|
Yagi Antenna Design
I had a WISP unit upgraded for better reception and they used a Yagi
antenna, at least I guess it's a Yagi. Here's a photo. http://www.netwifiworks.com/images/a.../Yagi/yagi.png This doesn't seem to fit the mold in a couple of ways. The elements are not spaced at all regularly. The spacing seems to vary around a bit. But more importantly, I've read that the director elements are *insulated* from the support beam while these are all welded. Obviously it works. I'm getting about 6 dB stronger signal than before although it's a bit hard to compare as the location changed and I measured about a 3 dB gain with the old unit in that location. But more importantly, with the signal rising by 6 dB, the reported background noise also rose 6 dB. Isn't SNR what is important that the antenna should have improved? This Yagi claims something like 20 or 25 degree beam while the old antenna had a 60 degree beam. -- Rick C |
Yagi Antenna Design
On 27/01/17 13:22, rickman wrote:
This Yagi claims something like 20 or 25 degree beam while the old antenna had a 60 degree beam. ======= That power is directed within a lower beam angle , hence more power in the set direction of the antenna .......a favourable change. Frank , GM0CSZ |
Yagi Antenna Design
On Fri, 27 Jan 2017 08:22:43 -0500, rickman wrote:
I had a WISP unit upgraded for better reception and they used a Yagi antenna, at least I guess it's a Yagi. Here's a photo. http://www.netwifiworks.com/images/a.../Yagi/yagi.png Ok. That's an Ubiquiti AirMax AMY-9M16 900MHz antenna. 16dBi gain and dual simultaneous polarization (i.e. not switched): https://www.ubnt.com/airmax/airmax-yagi-antenna/ https://dl.ubnt.com/datasheets/airmaxyagi/airMAX_900MHz_YAGI_Antenna.pdf You need the dual polarization to get double the normal speed by using 2x2 MIMO streams, one per polarization. This doesn't seem to fit the mold in a couple of ways. The elements are not spaced at all regularly. The spacing seems to vary around a bit. I agree. It does look weird. However, having extra aluminum near the antenna in the form of the other polarization, and getting sufficient isolation between the two polarizations, is going to do strange things to the design. Send me dimensions and I'll analyze it (time permitting), like I did with the 2.4GHz MFJ1800 yagi: http://802.11junk.com/jeffl/antennas/mfj1800/index.html But more importantly, I've read that the director elements are *insulated* from the support beam while these are all welded. That's done so that the mounting boom does not become part of the element length. Were it not insulated, half the circumference of the boom would need to be added to the element lengths. Insulating the elements also provides slightly fewer sidelobes and possibly (not sure) better isolation between polarization. Looking at the patterns on the data sheet, it looks much better than I would normally expect from a single polarization yagi. Obviously it works. Assumption, the mother of all screwups. However, the data sheet does seem to show that they actually made some measurements. I'm getting about 6 dB stronger signal than before although it's a bit hard to compare as the location changed and I measured about a 3 dB gain with the old unit in that location. But more importantly, with the signal rising by 6 dB, the reported background noise also rose 6 dB. Isn't SNR what is important that the antenna should have improved? Yep. You want to maximize the SNR. Increasing both equally is about what I would expect if your antenna were also pointed at other sources of interference. The 900MHz smartmeters are a likely culprit. Plenty of other possibilities. Can you move your new yagi around a little to see if you can minimize the background noise? This Yagi claims something like 20 or 25 degree beam while the old antenna had a 60 degree beam. A narrow beamwidth is good for reducing interference coming from off axis interference sources. However, if the source of interference is along the antenna axis, or in your case, within less than +/-10 degrees off axis, you can easily make things worse. Got a 900MHz spectrum analyzer handy? Any of the USB RTL-SDR (RTL2832U) dongles should do the trick, although a 900MHz RF amp will probably be needed. Use it to see what you're dealing with. http://www.rtl-sdr.com/?s=spectrum+analyzer -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Yagi Antenna Design
I had a WISP unit upgraded for better reception and they used a Yagi
