Tropospheric propogation?
Lately I've been trying to pull in WFFF (Fox affiliate), which has a NM=-5.8 dB on my Tvfool report (borderline "extreme measures required"). I'm well aware of the difficulties of pulling in a 2+ edge signal 70.5 miles away. Well, this past Saturday in preparation for the Super Bowl, I vertically stacked two SolidSignal HDB8x's, walked the roof to find a "hot-spot", and finally had success!, sort of... I was able to receive WFFF all night Saturday, into the afternoon on Sunday, and then by 2pm, the signal was gone. Bummer, no Superbowl from the comfort of my own living room...
Anyway, I have two questions about this situation: 1) Given that reception lasted for 20+ hours could this have been a "tropospheric" reception phenomenon? I haven't re-established reception since it went out, but it's because the wind blew the antenna out of position on Sunday night and then it snowed later, so I haven't been able to climb up on the roof to re-aim it and secure things better. I am sure that it was not a change in aim that caused LOS on Sunday afternoon. 2) The combined capture area of my two stacked HDB8x's 1728 sq-in. This is exactly the same area as a single DB8e. Do you guys think a single DB8e will perform as well (or maybe even better) than my stacked HDB8X setup? Thanks in advance, as always. |
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The signal path for WFFF is very similar to the WCAX signal path, but WFFF is running much less power and its antenna is a little lower on a separate tower.
http://forum.tvfool.com/attachment.p...1&d=1486689565 http://forum.tvfool.com/attachment.p...1&d=1486689565 You are on the extreme fringe of coverage for WFFF http://forum.tvfool.com/attachment.p...1&d=1486692691 A closeup of WFFF coverage; purple is very weak, no color is dead zone http://forum.tvfool.com/attachment.p...1&d=1486692691 Quote:
http://www.dxinfocentre.com/tropo.html Other local changes in atmospheric conditions can also affect reception of WFFF. Quote:
When you have a vertical stack of two 8-bays, the vertical beamwidth is even more narrow than one 8-bay. This means the azimuth aim AND the elevation aim are very critical. It might be necessary to tilt the top of the antenna back to aim slightly above horizontal for peak signal. One of my antenna test locations has a clear path across water, but I found it necessary to tilt my 4-bay for max signal. http://forum.tvfool.com/attachment.p...3&d=1477409166 |
Thanks very much Rabbit for the dxinfo URL.
How about 2xHDB8x vs. 1xDB8e? Thinking in terms of the capture area. I ordered a DB8e on sale, with VHF dipole (maybe it'll pick up WVNY) for $160, free shipping. |
Two 8-bay antennas will have a larger capture area, but that doesn't guarantee signal increase, as I mentioned in post #9. The larger capture area theory assumes that the wave front is uniform across the whole antenna; that is rarely true especially with weak 2Edge signals that have been scattered by terrain interference.
The DB8e has been optimized for the latest 14-51 band. I have no idea about the actual gain of the HDB8X based on range tests. http://forum.tvfool.com/attachment.p...5&d=1466633825 http://forum.tvfool.com/attachment.p...6&d=1446858514 In this case, a smaller capture gives a stronger signal: http://forum.tvfool.com/attachment.p...1&d=1475692853 |
In my latest experiment, I combined a Stellar Labs 30-2476 VHF yagi with a DB8e 8-bay using a UVSJ combiner (Stellar labs 33-2230 UVSJ). Real channel 25 (WNNE) is strong enough that it is separately received by both antennas, even though I point them 90-degrees off from the Real-25 tower to pick up Burlington stations. I confirmed this by separately removing UHF and VHF feeds to the UVSJ, and I receive Real-25 in both cases. Strangely, when both feeds to the UVSJ are populated, the UVSJ does not allow Real-25 to pass through to the output.
Any thoughts on what might be going on here? Is this some form of destructive interference where some very low amplitude CH-25 signal passes through the VHF-pass filter and destructively interferes with the CH-25 coming through the UHF-pass section? Is this an example of UVSJ's "not always doing what they're supposed to" and why I've seen several people on this forum recommend using separate coax runs and an A/B switch for UHF and VHF instead of using a UVSJ combiner? |
The UVSJ you used is an unknown quantity. I've not made nor have I ever seen a detailed analysis of its performance.
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Which UVSJ one would you recommend ADTech?
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the field so many, many times.... In theory, a good UVSJ should work under all conditions but in practice, that is not so. That is why I always recommend keeping separate coax runs and using an A/B switch..... |
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I don't recall, but are you using a preamp with this arrangement. Have you tried amplifying only the UHF signals? IIRC, your combiner has a switch that allows pass-through on the UHF-only port and, if implemented, that would overcome insertion loss of the combiner's UHF port. |
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http://forum.tvfool.com/attachment.p...1&d=1497985402 As ADTech said, their UVSJ is the only one currently available with known performance. http://forum.tvfool.com/attachment.p...1&d=1497986210 http://forum.tvfool.com/attachment.p...1&d=1497990764 There are a few Radio Shack 15-2586 UVSJs still left; the last one I measured did well. http://forum.tvfool.com/attachment.p...1&d=1497987107 http://forum.tvfool.com/attachment.p...1&d=1497987107 I opened up the MCM 33-2230 and wasn't impressed, but haven't measured it yet. They are using an all purpose board modified for use as a UVSJ, with a lot of empty pads for components. http://forum.tvfool.com/attachment.p...1&d=1497987508 http://forum.tvfool.com/attachment.p...1&d=1497987508 http://forum.tvfool.com/attachment.p...1&d=1497987508 |
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If you want reliable reception of WNNE, the antenna must be aimed at WNNE. |
Ad Tech and Rabbit,
The current ambient outdoor temperature at 5,600 feet is almost 100f. In the lower deserts, the ambient temperature is over 120f. Now, take a small, enclosed case, filled with rather delicate electronics...... See how long they hold up..... I've seen melted circuit boards, melted plastics, and melted and burned electronic components. Know matter how good the quality, heat is the enemy of electronics. That is why auto manufacturers have moved the most expensive and most delicate electronics inside the car, usually under a seat, where the heat impact is lessened...... |
A car alternator is designed to run with a case temperature of 200°F, according to a GM tech in Detroit that I consulted. He had done many measurements on car and truck alternators using thermocouples attached with thermal epoxy. I measured car alternators with a Fluke thermocouple probe when I was installing transmitters in cars to find out how much extra current could be drawn by the transmitter without damaging the alternator. For every 10 degrees C rise in temperature above 212°F (100°C), the life of the alternator is cut in half. The insulation on the wires starts to soften at about 120°C, depending upon the insulation Class. The diodes get pretty hot, too.
