[GreenKeys] Silent 700 Terminal with a 43 TTY (TDU) ?

[Mike]

Hmmmm.... Good point. Darn dust bunnies! We were working with full duplex leased line modems, no originate / answer functions to worry about.

Mike O'Day
N9ODM


On Apr 11, 2013, at 11:15, Chris Elmquist <chrise at pobox.com> wrote:

> Ya...  I think you'd still have trouble.  Cross connect would allow an
> electrical connection between two modems IF they were direct connect
> (ie, have a DAA).  Acoustic coupled units will need a telephone handset
> added to the equation...   but you will still have the wrong tones.
> 
> Two originate modems can't talk to each other.   You can only talk
> originate to answer because of the tone pairs used in each direction.
> It's key to remember that these were duplex connections too...  data was
> moving inbound at the same time it was moving outbound and so they had to
> keep the transmit FSK pairs from interfering with the receive FSK pairs.
> 
> For reference,
> 
> http://en.wikipedia.org/wiki/Bell_103_modem
> 
> "The originating station used a mark tone of 1,270 Hz and a space tone
> of 1,070 Hz."
> 
> "The answering station used a mark tone of 2,225 Hz and a space tone of
> 2,025 Hz"
> 
> In other words,
> 
> originate modem        answer modem
> ---------------        ------------
> send 1070/1270        listen 1070/1270
> listen 2025/2225    send 2025/2225
> 
> So, the Silent 700 or M43 with either direct connect or acoustically
> coupled modem is going to send to and listen from an answer modem peer.
> It won't hear an originate modem used as a peer.
> 
> Therefore, I think you have to get at them before the modem and make
> your connection to the serial interface there with either 20mA or RS232.
> 
> There were Bell 103 modems (both direct connect and acoustically coupled)
> that were switchable between originate and answer mode to solve this
> very problem but I do not believe those were normally built into the
> two terminals being discussed here.
> 
> Chris N0JCF
> 
> On Wednesday (04/10/2013 at 01:57PM -0700), Michael O'Day wrote:
>> Chris' description of the "originate" modem setup kicked loose an old Dust Bunny of a memory. We used to have to connect leased line modems together (at 1800 baud) to test our equipment in order to determine if comm problems were internal or external. One FE had a "Ma Bell" cable, complete with D-blocks, that would cross connect the modems. We would be monitor the RS-232 signals to verify everything was working.
>> Could you use a similar setup to connect the Silent 700 to the model 43?  If needed you could run the signals through an isolating interface using an opto-isolater chip to avoid voltage level conflicts. We used to connect TD-830 data terminals to loop current driven dot matrix printers the same way (the isolator circuit was built into the printer), and never had a problem.
>> 
>> 
>>  
>> Mike - N9ODM
>> 
>> 
>> ASCII and ye shall receive.
>> 
>> 
>> 
>