antenna, at least I guess it's a Yagi. Here's a photo. http://www.netwifiworks.com/images/a.../Yagi/yagi.png This doesn't seem to fit the mold in a couple of ways. The elements are not spaced at all regularly. The spacing seems to vary around a bit. Yagi-Uda antennas can be designed with all sorts of variations in element spacing. There are complex interactions between the element locations and lengths, leading to numerous tradeoffs between maximum forward gain, bandwidth, front/back ratio, and cleanliness of pattern (i.e. size and direction of side-lobes). But more importantly, I've read that the director elements are *insulated* from the support beam while these are all welded. It's possible to build a Yagi with the director, driven, and reflector elements either insulated from the boom, or connected to it electrically... and not all elements have to be of the same style. In general, if you connect an element to the boom, you do it right at the element's center (so that the ground connection is balanced). Connecting the element to the boom has the effect of "fattening" the element where it passes through the boom, and makes it look "longer" electrically than it is physically... so, in order to keep its resonant frequency unchanged, you must shorten it somewhat. Welding the elements to the beam makes good sense for physical longevity... there are no insulators to age and crack in the sun and weather, and no possibility of intermittent current leaks or arcing (which can cause noise or intermodulation problems in higher-power use). But more importantly, with the signal rising by 6 dB, the reported background noise also rose 6 dB. That could indicate a couple of things. It could mean that the predominent noise sources affecting you, are in the same direction as the WISP transmitter... and so they're being boosted by the same amount as the desired signal. It could also indicate that your old antenna or feed-line was electrically "lossy", and that you were losing some signal (and received noise) to resistive losses. |
Yagi Antenna Design
On 1/27/2017 11:52 AM, Jeff Liebermann wrote:
On Fri, 27 Jan 2017 08:22:43 -0500, rickman wrote: I had a WISP unit upgraded for better reception and they used a Yagi antenna, at least I guess it's a Yagi. Here's a photo. http://www.netwifiworks.com/images/a.../Yagi/yagi.png Ok. That's an Ubiquiti AirMax AMY-9M16 900MHz antenna. 16dBi gain and dual simultaneous polarization (i.e. not switched): https://www.ubnt.com/airmax/airmax-yagi-antenna/ https://dl.ubnt.com/datasheets/airmaxyagi/airMAX_900MHz_YAGI_Antenna.pdf You need the dual polarization to get double the normal speed by using 2x2 MIMO streams, one per polarization. I got a whole new setup. The old unit was one piece with what must have been a panel antenna as the case was flat and broad. You can see what a monster this one is. The beam is nearly three feet... no, I just checked the data sheet and it around 4 feet long! It's not hugely heavy, but to move it around I have to unbolt the mounting bracket and it's a PITA while on a ladder. This doesn't seem to fit the mold in a couple of ways. The elements are not spaced at all regularly. The spacing seems to vary around a bit. I agree. It does look weird. However, having extra aluminum near the antenna in the form of the other polarization, and getting sufficient isolation between the two polarizations, is going to do strange things to the design. Send me dimensions and I'll analyze it (time permitting), like I did with the 2.4GHz MFJ1800 yagi: http://802.11junk.com/jeffl/antennas/mfj1800/index.html If we get a warm day when I feel like messing with it I will. I spent over an hour yesterday trying to optimize the orientation. I had mounted a bracket under the deck thinking they would just move my existing unit (NanoStation M900 Loco). I spent some time positioning the unit and found a sweet spot that was two or three dB higher than the surrounding area, next to a pole. Ok for this unit, but in the way for the Yagi so it couldn't be aimed optimally. So I spent the time to unbolt the bracket (everything was in the way of everything else so it nearly all had to be dismounted) and move it to the other side of the post. It can be pointed perfectly, but now it may be out of the sweet spot so the numbers didn't change. When the weather is better, I'll try moving it back to the sweet spot in a way it can be aimed better. The old unit was easy to hold with your hand and test. The Yagi is not so light