Dual Antennas

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Tlanglais

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Is it possible to run two antennas at the same time on one receiver? I've been thinking of running an 800 MHz antenna along side the multiband the scanner (Uniden Home Patrol) came with.
 

gewecke

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Is it possible to run two antennas at the same time on one receiver? I've been thinking of running an 800 MHz antenna along side the multiband the scanner (Uniden Home Patrol) came with.
Yep, part of the fun is experimenting with different antennas to see what works! ;)

73,
n9zas
 

kb2vxa

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Uh oh, coupling two antennas into one receiver will result in an unpredictable, undesirable directional effect. Co-phased antennas are often used for directionality but careful calculations must be made for predictability. I use a system similar to that which you outlined, one antenna for VHF/UHF/T-Band and another for 800MHz but to keep them separate I use a custom diplexer with a 600MHz crossover point.
 

gewecke

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Uh oh, coupling two antennas into one receiver will result in an unpredictable, undesirable directional effect. Co-phased antennas are often used for directionality but careful calculations must be made for predictability. I use a system similar to that which you outlined, one antenna for VHF/UHF/T-Band and another for 800MHz but to keep them separate I use a custom diplexer with a 600MHz crossover point.
Yeah, but you're a purist and geek like me ! :D

There are folk who wanna do it, just to see if it'll work!

73,
n9zas
 

N8IAA

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Is it possible to run two antennas at the same time on one receiver? I've been thinking of running an 800 MHz antenna along side the multiband the scanner (Uniden Home Patrol) came with.
Yes, but don't use a tv splitter. Get a antenna multicoupler like the Stridsberg. Also, keep the antennas apart by at least 1.5'.
Larry
 

kb2vxa

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"Yeah, but you're a purist and geek like me!"
You can smelt copper but you need electricity to make it pure. (;->)

"There are folk who wanna do it, just to see if it'll work!"
Oh it'll work alright but with unexpected results. I used to hear that station, with two antennas it should be twice as strong... but wha hoppin Lucy? <razz>

Just to geekify Larry's advice, the un-amplified Stridsburg couplers are the 50 ohm version of the 75 ohm TV splitters and are ridiculously overpriced. The slight difference in impedance matters not, the 3dB loss per port matters a lot. If it doesn't matter to you go the cheap way with a TV splitter used backward as a combiner, you'll just need adapters for the female F connectors. The trouble with amplified ones is they can only be used as splitters running more than one scanner off one antenna. The preamp only works one way, try using one as a combiner and you won't hear anything at all.
 

N5TWB

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Not to fly in the face of Warren or John who clearly have more education and experience in radio than me, I'll tell you what I did back in the 70s in Oklahoma. The Highway Patrol was on VHF-Lo while everything else I wanted to monitor was on VHF-Hi and I was not pleased with the performance of the single A/S antenna (MON-31, IIRC) feeding the scanner in the car. I went to a commercial radio shop, bought one low-band and one high-band Antenna Specialists antenna, two mounts w/coax, and a T-connector. I ran both antennas to the T-connector and one short jumper to the scanner and got significant improvement on receiving, especially for low band. I never noticed any reduction in performance or interaction between the two antennas with the scanner. Being in the 70s, the scanner was a crystal-controlled model, a Regency ACT-R-10H/L/U that I still have today.
 

kb2vxa

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Of course you'll get better results with band specific antennas, performance is always a sacrifice to bandwidth. Look at it this way, two hoses with narrow nozzles fed from a Y connector vs. one with a spray nozzle. Now which will shoot farther?

As far as interaction is concerned, with so many complex variables involved it's impossible to predict how a slap-dash antenna system will behave. In the mobile with signals constantly changing there's another complex variable, I'm not the least surprised you didn't notice any interaction even if there was one.

Hey, where hams are concerned education and experience is a conflict in terms, what looks good on paper never works until you give it a good smack. My motto is "throw away the book and go with whatever works".
 
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jackj

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A log-periodic antenna is just what you describe, a serious of antennas, cut for different frequencies and feeding the same feed line. They work pretty well and give a pretty broad bandwidth. They are not something that you can throw together in an hour or so. They require some pretty heavy math to get the characteristics you want but there are web sites that will do the math for you. Search for log-periodic. I used to use a trap dipole on 10, 15, 20, 40 & 75 meters, one feed line feeding 5 antennas. Other than having a narrow bandwidth on each of the bands, it worked well. The ARRL's antenna handbook gives information on several multiband antennas and instructions on how to build them.

So the answer to your question is yes, it is possible.
 

n5ims

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And don't forget the #1 rule on antenna testing. If you've got a great antenna when you test the band will be totally dead so no signals will make it beyond a few hundred feet. If you've got a horrible antenna, the band will be totally open and signals will be flying in from all over even if you use just a wet toothpick for your antenna. If your antenna is somewhere between perfect and horrible, results will be somewhere between these two extremes with no relation as to the quality of your antenna design/installation.

The first corollary for this rule is that if you take this rule into account during your testing, your results will be totally random and not follow this or any other rule as they relate to antennas and their testing.
 

kb2vxa

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"After reading all this I think my head is gonna explode."

Baby zombie food, puree of brain... yum.
 
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