[time-nuts] GPS Filter

[J. Forster]

There are far more portable GPS units than fixed, timing units.
Furthermore, the consequences of a position error are far greater.

Hence, a filter option may well not get rid of LightSquared issues for the
majority of users users.

-John

===============


> I used the 0.5 dB number for loss as a worst case. Of course they are
> available. They are available even lower, and even at higher frequencies.
> Whether or not is trivial is not relevant. What is required is relevant.
> This would of course be relevant in small handheld disadvantaged GPS
> receivers, but, for roof mounted time-nuts use it should not be a problem.
> Even some indoor use it would be fine. If you really feel that you need
> less
> than 0.5 dB of NF, get the numbers. What is the typical RIP from the
> various
> birds at various locations? Then knowing Ga and NF you can calculate C/N
> and
> Eb/No required for the processors to work with acceptable error. Anyway,
> enough on this. This is something I can personally handle and am not
> worried. Besides, imagine if all of the sudden millions of Cell phones
> became useless. Just not going to happen. - Mike
>
> Mike B. Feher, EOZ Inc.
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960 office
> 908-902-3831 cell
>
>
> -----Original Message-----
> From: J. Forster [mailto:jfor at quik.com]
> Sent: Friday, March 04, 2011 9:09 PM
> To: Mike Feher
> Cc: 'Discussion of precise time and frequency measurement'
> Subject: RE: [time-nuts] GPS Filter
>
> Preamps with NFs under 0.5 dB are available for the 1.5 GHz region. IMO a
> doubling of system noise temperature is non-trivial.
>
> -John
>
> ===============
>
>
>> Well, as you said John, for FWIW. In this case not much. As said low
>> loss,
>> so increase in noise temp would be minimal, and, if it makes a
>> difference
>> between an overloaded front end or a 0.5 dB loss in NF, it will be
>> welcome.
>> Heck, we use filters in front of most of our Satcom LNBs at 21 GHz with
>> minimal effect. Been there and done that, as the saying goes. If
>> necessary
>> the small increase in noise temp can easily be overcome by a slightly
>> larger
>> aperture, especially since a view of the full sky is not really
>> necessary
>> and birds below certain elevation angles are typically ignored by
>> software
>> settings of one's own choosing. And again, I was talking about people
>> who
>> have done this and can do it again. It would not be an issue for me.
>> Regards
>> - Mike
>>
>> Mike B. Feher, EOZ Inc.
>> 89 Arnold Blvd.
>> Howell, NJ, 07731
>> 732-886-5960 office
>> 908-902-3831 cell
>>
>>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of J. Forster
>> Sent: Friday, March 04, 2011 8:47 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] GPS Filter
>>
>> I'm not so sure.
>>
>> A filter ahead of a preamp significantly increases the system Noise
>> Temperature.
>>
>> GPS signals are weak and link margins are small. The receiver preamps
>> are
>> already very low noise.
>>
>> I'd think that a narrow filter might well drive up the systen NF to the
>> point it'd be useless.
>>
>> FWIW,
>>
>> -John
>>
>> =============
>>
>>
>>> I used to make some interdigital filters and amplifiers in the early
>>> 80's
>>> for MDS TV reception in the 2.3 GHz range. One can easily fabricate a
>>> low
>>> loss narrow band filter at 1.5 GHz if need be, and as mentioned before,
>>> antennas should be easy as well. If this really becomes an issue, I am
>>> sure
>>> there will be a lot of solutions offered and anyone with some RF
>>> experience
>>> will also be able to handle it themselves. Regards - Mike
>>>
>>> Mike B. Feher, EOZ Inc.
>>> 89 Arnold Blvd.
>>> Howell, NJ, 07731
>>> 732-886-5960 office
>>> 908-902-3831 cell
>
>
>