And your point is, for the current topic? |
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rather delicate electronics...... See how long they hold up..... I've seen melted circuit boards, melted plastics, and melted and burned electronic components. Know matter how good the quality, heat is the enemy of electronics." My point is that electrical components like USVJ's, are the most likely to fail and the most problematic...... And when would you possibly see a 200f under hood temperature in a modern car???? None I know of.... and certainly not when the ambient temperature is above 120f.... That is why we see so many car fires these days........... |
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I consider the UVSJ one of the most reliable components in an antenna system. It is so rare for a UVSJ to fail that I have never heard of it, but many preamps do fail. I can imagine any antenna system component can fail from a lightning strike, but they are not expected to survive a strike. Even coax will fail outside when it gets old or corroded from water entry. Just exactly how, in detail, do you think the OP should set up his system using an A/B switch; which antennas aimed where, to get what he wants? What happens when the viewer at TV #1 wants the switch set to "A", but the viewer at TV #2 wants the switch set to "B"? A system with an A/B switch IS very reliable (until the switch fails), but if the TV tuners are not able to add a channel after scan, then it is necessary to rescan after switching to the other antenna. User convenience is just as important as reliability. |
I did some more tests this evening, (all in the last 30 minutes before sunset, for what it's worth). It seems that the 33-2230 UVSJ is greatly attenuating my UHF signals. I was using my Solid Signal HDB91X UHF yagi mounted at 30 feet AGL, with a CM-7778 pre-amp at the mast. In Configuration#1, I sent the HDB91X signal directly to the pre-amp (no UVSJ). In Configuration #2, I combined the HDB91X with the StellarLabs 30-2476 VHF yagi using the UVSJ, and then fed that to the pre-amp. Here are the SNRs as reported by my Sony Bravia (typically need SNR>14 to receive channel):
Real Ch____Config#1 (no UVSJ)___Config#2 (with UVSJ + VHF yagi) 13___________0 (no VHF ant)________18 14___________20__________________15 22___________19__________________6 24___________24__________________9 25___________21__________________8 32___________18__________________10 50___________29__________________17 I repeated configuration #1 a second time and confirmed this wasn't a temporal effect. I also did configuration #2 again, but left the VHF input to the UVSJ empty. The results were the same as with the 30-2476 VHF yagi feeding the UVSJ (except of course no Real 13 reception). Leaving the UVSJ out of the picture (HDB91X and pre-amp only) and signal strengths seem to be unchanged as i write this, even though it is now over 1 hour after sunset. One thing I didn't try was to see how Real13 is affected by the UVSJ. It comes in with the UVSJ (SNR=18), but I didn't measure the signal strength if I use the VHF yagi directly, with no UVSJ. Maybe it would be a fair bit higher. Also, FWIW, there is about 100 feet of RG-6 between my mast mounted pre-amp and the power inserter. It would seem that I should try a different brand of UVSJ. I would rather like to avoid two lines and an A/B switch. |
Thanks for the test results.
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has weatherproof housing https://www.antennasdirect.com/store...Combiners.html no housing https://www.radioshack.com/products/...itter-combiner maybe try both? |
What about the RCA TVPRAMP1Z Preamp, instead of a new UVSJ?
www.amazon.com/RCA-TVPRAMP1Z-Preamplifier-... This preamp serves dual purpose, replacing the UVSJ and my CM-7778 pre-amp. Generally speaking, are folks having good experiences with these? |
The RCA TVPRAMP1R does have dual inputs and is inexpensive. It seems to do well; I'm using one with a GE 34792 Attic Indoor antenna.
There are reports about QC problems, in particular about the combined/separate switch not making good contact with the VHF antenna with the switch in the separate position. The fix is to set the switch to combined and use a UVSJ, which brings you back to where you started. There is also a review by an installer (Robert Hughes) on Amazon who likes the RCA preamp, and has bought many of them as Amazon Warehouse Deals. The power inserters have a high DOA rate, probably because they were returns that were never tested. I'm seeing a similar pattern with Duracell batteries on Amazon. Amazon is shipping them in plain packaging instead of the original packaging; many batteries are old, DOA, or leaking. I suggest you try the RCA preamp, but order from Walmart instead of Amazon. I'm still confident about the AD and RS UVSJs, but not the MCM. Maybe I'll make some tests of the MCM to see how it compares with your results. |
If you buy the RCA preamp, buy two of them and keep your receipts.... Just saying.
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