[Collins] KWS-1 Upper/lower sideband supression

[Bill Riches]

Checked sideband suppression today - lower is -20 db when checking on upper
and upper is good at - 40 db when checking on lower.  Also upper sideband
sounds a lot better than lower does.  I believe problem is that the lsb
crystal fx is too high on the filter slope. (-2 db down)  Going to
experiment with moving crystal further down on the filter slope and maybe
that will help.  I do have another KWS -1 filter in one of the kws-1 units
that I have not done anything with yet.  May play with that filter after the
xtal experiment.  Film at 11.

73,

Bill 

-----Original Message-----
From: Bill Riches [mailto:bill.riches at verizon.net] 
Sent: Saturday, July 05, 2014 9:23 PM
To: 'geraldj at netins.net'
Cc: Bill Riches
Subject: RE: [Collins] KWS-1 Upper/lower sideband supression

Hi Jerry,

Swept the filter using a 3586 driving the filter before C107 and ground and
measuring the output thru a 10/1 probe. - 6 db points are centered 250.0
(251.7 and 248.8). I only get a max attenuation of -30 db at (252.0 and
249.0).  Shouldn't I get 50 - 60 db? Lower SSB crystal fx is 251.25 and only
-2 db down.  Upper SSB crystal fx is 248.35 and is 30 db down on the slope.
That is weird.  I will measure lower and upper ssb rejection tomorrow
inserting 1 khz and measuring rejection.  Have not done anything with USB as
I have had the rig only on 40 and 75.  Any comments would be appreciated.  I
will try to fire it up on the collins pre net tomorrow if I am back in time.


73,

Bill, WA2DVU
Cape May

-----Original Message-----
From: Collins [mailto:collins-bounces at mailman.qth.net] On Behalf Of Dr.
Gerald N. Johnson
Sent: Saturday, July 05, 2014 3:32 PM
To: collins at mailman.qth.net
Subject: Re: [Collins] KWS-1 Upper/lower sideband supression

Carrier suppression comes from the balanced modulator balance, capacitive
and resistive.

Opposite side band rejection comes from the filter. What audio frequency are
you using to measure the side band rejection, 1 kHz is much better than 100
Hz? Are the carrier frequencies on the slopes of the SSB filter? You may
have to sweep (manually with signal generator or LF sweep generator) the
filter response and check the carrier frequencies with a counter. Filters
that old have been known to go bad as have crystals. Y101 and Y102. There
are some capacitors in the carrier oscillator circuit that could also have
moved the crystals into the filter pass band. Three things are critical. The
carrier frequencies should be set to about the 30 dB down point on the slope
of the filter, on opposite sides of the passband, and the filter must have
the predicted passband about 2.5 kHz wide with steep skirts. The sideband
suppression is dependent on those.

it sounds to me as if the filter is the primary problem. Its not longer as
selective as needed.

On 7/5/2014 1:14 PM, Bill Riches wrote:
> Just noticed that upper/lower sideband suppression is only about -15 db.
> Specs are -50 db.  Carrier suppression is about -55 db.  Any suggestions?
> 73,
>
> Bill, WA2DVU
>
> Cape May, NJ
>
73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association
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