double antennas?

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radingman

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hi guys, hoping someone can answer this question for me. i have a grecom psr700 scanner that works great. i have a diamond RH519 antenna and a RS800mhz antenna. the RH519 works great on the 150-174mhz band and decent on the 800 mhz system that i listen to. i am just out of reach of the 800mhz unless i use the RS800 antenna, then i can pick up the signal fairly decent. The RH519 i can pick up the 150-174 band pretty good but im out of range of the 800mhz band. the RS antenna is kinda useless at the 150-174 bands which i knew since that antenna is specifically tuned for the 800 system. my question is this...would it be of any help to use a double duck antenna adapter and use both the RS800 and the RH519 at the same time or would there be some kind of interference? any help would be greatly appreciated. im not new to scanning at all tho i admit to being somewhat new to the different technologies that have to do with antennas. thanks again and hope to hear some good advice from you guys.
 

radingman

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thanks for the fast reply DDan.....appreciate the help. however, unless i missed something, i didnt see anything in that thread that really answered my question. it seems as tho that thread dealt w everyone using an external antennas or attic mounted antennas connected to the scanner via a coax cable. my question involves a handheld scanner using handheld antennas. the particular setup i would like to use is something like this - http://www.scannerworld.com/content/product/model/ANT96
 

W6KRU

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Yes but the reasons that two external antennas are not a very good idea also apply to two antennas like you are considering. Out of phase signals mixing and causing a lower overall signal, etc.
 

radingman

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ok, thanks DDan. as i said, im not really up on the technological side of antennas, but i understand the basis of what youre saying. let me add this.....is there any benefit to using the same setup, but with 2 identical antennas? say 2 RH519's or 2 Rs800"s ?
 

n5ims

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Unless they're correctly spaced and connected with the correct phasing harnes, you'll probably end up making things worse with two identical antennas. When correctly designed and mounted two identical antennas can provide a directional antenna, but when they're just randomly placed and connected with a random length of cable, you'll just as easily create a system that'll have one antenna picking up a signal and the other antenna cancelling that signal out so you'll end up with very little signal at your scanner.
 

n8zcc

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Unless they're correctly spaced and connected with the correct phasing harnes, you'll probably end up making things worse with two identical antennas. When correctly designed and mounted two identical antennas can provide a directional antenna, but when they're just randomly placed and connected with a random length of cable, you'll just as easily create a system that'll have one antenna picking up a signal and the other antenna cancelling that signal out so you'll end up with very little signal at your scanner.
And to add to the complexity, antenna separation distance and the length of the phasing harness is frequency dependent.

I took a look at the add at Scanner World and that is nothing but false advertizing or should I say, a lie designed to extort. Either way, it is irresponsible.
 

radingman

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thanks for your input but im talking about an actual dual bnc connector that mounts right to the bnc connector on my PSR700. the antennas would be spaced approx. 1/4 to 1/2 in apart.
 

radingman

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thanks N8ZCC.....that was my original thinking too, but again, im not up on the technical aspects of antenna wavelengths and separations and all that. i do understand that antennas are tuned for certain freq by using coiled wire and adjusting overall length of the antenna. thanks to everyone who replied. ill prob end up trying a Watson W889 to be able to pick up 150-174 and 800mhz without having to change antennas.
 

n8zcc

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thanks for your input but im talking about an actual dual bnc connector that mounts right to the bnc connector on my PSR700. the antennas would be spaced approx. 1/4 to 1/2 in apart.
Separation of the antennas has to be multiple of the wave length (usually 1 full wave length or more) of the frequency of interest. Then the harness that connects the two antennas to the radio has to be sized based on the frequency of interest with respect to the velocity factor of the coax.
 

VO1GXG

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it all comes down to simple math, never mind the signals " mixing" and what not, two 50ohm loads would be 50/2=25ohms which means you'll have a dampening factor of 1/2, think of it this way can you fit a 1inch bolt into a 1/2 inch nut? you're much better off getting an antenna switch!
 

