used it. Once again confusion reigned. I avoided the option entirely while working DX during both contests.
After each contest many forgot to deselect the option. They had little luck working anybody! Eventually normalcy returned to the bands.
Unfortunately when I did try CW and SSB in the CQ WW contest I logged exactly zero contacts. I heard a few stations fading in and out, but failed to work the few that were present. Ten minutes of continuous CQing netted no replies at all. Yet FT8 activity was high. Perhaps I'll avoid VHF contests for a year or two until something changes to rekindle my interest.
50.323 MHz
Used a great deal for intercontinental openings early in the season its use recently has been almost nil. During the exceptional opening to Europe on August 4 the 50.313 MHz segment was packed with signals from 200 Hz to 3,000 Hz. During each of the several times I checked 50.323 MHz there were no signals found. Neither did my band scope show a blip +10 kHz the many times I glanced at it while active on 50.313 MHz.
Is the idea behind 50.323 MHz dead? We'll have to wait and see how this develops. My suspicion is that for the majority the importance of discovery (discussed earlier) is greater than reduced QRM from intracontinental activity. As matter stand I see no reason to monitor 50.323 MHz.
Signal quality
Monitor FT8 on any band and you'll soon discover poor signals. Perhaps because these digital modes are new, the software unfamiliar or the operator carries on with poor practices learned on other modes many seem unable to consistently transmit a clean FT8 signal. This not only hurts them but everyone using FT8.
Based on the WSJT-X spectrum display and other displayed data it is possible in many cases to make a good guess what they're doing wrong. Some that I'm aware of include:
- Misadjusted clock: WSJT-X will forgive small clock errors but can be intolerant of errors greater than 1 second. It is mystifying that many operators don't know they have a problem since WSJT-X displays the clock error on every message. You'd think they'd notice that every signal has substantial error. Either they don't notice, imagine everyone else is wrong or don't understand the importance. The most common consequence is that they can successfully monitor but their transmissions overlap with others resulting failed decoding when a QSO is attempted.
- Drift: In this era of rock solid digital oscillators we have grown used to frequency accuracy of 10 Hz or better. Imagine my surprise to see that a small fraction of signals drift. Sometimes the drift is only 1 to 2 Hz every 30 seconds, and in extreme cases I have seen drift of up to 10 Hz. Since WSJT-X highlights messages addressed to you (your call sign) you still see messages that drift outside your receive window, so it is usually not a serious problem.
- Compression: Speech compressors by their nature -- both AF and RF -- are non-linear devices. When properly adjusted on SSB they achieve a balance between distortion and comprehensibility while improving average talk power. On FT8 the compressor produces mixing products that create QRM and reduce the power of their fundamental audio signal.
- Transmitter ALC: When the ALC meter moves there are distortion products due to the introduction of non-linearity in the RF amplification chain. This may be tolerable at very slight ALC action but is always dangerous. When it kicks a lot you can be certain that you are generating spurious signals.
- Amplifier over-driven: In the quest for squeezing out those elusive DX QSOs many run a lot of power on 6 meter FT8, and it is no surprise that those amplifiers are sometimes over-driven. Since negative feedback to the transmitter ALC is frequently not used there may be no immediate indication to the operator that there is a problem. But as we've seen ALC is not the cure for a poor FT8 signal. Carefully adjust the transmitter power, and observe its ALC meter if it has one, to ensure the amplifier remains in its linear range.
WSJT-X decoding is so good at discarding distortion products that most of us can survive the onslaught of QRM. However that is no excuse for transmitting a poor signal.
CW and SSB
Well, what about CW and SSB? Once I made the move to FT8 in early June I have worked very little CW and SSB. Not only has FT8 been far more productive for my primary objective to work DX -- despite the painfully lengthy QSOs and sudden QSB -- when I switch to CW and SSB there is often no one there. Few signals other than beacons are heard and CQs go unanswered. Yet 50.313 MHz is bursting with activity.
I have no answer to this issue, and I can't even claim that it is an issue. There are many who shun FT8 and similar digital modes. To them it can be annoying to have fewer stations to work. I felt the same before June. As a practical matter, when I'm set up for FT8 it is not convenient to tune the CW and SSB segments. I would have to come up with a system whereby a second rig can share the antenna.
While I am not prepared to give up on the "legacy" modes there seem to be fewer reasons to use them as time progresses. In this I refer only to 6 meters, not HF. On HF my interest in FT8 is very low. The only band I may play with it is 160 meters, if only to see what it can do.
My plans
My move to FT8 on 6 meters was one of necessity. It was that or make far fewer QSOs. After one season on FT8 I've become a believer. FT8 delivers the goods: an astounding amount of DX, which is my primary operating objective on 6 meters.
This success motivates me to improve my performance on 6 meters in 2019. First up is to replace the poor coax with low loss Heliax. That will improve my signal by at least 3 db. When I shop for an amplifier I would now like one that includes 6 meters. In time I may add one or two more antennas, for stacking and elevation angle diversity.
Together these measures should improve my DX results on 6 meters. Despite my renewed enthusiasm for 6 meters this work remains lower priority than towers and antennas for HF contesting. We'll just have to see how far I get by next spring. I am also considering playing with other WSJT-X modes to try out other forms of VHF propagation such as meteor scatter.
Despite FT8 being less hands-on that traditional modes it has earned a place in my station. That is perhaps the biggest surprise to me this year. Who knows, 6 meter DXCC in another year or two could be mine thanks to FT8. That this is possible during a solar minimum is extraordinary.
No comments:
Post a Comment
All comments are moderated, and should appear within one day of submission.