[time-nuts] GPS down converter question

[Magnus Danielson]

Hi Bob,

For some magic reason, there exists off the shelf SAW-filters with 
matching parameters. Not to expensive.

A saw before the LNA helps to protect the LNA input from strong 
interference.

Cheers,
Magnus

On 12/01/2015 11:57 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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