[gnosys]

Unfortunately, I am now in the position of having to either find a better multipath rejection antenna, or remote my antenna via hardline to my ham tower 200 feet higher than my house, and nearly 1/4 mile away. That's a lotta hardline.


If anyone has had measurable success with commercial designs in HEAVY multipath environments, I'd appreciate input. I'm talking about NO way to get a ghost free picture on strong VHF stations. I'm presently using a Radio Shack VU-190 with 60 feet of RG-6, and a rotor, at 35 feet. A clear shot at applicable horizon, but the horizon is a mountainside!


I may end up building a custom single-channel antenna for Channel 18 if nothing commercial works. Thanks.

 

[Headtalk]

A collection of 'the-best-of-the-best' in reception solutions

http://www.atechfabrication.com/

 

[jhe]

Key for me was horizontal stacked Blake JBX21 antennas.


If you need VHF not sure what would be good with a narrow beam but the big Delhi has a good F/B ratio.


And for my weakest station I had to switch to a Samsung tuner in place of the RCA DTC-100 or Panasonic DST-50.


And if I had the option of going 200 ft higher, I would have and saved myself a lot of hassle. At that height I would have had line of sight.

 

[Glenn_L]

Blake has a group "A" version of their JBX21 that covers US channels 15-35, this might give you a little extra gain for ch 18.

If that does not do it, then stacking two of them horizontally will give you significant multipath rejection.

http://www.blake-aerials.co.uk/JBX.HTM

 

[NightowlKY]

Is there a chart somewhere that better shows what channels are in each "group"?


Also, what about the DY 28 Element yagi Blake offers? It seems to offer even higher foward gain but not as much back-to-front vs. the JBX models.

 

[jhe]

The Blake web site has nice charts showing the channels in each group. It lists them by British channel numbers though.


See: http://www.blake-aerials.co.uk/


or even better, here they show some Group info for US channels:

http://www.blake-aerials.co.uk/chann...version_us.htm


Key info for USA is:


To cover everything in the new UHF band (up to 51) you just need two antennas for UHF a group A and a group B.


Group A for low UHF 14-35

Group B for upper UHF 33-57

Grouk C/D for upper old UHF 50-69

Group E for more of upper old UHF 33-69

Group K ideal for W/B 14-50


(Have not seen antennas being sold for the last two groups.)


If you need lots of low UHF gain you might want to look at the Televes antennas too.


I have the Blake JBX series group B because I need gain for the high UHF and have severe multipath. It works fine for me with some gain loss down to channel 19 which is our current lowest on the air.

 

[Glenn_L]

I found the DY28A to have good gain, but poor multipath rejection. It did well in this test where gain was important:
http://www.atechfabrication.com/test...ange_tests.htm


but did pretty bad in this test where multipath is a problem:
http://www.atechfabrication.com/test...st_results.htm

 

[NightowlKY]

Thanks, jhe.


That 2nd link is what I've been seeking. My primary goal is picking up Cincinnati DTV signals (78 miles). With dead tropo conditions, I can still get faint signals from most of the analogs and blips on the digital channels. The digitals are 10 (which I'll use a VHF-only for), 29, 31, and 35. My locals are about 20 miles away and the roof-based RS VU210 does just fine for them. I might even add some filters to block most of my big locals for helping out during DXing efforts.


Ideal would be something like 29 - 46 (that would cover Indy). I wonder what the dropoff is below 33 on that Group B antenna? Ch. 31 comes in first and 29 is the Cincy FOX which will probably never get any 480p done properly so I could do without that.


Decisions...decisions...decisions.


Hmm...actually, looks like the JBX14 is WB so that's the whole UHF range. I'd like to avoid the JBX21 as it's quite a bit bigger and heavier, I'm sure, and I want to miniwize weight/wind load.

 

[cymro]

As in jhe's case, for me the key difference was horizontal stacking of JBX21WB's, combined with remote rotator and tilt control.


Thanks to jhe for pioneering the horizontal stacking tests on the JBX's and to Glenn for helping me out with my installation with his superior kits.(results of tests at my location are on Glenn's website)

 

[NightowlKY]

Glenn,


Thanks for the info on the DY. If it's that long (14')...ooof...that's a bit large.


The JBX21, I see, is from 8-11' long and the JBX14 appears to chime in at about 7-8' or so.


What's the weight differential between the two? Haven't come across that info.


And, on the Group B antenna, does it just not pick up anything below US channel 33? How bad would Ch. 31 be? The Group A and Group B appear to offer much better gain than the WB version and that's what I need. Looks to have about 5-6dB gain over the Radio Shack UHF-only I have now.


Also, what would you recommend for low-loss baluns (or do the Blakes have 75ohm connectors) and low-loss combiner? I need to push as much signal down that line as I can (duh...who doesn't? )


Multi-path isn't much of an issue here. I can get to 50% signal indicator on the DISH 6000 from, say, WKRC-DT 31 Cincinnati (78 miles) and it will have few, if any, dropouts. Same for Indy. In fact, the other morning I locked on WRTV-DT 25 from Indy in the low 50s and it was steady until it faded when the tropo dissipated. Going to a horizontal stack, I think, reduces any multipath that may be in existence. I'm in a relative high spot for my area for at least a half-mile around (with the areas higher behind me or to the north and not in the direct path toward Cincy).

 

[cymro]

Jerry:


Use a Channel Master model 0538 ferrite "hybrid" coupler to combine two identical antennas. Do not use a resistive combiner such as Radio Shack sells. The length of the coax from each antenna to the combiner should be matched within a fraction of an inch.


The JBX antennas come with an integrated balun whose output is 75 ohm matched.

 

[NightowlKY]

Thanks for the info on the baluns and coupler, Cymro.



Any idea on the dropoff in gain on channels outside of Group B?

 

[Glenn_L]

Jerry,


The JBX14 weighs about 2/3 as much as the JBX21. For long distance I would go with one JBX21 over two 14's. It has about the same gain, but with less complications. If you were 30 miles or less from transmitters with multipath, the two 14's would work much better than a single 21.


The gain outside the group range falls off. If you have strong signals outside the range you would be ok, but if the channel outside the range is real weak you probably won't get it.


I have found that if you tune the antenna for the weakest channels, the strong ones will usually be just fine. So pick the range to cover your weakest channels.


The CM-0538 has F-connectors. I just got some combiners from LabGear (a UK company recomended by Blake) that are supposed to be low loss. They use the same type of coax clamp as the Blake baluns, so they may provide a better connection.


If you are looking to squeeze every bit of gain from the signal, you might want to use RG-11 for the main feed line. It has almost half the loss of regular RG-6.

 

[NightowlKY]

Thanks for the info, Glenn.


I may end up going with the WB version, then. Otherwise, sounds like I could write off DXing and it would also seem that my own locals wouldn't do well (other than off my attic-based VU210).


If I lived further out in the country and had a bit of land, I'd probably do multiple masts with a horizontal stack each. One setup would be for DXing and could use the WB JBX21 and the other would be primary for the Cincy DT stations (29, 31, 35...oh, and 10 but that's VHF and another matter entirely). The JBX -K would be ideal as that would cover the Indy digitals for me, too, but the PDF at the Blake site doesn't include the K group in their gain charts.


Either way, it looks like the JBX21 offers at least 3-4 and maybe as much 6-7dB gain over the U75R from Radio Shack. Add in that low-loss combiner and switching to 75' of RG11 and I'm looking at maybe 5-10dB increase over what I have now.

 

[SeanKelly]

Another option might be to exercise patience: next-generation receiver chips are apparently using multipath to an advantage in order to reassemble as much of the original digital signal as possible.