[aprssig] Fast SSTV for on-air presentations

[Stephen H. Smith]

On 5/4/2020 12:45 PM, Robert Bruninga wrote:
> The local radio club wants to move to on-line technical talks but got bogged 
> down in arguments over teleconferingin  protocols and security..
> 
> I's like to transmit my presentation as SSTV FAST mode (13 seconds per slide) 
> and give the talk on the local repeater.  The FAST FM mode premiered in the 
> (decades ahead of its time) Kenwood VC-H1 And generally has to connect to the 
> modulator and discriminator and not the voice circuits.
> 
> Has anyone used FAST FM mode for SSTV?  Can it be received by most folks 
> without having to get to the discriminator for receive?
> 


1)    NO!  The fast mode is a failed protocol that never gained acceptance.  No 
one except owners of the now rare VC-H1 that also have the only radio that 
worked with the VC-H1 in fast mode (the TH-D700) can send/receive it.  NO SSTV 
software supports the fast mode.


2)    The resolution of any normal SSTV frame (including the fast mode) is only 
320x240 pixels -- far far too low to reproduce any kind of presentation with 
text or detailed graphics such as maps or schematic diagrams.

The only modes to go above the quarter-VGA 320x240 are some of the PD modes 
that can do a standard 640x480 VGA (2-3 mins/frame) or SVGA 800x600 (4.5 
mins/frame) image.

Consider that normal PowerPoint presentations typically expect a 1024x768 XGA, 
1280x1024 SXGA, 1280x720 half-HD or even 1920x1080 full HD display.  At least 
3/4 of them use far too small text (to cram more onto each page), resulting in 
the text being unreadable to anyone but the first row of the audience .   Sent 
over low-def bandwidth-limited 320x240 analog SSTV will guarantee that NO one 
will be able to read them!

Further, the only way to create "fast mode" images is the unbelievably bad 
low-res camera head of the VH-C1.  I radically improved the sent image quality 
of the VC-H1 (on standard SSTV modes) by connecting an external NTSC camera to 
it in place of the OEM head. (The jack on the VC-H1 for the camera is actually 
a standard NTSC 1-volt P-P composite video input.)


3)    The only way to get the fast mode out of a radio is via the raw FM 
discriminator.  Radios that have the 6-pin mini-DIN "packet" or "data" port 
make this easily - one of the 6 pins is the discriminator-out connection, 
sometimes labeled "9600 baud packet".  Full details on the port here on my website:
    <http://WA8LMF.net/6-Pin-MiniDin-Data-Connector>

Unfortunately, fewer and fewer radios are now coming with this port.   I am 
painfully aware of this as I struggle to acquire basic monoband radios with the 
din port for APRS applications. NONE of the Chinese radios now flooding the ham 
market have the DIN port.   Not to mention the god-awful BaoFeng disposable 
handhelds that more and more entry-level hams struggle to use on non-voice 
modes, usually with lousy results.

FM/digital Transceivers are evolving toward entire radio-systems-on-a-chip that 
include RF, synthesizer, mixers, detector and audio on a single IC,  These 
chip-sets are intended for high-volume cellular devices, but are now 
increasingly appearing in two-way radios as well. This type of design makes it 
increasing difficult to "tap the discriminator" (if in fact they even have an 
IF & discriminator).  More often they are now direct-conversion DSP devices. 
(Nearly all the cheap Chinese radios are of this type.)

I wind up having to pick up second-hand Yaesu FT-1500 2M monobanders off eBay 
or at swapmeets for building ammo-can trackers or ammo-can porta-digis.  Jusat 
last month, I discovered that one of the last small-footprint VHF-UHF FM-only 
radios with the DIN port (the Yaesu FT-8900 10-6-2-70cm quad-bander) has just 
been discontinued with no replacement in sight.

_____________________________________________
Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

-----   NEW!    60-Meter APRS!   HF NVIS APRS Igate Now Operating  ------
    <http://wa8lmf.ddns.net:14447/>



Live Off-The-Air APRS Activity Maps
    <http://wa8lmf.net/map>

Long-Range APRS on 30 Meters HF
    <http://wa8lmf.net/aprs/HF_APRS_Notes.htm>