[RTTY] A Wikipedia quote.

[Eric - VE3GSI]

Chen,

A friend (VE3IWB) and I experimented with the higher baud rates around that
time. It should be pointed out at that time the TU's we were using were of
the LC construction using the old 88 mH coils and tuning caps, very much
along the line of the HAL ST-6 TU's. And, indeed the higher bandwidth
filters were required when using the LC circuits. Using 170 Hz shift and LC
filters we could not work RTTY with any kind of reliability at 110 baud.
When the filters were looked at with a scope there was a lot of 'skew type'
distortion with LC filters at the higher baud rate. LC demodulators at
higher speeds we also not reliable.

Also about that time we started building active band pass filters using
OP-amps and also XR(?) series demodulator chips for TU's. The switch to
active components allowed us to use filters with a reasonable bandwidth as
low as 250 to 300 Hz, quite an improvement from our first experiments with
LC circuits.

Using our new found active circuit designs we even did experiments with 300
Baud ASCII on 2 meters using a wider shift, which actually was a lot of fun.
Eventually we gave up with higher baud speeds on HF, mostly due to lack of
other Hams to experiment with.

Just reminiscing,
Eric - VE3GSI



> -----Original Message-----
> From: rtty-bounces at contesting.com [mailto:rtty-bounces at contesting.com]
> On Behalf Of Kok Chen
> Sent: January-29-10 2:52 AM
> To: RTTY Reflector
> Subject: [RTTY] A Wikipedia quote.
> 
> While searching for references to ASCII radioteletype, I found this
> quote at http://en.wikipedia.org/wiki/Radioteletype :
> 
> > On January 7, 1972, the FCC amended Part 97 to allow faster RTTY
> speeds. Four standard RTTY speeds were authorized, namely, 60 (45
> baud), 67 (50 baud), 75 (56.25 baud) and 100 (75 baud) words per
> minute. Many Amateur Radio operators had equipment that was capable of
> being upgraded to 75 and 100 words per minute by changing teleprinter
> gears. While there was an initial interest in 100 words per minute
> operation, many Amateur Radio operators moved back to 60 words per
> minute. Some of the reasons for the failure of 100 words per minute HF
> RTTY included poor operation of improperly maintained mechanical
> teleprinters, narrow bandwidth terminal units, continued use of 170 Hz
> shift at 100 words per minute and excessive error rates due to
> multipath distortion and the nature of ionospheric propagation.
> 
> I found the last sentence interesting :-).  Notice also the comment on
> "narrow bandwidth TU."  Be sure to open up the filter bandwidths if you
> try 110 baud ASCII and not fall into the same trap.
> 
> 73
> Chen, W7AY
> 
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