[time-nuts] GPS Filter

[Mike Feher]

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