[Collins] KWS-1 Upper/lower sideband supression

[Dr. Gerald N. Johnson]

20 is poor, 40 is not great when the filter should be 80 or more dB 
down. 40 might be intermod products.

2 db down is not the right place for the crystal on the slope, but the 
lack of USB rejection on LSB tells me that the filter is failing in the 
wide band mode on that side.

The 6 dB points ought to be more like 2.7 KHz apart. Maybe the crystal 
is wrong. That's a cheaper fix than the filter, but 20 dB down at 1 kHz 
tone is not a good sign for the filter.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 7/6/2014 1:16 PM, Bill Riches wrote:
> 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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