Re: [digitalradio] Some thoughts on antenna polarization for emergency use
I recall reading years ago horz TV may have been picked over vert because some test showed there to be less multipath and therefore less reflections and ghosts on the picture. I have no idea whether that is true. I remember seeing vert TV antennas in some other countries. AL7BX/ George
Re: [digitalradio] Some thoughts on antenna polarization for emergency use
Ted, I agree that in a single array configuration it does not have the gain realizable by a directive antenna, no omni-directional antenna will. But in those cases where a rotatable antenna is not feasible nor permitted (as on some public structures housing EOCs) This illustrates the core of the problem of not having enough total path gain to communicate with the EOC if the repeaters are down. Either the portable station in the disaster area, or the EOC 100 miles away, will have to have at least a 10-element beam in order for the portable station to be heard at all. I have a 13 element beam with 14 dBi of gain and several times, I have worked WO4DX on 2m mobile on SSB phone to his stacked loops and 100 watts. He periodically travels on business from the coastal town where I live (near Charleston, SC), to his home QTH in Dawsonville, GA, and I can consistently work him for 100 miles, going NW up I-26, until he turns and starts heading to Augusta, GA on I-20 and then I start losing him. I also periodically work rover NK4Q, also with 100 watts and stacked loops on his truck, up to 120 miles away, along I-20 as he heads east to the Outer Banks for the VHF contest, but to copy these stations, I must use my 13-element beam. If I switch to my skeleton-slot antenna, which I use for the local PSK63 net (6 dB down from the beam), I cannot copy either of them. If NK4Q switches from stacked square loops to the skeleton-slot antenna I made for him, picking up 6 dB more gain, I can again copy him until he gets over 120 miles away. When he arrives at the Outer Banks, I again cannot copy him unless I switch to the 13-element beam, and copy is still marginal on phone. However, if we switch to PSK63, print is over 50%. If NK4Q then switches to a 10-element beam, picking up another 3 dB, print improves to 100%. This is a distance of 300 miles, with both stations at sea level. So, if the EOC is not able to either have extra height, or to use a higher-gain antenna, or if I cannot set up a beam outside the hurricane shelter, I will simply be unable to reach the state EOC in Columbia from a hurricane shelter in Charleston, 100 miles away, if the repeaters are down locally, and we will have no commumications except hopefully on 80m or 40m using NVIS antennas, which takes more real estate to set up, and is more susceptible to QRN. I do realize it is going to take time for a substantial number of stations to discover 2m VHF SSB phone and digital for both emcomm and casual operating, but in the end, 2m VHF SSB digital, with sufficient antenna gain, is the most practical and reliable emcomm alternative to using repeaters, which may not be operational when we need them. If anybody reading this is within 200 miles of Charleston, SC, and would like to try 2m PSK63, you are invited to beam toward Charleston and check in to our informal ragchew net on 144.144 MHz, USB, around1500 Hz tone frequency, at 8 PM on Wednesday nights and 9 PM on Sunday nights. 73, Skip KH6TY
Re: [digitalradio] Some thoughts on antenna polarization for emergency use
Lots of interesting things. I completely accept that VHF SSB (which can also mean digital) communication is really the only practical longer distance VHF mode that works without infrastructure. But will we have a turn around in the number of operators who actually use these modes? There is no question that an increasing number of hams have the equipment now. But very few are using them for 6 and 2 meter SSB. Fewer hams are operating weak signal SSB, which has caused a significant drop in interest considering that there are several times as many hams today than when this was much more popular. A local weak signal ham (50 miles north) said to me recently that years ago (decade or more) there used to be many midwest U.S. stations on 2 meter SSB, both fixed and mobile. But that is no longer true. And there does not seem to be any improvement as of late. Maybe other areas are seeing some increase? But the unaswered question is, how much different would the path gain be between horizontal and vertical polarization? And that might depend on the distance since it seems that the farther out you go, perhaps the horizontal polarization gives a slight edge. But really how much of an edge? Isn't it really the gain of the antenna over the polarization of the antenna? Just because weak signal operators use horizontal does not mean that emergency and local SSB operators need to do this. We have many stations (most stations) that have gain on vertical and nothing available on horizontal and never will have anything on horizontal. Even hams who buy a multimode/multiband rig and now might want to try SSB or digital are rarely buying a new beam just for 2 meter SSB. Partly because of cost, partly because they can not due to local restrictions, and partly because they often have upgraded and also want to put energy into HF. The other factor that seems to be in play, is that there does not seem to be much correlation between hams who do weak signal and also do public service, compared with the ham who is primarily involved in public service and might add an new dimension to their operation if asked to provide this needed service providing that they could use their existing antenna or at least not have to have two separate antennas. Consider the number of FM hams who have beams on vertical polarization including fairly high gain antennas such as the double 13 element Cushcrafts. Using vertical polarization, they can often use FM to access repeaters from one side of our state to the other but unlike SSB they can drop below the threshold at