[Elecraft] KPA1500 XCVR serial connection

[Don Wilhelm]

Paul,

It is possible that short runs of "RS-232" can operate on TTL levels.
There certainly is no problem at the 5 volt level, that is entirely 
within the range of the + level valid RS-232 signals.

The possible problem is with the low level.  A proper RS-232 receiver 
should ignore levels between -3 volts and +3 volts because it could be 
in a range defined as noise.
However, all receivers are not designed to ignore a 0 volts low level. 
The receiver on the KX2 and KX3 as well as the XG3 (and probably others 
as well) will interpret 0 volts as a low level.

Note that the 'real' RS-232 spec is written for very long communications 
lines.  Short lines (10 feet or so) can take liberties with the levels 
if the receivers are such that they can tolerate those switching levels 
yet will accept signals with the full RS-232 voltage swings.

Properly connected, you would need to have the KPA1500 TxD disconnected 
and depend on the PC application to poll the radio while the KPA1500 
'listens' in to get its frequency information.
Without the PC connection (and the KPA1500 TxD connected, the KPA1500 
will poll the radio for that information.

RS-232 is point to point communications and not multipoint, although 
there can be multiple receivers listening to the communications, there 
can only be one driver.
Sort of like ham radio - everybody can listen, but if two operators 
transmit on the same frequency, they will QRM each other and "data 
corruption" occurs.

73,
Don W3FPR

On 2/28/2018 6:30 PM, Paul Baldock wrote:
> The manual on page 24 says:
> 
> Serial: A Kenwood, Yaesu, Elecraft K2, K3, K3S, KX2, or KX3, or 
> FlexRadio® transceiver that responds to IF; FA; FB; FT; polls with 
> frequency and VFO information. The XCVR SERIAL connector is configured 
> as TTL-level RS-232
> 
> Is it really TTL?. I planned to use this connected to the serial data 
> line that goes between my Kenwood TS-990 and PC, such that the KPA1500 
> will catch the frequency data triggered by my logging program. This 
> works great with the KPA500 which I assume  uses true RS232 levels. If 
> the KPA1500 does indeed use TTL levels will it capture the data, and 
> will it not corrupt the RS232 levels between the PC and TS-990?