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#1
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Looking for groundwave propagation experience on 20m
Hi all
I am gradually working up to a project to TX telemetry from the car at very low QRSS type data rates. Because of the unattended nature of the system I am going to start using the HiFER freq of 13.56Mhz rather than a "real" amateur allocation. This of course means very low output power and no doubt a number of other limitations for the TX. I really only need the system to work predominately 10 miles from the base. Yes I am aware of the frequency stability issues for very narrow band signals. No doubt the vehicle bouncing around wont help either! May end up using a Picollo type system where the freq difference between two states is used to send data. I am after some feedback and ideas about antenna systems to use. I suspect the car TX antenna will only be a wire draped across the rear window or a loaded broadcast antenna. The RX base antenna was going to be just a dipole but I reasoned that this would be great for DX but terrible for groundwave. Then thought about a vertical dipole, but am concerned about the higher noise level. I'll probably end up trying both. Initial tests are only going to be looking for a CW signal on a waterfall. Would also consider experimenting at a MedFER freq around 1700KHz but base antenna efficiency might be pretty bad. There is also a lot more RFI there. Ideas welcome. If however you want to say it "wont work" please back it up with some maths/calcs or your own direct experiences. Cheers Bob VK2YQA |
#2
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Looking for groundwave propagation experience on 20m
here in the states we call 13.56MHz an ISM frequency. Meaning Industrial,
Scientific, and Medical. near any populated area you are liable to run into diathermy machines, plasma ovens, rfid tag readers, and a host of other noise generators there. i would suspect your environment may be similar. for ground wave the vertical would probably be best, especially for omnidirectional covereage... though a low dipole would likely work almost as well. frequency stability with modern equipment shouldn't be a problem, just be sure to build everything nice an solid so it doesn't 'bounce around' and it shouldn't be a problem... not like bouncing around tubes with mechanical elements that would vibrate and move in the distant past. "Bob Bob" wrote in message news Hi all I am gradually working up to a project to TX telemetry from the car at very low QRSS type data rates. Because of the unattended nature of the system I am going to start using the HiFER freq of 13.56Mhz rather than a "real" amateur allocation. This of course means very low output power and no doubt a number of other limitations for the TX. I really only need the system to work predominately 10 miles from the base. Yes I am aware of the frequency stability issues for very narrow band signals. No doubt the vehicle bouncing around wont help either! May end up using a Picollo type system where the freq difference between two states is used to send data. I am after some feedback and ideas about antenna systems to use. I suspect the car TX antenna will only be a wire draped across the rear window or a loaded broadcast antenna. The RX base antenna was going to be just a dipole but I reasoned that this would be great for DX but terrible for groundwave. Then thought about a vertical dipole, but am concerned about the higher noise level. I'll probably end up trying both. Initial tests are only going to be looking for a CW signal on a waterfall. Would also consider experimenting at a MedFER freq around 1700KHz but base antenna efficiency might be pretty bad. There is also a lot more RFI there. Ideas welcome. If however you want to say it "wont work" please back it up with some maths/calcs or your own direct experiences. Cheers Bob VK2YQA |
#3
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Looking for groundwave propagation experience on 20m
On Sep 29, 8:48 pm, "Dave" wrote:
here in the states we call 13.56MHz an ISM frequency. Meaning Industrial, Scientific, and Medical. near any populated area you are liable to run into diathermy machines, plasma ovens, rfid tag readers, and a host of other noise generators there. i would suspect your environment may be similar. for ground wave the vertical would probably be best, especially for omnidirectional covereage... though a low dipole would likely work almost as well. frequency stability with modern equipment shouldn't be a problem, just be sure to build everything nice an solid so it doesn't 'bounce around' and it shouldn't be a problem... not like bouncing around tubes with mechanical elements that would vibrate and move in the distant past. "Bob Bob" wrote in message news Hi all I am gradually working up to a project to TX telemetry from the car at very low QRSS type data rates. Because of the unattended nature of the system I am going to start using the HiFER freq of 13.56Mhz rather than a "real" amateur allocation. This of course means very low output power and no doubt a number of other limitations for the TX. I really only need the system to work predominately 10 miles from the base. Yes I am aware of the frequency stability issues for very narrow band signals. No doubt the vehicle bouncing around wont help either! May end up using a Picollo type system where the freq difference between two states is used to send data. I am after some feedback and ideas about antenna systems to use. I suspect the car TX antenna will only be a wire draped across the rear window or a loaded broadcast antenna. The RX base antenna was going to be just a dipole but I reasoned that this would be great for DX but terrible for groundwave. Then thought about a vertical dipole, but am concerned about the higher noise level. I'll probably end up trying both. Initial tests are only going to be looking for a CW signal on a waterfall. Would also consider experimenting at a MedFER freq around 1700KHz but base antenna efficiency might be pretty bad. There is also a lot more RFI there. Ideas welcome. If however you want to say it "wont work" please back it up with some maths/calcs or your own direct experiences. Cheers Bob VK2YQA- Hide quoted text - - Show quoted text - 10 miles ground wave at 14 meg is going to be iffy.... denny / k8do |
#4
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Looking for groundwave propagation experience on 20m
Bob Bob wrote:
Hi all snip Ideas welcome. If however you want to say it "wont work" please back it up with some maths/calcs or your own direct experiences. Cheers Bob VK2YQA I am able to work 40 to 45 miles from my mobile, using a 20m Hamstick in the center of the sedan roof, to a friend who is using a ground mounted vertical made from half a driven element from an old tribander. We are both running 100W SSB, and the received signal levels are just enough above the noise level to communicate. The terrain is relatively level, and the path is from the western Minneapolis suburbs to a town southwest of Minneapolis. tom K0TAR |
#5
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Looking for groundwave propagation experience on 20m
Hi Denny
Pls elaborate. Are you talking about a SSB voice situation or bandwidths that will yield maybe 20-30dB better conditions? Also what power level are you talking about? Pls be specific. Denny wrote: 10 miles ground wave at 14 meg is going to be iffy.... denny / k8do |
#6
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Looking for groundwave propagation experience on 20m
Many thanks Tom
I can probably extrapolate from those numbers. I haven't looked at the ISM/HiFER rules/regs but the QRSS type mode itself is going to be maybe 20-30dB "better" than SSB. I guess I'd be on par with your numbers at 100-200mW o/p Cheers Bob Tom Ring wrote: I am able to work 40 to 45 miles from my mobile, using a 20m Hamstick in the center of the sedan roof, to a friend who is using a ground mounted vertical made from half a driven element from an old tribander. We are both running 100W SSB, and the received signal levels are just enough above the noise level to communicate. The terrain is relatively level, and the path is from the western Minneapolis suburbs to a town southwest of Minneapolis. tom K0TAR |
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