DB4e vs DB4-PRO vs ClearStream 4V
Anyone have experience with these models listed in title from Antennas Direct?
In particular, I'm curious about: 1) differences between DB4e and DB4-PRO (other than stainless steel construction, and, ahem, price) 2) beam width of ClearStream 4V (vs 2V)? Both indicate "70 degrees" on the company website, but I can only find technical data on the website for the 2V. Maybe ADTech can answer these questions? Thanks! --Tristan |
1. The PRO is all stainless, that's it. It was extraordinarily expensive to manufacture compared to a stock DB4e and was a one-time only production item. There are no plans to make more as of this time. Its performance parameters are close enough to the stock DB4e that no separate technical data was produced. There is a formal technical data sheet for the DB4e, it's on the website. If you live by the ocean where salt air eats everything, get the PRO. Otherwise, stick with the standard version.
2. I don't see any beamwidth numbers for the C4 or C4V on the website but that thing can be a real potpourri of old and new stuff. Link where you saw it? For the C4, the calculated UHF BW is ~43° at 470 MHz which narrows with increasing frequency to 31° at 698 MHz. There is no formal data sheet for the C4 (or C4V) although I do have calculated polar plots and a gain vs frequency chart somewhere on my computer at work. I'll see if I can dig them up. Performance of the VHF dipole will be considered to be the same as for the C2V, it's the same module. |
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From the overview: "...The ClearStream™ 4V has a 70+ mile range and a generous beam width of 70 degrees..." I thought this was a little suspicious, as the Clearstream 4 has no such description, and should be the same (other than the included VHF dipole). Also, there is this: http://www.hdtvprimer.com/ANTENNAS/ClearStream4.html Quote:
What I would be curious about however is how exactly do you define 70 degrees? or 60 degrees? Is there some industry standard, or do you choose an "arbitrary" dBi cutoff to define this? Thank you! |
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Thanks for the link to the beamwidth, I overlooked that this morning. Silly me, I looked in the "Specifications" but didn't read the "Overview" carefully. I suspect someone used the verbiage from another model but didn't catch the different BW. I'll notify the marketing manager about it. Horizontal beamwidth is technically defined as the "Half-Power Beam Width (HPBW)". This is the arc that covers the peak lobe and defines where the reception is 1/2 the peak on either side of maximum, also known as the -3 dB points. A good tutorial is available at http://www.antenna-theory.com/basics/radPatDefs.php Should you need the wide BW of a C4 but desire a bit more gain, you can stack two C2s vertically on the same mast and combine them with a reversed splitter and two equal length coax segments. This will compress the radiation pattern vertically and will provide a 2-3 dB increase in forward gain while maintaining horizontal HPBW. This is the same as what happens when we go from our C1 to the C2 UHF loops or from a DB2e to a DB4e. |
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Thanks again, your input is always helpful |
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This is the C4 spec sheet I had found thanks to Google. I'm thinking the 70 degree width is from the to bubbles on the higher UHF channels. C4 spec sheet |
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When you use a splitter in reverse as a combiner, the loss is about 0.5 dB, which means that the most gain you can get when combining two identical antennas aimed in the same direction is 2.5 dB. When a splitter is used as a splitter, the loss about 3.5 dB because you are dividing the power in half. It is possible to make a lower-loss combiner by connecting the coax lines from each antenna in parallel, which gives 37.5 ohms. This can be converted to 75 ohms by using a quarter wave matching section of 50 ohm coax. It is also possible to make a half-wave coaxial balun that has less loss than a conventional ferrite core balun. Any losses between the antenna and the input of the preamp subtract directly from the antenna gain. Calaveras at AVS Forum used the parallel combiner and half-wave coaxial baluns for the lowest losses when combining his two 91XG UHF antennas. http://www.aa6g.org/DTV/index.html http://www.aa6g.org/DTV/ABD/Antenna_Block_Diagram.html http://i496.photobucket.com/albums/r...psxfrsrcqn.jpg |
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When I combined two 4-bay antennas to give more gain for channel 15, I tried about 20 different baluns. I found that the loss on that channel varied about 5 dB between the best and worst baluns. OTA signals constantly vary in strength, sometimes as much as 10 dB in a half hour. The only valid test would be with a constant strength test signal and a signal level meter which gives a reading in dB. These are the signal level meters (SLMs) that I use for measurements: http://i496.photobucket.com/albums/r...G_0144_1_1.jpg |
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Is there a way to test the balun prior to installing? Never mind. I was going to try it but the parts are almost 35 bucks so I ordered a DB4e to try instead. |
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