There are several problems. First energy from the offending signal leaking into the protected GPS band and second the GPS receivers having a bandwidth greater than the protected GPS band in order to reduce phase errors, acquire GPS signal energy present outside the protected GPS band to have a higher bandwidth signal, and to reduce production costs. The GPS industry is part of the problem. I firmly believe the protected band needs to be increased. I will always favor better time and frequency dissemination over social networking. John WA4WDL -------------------------------------------------- From: "Bob Bownes" <bownes@gmail.com> Sent: Friday, September 30, 2011 11:11 AM To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Subject: Re: [time-nuts] GPS Interference Question > Exactly. The narrower the filter, the more it will cost. In general. > > > > On Fri, Sep 30, 2011 at 11:10 AM, Tom Holmes <tholmes@woh.rr.com> wrote: >> Sticking with the intent to keep this non-political, what good is a >> filter >> if the offending signal is within the necessary passband? >> >> Tom Holmes, N8ZM >> Tipp City, OH >> EM79 > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >

My question had nothing to do with cost or design, but only that you can't filter out a signal that is in the passband you need for your own channel. Even a square passband won't help that problem, fantasy that it is. Tom Holmes, N8ZM Tipp City, OH EM79 > -----Original Message----- > From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On > Behalf Of Chuck Forsberg WA7KGX N2469R > Sent: Friday, September 30, 2011 11:20 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] GPS Interference Question > > A wider filter with steep skirts tends to cost more. > Constraints on noise figure, dynamic range, group delay. and flatness > add more cost > and power consumption. > > > On 09/30/2011 08:11 AM, Bob Bownes wrote: > > Exactly. The narrower the filter, the more it will cost. In general. > > > > > > > > On Fri, Sep 30, 2011 at 11:10 AM, Tom Holmes<tholmes@woh.rr.com> wrote: > >> Sticking with the intent to keep this non-political, what good is a filter > >> if the offending signal is within the necessary passband? > >> > >> Tom Holmes, N8ZM > >> Tipp City, OH > >> EM79 > >> > >> > >>> -----Original Message----- > >>> From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] > On > >>> Behalf Of Chuck Forsberg WA7KGX N2469R > >>> Sent: Friday, September 30, 2011 10:55 AM > >>> To: Discussion of precise time and frequency measurement > >>> Subject: Re: [time-nuts] GPS Interference Question > >>> > >>> If LightSquared deploys their high powered LTE network in the satellite > >> band > >>> the GPS world will become very interesting indeed. Are LightSquared > >> willing > >>> to spend $20,000 to upgrade the GPS on my Skylane to a new model which > >>> does not yet exist? > >>> > >>> With that many transmitters we may experience areas where RF from > multiple > >>> high power transmitters creates hot spots. In some places pieces of metal > >>> with non Ohmic bonds will create mixing products, some of which may fall > >>> directly within GPS bands. These effects have not been simulated. > >>> > >>> Who knows who the FCC is listening to - the GPS industry including > >> millions > >>> of current users, or those who appear to have bought under the table > >> favor. > >>> This could make Solyndra look like small change. Film at 11. > >>> > >>> > >>> On 09/30/2011 07:02 AM, Marco IK1ODO -2 wrote: > >>>> At 15:44 30-09-11, Jason wrote: > >>>> > >>>>> To filter out the L2 signal, would an actual GPS receiver have to be > >>>>> replaced / modified? > >>>>> > >>>>> Or would a more simple and cheaper alternative be to get a new > >>>>> antenna (with fancy filtering) to replace my existing roof-top > >>>>> antenna and expect all my old equipment to be happy? > >>>> I think that a new antenna/filter/amplifier unit would be ok. But the > >>>> problem is the installed base of receivers, including all those costly > >>>> units used for geodesy or navigation, that have embedded antennas. > >>>> Those will be hard to modify. > >>>> > >>>> 73 - Marco IK1ODO > >>>> > >>>> > >>>> > >>>> _______________________________________________ > >>>> time-nuts mailing list -- time-nuts@febo.com > >>>> To unsubscribe, go to > >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >>>> and follow the instructions there. > >>>> > >>> -- > >>> Chuck Forsberg WA7KGX N2469R caf@omen.com www.omen.com > >>> Developer of Industrial ZMODEM(Tm) for Embedded Applications > >>> Omen Technology Inc "The High Reliability Software" > >>> 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430 > >>> > >>> > >>> _______________________________________________ > >>> time-nuts mailing list -- time-nuts@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@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@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > -- > Chuck Forsberg WA7KGX N2469R caf@omen.com www.omen.com > Developer of Industrial ZMODEM(Tm) for Embedded Applications > Omen Technology Inc "The High Reliability Software" > 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430 > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

