[RTTY] Time wave 599zx

[Kok Chen]

On Dec 5, 2004, at 4:09 PM, NOEL POULIN wrote:
> I would like to know if somebody using the Time Wave 599zx in RTTY 
> mode.
> I have in mind buying one, but would like to have user's advice before
> I would appreciate your comments very much

Good choice.  I had been using one for a couple of years now.

It is one of the better hardware modems around.  But if you are 
currently using a software modem, this unit will probably not provide 
any better copy (depending on the software modem and how carefully you 
have set up the audio level, of course).  But it will readily outshoot 
the KAM Pluses and PK-232s of the world.

If you are currently using a TNC and are happy with your computer's 
interface to it, then I would recommend using the 599zx as a 
Remodulator to your current modem (the manual describes how -- 
basically you insert it in the audio path from your rig to the original 
modem, just two audio cables), while keeping transmitting with your 
current modem/TNC and also receiving the ASCII through the current 
modem/TNC.

As a remodulator, you don't need to change software configuration nor 
the transmitter interface.  When wired and used this way, the 599zx 
does the actual heavy lifting of RTTY demodulation, and with a press of 
a button, you can use the 599zx as just a sharp filter (plus audio AGC) 
for the existing TNC, where the TNC is actually doing the demodulation.

The 599zx provides an AGC stage which is very good with moderately slow 
QSB.  However, in a contest situation where there are some really loud 
stations who don't transmit at least a few diddles or carriage return 
before sending their exchanges, the AGC action might cause the first 
few characters of an exchange to be lost.  I have had this happen in 
DXpedition style exchanges too, that is why I love N6TQS who also sends 
your call at the end of his exchanges (I've just yesterday received the 
TZ6RD card through the buro; thanks, Doug!).  Just remember to turn off 
the AGC in such situations.

One of the neat aspects of the 599zx is its use as an audio 
millivoltmeter.  By hitting a few buttons, you can use it to measure 
the audio level from the rig.  The built in AFSK generator can also be 
set to put out a steady stream of diddles or RYRY for testing purposes.

Having a digital front end (just like the HAL 4100 and DXP-38), the 
599zx needs to have the audio level from the rig set as perfectly as 
you can make it, just as you need to with the software modems (one of 
the prime reasons people cannot print well with software modems is that 
the sound levels are simply not set up properly).  The AGC circuitry 
(analog) on the 599zx helps some, but you should attempt to provide the 
exact audio level to it that the manual recommends.  The built in meter 
will help a lot with doing it right.  A level that is too high or too 
low will reduce the effective dynamic range the modem will work under 
(it is like working with an A/D converter with fewer bits).  
Overloading the A/D is a much worse problem than too weak a signal 
unless you are using a 250 to 300 Hz IF filter in your rig (i.e., 
absolutely only one RTTY signal is coming through the audio pipe); in 
which case, erring on the overloading side is tolerable.

Finally, a warning... using a good modem can be very frustrating...  
with them, you will be able to print more stations than before; but the 
ones that could not print you before still will not be able to print 
you, HI HI.

73
Chen, W7AY