[time-nuts] GPS down converter question

paul swed paulswedb at gmail.com
Wed Dec 2 15:32:14 UTC 2015 

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 <paulswedb at gmail.com> wrote:

> Sorry mouser electroncs.
>
> On Wed, Dec 2, 2015 at 8:10 AM, Herbert Poetzl <herbert at 13thfloor.at>
> 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 <paulswedb at gmail.com> 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 <alex at pcscons.com> 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 <paulswedb at gmail.com> 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 <
>> > >>>> magnus at rubidium.dyndns.org
>> > >>>>
>> > >>>>> 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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