[R-390] R-390a/SSB Convertor

[John Kolb]

On Mon, 18 Aug 2003, Tony Angerame wrote:

> I am using an R-390a and feeding the if output to a Rycom Selective
> Voltmeter. The Rycom has a product detector with selectable USB/LSB,
> bfo, am and fm detectors. I works well on all modes but I am skeptical
> that I actually have the received ssb signal centered in both the
> passband of the r-390a mechanical filters and the Rycom crystal filters.
> Right now I simply peak the Rycom on receiver noise, select the
> appropriate sideband and tune the r-390 for intelligibility but this
> cannot guarantee the ssb signal is centerted in the r-390a passband. I
> was thinking of using my xmter as a generator and injecting, say a 2.0
> khz audio and centering it in the 4kc passband just by carrier stregth.
> I have a feeling that because of this I am tuning signals on the r-390a
> at one end of the filter passband.

If using the 4 kHz filter in the R-390A, exact centering shouldn't
be necessary. If using the 2 kHz filter, centering would be rather
critical. How close can you set the Rycom? If a perfect 2 kHz
filter in the rx, filter corners at 454.00 and 456.00, setting
the Rycom to 453.70 for USB or 456.3 for LSB would  give you
an audio bandpass of 300 Hz to 2.3 kHz for . I assume the Rycom
has xtal controlled BFO's of the correct freq for it's filters,
which are probably about 3 kHz wide.

Of course the R-390A filters won't be perfect. The 2 Khz
filter is spec'ed at 2.1 kHz +/- 0.2 kHz at 25 deg C, +/- 0.3
over -55 to +85 deg C. A couple of 2 kHz filters I plotted recently
<http://members.cts.com/king/j/jlkolb/site/curves/F455N201.PDF>
<http://members.cts.com/king/j/jlkolb/site/curves/F455N202.PDF>
are a hair less than 2.0 kHz. 4 kHz filter at:
<http://members.cts.com/king/j/jlkolb/site/curves/F455N40.PDF>

At any rate, the perfect BFO freq for a 2 kHz filter will vary slight
depending on the voice you're listening to, lower or higher pitched.
Tune for what sounds most natural.

You can also use the Rycom as an awkward passband tuning by
offsetting it high or low from the perfect location, using
the sholder of one filter to cut into the bandpass of the other
filter and thus reducing the bandwidth below 2 kHz.

John  KK6IL  <http://members.cts.com/king/j/jlkolb>