Yagi w/ 296 in MD??

[doctordave]

Has anyone used a yagi w/ a 296 or 796 in the Baltimore County / Baltimore City area w/ success....specifically, avoiding major overload of the scanner? I'm having a bit of a tough time clearly copying Balt City 800 from Northern Balt Co...considering a commercial directional antenna for 800 MHZ....have concern that it may just ramp up Nextel/Cell interference w/out improving my reception. Anyone have experience w/ this?

Thanks.

Dave

 

[doctordave]

As a postscript to my above posting, I made a little homebrew directional antenna - using a large metal mixing bowl - fitted w/ an F connector at the base and a thick wire cut for 856 MHZ extending straight up from the bottom.....sorta looks like a poor man's sat dish......I basically aimed it away from a cluster of 800/900 MHZ paging/cell/?Nextel antennas that are positioned 1/4 mile from me....in an attempt to reduce intermod that has been destroying my reception of Balt City 800. Know what? There is definite improvement as compared to various helicals & high gain 800 antennas mounted high on my house. Still, there is clearcut intermod zapping out my reception intermittantly.

Here's my updated question....if I go with a yagi that has 7-plus elements, will I likely be able to get a focal enough "beam" to aim for a Balt city 800 tower and diminish the impact of the multitude of other cell/pager/Nextel towers scattered in the area? Most specs I've read for various commercial yagi products suggest that reception is strong in a pattern of approximately 30-40 degrees in the direction in which the thing is aimed.....I suspect that I would, therefore, get a great lock on the designated Balt City 800 tower, but would also be increasing the unfortunate impact of various commercial towers located in the nearby periphery. I don't suppose that there is a yagi of some sort that offers a super narrow cone of reception, with tremendous attenuation in the remainder of the pattern?

Perhaps getting good reception of Balt City 800 is a bit of a lost cause w/ all the heinous RF "pollution" in my area?

P.S. - If anyone would like to buy my high-tech, well-crafted salad bowl antenna....I'll start taking bids here

Dave

 

[crayon]

P.S. - If anyone would like to buy my high-tech, well-crafted salad bowl antenna....I'll start taking bids here

HUP!!

I start ya with two bits.

 

[TinEar]

27 cents is the bid.

Dave, I use a pair of co-phased 7-element Yagis for 800 mHz reception only. Not by choice on that band only but because that's the only band they work on. For everything else I stick with the radio whip which does just fine. I tried them on the other bands and get a little copy on the 494/495 band but by the time you get down to 460 they become worthless. And, of course, that's a good thing. I copy all of Baltimore County with the Yagis as clearly as my home county of Anne Arundel. Baltimore City is a piece of cake. It's only when I copy the Eastern Shore net that I have a bit of trouble because I can't seem to "see" the signal in a direct line. I have to point the beam to about 40 degrees off the signal to pick it up clearly. A single, 7-element beam gives about 10dbd of gain and 13dbd in a co-phased setup the way I have them. I co-phased them vertically (one atop the other) to allow a wider beam width. By co-phasing them next to each other, it would provide a very tight beam which I didn't want at the time I installed them. I'd like to try them the other way also but probably won't do that until next spring. I don't have much, if any, intermod problems with them although I was promised I would in this cluttered area. Comtelco had the 7-element Yagis on sale for around 50 bucks when I bought them. I'm in a very bad area to copy the DC 800 mHz fire signal and can't hear them at all with the radio whip but get them fine with the beams. I think they were a good investment.

 

[doctordave]

TinEar,

Thanks for the response. Perhaps I'll just try a yagi and see what happens. At least the $50 is not a huge investment. I suspect you and I have the same amount of RF cluttering to contend with....so this may just work for me.

Thanks again. I'll keep you posted.

Also, if there is a continued, huge demand for my high-tech salad bowl antennas, I have a kitchen-full of pots, pans and mugs and will happily continue to produce

Dave

 

[TinEar]

Dave, I'm not sure how many different nets you copy on a regular basis but let me tell you what else I have up there on the roof. On the same mast with the 7-element Yagis, I also have a pair of co-phased 3-element Yagis. I have the 7s and the 3s separated by 140 degrees on the mast which allows me to point one set at DC and the other at Baltimore without having to turn the rotor when my interests are hearing the two major cities. I run them into an A/B switch which makes it easy to change from one direction to the other without having to wait for a rotor to take its time turning. The pair of 3-element beams covers me real well for Baltimore City and County but I need the 7s to hit the Eastern Shore and DC. I use LMR400 coax to cut down on loss as much as possible. Both antennas, even the 7-element beams for 800 mHz, are fairly small sized and I have them on the roof at the back of the house and you can't even see them from the street. So, if you have to keep any outdoor antennas unobtrusive, this is the way to go.

