I'm not sure yet. Right now, I am learning how to use Protel DXP (our
program at work) to input all of the design date. I'm figuring 2 or 3 weeks
for the learning curve. The schematic input part is pretty similar to an
older version of Protel that I have, but different from the program that I
have been using for awhile but it should work out ok. It should take about a
week after that to input all of the schematic sections, and a few more weeks
for the complete layout. I still have to work out the details for the DAC
(to improve the settling time of the synthesizer), and the switching scheme
for the filters if I go for multiple I.F. bandwidths.
I work in a secluded industrial park, so I might string out a 500 foot
antenna. This should be a good test for strong signal handling.
As soon as our software guy gets freed up from his big project, we will get
the graphics display up an running.
Too bad you aren't in the Chicago area....................I would be able to
demonstrate the engineering unit for you!
Oh, on a very funny note............I did get the DDS based RF generator up
and running, at least for a little while. After about 10 minutes, the DDS
conks out. I am not sure if it is a bad device (ESD) or the board layout. I
didn't have any double-sided board stock left, so I got the bright idea to
lay copper tape on the reverse side, using feedthroughs to connect to the
copper flood on the reverse side. Anyway, I am working on a relayout of the
board, this time, using segmented power planes. It should work out ok,
especially since it is basically the DDS circuit I have been using for a few
years, except that I have added a modulated output stage.
Back to work!!!!!!!!!!!!
Pete
"Eric F. Richards" wrote in message
...
"Pete KE9OA" wrote:
Hi Eric,
It has come along pretty well. I just met with one of
the
vendors yesterday, and it looks as if they will be able to wind the
loopstick antennas on 8 inch rod stock. We just have to work out the
minimum
buy details.
Cool. Do you know how big your first run will be?
I tried several different I.F. transformers, to couple the mixer to the
ceramic filter, and was able to find a good source.
Toko looked promising at first..............I told them that we would
only
be ordering 500 of the transformers to begin with, and they said that
was
fine. After about 8 weeks, they sent me 20 samples. When I read the fine
print on the paperwork, they had submitted an annual usage of 100k. When
I
explained to them once again that we would only be needing 500 pieces to
start with, they said "is that all? We can't give good pricing on small
quantities".
I then explained that Mouser has just what I need in stock, at one
quarter
of the Digi-Key price. It looks like the Mouser unit is a winner. With
this
transformer, overload doesn't occur until a 140mV level is present at
the
antenna input.
I am not sure where Philips got that 500mV overload spec from, but I
tried
several different transformers, with impedance ratios from 3 to 1, up to
60
to 1. The Philips folks couldn't explain how to achieve that figure
either.
Later this week, I am going to string a 200 foot longwire, and do some
field
testing. I am fairly optimistic that the receiver will handle those
conditions pretty well.
We've been working on a 3 million dollar project for the past few
months, so
that put the radio on the back burner, as far as the software
development
goes. Hopefully, in the next couple of months, things will take shape.
All of the RF design work is completed....................I think I will
have a switchable attenuator ahead of the front end for those super
strong
signals.
Oh, one other thing about that overload point...............it only
occurs
on signals in the I.F. passband. As soon as you tune off center
frequency,
the strong signals are out of the picture. No desense problems.
That's good to know, although I'll bet I can find the 140mV signal
without problem.... :-)
The sync detector sounds so good that I don't know if the receiver even
needs an envelope detector.
I think it would be necessary for digging out the weakest of the weak.
Using the sync detector, 8 extra poles of
selectivity are cascaded at 455kHz, so the skirt selectivity is very
good.
Still, I would like to come up with some sort of phasing scheme, so that
the
receiver could have continously variable bandwidth, but I haven't
figured
out how to do that yet.
I needed a way to test the receivers at our facility, and I didn't want
to
bring any of my RF generators from home, so I designed an AD9851 based
signal generator. I will be building it up at work later
today..............I want to make some distortion measurements after I
get
it completed. Wouldn't that be a cool product, if it could sell for
under
200 dollars?
I still haven't convinced the boss about that one!
Do you have a release target date?
I recall some mention of LF/VLF capability -- is that still in the
design?
Eric
Pete
"Eric F. Richards" wrote in message
...
Hi, Pete,
Out here in the peanut gallery we want to know what's happening with
your new receiver and antenna -- how is it going?
Eric
--
Eric F. Richards
"The weird part is that I can feel productive even when I'm doomed."
- Dilbert
--
Eric F. Richards
"The weird part is that I can feel productive even when I'm doomed."
- Dilbert