and unwieldy, especially on a ladder. I also want to move it to a less conspicuous spot. That will be hard. I store kayaks under the deck mounted from pulleys. But more importantly, I've read that the director elements are *insulated* from the support beam while these are all welded. That's done so that the mounting boom does not become part of the element length. Were it not insulated, half the circumference of the boom would need to be added to the element lengths. Insulating the elements also provides slightly fewer sidelobes and possibly (not sure) better isolation between polarization. Looking at the patterns on the data sheet, it looks much better than I would normally expect from a single polarization yagi. Not sure if you understand me. This Yagi is *not* insulated. But remember, it has 17 passive elements! It's not like they were just fooling around. lol Obviously it works. Assumption, the mother of all screwups. However, the data sheet does seem to show that they actually made some measurements. I mean I'm getting some 6-7 dB better signal. Regardless of the SNR, the receiver provides quality indexes that show a lower bit error rate and higher overall throughput. That's why they put this up. It hasn't improved my throughput so much, but it lowers the retransmits and improves the utilization of their network. I'm getting about 6 dB stronger signal than before although it's a bit hard to compare as the location changed and I measured about a 3 dB gain with the old unit in that location. But more importantly, with the signal rising by 6 dB, the reported background noise also rose 6 dB. Isn't SNR what is important that the antenna should have improved? Yep. You want to maximize the SNR. Increasing both equally is about what I would expect if your antenna were also pointed at other sources of interference. The 900MHz smartmeters are a likely culprit. Plenty of other possibilities. Can you move your new yagi around a little to see if you can minimize the background noise? I'm not certain whether SNR or signal strength is most important. That would depend on the noise factor of the receiver, no? I know in lower frequencies the environmental noise is high enough the receiver noise nearly doesn't matter. At higher frequencies I thought the limitation was in the receiver front end. So until the noise gets to be high enough that it approaches the receiver noise, it won't matter. This Yagi claims something like 20 or 25 degree beam while the old antenna had a 60 degree beam. A narrow beamwidth is good for reducing interference coming from off axis interference sources. However, if the source of interference is along the antenna axis, or in your case, within less than +/-10 degrees off axis, you can easily make things worse. Got a 900MHz spectrum analyzer handy? Any of the USB RTL-SDR (RTL2832U) dongles should do the trick, although a 900MHz RF amp will probably be needed. Use it to see what you're dealing with. http://www.rtl-sdr.com/?s=spectrum+analyzer What would a spectrum analyzer show me that would be useful. No, I don't have one, but I could get one... :) -- Rick C |
Yagi Antenna Design
On 1/27/2017 3:59 PM, rickman wrote:
On 1/27/2017 11:52 AM, Jeff Liebermann wrote: On Fri, 27 Jan 2017 08:22:43 -0500, rickman wrote: I had a WISP unit upgraded for better reception and they used a Yagi antenna, at least I guess it's a Yagi. Here's a photo. http://www.netwifiworks.com/images/a.../Yagi/yagi.png Ok. That's an Ubiquiti AirMax AMY-9M16 900MHz antenna. 16dBi gain and dual simultaneous polarization (i.e. not switched): https://www.ubnt.com/airmax/airmax-yagi-antenna/ https://dl.ubnt.com/datasheets/airmaxyagi/airMAX_900MHz_YAGI_Antenna.pdf You need the dual polarization to get double the normal speed by using 2x2 MIMO streams, one per polarization. I got a whole new setup. The old unit was one piece with what must have been a panel antenna as the case was flat and broad. You can see what a monster this one is. The beam is nearly three feet... no, I just checked the data sheet and it around 4 feet long! It's not hugely heavy, but to move it around I have to unbolt the mounting bracket and it's a PITA while on a ladder. This doesn't seem to fit the mold in a couple of ways. The elements are not spaced at all regularly. The spacing seems to vary around a bit. I agree. It does look weird. However, having extra aluminum near the antenna in the form of the other polarization, and getting sufficient isolation between the two