My house is ringed with huge oak trees but I still manage to get good distance even with just the radio whip. I'm trying to find someone that will go up one of those 50-60 foot oaks, trim out the top and install a discone for me. I figure it should really get me out there since I'm already copying stuff from six states with just the radio whip. I actually enjoy listening to VHF signals more than I do all the trunked nets we have in this area. We shall see.

Hope you come up with something good that will work for you. You can always start with a single Yagi and then co-phase them if you need a little more punch.

 

[doctordave]

Tin Ear,

Sounds like you have a great setup down there! I really like the arrangement of yagis you've got. As of yet, I have an antenna "farm" in my attic and it serves me fairly well....can copy VHF-Low down to the mid-Shore nicely and VHF-Hi from all over, including the re-broadcast fire freqs out of Kent, DE. 800 MHZ, thus far, has been a real challenge due to the aforementioned issues. I wonder if mounting the yagi(s) near the peak of my A-Frame, inside the attic, would suffice? Balt City's nearest 800 towers are only a meager 15-20 air miles (albeit, there is some hilly terrain and lots of RF between me and there)....perhaps I might get through? I'd love to get the Upper Eastern Shore system, as well, with another Yagi....right now I get them variably w/ just a helical....imagine that will only get better as leaves begin to fall....my house is also ringed by enormous/thick trees. Think that Radio Shack RG-6u at only a 25 ft run would suffice? I already have an extra feedline in place and awaiting a yagi.....should only be losing about 2 db at 900 MHZ w/ such a run, compared with maybe 1 db loss for similar config w/ your high-grade cable.....

Thanks again.

Dave

 

[doctordave]

Tin Ear,

How about the Comtelco yagi, Y-2287 B06 model, listed on rfwiz.com.....is this fairly consistent w/ what you have used in a single yagi configuration? They also have the co-phased setups for $250+.....pricey, but quite nice!

http://www.rfwiz.com/Comtelco/ComtelcoYagi1.htm


Thanks.

Dave

 

[trimmerj]

"My house is ringed with huge oak trees"
Mine too, and they make good antenna supports. I used a slingshot and 1 oz fishing weight connected to fishing rod and spinning reel to get over limbs of choice. Once you have the fishing line over the limb, tie a rope to it.

 

[TinEar]

Dave, yes, the Y2287B is what I used. Rfwiz shows the heavy duty models in a stacked configuration but I went with the standard duty. One thing I wouldn't do again though...I bought that Comtelco made stacking bar which is way too expensive. If I did it again, I'd just go with a phasing harness made with short pieces of 75ohm coax to lead into the 50ohm long coax run into the house. You'll save a bunch of money. That's what I did with the 3-element pair. You can certainly try it in the attic but there will always be some loss compared with outside. Radio Shack's RG6U coax is 75 ohm, isn't it? I don't know what the loss is per 100 feet though. The LMR400 is, as you say, about 1 db loss at 25 feet at 900 mHz or 3.9 db at 100 feet. Maybe the impedence mismatch and high loss of that Radio Shack coax on such a short run won't make that much difference unless you're right at the edge of being able to hear a signal - or not.

There is a fantastic supplier of coax cable and bits and pieces for antenna installation right here in Maryland. They'll make whatever you want in any configuration you want, fast and professionally. They are great guys to work with. You can find them (The RF Connection) at:
http://users.erols.com/rfc/index1.htm

 

[doctordave]

Tin Ear,

Thanks for the additional feedback.....I'm going to order one and see what happens....certainly very suboptimal to mount it inside the attic, but perhaps it will do the trick. I think I will start w/ the RG-6 and upgrade if necessary....I should be losing 2 db w/ the length of cable involved....doubt that upgrading to cable w/ only 1 db loss will make a huge difference.

Appreciate your help. Maybe I'll even be able to start copying AA Co, as well.

Dave

 

[doctordave]

Tin Ear,

The yagi is on the way. We shall see. Either it will serve my purposes....or it may end up to be a rather expensive tie rack

Dave

 

[TinEar]

Very good. How are you going to install it? I know your plans are for the attic but will it be on a rotor or fixed mode at a particular signal? Let me know how it turns out once you get it up and running. The good thing is that it will cut out a lot of intermod from the 460 and below bands and should provide several orders of magnitude improvement on the signals of interest in the 850/860 band.

