[time-nuts] Re: GPS antenna locations

[Bob kb8tq]

Hi

Not knowing everything about the local environment there’s 
not much way to guess exactly what this or that location 
will do. The biggest thing I see on your plot is something 
due south of the current antenna location. 

In a “typical” setup, anything within 20 degrees of the horizon
gets tossed out for timing. The paths are long and with normal
clutter multi path is likely at low angles. 

The filters in the typical “telecom” antennas are set up to block
cell phone transmitters. The GPS and cell antennas are co-located
on the same tower so they can get hit pretty hard. That said, the
cell site isn’t running an ERP in the many hundreds of watts range. 

The longer your cable, the more likely you are to need a booster
amp. The telecom antennas typically don’t have a lot of gain. Yes,
fancy cable can help with this. RG-58 is a bad idea :) ….

If you have a better sky view at 60 to 80’ on the tower, then a side
mount in that range would be my vote. Lightning would be my 
biggest concern as you go higher. Assuming all the heights are 
to the same reference, moving the antenna up 40 to 60’ should 
do the trick. 

Bob

> On Apr 16, 2022, at 2:05 PM, N1BUG <paul at n1bug.com> wrote:
> 
> Hello time nuts,
> 
> I finally have my long awaited Trimble Thunderbolt up and running. I am not thrilled with the coverage using a Symmetricom 58532A antenna on the roof about 20 feet above ground level. Here is what I get after ~24 hours:
> 
> http://n1bug.com/gpssig.png
> 
> Sometimes I have 8 satellites with usable signal, sometimes as few as 5. The problem to the west is trees. I believe the chaotic signal strength in the east is due to reflections from a metal roof.
> 
> I have three options:
> 
> 1. Leave the antenna where it is.
> 
> 2. Side mount it at 80 to 90 feet on a radio tower that has yagis for 50/432/222/144 MHz at 105/110/115/120 feet. These antennas are used for high power transmitting. Potential interference to GPS reception? I don't know if the filter in the 58532A is before or after the amplifier. Blockage from the tower and/or yagis? I assume mounting a few feet off the south tower face would be best.
> 
> 3. Mount at the top of a mast on another radio tower, at 110 feet. This would have a completely unobstructed sky view but would have antennas for 7/10 MHz about 3 feet below and 14/18/21/24/28 MHz about 13 feet below. Those antennas are used for high power transmitting. There will at some point be a 10 GHz dish about 8 feet below the top of that mast.
> 
> Any comments on these options? Is it good enough where it is? I am only using it as a 10 MHz reference now, but I may care about the 1 PPS later.
> 
> Paul N1BUG
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