WRTH '94 and WJ-HF1000's filters

WRTH '94 and WJ-HF1000's filters

Post by Mohammed F. Ha » Mon, 10 Jan 1994 08:50:55

I just received my WRTH '94 copy via priority mail from Grove and one
bit of information surprised me. The book said that crystal filters
have a typical shape factor of 2:1 while the DSP (Digital Signal
Processing) filters of the Watkins-Johnson HF1000 have a shape factor
of 1.2:1!

If this is true then I think my next receiver will have a DSP chip in it.

By the way what is the typical shape factor of mechanical filters?

---barrak

PS. I placed my order for the book on November 18. Maybe that's why I
got it so soon. I guess I learned a lesson from PWBR '94; my local
store didn't get it until a month after it was first reported by fellow
SWLers on the net.

 
 
 

WRTH '94 and WJ-HF1000's filters

Post by Will Marti » Thu, 13 Jan 1994 19:54:32



>PS. I placed my order for the book on November 18. Maybe that's why I
>got it so soon.

I think Grove sent them all out at once -- I didn't order mine until
just before Christmas and it arrived Monday... The chargecard bill
hasn't arrived yet, so I'd advise that timing as the way to go... :-)

Re DSP -- I've seen some ads for standalone DSP filter boxes that
range from $150 up. They sound like neat add-ons -- automatic notch
filters, etc. What I'm wondering about is this:

Does anybody yet make a DSP filter unit that has two inputs, one for
each of two receivers. You use the main input for the receiver tuned
to the desired signal, and apply whatever notch and bandwidth filtering
you want to that signal. If you have another station splattering in
from an adjacent frequency, or something so strong that it overloads the
receiver's front end and appears in the background everywhere, you tune
the second receiver (which could be a much cheaper and simpler ordinary
receiver) to that strong un-desired signal and feed that audio into
the DSP's input #2. The DSP then INVERTS the unwanted signal and uses
that result to cancel out the interference on the desired signal.

I'm envisioning BCB/MW DXing on a channel next to a strong local being
possible without having to use a fancy loop to null out the local, for
example. Or getting rid of Gene Scott in the background of every other
WWCR broadcast... :-)

Anybody make such a toy yet? If not, and this inspires you with the idea
to make one and become rich selling them, send me one as a reward for
thinking of it... :-)

Regards, Will

 
 
 

WRTH '94 and WJ-HF1000's filters

Post by Mohammed F. Ha » Sat, 15 Jan 1994 03:44:20



Quote:

> >Re DSP -- I've seen some ads for standalone DSP filter boxes that
> >range from $150 up. They sound like neat add-ons -- automatic notch
> >filters, etc. What I'm wondering about is this:

> >Regards, Will

I've seen an ad for a similar filter but I thought that one worked only
on the audio signal of the receiver and not within the IF stage which
is more efficient as I read somewhere.

---barrak