[time-nuts] Difference in antennas

Fri Nov 22 18:02:21 UTC 2019

Interesting.  No, there was no data with it.

On Fri, Nov 22, 2019 at 12:00 PM Björn <bg at lysator.liu.se> wrote:

> The N for North is because the phase center offsets are not symmetrical.
> With a convention to orient the antennas the same way the offset could be
> corrected.
>
> /Björn
>
> Sent from my iPhone
>
> > On 22 Nov 2019, at 17:07, Bill Dailey <docdailey at gmail.com> 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 <k8yumdoober at gmail.com>
> 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 <
> >>> time-nuts at lists.febo.com> 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 <
> >>> kb8tq at n1k.org> 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 <jra at febo.com>
> 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 <
> >>> time-nuts at lists.febo.com> 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
> >>>>>> _______________________________________________
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> >>>>>> and follow the instructions there.
> >>>>>
> >>>>>
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> >>>>>
> >>>>
> >>>>
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-- 
Doc

Bill Dailey
KXØO