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Here's a sample that compares the RCA7511 to our clip-on VHF module which is tuned to 195 MHz, the center of the high-VHF band. See notes following. http://forum.tvfool.com/attachment.p...1&d=1495723497 Notes: 1) A hardware failure in my circuit that synchronizes the SA sweep to the rotor's start of rotation forced me to manually trigger the SA sweep using a manually activated micro-switch in conjunction with activating the rotor. Consequently, the data may be easily skewed by as much as a second or two (7.5-15 degrees). Kindly overlook this shortcoming, it's particularly noticeable in the 7511's pattern. 2) The data was normalized so that the maximum point in the paired data set was set to "0" and the rest of the data was adjusted by the same amount for the purposes of this comparison. Using Excel, there are, of course, a good number of possible data display methods possible, this happens to be the one I chose as I attempt to enhance my feeble Excel and VBA skills. ;) 3) The VHF module, if balun and insertion loss adjustments were included (they aren't at this point) would be about as close to a reference dipole as a no-budget measurement effort could produce. I may explore this later and then compare it to the BicoLOG just to see how close they are to each other. In the meantime, I'd assume a 1 dB insertion loss @195 MHz and that will get you better than in the ballpark (probably into the infield) for an estimate. 4) Using the above described F/B definition, the F/B of the dipole is measured a almost zero, the 7511 is measured at about 15 dB. 5) Using the above described gain definition and including the estimated insertion losses, I'd estimate that the forward gain of this antenna, as tested, is ~ 5 dBd (7.15 dBi) at 195 MHz. |
I spoke to an engineer for Arizona PBS, KAET, several years ago
while at the summit of Mingus Mtn. I mentioned that his translator, K42AC, was harder to receive than the others on Mingus. He told me that the signal was directed away from Prescott and Prescott Valley and that they were using circular polarization. He then told me to tilt the 4 Bay antennas from an "X" to a "+" which he said would help. It did help but not much..... It continues to be hard to receive through much of the area. |
K42AC shares a Jampro JA/LS-8 with K38AI and K40DD up on Mingus Mtn and the antenna is H-POL only, none of them are licensed for any vertical component in their signal. Their antenna is, however, highly directional to the east-northeast with a good amount of electrical down tilt (3°). K42AC, however, maxes out at only 5 KW ERP along its maximum strength signal path compared to 12-15 KW for the other two stations on the antenna. The worst case, if one were situated in one of the weakest nulls, would be that only 920 watts might be sent in that direction. By contrast, K38AI peaks out at 15 kW with a minimum of 2.65 KW in its deepest null.
I suspect the much lower ERP and the directional antenna are the root cause for the difficulty in receiving K42AC as compared with its neighbors, depending o the relative direction and distance of the receiving location relative to Mingus Mtn. The weaker UHF signal of K42AC will be much less capable of diffracting to lower elevations where terrain is an issue or even for simple longer distance locations, even with LOS. My interpretation, based on the antenna patterns and the City of License for each facility, is that KAET intends K42AC to cover the Cottonwood side of Mingus Mtn and for K43LW, located on Mt Francis, to cover the Prescott side. |
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http://www.tvfool.com/?option=com_wr...q=call%3dK42ac The use of circular polarization may not play a role with your spotty reception of K42AC. |
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hampered by the hills and terrain of Prescott. Additionally, there is another RF43 on Bill Willaims Mtn about 40 miles away. Many areas have LOS to Mingus and Williams but not Mt. Francis. That is why it is imperative to capture K42AC. There is another PBS translator in Flagstaff on RF14 but it cannot be received because there is also a translator for KUTP, RF 14 on Mt Francis, here in Prescott. It is what you could call " A MESS." |
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database is correct or if the engineer was mistaken. |
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The ability to pick up a signal while your antenna was mounted vertically indicates significant depolarization due to refraction off the mountains. In mountainous locations antenna height can make a huge difference. You can try moving your antenna up or down to see if reception improves. Scientifically, you can calculate the angle to to the mountain, determine the slope in front of the antenna, and use ray tracing techniques to get a good starting point. I don't know where you live in Prescott, but you may find that an antenna several feet off the ground with nothing in front of the antenna might be better than the roof. |
I'm going to go with the engineer either mis-poke or there was a miscommunication. There's nothing in the FCC file that indicates the digital facility was ever anything but what it still is.
