Hi
> On Apr 17, 2022, at 12:58 PM, N1BUG <p...@n1bug.com> wrote: > > 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 TBolt needs about 16 db in front of it to do a reasonable job. With a 30 db gain antenna and no splitters, that leaves you with about 14 db or so for cable and connector loss. Most of us accumulate multiple GPS gizmos. A 4 way splitter takes your 14 down to 8 db. That puts you “at the limit” with a bit over 100’ of LMR-400. > > 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. The filter is after the amplifier. However the antenna itself is pretty narrowband. If the filter was in front, getting a 2 db noise figure would be exciting. Bob > > 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 >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send >>> an email to time-nuts-le...@lists.febo.com >>> To unsubscribe, go to and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an >> email to time-nuts-le...@lists.febo.com >> To unsubscribe, go to and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
