[time-nuts] Rooftop antenna and splitter

[Bob kb8tq]

Hi

For a variety of reasons, a puck antenna is a bad choice for a lab timing receiver. 
Because the ground plane (and other issues like feed line) are a variable, getting a 
good pattern is a matter of luck. Multipath ( = low angle) rejection is rarely going to 
work well with them. They also are not really good at standing up to years and years
of exposure outdoors. 

Since “real” antennas are a sub $20 sort of thing at L1 and sub $70 at L1/L2 … why 
bother with the minor leagues? Get something that does the job properly and use 
that. 

No matter what you do, (survey or timing) multipath is what gets you. Rejecting it 
is what you design the antenna for. Stuff that is properly polarized, you keep. Stuff
that is not properly polarized you strongly reject. Very low angle stuff (especially below
zero degrees) you strongly reject. Your typical ground plane acts as a knife edge at low 
angles to “help” below zero degree stuff …. not good. 

Indeed some light weight antennas take off into spurious oscillation land under this or 
that condition. When they do nothing works well. The answer there is to get another 
antenna. We’re talking the price of a case of beer ….

Bob

> On Apr 30, 2019, at 6:52 PM, Taka Kamiya <tkamiya9 at yahoo.com> wrote:
> 
> Yes, I saw your particular mention of survey antennas.  My concern was that multi-path will affect any setup.  
> 
> I've seen pros and cons of placing a cookie sheets and pizza pans under antennas to enhance "efficiency".  I'm not exactly buying into this idea but I thought your discussions were similar.
> 
> I have two identical antennas and one is already installed in a manner I described.  I suppose I could purchase a pole and mount it all by itself in middle of my yard.  Comparison will be very interesting.
> 
> Thanks for your reply.
> 
> --------------------------------------- 
> (Mr.) Taka Kamiya
> I'm stuck in a wormhole....  Hello, worms!
> 
> 
> On Tuesday, April 30, 2019, 6:28:11 PM EDT, Bob kb8tq <kb8tq at n1k.org> wrote:
> 
> 
> Hi
> 
> The pictures shown earlier are of a “survey antenna”. In the post I was careful to refer to a “survey antenna”
> as the point of the post. Ideally you want to be meters away from any metal.
> 
> Bob
> 
> > On Apr 30, 2019, at 5:42 PM, Taka Kamiya via time-nuts <time-nuts at lists.febo.com <mailto:time-nuts at lists.febo.com>> wrote:
> > 
> > I can see that on survey situation but will it affect timing installations?
> > Will you give me an idea how far those bullet type antenna needs to be?  My antenna sits on a very short pole (2 feet?) and its base is mounted to frame of my screened in porch.  Roof and structure is aluminum, which is very much like ground plane and reflective.
> > 
> > --------------------------------------- 
> > (Mr.) Taka Kamiya
> > I'm stuck in a wormhole....  Hello, worms! 
> > 
> >  On Tuesday, April 30, 2019, 5:01:05 PM EDT, Bob kb8tq <kb8tq at n1k.org <mailto:kb8tq at n1k.org>> wrote:  
> > 
> > Hi
> > 
> > You very much do *not* want to put a ground plane on one of the modern survey
> > antennas.(Chinese or US or Canadian or …)  The better ones are very explicit 
> > about this. They are optimized to sit on a pole in free air. Anything else and the 
> > pattern is degraded. ( = multipath gets worse)
> > 
> > Bob
> > 
> >> On Apr 30, 2019, at 2:23 PM, David J Taylor via time-nuts <time-nuts at lists.febo.com <mailto:time-nuts at lists.febo.com>> wrote:
> >> 
> >> Hi David,
> >> 
> >> No, no ground plane. Don’t really have a lot of room for that in the window. Out of curiosity, how large of an impact have you found with a ground plane?
> >> 
> >> Btw, I love the pan!
> >> 
> >> Denny
> >> ============================
> >> 
> >> Yes, Denny, choosing the baking tray (IIRC) was fun - I wanted as large a flat area as I could reasonably get, but it has to be magnetic.  I don't recall what I took into the shop to test with!
> >> 
> >> Unfortunately I didn't make any specific measurements with and without the ground plane, but I did see a noticeable increase in SNR.  Even a small e.g. tobacco tin may help.
> >> 
> >> Cheers,
> >> David
> >> -- 
> >> SatSignal Software - Quality software for you
> >> Web: http://www.satsignal.eu <http://www.satsignal.eu/>
> >> Email: david-taylor at blueyonder.co.uk <mailto:david-taylor at blueyonder.co.uk>
> >> Twitter: @gm8arv 
> >> 
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> > 
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