My Opinion on Autoslant
With Autoslant on, you will receive all images straight.
The Autoslant feature works for received mode only With Autoslant on, the software
such as MMSSTV listens for some type sync pulse for every
line in the image and starts that line at the beginning every line. Your
computer works harder, it requires more horsepower but most
computers now days have plenty to do the job so no problem. Leave autoslant on. Again. You have no intentions helping others who are
transmitting slanted image. You can't help them because you will not know
they are transmitting slanted image. You have Autoslant on' and everything
you receive is straight. and perfect.
You will need to calibrate your soundcard clock or crystal. most soundcards use a
crystal. As you know, not all crystals are perfect.
Some use a capacitor for tuning as in a radio but on a soundcard we have
a timing fudge-factor we can add or subtract to tune it. We add or
subtract Hertz to fine tune the main frequency
11025.00. We will add or subtract from that to adjust the receive crystal.
Again Receive crystal. Best to use the WWV signal because that clock is
the most accurate clock in the world. It is available and free to use so
lets use that.
Assuming you have calibrated your receive as described in last paragraph.
Your RX is calibrated perfect now.
With Autoslant off, you are going to receive slanted pictures from time to
time. Wait. you just calibrated to WWV the most accurate clock in the world
and you are still receiving slanted images. If you have calibrated your
receive crystal and another station has not calibrated their transmit
offset, then you will see their slanted images. You have Autoslant off.
People sending slanted images you will see those slanted images. The
software only listens for the first initial sync pulses and then uses
timing for all the remaining lines. If the station transmitting has not
calibrated their transmit TX Offset, they are going to send slanted
images, you will receive each line slightly shifted from the last line
which looks like slant. They really are not slanted images. Each line is
shifted slightly which looks like it is slanted. Everyone calls is slant
which is fine. That same station who has not calibrated there soundcard will
transmit slanted images same slant until someone tells him about it or
they find out some other way maybe by seeing them on the internet SSTV
Cams who have Autoslant OFF.
Note you will not be able to help stations sending slanted images if you
have Autoslant ON. You receive all images straight by correcting them at
your end only with your Autoslant. Stations will still be sending slanted
images even though you don't see it.
Some soundcards, many of them use the same crystal for data out as for
data in and if you have calibrated your receive clock dead nuts to the WWV
clock, most accurate clock in the world, zero will usually work here. If
you never send pictures then again, you do not need to put any value here.
Zero or 0.00 is fine. Many soundcards, single crystal type
will have zero here if you have calibrated your receive.
Multi Crystal Soundcards:
Some soundcards use multiple crystals. A different crystal for TX
than RX and again as I stated
above, generally no two crystals are exactly the same. The TX crystal will
most likely need some fine adjustment and this is where the TX Offset comes into play. You
may need somebody's help or you can use the SSTV cams that are not using Autoslant.
Somebody who is not using Autoslant and has calibrated
their RX correctly is probably about the easiest way. Using an SSTV cam you know is
calibrated. such as KE5RS or W3MRC. Both these SSTV cams are
calibrated to WWV and have been checked over several hours for any drift.
You will find some SSTV Cams with Autoslant ON. They are reasonably easy to
spot. They never display slanted images. These SSTV Cam stations will
not help people calibrate their TX offset. I have contacted some of these
people and they are more interested in showing straight images rather than
helping others send straight images. To each their own. I like W3MRC and
mine, KE5RS to show exactly what the transmitting station has sent without
modifications. If a station is sending slanted images, W3MRC or KE5RS SSTV
cams will let you know that.
I hope this information helps
John de KE5RS