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[QUOTE=
In mountainous locations antenna height can make a huge difference. You can try moving your antenna up or down to see if reception improves. Scientifically, you can calculate the angle to to the mountain, determine the slope in front of the antenna, and use ray tracing techniques to get a good starting point. I don't know where you live in Prescott, but you may find that an antenna several feet off the ground with nothing in front of the antenna might be better than the roof.[/QUOTE] Agreed. In some locations I've lost RF13 but received RF22 which transmit from the same basic location. Moving the antenna a few feet, I was able to capture RF13, though weakly. |
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low band VHF will be used. There will be even more co-channel interference. Invariably, some channels will simply disappear. Trying to find as compact as possible antenna capable of RF 2-36 or Rf 2-51 is impossible..... |
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Personally, I'd expect the rural translator operators to do like all the majors and avoid low-VHF for the most part unless there's nothing less to pick from. IIRC, the filing window for the LP and translators being displaced is later this year so we'll have to see how it shakes out. |
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ADTech
I bought two EU385CF for evaluation. I opened the black enclosure, and something didn't look right. I opened the second enclosure and it did look right. I was able to figure it out, but if someone only purchased sample #1 with the upside down label, it might confuse them. Sample #1 was sealed at the rear with epoxy; sample #2 with solder and epoxy, so I didn't mess with it. Since you do QC, I thought you should know. I also called customer service to let them know, but didn't ask for an RMA because I wanted to look inside anyway to add to the AVS UVSJ thread. http://www.avsforum.com/forum/25-hdt...ombiner-8.html my post for the Antennas Direct EU385CF-1S UHF/VHF Diplexer (UVSJ): http://www.avsforum.com/forum/25-hdt...l#post53267506 |
Thanks for bringing that to my attention. Must have been a Monday morning at the factory!
I couldn't find any relevant tickets in our system. Any chance you received a ticket number? |
Sending ticket number in a PM on other forum.
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I found a convenient location in the bedroom for the antenna and made some measurements. In this location, CH 13 is picked up by the tuner, but there is picture freeze and many uncorrected errors, not too good: http://forum.tvfool.com/attachment.p...1&d=1496712910 The signal level meter shows adequate signal strength, but a bad channel scan: http://forum.tvfool.com/attachment.p...1&d=1496713140 |
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I suspected that multipath reflections were causing a problem and decided to add a reflector element to the VHF folded dipole. A cardboard box is used as a temporary support.
http://forum.tvfool.com/attachment.p...1&d=1496713473 The reflector is 13" behind the VHF dipole and consists of a 24" length of 1" aluminum tubing with a 12" length of 7/8" tubing in each end and clamps. The length has been adjusted to 27.7". I also tried a strip of aluminum foil on a yardstick with the same results: http://forum.tvfool.com/attachment.p...1&d=1496713915 The reflector improves the reception: http://forum.tvfool.com/attachment.p...1&d=1496714072 and the scan looks a lot better: http://forum.tvfool.com/attachment.p...1&d=1496714197 |
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Since the convenient location for the antenna had some problems, I tried other locations in the room. The best location for the signal was in the middle of the room in a high traffic area (of course it was).
http://forum.tvfool.com/attachment.p...1&d=1496715021 No reflector was needed in this location and the reception was excellent: http://forum.tvfool.com/attachment.p...1&d=1496715151 and the channel scan looks good, with increased signal strength: http://forum.tvfool.com/attachment.p...1&d=1496715270 |
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The Sadelco DislayMax 800 signal level meter makes 43 measurements across the channel and diplays the average of all readings. If one of the 43 measurements is below -20 dBmV, the meter says "Ur" for under range and doesn't give a reading. The scan covers about 5.3 MHz of the 6 MHz channel.
http://forum.tvfool.com/attachment.p...1&d=1496716036 If the meter is switched to the single frequency mode, it will measure down to -35 dBmV at the center of the channel, but the correction for a digital signal is not added; +6.8 dB IIRC. http://forum.tvfool.com/attachment.p...6761421http:// The screen on the meter actually shows a dark gray image on a dark green background and doesn't have much contrast. The image looks pretty good on a computer screen, but makes a muddy image on a print. analog channel: http://forum.tvfool.com/attachment.p...1&d=1496762257 digital channel: http://forum.tvfool.com/attachment.p...1&d=1496762257 To make an image that has more contrast and room for notes, I set my digital camera for a B&W image, and then edit in Photo Gallery to increase the contrast. http://forum.tvfool.com/attachment.p...1&d=1496769065 Photo Gallery will only allow me to increase the contrast one time, AFAIK, so I use Lunapic to increase the contrast 4x more: http://forum.tvfool.com/attachment.p...9&d=1496715329 |
Rca ant751
You may not have your outdoor antenna testing equipment available anymore, rabbit73, but your indoor results here are AMAZING!
As I'm beginning to understand much better now, indoor antenna set ups are even more complex and perhaps mysterious than their outdoor counterparts. LOS is a bit more straight forward out of doors, or so it seems. But like you previously mentioned, not everybody can put up an outdoor antenna. If you keep up grading that GE Indoor antenna of yours, you might want to seek a patent, make a ton of money and really retire in a manner you're unaccustomed too--LOL! But necessity is the mother of invention. I'm copying your attachments for possible future inventive use. Ha! Ha! Thanks for remembering my request here, rabbit73! I appreciate your dedication to this forum. It has been extremely enlightening. BTW, I've been watching your other posts. I'm learning something new every day! |
Thank you for your encouraging comments. I also learned a lot about indoor reception from this experiment.
Trip in VA, who runs the rabbitears.info web site and now works for the FCC, had an even more difficult time with reception of local signals. When he was living in Chattanooga he had to put his antenna inside a trash can to reject multipath reflections. http://forum.tvfool.com/attachment.p...3&d=1470521359 Background information on this technique: http://www.avsforum.com/forum/25-hdt...l#post21358820 http://forum.tvfool.com/showpost.php...27&postcount=7 |
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