I believe that's to avoid errors from phase center offset -- when the antenna calibrations are done, the measurements are taken with the antenna aligned that way so aiming it in the fields ensures releatability.
On Nov 22, 2019, 12:01 PM, at 12:01 PM, Bill Dailey <[email protected]> wrote: >I would like to tag on to this. I have a large Leica L1 choke ring >antenna. It has an indicator for “N”. Not sure why. I placed it on >the roof without respect to directionality. I will rotate it with “N” >facing north in a month or so to see if there is any effect. > >Bill Dailey > >Negativity always wins the short game. But positivity wins the long >game. - Gary Vaynerchuk > >Don’t be easy to understand, >Be impossible to misunderstand >- Steve Sims > >> On Nov 21, 2019, at 6:00 PM, Dana Whitlow <[email protected]> >wrote: >> >> Most modern GPS receivers are very quiet even barefoot. So, one >could >> argue that one should >> not have much more LNA gain in the antenna than required to make up >for >> feedline loss, which >> should be easily calculable. While excess gain in the antenna can >improve >> overall system noise >> figure a small amount, it will degrade intermod performance, which is >> likely to be a worse problem >> than simple weak signals. It's likely that the cure is worse than >the >> disease, as my doctor likes to >> say. >> >> Dana >> >> >> >>> On Thu, Nov 21, 2019 at 4:00 PM Taka Kamiya via time-nuts < >>> [email protected]> wrote: >>> >>> So.... concensus is, 50dB gain antenna is too much gain, unless feed >line >>> is too long, reception is poor, or there are other circumstances >extra gain >>> is desired? >>> >>> --------------------------------------- >>> (Mr.) Taka Kamiya >>> KB4EMF / ex JF2DKG >>> >>> >>> On Thursday, November 21, 2019, 3:00:14 PM EST, Bob kb8tq < >>> [email protected]> wrote: >>> >>> Hi >>> >>> That is indeed the gotcha. Once you get past a certain amount of >gain in >>> the >>> preamp, the C/N levels don’t change enough to notice. Looking today >vs >>> looking >>> tomorrow is unlikely to be of any help if you are after a fraction >of a >>> db. >>> >>> About the only way to check would be to fast switch an attenuator in >and >>> out of >>> the signal path. Watch things for a minute at one setting and then >do the >>> same at >>> another setting. Run for a while and log all the deltas. If you see >a >>> degradation of >>> more than a few tenths of a db, you are getting towards the minimum >gain >>> point. >>> >>> Indeed there are some receivers that have an AGC built in. *IF* your >>> receiver has one >>> and *IF* you can get at it, that would be a great way to work this >out. >>> Indeed anybody >>> who makes it past both of those constraints has a pretty unique >device. >>> >>> ==== >>> >>> Simple answer for a 50 db antenna is to put an attenuator in after >the DC >>> has >>> been eliminated from the circuit. It’s not idea, but it’s the best >you can >>> do. Running >>> a great big splitter is one great way to come up with attenuation >….. >>> >>> Bob >>> >>> >>>>> On Nov 21, 2019, at 10:29 AM, John Ackermann N8UR <[email protected]> >wrote: >>>> >>>> Bob, this is a great summary, thanks! >>>> >>>> One related question, especially with mixed systems -- how do you >tell >>>> if you have optimum signal level at the receiver? >>>> >>>> Most show some sort of SNR or Cn value. What should we look for? >What >>>> are the indication of *too much* signal? One issue in particular >is how >>>> to handle a modern GPS that expects modest antenna gain when it's >>>> plugged into a system with a 50dB gain antenna at the top. >>>> >>>> Thanks! >>>> John >>>> ---- >>>> >>>> On 11/21/19 8:00 AM, Bob kb8tq wrote: >>>>> Hi >>>>> >>>>> Way back in time, the first gear out there to use what we now look >at >>> as “normal” antennas >>>>> was survey gear. For various reasons they decided on a 12V power >supply >>> and 40 to 50 db >>>>> of gain in the preamp mounted in the antenna. They also got into >L1 / >>> L2 pretty quickly. >>>>> >>>>> A bit later the cell phone (and later broadcast) guys got into >this. In >>> a