[time-nuts] GPS down converter question
alex at pcscons.com
Tue Dec 1 19:53:45 EST 2015
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
That down up converter system is an interesting project but it is not
that simple as it looks
On 12/1/2015 2:57 PM, Bob Camp wrote:
> 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.
>> 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
>> 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.
>> On Tue, Dec 1, 2015 at 1:36 AM, Magnus Danielson <magnus at rubidium.dyndns.org
>>> 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
>>> 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.
>>>> time-nuts mailing list -- time-nuts at febo.com
>>>> To unsubscribe, go to
>>>> and follow the instructions there.
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to
>>> and follow the instructions there.
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2016.0.7227 / Virus Database: 4477/11098 - Release Date: 12/01/15
More information about the time-nuts