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.
