Thanks Bob.
I have no idea what makes that gap to the south. There is nothing to
block that direction above 15 degrees.
I am not concerned about cable losses. I have LMR-400 on this roof
mounted antenna because it is only a 50 foot run, but the smallest cable
I have to either tower is 1/2". The antenna spec sheet says 30 dB gain.
The data sheet on this antenna shows it being down >60 dB at +/- 50 MHz.
With a noise figure spec of 2.2 dB I suspect that filter is before the
amplifier, but I wish it actually said that. Add several tens of dB for
separation of antennas and I think it would be OK.
My only concern is with overload of the onboard amplifier in the
antenna. It is filtered again by a GPS Networking splitter (-60 dB at
+/- 60 MHz) before going to the Thunderbolt.
Side mounted at 80 feet on the VHF tower (60 feet higher than where the
one on the roof is), it would have a much better sky view, neglecting
any blockage to the north from the tower itself and at high elevation
angles from yagis on top of the tower).
I am leaning toward getting another of these antennas and side mounting
it on the tower, then doing a comparison of the signal strength vs az/el
plot against this roof mounted one. It is an extra expense I will have
to find a way to budget for, but certainly has educational value if
nothing else.
Paul
On 4/17/22 09:04, Bob kb8tq wrote:
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 <p...@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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