polarizations, is going to do strange things to the design. Send me dimensions and I'll analyze it (time permitting), like I did with the 2.4GHz MFJ1800 yagi: http://802.11junk.com/jeffl/antennas/mfj1800/index.html If we get a warm day when I feel like messing with it I will. I spent over an hour yesterday trying to optimize the orientation. I had mounted a bracket under the deck thinking they would just move my existing unit (NanoStation M900 Loco). I spent some time positioning the unit and found a sweet spot that was two or three dB higher than the surrounding area, next to a pole. Ok for this unit, but in the way for the Yagi so it couldn't be aimed optimally. So I spent the time to unbolt the bracket (everything was in the way of everything else so it nearly all had to be dismounted) and move it to the other side of the post. It can be pointed perfectly, but now it may be out of the sweet spot so the numbers didn't change. When the weather is better, I'll try moving it back to the sweet spot in a way it can be aimed better. The old unit was easy to hold with your hand and test. The Yagi is not so light and unwieldy, especially on a ladder. I also want to move it to a less conspicuous spot. That will be hard. I store kayaks under the deck mounted from pulleys. But more importantly, I've read that the director elements are *insulated* from the support beam while these are all welded. That's done so that the mounting boom does not become part of the element length. Were it not insulated, half the circumference of the boom would need to be added to the element lengths. Insulating the elements also provides slightly fewer sidelobes and possibly (not sure) better isolation between polarization. Looking at the patterns on the data sheet, it looks much better than I would normally expect from a single polarization yagi. Not sure if you understand me. This Yagi is *not* insulated. But remember, it has 17 passive elements! It's not like they were just fooling around. lol Obviously it works. Assumption, the mother of all screwups. However, the data sheet does seem to show that they actually made some measurements. I mean I'm getting some 6-7 dB better signal. Regardless of the SNR, the receiver provides quality indexes that show a lower bit error rate and higher overall throughput. That's why they put this up. It hasn't improved my throughput so much, but it lowers the retransmits and improves the utilization of their network. I'm getting about 6 dB stronger signal than before although it's a bit hard to compare as the location changed and I measured about a 3 dB gain with the old unit in that location. But more importantly, with the signal rising by 6 dB, the reported background noise also rose 6 dB. Isn't SNR what is important that the antenna should have improved? Yep. You want to maximize the SNR. Increasing both equally is about what I would expect if your antenna were also pointed at other sources of interference. The 900MHz smartmeters are a likely culprit. Plenty of other possibilities. Can you move your new yagi around a little to see if you can minimize the background noise? I'm not certain whether SNR or signal strength is most important. That would depend on the noise factor of the receiver, no? I know in lower frequencies the environmental noise is high enough the receiver noise nearly doesn't matter. At higher frequencies I thought the limitation was in the receiver front end. So until the noise gets to be high enough that it approaches the receiver noise, it won't matter. This Yagi claims something like 20 or 25 degree beam while the old antenna had a 60 degree beam. A narrow beamwidth is good for reducing interference coming from off axis interference sources. However, if the source of interference is along the antenna axis, or in your case, within less than +/-10 degrees off axis, you can easily make things worse. Got a 900MHz spectrum analyzer handy? Any of the USB RTL-SDR (RTL2832U) dongles should do the trick, although a 900MHz RF amp will probably be needed. Use it to see what you're dealing with. http://www.rtl-sdr.com/?s=spectrum+analyzer What would a spectrum analyzer show me that would be useful. No, I don't have one, but I could get one... :) A specific question about the USB RTL-SDR. Would it and the software allow me to get much detail in the LF band, specifically around 60 kHz? That's an area I would like to do some work in. -- Rick C |
Yagi Antenna Design
On Fri, 27 Jan 2017 16:13:30 -0500, rickman wrote:
A specific question about the USB RTL-SDR. Would it and the software allow me to get much detail in the LF band, specifically around 60 kHz? That's an area I would like to do some work in. Y're guilty of topic drift. Give yourself a slap across the knuckles with a wooden ruler. The RTL2832 and R820T2 tuner covers 24 - 1766 Mhz. You can buy upconverters but they typically bottom out at 100Khz. http://www.ebay.com/itm/182423524669 http://www.ebay.com/sch/i.html?_nkw=rtl-dsp+upconverter This is NOT the way to do WWVB. The best way is to use a PC and a sound card. I learned the hard and somewhat expensive way that an internal sound card is a great way to analyze the spectrum of all the crap being generated inside the computah. Therefore, I suggest an external USB sound card, that runs at 192Kbits/sec or 384Kbits/sec. http://www.ebay.com/sch/i.html?_nkw=192khz+sound+card+usb I don't actually have one of these, but was able to play with one for a few days with tolerable results. There are examples of sound card VLF receivers on YouTube: https://www.youtube.com/watch?v=L2W1x6Rb9hI https://www.youtube.com/watch?v=EwxdZ0fY8fM https://www.youtube.com/watch?v=UrJ77GiBNQw https://www.youtube.com/watch?v=L2W1x6Rb9hI https://www.youtube.com/watch?v=fKSOoZ2vhvo SDR-sharp is the most common software used. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Yagi Antenna Design
In article , rickman wrote:
A specific question about the USB RTL-SDR. Would it and the software allow me to get much detail in the LF band, specifically around 60 kHz? That's an area I would like to do some work in. Not directly. The tuner chips in these devices are designed to operate at VHF and UHF. The standard approach, when using these devices on HF, is to use an upconverter to shift the signal up to somewhere around 120 MHz. You could do the same with an LF signal, I imagine. Nooelec sells the "Ham It Up" upconverter for this purpose; I don't know if its input frequency response extends down to 60 kHz or not. Some of the display-and-control software (e.g. GQRX on Linux) lets you plug in a converter LO frequency number; it will then adjust the frequency numbers on the display accordingly. |
Yagi Antenna Design
On Fri, 27 Jan 2017 14:45:25 -0800, Jeff Liebermann
wrote: On Fri, 27 Jan 2017 16:13:30 -0500, rickman wrote: A specific question about the USB RTL-SDR. Would it and the software allow me to get much detail in the LF band, specifically around 60 kHz? That's an area I would like to do some work in. Y're guilty of topic drift. Give yourself a slap across the knuckles with a wooden ruler. +1 I am not aware of too many 60kHz yagi antennas ;) |
Yagi Antenna Design
On 1/27/2017 7:06 PM, Pat wrote:
On Fri, 27 Jan 2017 14:45:25 -0800, Jeff Liebermann wrote: On Fri, 27 Jan 2017 16:13:30 -0500, rickman wrote: A specific question about the USB RTL-SDR. Would it and the software allow me to get much detail in the LF band, specifically around 60 kHz? That's an area I would like to do some work in. Y're guilty of topic drift. Give yourself a slap across the knuckles with a wooden ruler. +1 I am not aware of too many 60kHz yagi antennas ;) You don't notice them sort of like not noticing the galactic super cluster we are in. -- Rick C |
Yagi Antenna Design
On Fri, 27 Jan 2017 19:32:33 -0500, rickman wrote:
You don't notice them sort of like not noticing the galactic super cluster we are in. Kinda like distracted driving. You don't notice things until you run into them. Anyway, 900 MHz yagi antennas are kinda pedestrian. Getting something to work at VLF frequencies is a real challenge. Incidentally, did you know that the original plan was for WWVB to transmit on 20KHz instead of 60KHz? 2.2% radiation efficiency at 20KHz: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4487279/#__sec8title Almost what Tesla was trying to build. Too bad WWVB doesn't have a voice announcement: http://www.lownoiserecords.com/wwv_the_tick.html (Click on the big yellow square) We return you now to sanity. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Yagi Antenna Design
In article ,
Jeff Liebermann wrote: Anyway, 900 MHz yagi antennas are kinda pedestrian. Getting something to work at VLF frequencies is a real challenge. Not all that hard, really. All you have to do is lay out a redundent pair of oil pipelines along the proper courses, and you can make a VLF rhombic large enough to be seen from geostationary orbit :-) |
Yagi Antenna Design
