[GreenKeys] Terminal unit (HAL ST-5000) adjustment

[Ralph Mowery]

-----Original Message-----
From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Ethan Blanton
Sent: Sunday, January 07, 2018 8:27 PM
To: greenkeys at mailman.qth.net
Subject: [GreenKeys] Terminal unit (HAL ST-5000) adjustment

This note is a plea for the voice of experience.  Hopefully someone can tell
me what I'm doing right and wrong!

The equipment:

Drake 2-B
HAL ST-5000
Model 28 KSR

The scenario:

I have no trouble copying RTTY signals with reasonably high SNR on a quiet
band.  (See, e.g., https://www.youtube.com/watch?v=g3VbeuTIgRk
and pleas forgive my fumbling tuning in front of the camera!)  I can finagle
in lower SNR signals on a noisier band, but it gets difficult.
I recognize that my receiver selectivity (and AGC action) will limit
reception performance, but on the bands today I felt like I should have been
able to copy some signals that I could not.

I normally use the 2-B 500 Hz pass band filter centered around something
near 2260 (I use low tones) on a busy band.  Receive signals are passed to
the TU in parallel with the 2-BQ speaker through a filament transformer (I
have an audio transformer for the job, but it's on my TODO).  This is the
setup I was using during the RTTY Roundup.

Furthermore, a 'scope on the ST-5000 showed greatly unbalanced mark and
space amplitudes, rather wide ellipses on the cross, and an angle between
the ellipse long axes of probably 15 degrees off perpendicular.  The needle
bounced significantly on a known good (i.e., generated locally on a computer
with a high quality sound card) signal.

>From what you are saying you are using low tones, but have a filter set at
2260.  That does not sound right at all.  


The normal high tones would be 2125 and 2295 and a filter around 2260 would
probably be ok for that, but the low tones are way below that.  Don't recall
and too lazy to look them up but are below 2125.  That means you are
filtering out almost all the audio tones.  The higher tone will be filtered
out the most.


I am not familiar with  the drake 2b and filtering arrangement ,but if it is
adjustable for center frequency, it should be much lower than 2000 if using
low tones.  If the ellipses are not at right angles to each other, then the
filters are not exactly  tuned, but if not off too far you should be able to
copy ok.