times as there can be QSB on these kinds of signals. SSB would give them at least 6 dB or more margin and digital should give quite a bit more. Your comment about PSK63 only working 50% of the time when you have marginal phone communication makes me wonder if the digital modes are able to work as deeply into the noise as claimed. Shouldn't there be solid copy in PSK modes, even PSK250 or at least PSK125 at a few dB below zero dB S/N? Phone communication, even SSB would need a bit over zero dB wouldn't it? 73, Rick, KV9U kh6ty wrote: This illustrates the core of the problem of not having enough total path gain to communicate with the EOC if the repeaters are down. Either the portable station in the disaster area, or the EOC 100 miles away, will have to have at least a 10-element beam in order for the portable station to be heard at all. I have a 13 element beam with 14 dBi of gain and several times, I have worked WO4DX on 2m mobile on SSB phone to his stacked loops and 100 watts. He periodically travels on business from the coastal town where I live (near Charleston, SC), to his home QTH in Dawsonville, GA, and I can consistently work him for 100 miles, going NW up I-26, until he turns and starts heading to Augusta, GA on I-20 and then I start losing him. I also periodically work rover NK4Q, also with 100 watts and stacked loops on his truck, up to 120 miles away, along I-20 as he heads east to the Outer Banks for the VHF contest, but to copy these stations, I must use my 13-element beam. If I switch to my skeleton-slot antenna, which I use for the local PSK63 net (6 dB down from the beam), I cannot copy either of them. If NK4Q switches from stacked square loops to the skeleton-slot antenna I made for him, picking up 6 dB more gain, I can again copy him until he gets over 120 miles away. When he arrives at the Outer Banks, I again cannot copy him unless I switch to the 13-element beam, and copy is still marginal on phone. However, if we switch to PSK63, print is over 50%. If NK4Q then switches to a 10-element beam, picking up another 3 dB, print improves to 100%. This is a distance of 300 miles, with both stations at sea level. So, if the EOC is not able to either have extra height, or to use a higher-gain antenna, or if I cannot set up a beam outside the hurricane shelter, I will simply
Re: [digitalradio] Some thoughts on antenna polarization for emergency use
Rick, I completely accept that VHF SSB (which can also mean digital) communication is really the only practical longer distance VHF mode that works without infrastructure. But will we have a turn around in the number of operators who actually use these modes? There is no question that an increasing number of hams have the equipment now. But very few are using them for 6 and 2 meter SSB. Fewer hams are operating weak signal SSB, which has caused a significant drop in interest considering that there are several times as many hams today than when this was much more popular. There are probably thousands of IC-706MKIIG's, IC-746's, FT-857's,FT-890's, or Kenwood TS-2000's in circulation that all have 2m SSB capability. Of course, it is sure that there are many more HT's and FM-only transceivers than those SSB transceivers. It is my understanding that weak signal operating is on the increase, mostly due to the introduction of WSJT, which is good, since the same digital interface can be used for 2m digital SSB. A local weak signal ham (50 miles north) said to me recently that years ago (decade or more) there used to be many midwest U.S. stations on 2 meter SSB, both fixed and mobile. But that is no longer true. And there does not seem to be any improvement as of late. Maybe other areas are seeing some increase? Don't know... Of course NBEMS on HF with NVIS antennas is still a viable alternative, but setting up point-to-point communications with EOC's on 2m is more reliable, and a 2m antenna, even a 10 foot long beam, is more portable than a long HF antenna for 80m or 40m. The advantage of medium range 2m (i.e. up to 100 miles) is that propagation is quite constant, whereas on 80m and 40m, it varies according to the time of day, and QRN can be distrupting to the ARQ transfer, slowing it down. There is little QRN (i.e. from static crashes) on 2m. But the unaswered question is, how much different would the path gain be between horizontal and vertical polarization? And that might depend on the distance since it seems that the farther out you go, perhaps the horizontal polarization gives a slight edge. But really how much of an edge? I guess only RCA knows, since they made the tests in the early days of TV. I wonder the same thing, and hope to find time to test, but just rotating an existing vertically polarized beam 90 degrees does the trick at no cost. Isn't it really the gain of the antenna over the polarization of the antenna? Just because weak signal operators use horizontal does not mean that emergency and local SSB operators need to do this. A local ham on our 2m net here designed and constructed a cycloid to see if random polarization was significant, and it turned out not to be. His work can be seen at KR1ST.com. Emergency and local SSB operators do not need to go horizontal, but if they do, then the existing weak signal operators can assist emcomm by being forwarding stations, and will have superior antenna gain to do that over longer distances. The antenna change from vertical to horizontal is much easier, and less expensive, than the change from FM-only to SSB. Perhaps a bigger problem is that many vertically-polarized beams are fixed in the direction of a desired repeater and do not have rotators. Once a rotator is added, it is easy to just rotate the beam 90 degrees at the same time. The catch-22 is that many of those 5-element beams are rear-mounted (to keep the metal mast out of the antenna field), and that puts an undesirable strain on a rotator, since it presents an unbalanced load, but it will probably not be a problem for a medium-duty rotator. Anyway, a non-metallic mast extension (like fiberglass) can be used to solve that problem and allow the beam to be center-mounted. We have many stations (most stations) that have gain on vertical and nothing available on horizontal and never will have anything on horizontal. Even hams who buy a multimode/multiband rig and now might want to try SSB or digital are rarely buying a new beam just for 2 meter SSB. Partly because of cost, partly because they can not due to local restrictions, and partly because they often have upgraded and also want to put energy into HF. They can just rotate the beam 90 degrees if they have a beam, but most probably do not, so they can just build the inexpensive design that will appear soon in QST, or use the latest three dipole Big Wheel in the March QST issue. The decision will depend upon how successful the ham is trying to use NBEMS or other messaging systems on HF with NVIS antennas compared to 2m. All my 2m antennas are in my attic (including my 13-element beam), due to restrictions barring outside antennas. The signals pass through the wood and shingles on 2m just fine, but there is some absorption on 70 cm. A 10-element 2m beam is around $100 and is the minimum amount of gain that should be considered. If one already has a multimode 2m
Re: [digitalradio] Some thoughts on antenna polarization for emergency use
Please correct FT-890 to read FT-897. Thanks, Skip KH6TY
Re: [digitalradio] Some thoughts on antenna polarization for emergency use
Moving on to mode/throughput, let me put on my Incident Commander cap... As an incident commander, I would rather have a printed/written message than one delivered verbally. If I know that you have a digital print system, I would want that and especially if you tell me its error free. The thing important to me is getting every word correct...no errors and sending/ receiving a message in a timely manner. Thus a PSK63/125/250 message that is error free is what you want to make me happy. If you use FlARQ with FlDigi or with DBdigi and at PSK125 or 250 then I shouldn't ask for anything more. how you accomplish the message exchange really becomes unimportant. When it comes to setting up a comm. unit, I ask the operators to tell me where they want to set up if the area I have recommended doesn't meet their needs. The IC should give you room for you HF antennas as well as assistance in setting them up. Putting on my communicator cap, I can set up a 40M Inverted V with counterpoise and fed with 50 ohm coax with the apex at 20 ft and cover most stations from 25-600 miles in the day and raising the antenna to 30 ft for 80/75M I can cover the same area at night. Two individuals can set up then 40M Inverted V in 15-20 minutes. Of course if you can set up a 10-12 element 2M beam at 30 feet in 30 minutes and have connectivity at the other end, then go for either one. What ever you do, just make sure that you contact on the other end of the string is on the same frequency/mode etc. :-) Good comments all around. 73, Walt/K5YFW
Re: [digitalradio] Some thoughts on antenna polarization for emergency use
Hi Ted, That's a good thought, but the problem is that achieving more than a 16 to 25 mile range without a repeater requires more gain (on at least one end - usually the home station end) than you can get from a lindenblad antenna, a big wheel, a ground plane, or even a 5/8 wavelength vertical. The portable end will also generally be at a lower elevation than the home stations. According to Cebik (http://www.cebik.com/ao/ao16a.html), the Lindenblad antenna has about 6 dBi of gain, and the big wheel about 7 dBi. Those antennas will work at the portable end, but on the home station end, more antenna gain (approximately 10 dBi or greater) is needed to ensure spanning a wide disaster area up to 100 miles without a repeater. For exceeding the distant obtainable by repeaters, which are usually positioned as high as possible, and usually higher than the typical home station antenna, even 3 dB of extra gain can make the difference between 100% copy and no copy. The Lindenblad is most useful for satellite work, where it can accomodate circular polarization and a high angle of reception. For operators already using repeaters with FM-only transceivers, the move to SSB is the major change (i.e., a new transceiver!), and the antenna change to horizontal polarization is relatively minor. In many cases, where 5-element vertically polarized beams are being used to hit repeaters, it only involves fliping the beam 90 degrees. In fact, any such beam can also just be rotated 45 degrees and handle both vertical and horizontal polarizations, but with a 3 dB loss in gain for each polarization. There is a whole new world of fun available on 2m SSB and digital that those who only work VHF via repeaters are missing. Instead of collecting countries, VHF SSB stations collect grid squares, counties, and states, so there is quite a reward to be had for joining the horizontally-polarized VHF world on 2m as well as being ready to assist with emcomm. 2m SSB is not all weak signal operating. Using my 13 element 2m beam, I have consistently worked horizontally-polarized mobiles over distances just exceeding 100 miles, when the elevations of both myself and the mobile do not exceed 30 feet ASL. 73, Skip KH6TY - Original Message - From: Theodore A. Antanaitis To: digitalradio@yahoogroups.com Sent: Friday, February 29, 2008 4:16 PM Subject: Re: [digitalradio] Some thoughts on antenna polarization for emergency use How about the best of both worlds (or at least an approximation thereof). I would suggest for two meter home station applications that a lindenblad antenna is a versatile compromise omni-directional antenna that works equally well with both vertical and horizontal polarizations. The complexity of construction is not that much greater than for a big-wheel or three dipole array. One source for more info: http://www.amsat.org/amsat/articles/w6shp/lindy.html 73 Ted WA7ZZB -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.21.2/1304 - Release Date: 2/29/2008 8:18 AM