AC9BX

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It just doesn't work well at all without filtering and/or phasing.
Impedance match isn't really a problem if proper band filtering is applied. You can't "never mind" the mixing. Because we're dealing with radio frequencies and not DC simply using two 50Ohm antennas in parallel doesn't mean you have an effective 25Ohms. It would if they're identical and phased. If not the resultant impedance can be almost anything. This is impedance, not resistance, frequency and phase is everything. An antenna with 50Ohm impedance is only 50Ohms over a range of frequencies.
If the intention is two different portions of spectrum and there's a filtering-mixer to connect them you still have a 50Ohm system. Say we have one antenna for below 300MHz and one for above 300 and we connect them through a band filtered combiner (dixplexer) designed for this as far as the radio is concerned there is one wide band antenna connected. Since this won't be how it works by simply connecting two antennas with a BNC "T" connector we'd just have a mess, some random metal attached to the antenna connector. It might work, might not, well here, poor there. All bets are off.
 

radingman

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ok, thanks everyone for explaining this to me. i had assumed it was a gimmick since you never see anyone actually using a double duck setup. if this was a viable working solution to picking up multiple bands, then more people would be using it and more posts would be suggesting such. its still a bit above my head but i do understand the basic idea that you guys are telling me. great forum and great advice !!
 

SCPD

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I wouldn't completely discount their product, it looks like more than a simple T. It may actually have bandpass filters in it. But hard to really know.
But if it's just a splitter it'll probably make your signal worse. There are several threads on here about them but no posts from anyone that has actually tried one.
 
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mm

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NAR6591 Dual band VHF, 700/800 MHz antenna - Magnum Electronics Inc.

The antenna above works very well on VHF and 700/800 MHz, just ignore the GPS capability if you don't need it.

It uses a female SMA connector so you will also need a male to male SMA barrel like this one.

http://www.rfstuff.com/store/comersus_viewItem.asp?idProduct=210.

You will pay more for the Motorola but remember that it is properly matched for VHF (150-174MHz) and 700/800MHz operation and well worth it.

I use stock Motorola handheld antennas like these on my scanners and two way radios with excellent results.

Mike
 
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radingman

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looks like a great solution...but yeah.....$64 is a tad steep....wow. thanks for looking for me tho...always good to see the various options
 

nathancarlson

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I tried that, using the T connector with the stock rubber ducky antenna and the 800 rubber ducky, and my kids ended up spinning the antennas around for fun like a helicopter, and breaking the internal BNC connection, costing me about $50 and being without my scanner for almost a month. Your best bet may be a telescoping, or multi band antenna. I got the Radio Shack BNC telescoping antenna, and have improved performance even without always expanding it to the various lengths for the various bands. On my car, I have the Austin Spectra. It does decent on all bands, but best on 800mhz. I have tried the T-connector in my car, using two different mobile antennas and it didn't seem to work as well as I hoped it would (probably for the technical reasons above).

Do you need the antenna to be portable? You may be better off trying different antennas if you use it in your house a lot. They have a lot of decorative cool ones like dipoles, ect that look neat and will probably work better than the rubber ducky, but of course not perfect on all the bands at once. You may also try to find ways to ground it. I have found that even a cheap mag mount on a cookie sheet does wonders for rx in the house.

Improving your reception doesn't always have to be expensive, or a perfect match with the length, ect. Simple improvements that aren't perfect can still make a difference when you are just receiving and not needing to transmit.

Don't forget to consider nearby interference that may be causing issues on some bands that wouldn't effect the other bands as bad.
 

radingman

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this set up needs to be portable. i live approx 12 miles from utica that uses an 800mhz edacs trunking system. i tend to travel to utica at least 3-4 times a week. the main issue is i have is that i live in a valley and the road to utica goes approx 3/8 mile uphill just outside of my town. so while im home i get very little 800mhz signal and as i get to the top of the hill on my way to utica, my signal improves dramatically. now of course, my 150-174 signal is better where i live and even better on my way to utica. what id like is to not have to swtich antennas halfway to utica every time i go there. just driving around the valley i can get some signal w the RS800 for the 800mhz system but the low band suffers.
 
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