FAX480 FREQUENTLY-ASKED QUESTIONS
Why Create another SSTV mode?
Most of our present SSTV modes are designed to transmit color images at relatively low resolution. Much of the proliferation of modes is due to the fact that different experimenters have strongly-held opinions about the best way to do that. Hence, most of our modes represent different ways to accomplish the same task. Fax480 was developed with the single objective of transmitting higher resolution pictures in essentially the same time required for the common color modes. When Fax480 was developed in 1983, there were almost no options for handling images with greater detail.
So why not use one of the new color high-resolution modes?
The simple answer is time! A Fax480 image requires just 2 minutes and 18 seconds to transmit. A high-resolution color image will take anywhere from 3 to 7 minutes or more, and you will need at least 5 minutes if you really want to see the increase in resolution. The color high-res modes are great - I use them myself on 15 meters and higher when conditions are good and the band isn't crowded. However, under normal band conditions, Fax480 is a better choice under more typical band conditions.
So why black and white? Isn't that a step backwards?
Not really! I like the various color modes, but high-resolution color takes too much time in most situations (see the previous question). In the presence of QRM or QRN, a black and white image will always look better than the same image in color, since the "junk" on a color image will appear as colored specks or streaks which the eye picks up rather easily. In contrast, noise and QRM impacts a Fax480 image as speckles and streaks in various shades of gray - far less obvious and distracting! It is also worth noting that many things, including multipath, can impact registration in a color image - something which isn't a problem with grayscale images. In addition, as photographers have known for years, some subjects simply make a better black and white picture than they do in color.
Fax480 has a reputation for getting through noise, QRM, and multipath better than standard SSTV. Why is this the case?
Part of the answer here is covered in the previous question, but the rest of the story concerns resolution. An image is degraded by loss of information. Since a Fax480 image contains almost four times the information (resolution) of a standard SSTV image, you can lose more to QRM and QRN and still have an acceptable picture.
So should Fax480 be considered a replacement for our current modes?
Of course not! The standard color modes are the ones that will always be used most-often, but the issue is one of options. When you have a picture with a lot of detail, or conditions are less than ideal, then it is nice to have a mode like Fax480 available.
So which SSTV systems support Fax480?
The best way to know is to check Fax480 Hardware and Software for an update on the systems and programs that support Fax480.
What if my SSTV system doesn't support the mode?
You have two options:
Developers want to sell their programs and, if enough people ask for a new option, most developers will try to accomodate them. If the developer doesn't know about Fax480, direct them to my website, which has all the information needed. If they still have questions, I would be happy to discuss the issues, via e-mail or via phone. I have no commercial objectives with respect to the mode, so I don't charge in any form for consultation on the subject!
If I get new questions, I will be happy to post them here. Simply drop me an e-mail at the address shown below.
Ralph E. Taggart (firstname.lastname@example.org)