One sure-fire "fix" to the problem is to open up the military frequencies to everyone. GPS broadcasts on more than just the common L1 freq. but also on 1.2Ghz. Again, not really pratical because of the huge cost of conversion -- Chris Albertson Redondo Beach, California

Björn

Hi Chris, > One sure-fire "fix" to the problem is to open up the military frequencies > to everyone. GPS broadcasts on more than just the common L1 freq. > but also on 1.2Ghz. It is not military frequencies, it is military codes, the spread spectrum sequence is encrypted. There are different generation GPS satellites. Older generations are still on orbit, thanks to a working life of a decade or more. General replacement strategy is to launch a new to replace a dying satellite. The classic GPS signals available is L1 CA open signal L1 P(Y) has been sent unencrypted in P form in the past, now encrypted Y L2 P(Y) same as above Even when encrypted there are relations between the signals enabling geodetic quality receivers to make measurements on L2 too. With the GPS IIR-m satellites a new open signal on L2, called L2C is broadcasted. We have 8 IIR-m on orbit now. [1] We have one IIF satellite in the constellation, adding also an open signal on L5. > Again, not really pratical because of the huge cost of conversion It will be interesting to see if consumer GPS receivers will do more than one frequency. Perhaps interference on L1 will make that happen. ;-) [1] ftp://tycho.usno.navy.mil/pub/gps/gpsb2.txt -- Björn

On 30/09/11 18:06, Chris Albertson wrote: > One sure-fire "fix" to the problem is to open up the military frequencies > to everyone. GPS broadcasts on more than just the common L1 freq. > but also on 1.2Ghz. > > Again, not really pratical because of the huge cost of conversion L2C is already being roled out, but relying only on that is to early as only 8 birds transmitt it. L5 is also an option in the future. Only one bird transmits it. In a distant future it would be possible to build devices with L2C & L5 only. They are so close in frequency that a common RF chain would not be too hard. What Lightsquared may force is the development of double or tripple receivers. It is the next challenge for commercial GPS chip designers. Just doing L1 C/A and L2C could shift the precision of the receivers significantly as it now could be doing it's own ionspheric compensation. Just a single L2C channel would achieve that. L1 C/A and L2C capable receiver would provide frequency disparity but when not needed increase the precision. Cheers, Magnus

On 10/1/11 1:38 AM, Magnus Danielson wrote: > On 30/09/11 18:06, Chris Albertson wrote: >> One sure-fire "fix" to the problem is to open up the military frequencies >> to everyone. GPS broadcasts on more than just the common L1 freq. >> but also on 1.2Ghz. >> >> Again, not really pratical because of the huge cost of conversion > > L2C is already being roled out, but relying only on that is to early as > only 8 birds transmitt it. > > L5 is also an option in the future. Only one bird transmits it. I think there's actually two, but not turned on all the time. Not sure though. > > In a distant future it would be possible to build devices with L2C & L5 > only. They are so close in frequency that a common RF chain would not be > too hard. > But you lose the ability to measure ionospheric delays as well, when the two frequencies are close. L5 is all about safety of life applications, since the spectrum for L2 isn't protected as well as that for L5.

Hi Jim, On 01/10/11 16:46, Jim Lux wrote: > On 10/1/11 1:38 AM, Magnus Danielson wrote: >> On 30/09/11 18:06, Chris Albertson wrote: >>> One sure-fire "fix" to the problem is to open up the military >>> frequencies >>> to everyone. GPS broadcasts on more than just the common L1 freq. >>> but also on 1.2Ghz. >>> >>> Again, not really pratical because of the huge cost of conversion >> >> L2C is already being roled out, but relying only on that is to early as >> only 8 birds transmitt it. >> >> L5 is also an option in the future. Only one bird transmits it. > > I think there's actually two, but not turned on all the time. Not sure > though. They sent one up with a "demostrator signal" which had issues... on L1 already. Will check it properly myself as my memory is hazy... seems one of the IIF sats (IIF-2 launched in July) has not been brought into constellation yet. >> In a distant future it would be possible to build devices with L2C & L5 >> only. They are so close in frequency that a common RF chain would not be >> too hard. >> > > But you lose the ability to measure ionospheric delays as well, when the > two frequencies are close. You don't loose it, you just doesn't get the same precision. However, recall where we are comming from... not real observation at all but approximate models being parametriced. Still, L1, L2 and L5 would be the ideal. > L5 is all about safety of life applications, since the spectrum for L2 > isn't protected as well as that for L5. Indeed. Cheers, Magnus