 

[ka3jjz]

Very good. How are you going to install it? I know your plans are for the attic but will it be on a rotor or fixed mode at a particular signal? Let me know how it turns out once you get it up and running. The good thing is that it will cut out a lot of intermod from the 460 and below bands and should provide several orders of magnitude improvement on the signals of interest in the 850/860 band.

Yeah, but Nex-hell and other cell pager services are just a bit higher in freq; it might be close enough that some overload may still occur. Still, it's worth a try, particularly if you can turn the beam in a less favorable direction away from all that trash....73s Mike

 

[doctordave]

Yep - going to be a bit of a gamble. Primary goal is to get Baltimore City 800, mainly by attenuating all of the other RF garbage in the area. I'm hopeful, since I've identified the 2 cell/paging/Nextel towers causing my intermod probs and they are almost 180 degrees apart relative to my house....I think I may be able to aim reasonably away from them and still be pointing toward Balt City. We'll see. Also very curious if I can get better locks on the UES system. With a whip, I'm pulling in that system variably. Then again....who knows what other cellular, etc towers I may soon feel the effects of down in that direction w/ the yagi pulling signals in.

Planning on starting w/ a fixed, in-attic mount - but will quickly move to an above-roof mount if essential. If that doesn't work, I'll promptly move it into a closet and see how many neckties I can hang from it

Dave

 

[doctordave]

Success!! Received the Comtelco yagi yesterday and mounted it in a fixed position in my attic w/ just a 20' run of plain old RG-6...and the intermod from some area Nextel & cellular towers that was killing my Balt City 800 is nearly gone. Very impressive and well worth the $60'ish investment. Interestingly, there are a few freqs (out of the many) on Balt 800 that still suffer from some mild intermod - presumably these are the freqs closest to those of Nextel. Unable to pull in the Eastern Shore system, because I am aiming essentially right at a few intermod sources in order to point at the Shore....although just driving a few miles from my house (and thus getting East of the Nextel tower) affords me great reception of UES w/ my 796. Perhaps I'll figure a creative way to overcome the issue w/ UES....or if there truly is to be a Nextel-Public Safety frequency re-alignment sometime in the future, I may get the Shore system after all.

Overall, I'm very pleased. Thanks to TinEar for input on yagi selection.

Dave

 

[TinEar]

Dave, I'm extremely glad to hear this antenna is working for you. You'll find out really how much difference it makes once you get a chance to play with it for a bit. As I mentioned earlier, to reach the UES net, I have to point about 40 degrees off a direct line so you may still be able to do something after playing around. Just as an experiment on the Baltimore City freqs, point the antenna about 90 degrees off a direct line and see if that doesn't still allow the signal to be received but kill the intermod. I don't really need the Yagi to hear AA County but when I do use it there is a spot that I get terrible intermod from and simply point away from but still receive the AA signal very well. There are lots of things you can do since it's in your attic. You may also want to try about a 10-20 degree upward tilt on the antenna too - especially when you're trying to hit the UES. That works wonders on more distant signals although it's not something I can do easily with mine being on the roof.

Alan

 

[doctordave]

Alan,

Yep - I'm looking forward to working w/ the yagi some more. I did notice that aiming up or down about 20-30 degrees makes a big difference, in addition to changing compass direction. Was very curious that I seemed to get the best reception by aiming Northwesterly - quite away from the City.....most importantly, it is the direction most away from the 2 major sources of intermod....really goes to show you how powerful the Nextel/cellular interference is in my locality. Of note, prior attempts at using attenuation added little benefit.....I will try that setting AND use the yagi and see what results I get.

Must admit, I am curious about cable upgrade. I have 20' of RG-6....likely to represent about 1.5 - 1.7 db of loss at 900 MHZ for this length.....but I wonder if the mismatch (50 - 75 ohm) factors in much? Wonder if low-loss 50 ohm would make any difference here?

I am determined to get UES......more than likely, I will end up pursuing some above-the-roof mount, just to see what I can pull in.

Thanks again for your imput!

Dave

 

[TinEar]

Dave, I used to know the math to figure that impedance mismatch you've got but it's gone from memory. It can't help but you've got a very short run of coax and the extra loss is probably slight. It will only make a difference when you're right on the edge of receiving or not receiving a particular signal. Your plan to point away from the interference is a good one. You're not all that far from the City and still have plenty of gain in that antenna even pointed away from a direct line. It should be fun playing with elevation and direction - assuming the path to the attic is not complicated. Enjoy.

Alan