I have access to a Hiper setup that I assume is toast or will have to be "fixed". I'm wondering about the Older L1 only (non-RTK) units I have... I have a set of Sokkia Stratus and Ashtech Locus for short baseline static. Any chance of those not being affected if Lightsquared stays in it's lower bands, as promised? It's been said that RTK gear looks at a wider band and in some cases were made to look deep into lightsquared's band for Omnistar. Haven't heard much about L1 only gear. Anyone know?
> I'm wondering about the Older L1 only (non-RTK) units I have... I have a set of Sokkia Stratus and Ashtech Locus for short baseline static. Any chance of those not being affected if Lightsquared stays in it's lower bands, as promised?
Hmmm. That's a good question. I suppose it mainly is one of antenna design, i.e. how finely tuned the antenna is for the L1 frequency. The Trimble L1-only 4600LS units I use have micro-strip antennas, which insofar as I can tell from what's available are optimized for one specific frequency and don't "listen" across several frequencies, which ought to be a good characteristic.
Yea, I'm worried about my Promark 3 units. I just paid one off, and am halfway through the lease on my second unit. I really do not want them to be obsolete. They are awesome units for what I use them for.
I assume that my 2002 vintage Hipers (L1/L2) RTK Base and Rover can be retrofitted with the "filters".
Let's hope that it is not as bad as they say it will be. Most of my work is in rural areas, so maybe I'll be less affected than someone in a heavier populated area? I am not as up to speed on this as I should be.
The L1 frequency is 1575.42 Mhz, and L1 is precisely the frequency that will be jammed by LightSquared, who has a license to operate in the 1525 to 1559 Mhz range.
> The L1 frequency is 1575.42 Mhz, and L1 is precisely the frequency that will be jammed by LightSquared, who has a license to operate in the 1525 to 1559 Mhz range.
It pretty much depends on the bandwidth of the L1 receiver's antenna, though, doesn't it? This source on antenna design gives a typical bandwidth of about 3% for rectangular microstrip antennas. Assuming that's a fair estimate for the inexpensive L1 antennas under discussion, that would mean that their bandwidth would be about 1574.42 +/-24 MHz.
If so, the problem for those L1-only antennas would be in the 9MHz of overlap at the upper end of the LightSquared frequency assignments. If the antenna bandwidth is significantly less than 3% or if the upper 9MHz of the LightSquared frequency assignments is withdrawn, then the picture looks better.
The percentage bandwidth usually quoted would be the range of frequencies that pass without undue loss so that they can be received if desired.
That is where the curve is just starting to go seriously downhill. It takes a lot more frequency separation before the antenna or filter has enough loss to strongly reject undesired frequencies, particularly ones that are so strong they need LOTS of rejection.
So it is unlikely an antenna with those specs would do much to get rid of terrestrial strength signals in even the lower LS band.
You seem to be counting on a microstrip antenna to be so narrow banded that it acts like a band filter. This is not reality. Here is an explanation I ran across.
> You seem to be counting on a microstrip antenna to be so narrow banded that it acts like a band filter. This is not reality. Here is an explanation I ran across.
>
>> http://www.tvtechnology.com/article/124620br >
Perhaps I'm misreading that article, but what I get from it is the technical difficulty that LightSquared's proposed ground-based transmitters would have staying perfectly within the allocated frequency.
> The percentage bandwidth usually quoted would be the range of frequencies that pass without undue loss so that they can be received if desired.
>
> That is where the curve is just starting to go seriously downhill. It takes a lot more frequency separation before the antenna or filter has enough loss to strongly reject undesired frequencies, particularly ones that are so strong they need LOTS of rejection.
>
> So it is unlikely an antenna with those specs would do much to get rid of terrestrial strength signals in even the lower LS band.
What I get from a cursory reading of some material about the design of microstrip antennas is that (a) they have a natural resonant frequency and (b) the bandwidth associated with the antenna varies considerably with the details of construction such as the substrate that is used. So, a GPS antenna designed for L1-only receivers might be expected to have a resonant frequency centered on the L1 frequency and to have a very narrow bandwidth.
If the LightSquared signal doesn't run over into the narrow range of bandwidth of an L1-only antenna, are you saying that the antenna will pick up frequencies well outside the natural resonant frequency and the bandwidth to either side of it anyway?
A bandwidth isn't an all-or-nothing proposition. The further you get from the resonant frequency, the less signal gets through, according to a response curve that depends on how complicated the antenna or filter is. If the signal you don't want is very strong, then you either have to move it further from your desired band or else build a filter that has a steeper curve.
That's fundamental to radio receiver design. It's why the FCC in their prior days of wisdom didn't assign an AM (or FM or TV) broadcast station in the same town on adjacent channels - it would require too complicated a filter for an economical receiver to separate them if you were physically closer to the one you didn't want to hear.
An antenna won't have a very steep curve. Almost any receiver will have a filter inside with a steeper curve than the antenna.
That's why Javad's recent press release was talking about a new improved filter inside the receiver - better than previous filters. The release had some interesting curves that illustrate the point.
We should check how our antenna's Return Loss is behaving between 1525-1559 frequencies.
Return low is also known as S11 parameter, or can be calculated from VSWR. My antenna's return loss at 1525 is -2.97dB and at 1559 MHz is -14.72dB, which is a bad news, I have to build a filter to get rid of this new fricking neighbor, sooner or later they will get to europe.
If you have radiation parameters plots (a returnl loss, or VSWR plots) for your Stratuses, Locuses, 4600LSs atc check its antenna return loss between 1525-1559 MHz frequensies.
I do not know if RF part of a receiver does any filtering, I think this entirely antenna part problem.
Javad should be on our side not on Lighsquared's!
What does US DOD think about Lighsquared getting that close to their frequencies?, what about antennas in military handhelds, are they so much narrow banded around 1575.42MHz ?.
my antenna is a patch antenna and it is wideband around L1.
if you have plots for you antennas could you please email them to me: info@mirapract.com
if I have more free time I can prepare a report on my webpage of the antennas affected.
