[time-nuts] Re: GPS antenna locations
On 4/17/22 13:08, Bob kb8tq wrote: 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. I currently have three GPS gizmos and expect to hold at that number. I use a GPS Networking LNFA1X4-N filtered amplified splitter spec'd at 0 dB gain/loss. With the side mount option, the worst case cable loss would be around 10 dB, but probably a few dB less. It depends on which available cable I use. 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. Well then, possibly a concern but I suspect a GPS antenna doesn't pick up RF below 500 MHz very efficiently. I guess the only way to know for certain is to try it. Paul ___ 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] Re: GPS antenna locations
Hi > On Apr 17, 2022, at 12:58 PM, N1BUG 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 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...@li
[time-nuts] Re: GPS antenna locations
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 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] Re: GPS antenna locations
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 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.
