cure for my simulcast distortion??

[kb0gus]

Can anyone comment on this antenna as a potential "cure" for my simulcast digital distortion issues?

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The price sure is right. I'm going to mount a yagi outside to see if that'll help but that will only provide help in one listening position... Unfortunately I typically have 3-4 areas in the house that I could be listening.

I'd like to have something smaller that I can "point" a bit easer..

I was even thinking about building a half square for 700mhz and somehow attaching it to a BNC connector...

Has anyone had any success with ANYTHING on these simulcast systems?

thanks!

 

[n5ims]

That price does sound good, but 80 degrees of beam width is pretty wide and the gain may make things worse as well.

Quite often there are two ways to resolve the issue. First is to use a directional antenna (like you're thinking about) to isolate one tower so you get the signal from that tower (and only that tower). Second is to reduce your signal strength so the other towers (from further away, generally) have weaker signals and cause less distortion.

What you may try (at little to no cost) is to use an indoor antenna to see if that helps. If not (or not completely) check to see if you're getting enough signals, but from multiple towers (vs not enough signal at all). It may also be useful while testing to use you hand to shield the antenna to help further reduce the signal strength. If any of this works, you know that the issue can be resolved by reducing your signal strength (using attenuators or other tricks like foil on your antenna, a foil shield - tin foil glued to some poster board and folded to block signals from that direction, etc.).

While mobile listening to my main simulcast system I have good results grabbing the antenna (a RS 800 MHz duck) to block much of the signal. Since the system is still strong, this lets enough signal in to correctly decode, but blocks the other tower's signals and eliminates the distortion. Once I leave the area of bad distortion, I simply let go of the antenna and let things work normally. One friend that lives in that area simply removes his antenna to resolve the issue since the closest tower's signal is strong enough to pick up with just the BNC connector.

Check these threads for additional tips in resolving this issues as well (it's a common problem!):
http://forums.radioreference.com/antennas-coax-forum/218290-fixing-simulcast-p25-issue.html
http://forums.radioreference.com/antennas-coax-forum/218798-st2-antenna-digital-800mhz.html
http://forums.radioreference.com/antennas-coax-forum/217910-discone-antenna-problems.html

 

[nanZor]

For the quickie indoor test, how about a homebrew corner reflector? I did a search for

N6GN cardboard corner reflector

and found an interesting pdf showing it built with cardboard and foil - placing the unit inside the box at the focal point. I have never tried one, and it looks like it could get you kicked out of the house. Indoors with reflections it might be impossible - but might be worth at try..

 

[popnokick]

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I would think two directional antennas pointed in different directions and an adjustable phase adapter connecting them to a single coax would work. Then just turn the dial until the distortion induced by the signal from the other tower is phased out. Something like this:
http://www.dxtools.com/Phaser.htm
EDIT- oops! Wrong freq range. This device is for MW, not VHF or UHF. Haven't got time at the moment to look, but must be one for VHF/UHF.

 

[W8RMH]

The price is tempting but I think you will be happier with a yagi.
Scannermaster has a nice selection at reasonable prices.

I think these planar antennas are designed to communicate with each another, namely another directional antenna pointed toward it. I don't know how well it would receive a signal from an omni-directional base antenna.

 

[n5ims]

I think these planar antennas are designed to communicate with each another, namely another directional antenna pointed toward it. I don't know how well it would receive a signal from an omni-directional base antenna.

Actually they're designed to isolate an area for specific coverage (often for cell phone use to allow a single site to handle more calls by dividing the area up into multiple virtual sites). What they'd end up with is 4 or 5 groups of these around a tower so a single tower would than handle 4 to 5 times the number of calls it would by using onmi-directional antennas. They are also used for point-to-point communications to allow several links to use the same frequency since they restrict beamwidth, but are easier to install (and less expensive) than the typical microwave dish. They also tend to have fewer wind-related outages since the beamwidth is wider than a dish would be.

Since the antenna in question has an 80 degree coverage area, the company would place 4 around the tower, 1 each facing north, east, south, and west. With the same frequencies being directed in each direction, but each on their own antenna (now often they'd vary the frequencies, time slices, etc. but we're keeping it simple here). With an omni antenna 1 person north of the tower on that frequency and it's full the next person would get the dreaded 'no bars'. With the 4 antenna setup, only the northern folks would get 'no bars' while east, south, and west could still get folks to make their calls.

If used on a scanner and the system used an omni-directional base antenna what would happen if you used this antenna is that if the planar antenna is pointed within 80 degrees of that omni antenna you'd hear fine, if not you'd get nothing (or possibly only minimal signal depending on how far off that 80 degree mark the omni transmitter was).

 

[popnokick]

THIS is what I was looking for (see my previous post above). Connect two directional antennas (one of them pointed away from the site you want to receive) and tune out the intermod from the 2nd site. RF Phase Shifters RF Phase Shifter What you'll be doing is adjusting the 2nd site to be out of phase with the main site.... or adjusted to the point where the phase relationship is complementary rather than destructive.