location with a lot of >>>>> RF (like a cell site) having a lot of gain at the antenna didn’t >work >>> all that well. IMD issues >>>>> got into the act pretty quickly. In addition, front end filtering >was >>> required to reduce overload >>>>> issues. The focus was on L1 only so filtering was relatively easy. >>>>> >>>>> There is a whole separate set of antennas that put a big chunk of >the >>> RF portion of the radio >>>>> in the antenna. Those still survive here and there. I have one of >them >>> and probably a couple >>>>> of dozen of the more “normal” antennas. >>>>> >>>>> As time marched on, supplying 12V to antennas became a bit less >>> popular. Most of the cell >>>>> guys went over to a 5V antenna supply. The net result was 12V 50 >db >>> survey antennas that did >>>>> L1/L2 and much smaller 5V 25 db antennas for “timing”. The timing >>> antennas didn’t do L1/L2 so >>>>> not going to work for survey. The survey antennas had way to much >gain >>> and no filtering so >>>>> not going to work for a cell site. >>>>> >>>>> Indeed things did and do get crossed up in various pro and >basement >>> systems. With care and >>>>> the right set of circumstances things may work. In other cases the >>> result can be an ongoing set >>>>> of systems issues over an entire network of stations. >>>>> >>>>> Prices for a good new survey antenna are up in the many thousands >of >>> dollars range. They have >>>>> very stable phase centers and (usually) test results to allow >>> correction of any residual phase >>>>> issues. This is part of what lets you get into the “couple of mm” >range >>> on a survey. >>>>> >>>>> For timing, you have to dig a bit and answer a few questions. Is >your >>> concern how close you >>>>> are to BIH? If so you will need to know all the delays in your >system. >>> This includes the delays >>>>> in the antenna filters and the preamp. Is your concern (or >measure) the >>> ADEV at 1 second? >>>>> If so the delays are not a concern. Your antenna choice may be a >bit >>> different depending on >>>>> this focus. >>>>> >>>>> Bob >>>>> >>>>> >>>>> >>>>>> On Nov 21, 2019, at 1:25 AM, Taka Kamiya via time-nuts < >>> [email protected]> wrote: >>>>>> >>>>>> I have been looking antennas. Prices seem to range less than 30 >>> dollars to more than 500 dollars. Some are 20db gain and some are >40 db >>> gain. Some are specified as marine use only. Some are specified as >timing >>> use. Some doesn't say anything at all. Power supplies are >different. >>>>>> Other than obvious, antenna is an antenna, isn't it? It captures >L1 >>> signal, amplify it and send it down the coax. What makes one more >costly >>> than others? What makes one timing antenna and one navigation >antenna? It >>> doesn't make sense to me. >>>>>> >>>>>> I did some simple experiment with 26db, 40db, and magnetic stick >on >>> type. I didn't really see significant difference. Signal level >itself >>> even wasn't all that different. I have nearly a clear sky view 360 >degrees >>> above 30 degrees above horizon. In some directions, clear view to >>> horizon. My feed is Timewave type. So It may not be the best but >nearly >>> ideal. >>>>>> >>>>>> Can someone shed light on this topic? (of course, I know some >antenna >>> has integrated receiver. I am not talking about those) >>>>>> >>>>>> --------------------------------------- >>>>>> (Mr.) Taka Kamiya >>>>>> KB4EMF / ex JF2DKG >>>>>> _______________________________________________ >>>>>> time-nuts mailing list -- [email protected] >>>>>> To unsubscribe, go to >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>> and follow the instructions there. >>>>> >>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list -- [email protected] >>>>> To unsubscribe, go to >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>> and follow the instructions there. >>>>> >>>> >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>> and follow the instructions there. >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >>> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to >http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