On Fri, 27 Jan 2017 15:59:18 -0500, rickman wrote:
On 1/27/2017 11:52 AM, Jeff Liebermann wrote: https://www.ubnt.com/airmax/airmax-yagi-antenna/ https://dl.ubnt.com/datasheets/airmaxyagi/airMAX_900MHz_YAGI_Antenna.pdf I got a whole new setup. The old unit was one piece with what must have been a panel antenna as the case was flat and broad. You can see what a monster this one is. The beam is nearly three feet... no, I just checked the data sheet and it around 4 feet long! It's not hugely heavy, but to move it around I have to unbolt the mounting bracket and it's a PITA while on a ladder. 900 MHz panel (patch) antennas have about 8dBi gain but are fairly small. The larger variety with 4 patches might squeeze out 12dBi gain, but will be huge. Remember, with antennas, the bigger and uglier they are, the better they work. But more importantly, I've read that the director elements are *insulated* from the support beam while these are all welded. Not sure if you understand me. This Yagi is *not* insulated. But remember, it has 17 passive elements! It's not like they were just fooling around. lol Sorry. I misread your statement. 4ft long is not a big antenna. If it requires a crane, I would call it a big antenna. I mean I'm getting some 6-7 dB better signal. Regardless of the SNR, the receiver provides quality indexes that show a lower bit error rate and higher overall throughput. That's why they put this up. It hasn't improved my throughput so much, but it lowers the retransmits and improves the utilization of their network. Retransmissions can be a sign of too much noise (low signal), interference, or collisions with packets from other users. If the system is heavily subscribed, and your noise level looks about the same as before, I would suspect collisions. Got any other users nearby? I'm not certain whether SNR or signal strength is most important. SNR is most important. Having a strong signal isn't very useful if the noise level is as strong as the signal (ignoring spread spectrum processing gain). That would depend on the noise factor of the receiver, no? Noise figure is part of it. A noisy front end will do as much to bury a signal with noise, as will interference from other stations. However, todays receiver front ends are quite good and are not the horrid noise generators I recall from the vacuum tube days. I would say that interference is far more important than receiver noise figure. I know in lower frequencies the environmental noise is high enough the receiver noise nearly doesn't matter. True. However the problem is a bit different at HF frequencies. The noise level can be so high, that if the receiver had too much front end gain, it would overload on the noise alone, producing zero dynamic range. That's why many HF radios have a 20dB attenuator switch on the front panel. At higher frequencies I thought the limitation was in the receiver front end. As I mumbled a few paragraphs up, it's a system problem. The demodulator doesn't care if the noise if thermal, shot noise, or interference. I can make any of these be predominant by committing some kind of design screwup, but if the radio is reasonably well designed, it's interference and collisions with other users packets, that limits the throughput. So until the noise gets to be high enough that it approaches the receiver noise, it won't matter. If your receiver shows an increase in base line noise level when the antenna is connected but there's no receive signal, the noise is higher than the receiver noise. What would a spectrum analyzer show me that would be useful. No, I don't have one, but I could get one... :) You'll be amazed at what you can "see" on the 902-928 band. Most of this crap will be visible: http://www.ccrane.com/AM-Antennas?by=Category However, I think you'll see quite a bit of junk from the utility Smartmeters. Around here, we had to move the 900MHz ham radio repeater input frequencies to the bottom of the band, where PG&E has gratiously left a few MHz unpolluted by their wireless metering system. BTW, I think your Nanostation M900 has a built in spectrum analyzer. Not sure about your unspecified model replacement. I think that would be the easiest test for intereference. Gotta run. I'm late as usual... -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Yagi Antenna Design
On 1/27/2017 9:51 PM, Jeff Liebermann wrote:
