[AMRadio] SP-600 IF Bandwith Specification


Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Mon Oct 2 08:18:17 EDT 2006


As far as my results go, I would rate them
better then the mechanical filters.
They are real easy to add to a receiver since they are zero
loss and are not particular about the impedance
they look into.

In most cases, you can just lift a wire off an IF
transformer and insert the filter.
Just after the mixer would be best.

Has to be 455 kHz IF though, some Collins stuff used
500 Kc, some other stuff used 262 KHz, etc.

Heath kit used some crazy IF frequencies like 9 Mhz and so on...

With the mechanical filters, you need to make up for the loss
through the filter, and have to terminate it carefully, 
and pay attention to the in and out to prevent pass through.

If you just replaced a mechanical filter with a Kiwa, you would get
about 6db of gain? through the circuit, so you might want to
experiment with bypassing one tube amp that drives the mechanical
filter.
Kiwa also makes a better filter, that has some loss through it,
which might make a better direct mechanical filter substitute.

The Kiwa filters are little cubes with pig tail shielded wires
you just tack on, you can also buy a switch board that holds
2 filters, and can pick whatever bandwidth you want in .5 Kc
increments.

I don't know about any phase shift distortion and so on, but
to my ear, they work just as well as a mechanical filter.

With the 5.5Kc filter, as I tune across a steady carrier,
you can see the 3 filters inside that give the bandwidth
you picked, you see three slight peaks of each filter as you
tune across the signal.
Kiwa uses an op amp into 3 separate narrow filters of
slightly different frequencies, and an op amp output.

If there is a S9+50 db signal just out of the passband,
you wont hear it at all with the Kiwa filters.

With the 5.5Kc filter switched in, a clean AM qso
on 7295 will not bother me on 7290, if its clean and the
highs are somewhat limited.

For $50.00 you wont do any better...

 
Brett
N2DTS
> 
> I'm curious, how well these filters would work in lieu of the Collins 
> filters? I have a 75A3 with just the 3.2 Kcs mechanical 
> filter and it just 
> plain sucks. Maybe if it had something along the lines of a 
> 5.5~6.0 Kc 
> might make it a little more tolerable.
> Mod-U-Lator,
> Mike(y)
> W3SLK
> ----- Original Message ----- 
> From: "Brett gazdzinski" <brett.gazdzinski at verizonbusiness.com>
> To: "'Jim Candela'" <jcandela at prodigy.net>; "'Discussion of 
> AM Radio in the 
> Amateur Service'" <amradio at mailman.qth.net>
> Sent: Sunday, October 01, 2006 8:25 PM
> Subject: RE: [AMRadio] SP-600 IF Bandwith Specification
> 
> 
> Yes, the Kiwa filters are something like
> 5.5Kc at -6db, and 6 Kc at -60 db!
> 
> Brett
> N2DTS
> 
> 
> 
> > -----Original Message-----
> > From: amradio-bounces at mailman.qth.net
> > [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Jim Candela
> > Sent: Sunday, October 01, 2006 7:34 PM
> > To: Discussion of AM Radio in the Amateur Service
> > Subject: [AMRadio] SP-600 IF Bandwith Specification
> >
> >
> >
> > I stumbled on a good mechanical filter article that goes into
> > upgrading the SX-42 and SP-600. I found this pretty interesting.
> >
> > This is how it starts:
> >
> > A complaint many shortwave receiver owners have is the
> > inadequate skirt selectivity in their equipment. This is not
> > just a problem in old or inexpensive units. The skirt
> > selectivity of even some modem, top-priced receivers is less
> > than what it could be for dealing with current crowded band
> > conditions. Mechanical filters are often expensive, and they
> > may need accompanying resonating capacitors. Sometimes a good
> > drop-in substitute filter can be found; otherwise
> > installation may be difficult. Even with a new filter
> > successfully in place, an insertion loss can result because
> > of impedance mismatch. Such a loss, averaging 6 dB, is not
> > important for strong signals, but for weak ones it makes all
> > the difference in readability.
> >
> >
> >
> > http://www.kiwa.com/goodwin.htm
> >
> > The -6/-6OdB band widths for the SX-42 are about 4/21 kHz and
> > for the SP-600J about 3/18 kHz - good in their respective
> > times, but most inadequate for today's conditions.
> >
> > SP-600:
> >
> > '3' means 3.0 Khz at -6db, and 18 Khz at -60db
> > '8' means 8.0 Khz at -6 db, and 26 Khz at -60db
> > '13' means 13.0 Khz at -6db, and 35 Khz at -60db
> >
> > Jim
> > JKO
> >
> >
> >
> >
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