FAQ's
Q. The output of my 1278 sounds like a buzzsaw
rather than a pure tone.
A. Check the transmit level on the side of the
TNC...you may have it set too high, causing the audio amplifier to be
overdriven. I have seen at least one early 1278 that could not be
cured.... apparently it was a component problem.
Q. Sometimes I can't receive well on RTTY, even though
I have a really good signal.
A. If the TNC is set correctly, this can usually be
traced to one of three things...either it's in the other guys
transmitter, or your receiver, or propagation. Take a look at his
signal using a program like Spectrogram. Is it a clean signal? By
clean, most of the energy should be concentrated in two locations--at
2125 and 2295 Hz. Or is he overdriving the transmitter, generating
wideband hash? Or maybe he has power supply problems and has a
ripple? These things you can't cure. On the other hand, on your end,
especially with tight CW filters, the tendency for the filters to
"ring" may cause problems. Or your receiver may introduce
distortion on strong signals. The solution: reduce the RF gain on the
receiver. The best way to comprehend how much of a difference this
makes is to switch to Pactor mode using Skyrider and make a contact,
and monitor the link speed as you adjust. By reducing my drive level
from the top edge of the ALC zone to 50 percent of the full ALC zone,
and by reducing my RF gain by 25%, I can usually increase my link
speed by anywhere from 200 to 800 percent! Propagation also plays a
certain part, especially on DX contacts. Multipath propagation can
wreak havoc with a digital signal. If the other station sounds
"watery"...you might as well forget it.
Q. In PACTOR, people can connect to me, but then get
stuck and have to abort the QSO. In RTTY I don't have any problems at all.
A. This is usually due to a TXDELAY problem. For
instance, let's suppose the TXDELAY setting is set to 0. The TNC keys
the PTT line, and immediately sends out the data stream to be
transmitted. Not a problem, if the radio switches from RX to TX
instantaneously. But if the radio is typical, it will take from 20 to
40 milliseconds to key the PTT line and come up to full TX. Now if
the TXDELAY is 0 and the radio delay is 30 milliseconds...the first
30 milliseconds of each packet is being chopped off.
The solution: increase your TXDELAY to 40 by typing TXDELAY 40 at the cmd: prompt.
Q. I can "hear" the TNC on the radio--it's
generating RFI.
A. Here's some suggestions. Place chokes on the
line(s) running between the radio and TNC. Install a grounding lug on
the back of the TNC and ground it (just like your transmitter). Plus,
take off the cover and scrape off the paint where the cabinet halves
meet. Check and make sure
all the screws securing the main board to the chassis are tight--this
was the cause of my RFI. Change power supplies--the
"wall-wart" type may be causing trouble. Lastly, separate
the radio and TNC physically--1 foot is usually sufficient. Right
now, I'm doing an investigation of RFI with the 1278B, so in the
future I may have an RFI page specifically devoted to the problem,
along with solutions.
Q. My Pactor connects are really slow, even with good
band conditions.
A. This could be caused by a couple of things...see
the above question on reception. However, there might be another
cause while using Pactor. In Pactor, there is the ability to speed up
or speed down depending on band conditions. For example, suppose I am
working a station at 200 baud, and my neighbor turns on a hair dryer,
generating noise on my quiet band. The TNC will begin to receive
errors. After a certain number of packets, set by the MAXDOWN
command, the TNC will request the sending station
"downshift" to 100 baud. The QSO continues as before, until
my neighbor turns off the hairdryer. Now the band is clear again, and
I begin receiving error-free packets. After a certain number of
error-free packets, determined by the MAXUP command, the TNC will
request that the sending station "upshift" to 200 baud.
All this is done automatically behind the scenes. Speed up and speed down are enabled by the NO200 command..it should be OFF for maximum performance. MAXUP and MAXDOWN can be adjusted to suit your individual preference. Setting MAXDOWN and MAXUP is a balancing act...it is basically two questions: a) How willing are you to give up on 200 baud in bad conditions? and b) How sure are you that 200 baud will work after x number of good 100 baud packets?