[SignalOne] CX-7 Filters

[Peter Sundberg]

Hi guys and thanks for the feedback.

Actually the ladder filter is an interesting concept as a substitute 
for the real deal. Ordering crystals for specific frequencies is not 
that expensive these days.

I note that QuartsLab http://www.quartslab.com/ can provide custom 
made crystals at reasonable prices and there is a very good article 
how to design ladder filters in QEX November-December 2009 - "Crystal 
Ladder Filters for All".

At present I do have some very good audiofilters in my shack and 
there is a very sharp one already built in to the CX7, activated via 
the modified FSK Shift knob  where I select different BW. But for 
crowed CW bands there is definitely a need for a more narrow IF 
filter to cut the QRM.

As always, plenty of food for thoughts.. hi!

73
Peter SM2CEW




At 00:04 2017-01-09, Ka9p--- via SignalOne wrote:


>This list is for discussions regarding collecting, repair, use and 
>sale of Signal/One radios and accessories.
>
>Documentation on Signal/One radios can be found at 
>http://www.hamanuals.com and several other sites on the Web.
>
>.
>They are hard to find, I finally got one cw filter by buying a barn find
>radio for about what a filter should cost and still haven't found time to
>test  it...
>
>.....but before that I had spent a lot of time looking at the more recent
>ladder filter design articles, and thought if I could find a source of 8815
>khz crystals in quantity it shouldn't be that bad a project, and you could
>make a few of varying bandwidths.......the set up of the radio looks like
>there  is plenty of room for a few homebrew ladder filters.  in fact I was so
>  desperate that I did collect up all the 8 meg FT-241 crystals I could find
>at  hamfests and was going to try to grind them into submission (like in my
>novice  days) to try get 4-6 close enough for a decent homebrew.  Obviously
>I'm  retired with way too much time on my hands, and doubt that would work
>very well,  although it might be easier to get some crystals close enough to
>do a lattice  filter.
>
>I have no idea what suitable crystals would cost in quantity but if anyone
>is interested in looking at a quantity crystal order, I'd be interested as
>well....
>
>good luck with the hunt.
>
>73 Scott ka9p
>
>
>In a message dated 1/8/2017 4:28:01 P.M. Central Standard Time,
>signalone at mailman.qth.net writes:
>
>
>
>This list is for discussions regarding collecting, repair,  use and sale of
>Signal/One radios and accessories.
>
>Documentation on  Signal/One radios can be found at
>http://www.hamanuals.com and several other  sites on the Web.
>
>.
>Hello, Peter,
>I also never saw any  satisfactory solutions to additional filters. You may
>have already noticed in  the news letters that the factory ones were less
>than satisfactory due to  filter matching/alignment problems. I also followed
>the issue of trying to add  audio filtering and even found one of the MFJ
>filters at a hamfest for $1!  This was many years after the newsletters ended
>making it all the more amazing  to find one of these filters. After
>studying the letters I decided my best  option was to use a dsp unit 
>I had built
>and used on my Ten Tec Paragon. I  mainly used it for the noise and notch
>functions which the Paragon lacked.  These out board dsp units were popular
>before manufacturers started building  the technology in to the radios.
>My unit also offered several very sharp  audio filter choices so I decided
>to use this device which was now sitting  unused. It works great with the
>CX-7 and while it cannot always help with  strong close in interference
>signals, it is plenty good for regular operating.  If you can lay 
>your hands on
>one of these old outboard dsp units that does  notch/noise/filter
>functionality I would do that and not have to cut into the  radio 
>itself. Hope this
>helps.
>73 ...  Ed
>
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