On Fri, 27 Jan 2017 15:59:18 -0500, rickman wrote: On 1/27/2017 11:52 AM, Jeff Liebermann wrote: https://www.ubnt.com/airmax/airmax-yagi-antenna/ https://dl.ubnt.com/datasheets/airmaxyagi/airMAX_900MHz_YAGI_Antenna.pdf I got a whole new setup. The old unit was one piece with what must have been a panel antenna as the case was flat and broad. You can see what a monster this one is. The beam is nearly three feet... no, I just checked the data sheet and it around 4 feet long! It's not hugely heavy, but to move it around I have to unbolt the mounting bracket and it's a PITA while on a ladder. 900 MHz panel (patch) antennas have about 8dBi gain but are fairly small. The larger variety with 4 patches might squeeze out 12dBi gain, but will be huge. Remember, with antennas, the bigger and uglier they are, the better they work. But more importantly, I've read that the director elements are *insulated* from the support beam while these are all welded. Not sure if you understand me. This Yagi is *not* insulated. But remember, it has 17 passive elements! It's not like they were just fooling around. lol Sorry. I misread your statement. 4ft long is not a big antenna. If it requires a crane, I would call it a big antenna. I mean I'm getting some 6-7 dB better signal. Regardless of the SNR, the receiver provides quality indexes that show a lower bit error rate and higher overall throughput. That's why they put this up. It hasn't improved my throughput so much, but it lowers the retransmits and improves the utilization of their network. Retransmissions can be a sign of too much noise (low signal), interference, or collisions with packets from other users. If the system is heavily subscribed, and your noise level looks about the same as before, I would suspect collisions. Got any other users nearby? I'm not certain whether SNR or signal strength is most important. SNR is most important. Having a strong signal isn't very useful if the noise level is as strong as the signal (ignoring spread spectrum processing gain). That would depend on the noise factor of the receiver, no? Noise figure is part of it. A noisy front end will do as much to bury a signal with noise, as will interference from other stations. However, todays receiver front ends are quite good and are not the horrid noise generators I recall from the vacuum tube days. I would say that interference is far more important than receiver noise figure. I know in lower frequencies the environmental noise is high enough the receiver noise nearly doesn't matter. True. However the problem is a bit different at HF frequencies. The noise level can be so high, that if the receiver had too much front end gain, it would overload on the noise alone, producing zero dynamic range. That's why many HF radios have a 20dB attenuator switch on the front panel. At higher frequencies I thought the limitation was in the receiver front end. As I mumbled a few paragraphs up, it's a system problem. The demodulator doesn't care if the noise if thermal, shot noise, or interference. I can make any of these be predominant by committing some kind of design screwup, but if the radio is reasonably well designed, it's interference and collisions with other users packets, that limits the throughput. So until the noise gets to be high enough that it approaches the receiver noise, it won't matter. If your receiver shows an increase in base line noise level when the antenna is connected but there's no receive signal, the noise is higher than the receiver noise. I'm not going to mess with this setup. The antenna connects to the receiver with some rubber booted connectors I'm not familiar with and I'm leaving them alone. So this will have to remain a thought experiment. But your point above that if the noise from the environment were below the receiver noise, I wouldn't see it change... however, I was comparing two units which may well be calibrated differently or something... too many variables. What would a spectrum analyzer show me that would be useful. No, I don't have one, but I could get one... :) You'll be amazed at what you can "see" on the 902-928 band. Most of this crap will be visible: http://www.ccrane.com/AM-Antennas?by=Category However, I think you'll see quite a bit of junk from the utility Smartmeters. Around here, we had to move the 900MHz ham radio repeater input frequencies to the bottom of the band, where PG&E has gratiously left a few MHz unpolluted by their wireless metering system. This is what I'd like to see around 60 kHz. If I ever get the thing built it should have a *lot* of DSP filtering to give it a very narrow bandwidth. But the question remains if that will be good enough. Joerg seems to feel that a 1 bit ADC can still be overloaded by out of band noise. I think the signal will still show up and can be dug from the dirt. BTW, I think your Nanostation M900 has a built in spectrum analyzer. Not sure about your unspecified model replacement. I think that would be the easiest test for intereference. I listed the new receiver model somewhere, Rocket M900. Actually they are sold together I believe. The data sheet covers them both anyway. -- Rick C |
