[time-nuts] GPS first LO need to be locked?
kb8tq at n1k.org
Sat Apr 1 13:23:52 EDT 2017
> On Apr 1, 2017, at 11:18 AM, paul swed <paulswedb at gmail.com> wrote:
> Thanks everyone but I am working on an austron 2201a so all the discussions
> on modern methods won't help. Whats is interesting is indeed the 2201 down
> converts to 80KHz and the does sample in an IQ fashion. Its all discreet
> chips and such.
If you have a free running VCO in the head end, then indeed you need to lock it to
something. An unlocked VCO will not be close enough to frequency to do you any good.
The 8660 may or may not be close enough in free run mode. It depends a lot on
what standard you have in yours.
> Easily traceable and logical.
> I think I have what I asked for and am experimenting with active mixers and
> IFs made of minicircuit gain stages.
> I am using a commercial antenna with 34 db of gain. It says 50db I question
That is a very normal antenna gain spec and it was quite common in the era the
device you have was designed. I run a number of GPS gizmos that need a 50
db antenna on them. They *might* work with a 40 db setup. They do not work
with something in the 20 to 30 db range. If you watch for a while (as in 6 to 12
months) you can indeed get good old 50 db gain antennas on eBay pretty cheap.
> But lots of gain to a HP IAM 81008 active mixer low drive LO. Then a 40db
> at least 75 MHz IF. (Pretty sure this is overkill.)
> The LO is a HP 8660c for now. Locked to a TBolt.
> Thats the reason for the question. I can shift the 8660 to the ausytron 10
> On Fri, Mar 31, 2017 at 7:47 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
>> There are a lot of GPS chips that do an I/Q mix down to a low IF. It’s
>> then (re) sampled from there. The “LO” in this case would down convert to
>> the low IF ….
>>> On Mar 31, 2017, at 6:08 PM, Magnus Danielson <
>> magnus at rubidium.dyndns.org> wrote:
>>> God natt Attila,
>>> On 03/31/2017 11:29 PM, Attila Kinali wrote:
>>>> God kväll Magnus,
>>>> On Fri, 31 Mar 2017 21:19:00 +0200
>>>> Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>>>>> Still fills the function of LO, as the sample and hold operates as a
>>>>> mixer and the fold-down can be seen as an overtone mix followed by a
>>>>> sampling of the mix product, so well, it's about the same thing.
>>>> "Harmonic mixer" is the word you are looking for :-)
>>> Not necessarily. It could be a locked oscillator too.
>>> Harmonic mixer is another way to go.
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