actually the 34MHz filter [Meinberg scheme ]could be made at home, by
using old 10,7MHz FM-IF filters magnetic material, once upon the time I
made some 27MHz filters that way, for 70MHz is bit risky, since there is
no salvageable out there,
perhaps by using some "binocular" cores made for 100MHz from old FM
radios input or some Amidon parts with trim-cap tuning could work
73
KJ6UHN
Alex
On 12/2/2015 2:42 PM, Bob Camp wrote:
Hi
Indeed (as I suspected) that 75 MHz filter runs up the total parts cost quite a
bit.
First thing I’d do is take a look at the board this connects to. Does it
already have
a narrowband filter (at 75 MHz) on it?
Bob
On Dec 2, 2015, at 10:36 AM, paul swed <[email protected]> wrote:
To Bobs comments your right. That 75 MHz may not be needed because of the
1575 input filter. That would save $29.
By the way I was shocked to see for all of $3 complete 1575 filter and LNA
chips. The only nasty challenge is the chips are extremely small. The cost
is low enough I can purchase several in case I screw it up. Its clearly
going to be at my maximum soldering skills.
Regards
Paul
WB8TSL
On Wed, Dec 2, 2015 at 10:32 AM, paul swed <[email protected]> wrote:
My bad mixing threads here the 1575 filter is in mouser and digikey has
them.
The 75 MHz is straight from mini-circuits.
Regards
Paul
WB8TSL
On Wed, Dec 2, 2015 at 10:31 AM, paul swed <[email protected]> wrote:
Sorry mouser electroncs.
On Wed, Dec 2, 2015 at 8:10 AM, Herbert Poetzl <[email protected]>
wrote:
On Tue, Dec 01, 2015 at 08:33:05PM -0500, paul swed wrote:
Digikey was a strike out with 1 filter for 86 cents but
order was 1000 units.
Sorry, but could you point me to the filter in question
please, I couldn't find anything on digikey, but probably
I was searching for the wrong keywords.
Thanks in advance,
Herbert
Mouser however has a wide assortment very reasonable and
by the single units.
Hardest thing will be soldering them.
Regards
Paul
WB8TSL
On Tue, Dec 1, 2015 at 8:29 PM, paul swed <[email protected]> wrote:
Hello to the group have indeed done the 1575 down to 35.42 to 75.42
and
upconverter trick.
Thats what I used for 2-3 years now and thought it was time to move
beyond
that approach. Especially due to the earlier conversation on old
receivers
and that they should still work just fine if you do not care about
the date.
I actually have 2 versions of the 35 to 75 converter. One using an
odetics
down converter and another using a starlink gps receiver. Both have
35.42
MHz IFs. Old stuff you can get a soldering iron into.
No intention to put this on the tower and mini-circuits makes a good
BPF
for the 75 MHz IF. Since I will believe the actual antenna has a 1571
filter in it I was thinking of skipping it down in the shack.
Will see what digikey and mouser has in the way of filters and if
inexpensive may buy one. I keep thinking I may actually have one
also.
Thanks again everyone.
Paul
WB8TSL
On Tue, Dec 1, 2015 at 7:53 PM, Alex Pummer <[email protected]>
wrote:
for 70MHz it does not hurt to match the cable to the filter at the
antenna unit [down converter] end and also match the filter at the
receiver upconverter end, the cable will pick up enough noise to
overdrive
the 70 something receiver's input [ the "outside" field will drive
a
current in the cable's shield, but not in the center conductor, that
current causes noise voltage between the two end of the cable's
shield
which will end up at the input of the receiver, therefore it need
to be
filtered out before it hits the mixer......also the down
converter's LO's
reference is sensitive to the noise which the cable will pick up [
will
cause phase noise ], therefore it needs to be filtered .....
That down up converter system is an interesting project but it is
not
that simple as it looks
73
KJ6UHN
Alex
On 12/1/2015 2:57 PM, Bob Camp wrote:
Hi
Here’s sort of a backwards look at it:
Do you *need* an IF filter in the downconverter? By that I’m asking
about a
filter better than a simple LC tank. Did they put the filter in the
downconverter
or in the main box? I would think that putting a fancy filter up
by the
antenna
would have been a less likely thing to do than putting it down in
the
main box.
Bob
On Dec 1, 2015, at 9:48 AM, paul swed <[email protected]> wrote:
Thanks everyone. The Meinberg is nice and maybe available from
Ebay by
Alex's link. But its 35.42 much as the Odetics down converter. I
am
looking
to create a 75.42 Mhz IF.
Mini-circuits makes just the right parts. But had several IF
bandwidths
available.
So will go with the 2 or so MHz filter as suggested.
I have the typical GPS better quality high gain antenna 1/2"
Heliax
feed to
a low noise gain block that makes up for the loss of a 8 X
splitter.
I may add a 1575 filter ahead of the 10 db amplifier and then hit
the
mixer. I think I have a filter. I actually question that I need
the
filter
or 10 db amp. May build without it to see what happens. Can
easily add
it.
The LO will be a mini-circuits dsn-2036 followed by a 10 db amp
to drive
the mixer another mini-circuit DBM. The IF drives a bpf-a76+ and
then
will
follow that with 30 db of gain at 75 MHz.
At least thats my thinking.
Regards
Paul
WB8TSL
On Tue, Dec 1, 2015 at 1:36 AM, Magnus Danielson <
[email protected]
wrote:
Hi,
This is a side-track to Pauls original question, but maybe a nice
little
point to make now that Peter touched on the subject.
To elaborate a little on C/A and multipath surpression.
The multipath surpression of the receiver depends on code rate,
bandwidth
and correlator spacing. P-code is able to surpress more, and the
C/A
code
errors look about the same as the P-code, but scaled accordingly.
Increasing the bandwidth helps to reduce the C/A errors, but
taking the
next step of using narrow correlators further reduces the error.
This
is
shown already in the classical Spiliker book, but further
readings from
Novatel could be nice.
Increasing the bandwidth and narrowing the early and late
correlator
taps
both have the effect of reducing the time over which energy goes
into
the
E-L difference, and hence reducing the impact of multipath into
the
solution.
Cheers,
Magnus
On 12/01/2015 06:00 AM, Peter Monta wrote:
What should the IF pass band bandwidth be?
For GPS C/A with wide correlator, about 2 MHz; if you want
Galileo
BOC and
(eventually) GPS L1C, or legacy C/A with narrow correlator,
about 8
MHz;
for GPS P code about 20 MHz. Books on GNSS software receivers
will
detail
the many tradeoffs available---if you're starting out with a
proof-of-concept lab receiver, go for 8 MHz.
Cheers,
Peter
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