Yagi Antenna Design
On Fri, 27 Jan 2017, Jeff Liebermann wrote:
On Fri, 27 Jan 2017 19:32:33 -0500, rickman wrote: You don't notice them sort of like not noticing the galactic super cluster we are in. Kinda like distracted driving. You don't notice things until you run into them. Anyway, 900 MHz yagi antennas are kinda pedestrian. Getting something to work at VLF frequencies is a real challenge. Incidentally, did you know that the original plan was for WWVB to transmit on 20KHz instead of 60KHz? 2.2% radiation efficiency at 20KHz: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4487279/#__sec8title Almost what Tesla was trying to build. For a long time, there was WWVL at 20KHz. References to that may have been more common in the sixties than to WWVB, which seemed to get attention in the seventies especially since it sent out time code. References to WWVL seem to be mostly erased at this point. Michael |
Yagi Antenna Design
On Fri, 27 Jan 2017, Dave Platt wrote:
In article , Jeff Liebermann wrote: Anyway, 900 MHz yagi antennas are kinda pedestrian. Getting something to work at VLF frequencies is a real challenge. Not all that hard, really. All you have to do is lay out a redundent pair of oil pipelines along the proper courses, and you can make a VLF rhombic large enough to be seen from geostationary orbit :-) I think it wsa in the surplus column in CQ in the sixties, someone wrote about a long wave station up for sale, and added that they had to keep replacing the buried ground wires, because treasure hunters would stumble on it and take some. A little hard to contain that sort of thing when it's so big. Then there was VK3ATN who did moonbounce from Australia in the sixties, with rhombics. He could make slight adjustments because he'd had some rigging to adjust something, so he got a bit more time, but it was limited to a few days a month. But with the 100W limit of Australia (it was something like that) he did fine with the rhombics. Of course, he lived in the outback, so he had endless space, just needed telephone poles and wire. He had rhombics for a few bands. Michael |
Yagi Antenna Design
On 1/28/2017 10:19 AM, Michael Black wrote:
On Fri, 27 Jan 2017, Dave Platt wrote: In article , Jeff Liebermann wrote: Anyway, 900 MHz yagi antennas are kinda pedestrian. Getting something to work at VLF frequencies is a real challenge. Not all that hard, really. All you have to do is lay out a redundent pair of oil pipelines along the proper courses, and you can make a VLF rhombic large enough to be seen from geostationary orbit :-) I think it wsa in the surplus column in CQ in the sixties, someone wrote about a long wave station up for sale, and added that they had to keep replacing the buried ground wires, because treasure hunters would stumble on it and take some. A little hard to contain that sort of thing when it's so big. Then there was VK3ATN who did moonbounce from Australia in the sixties, with rhombics. He could make slight adjustments because he'd had some rigging to adjust something, so he got a bit more time, but it was limited to a few days a month. But with the 100W limit of Australia (it was something like that) he did fine with the rhombics. Of course, he lived in the outback, so he had endless space, just needed telephone poles and wire. He had rhombics for a few bands. A friend bought a house some 10 years ago and I looked it up on Google. The pictures showed a humongous Yagi over the house which must have been for 20 meters or maybe 40. The 4 element antenna was much larger than the house! There were (and still are) three guy points which are huge I beams in concrete around the house. In the basement there was what had been his radio shack with sound proofing and EMI screen. I was impressed, but everything other than the guy points is gone now. -- Rick C |
| All times are GMT +1. The time now is 05:50 AM. |
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
RadioBanter.com