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Scanner / Receiver Antennas - For discussion of any type of receiving antenna used by a scanner or receiver base, mobile or handheld.

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  #61 (permalink)  
Old 08-16-2005, 6:12 PM
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Using the ribbon cable, it should look more like this (no need to "fan"):

Code:
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 +------ Center
 +------ Shield
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Strip all the ends about 1/2", twist them together, and solder them to the appropriate side of the coax.
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  #62 (permalink)  
Old 08-16-2005, 10:37 PM
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Cool works for me.

I am going to be using some older ribbon cable. Its 40 conductor. So I will just be slicing it down to the 3 wires for the 3 bands I plan to make it up for.

I will make sure ot take some pictures for the Wiki as I do it.

Thanks for all the help. I am sure I will have more questions. Oh and my ARRL handbook is on its way. I ordered the 2006 edition also.
Does anyone have a website with descriptions (with pictures) of the different types of antennas. I searh google and I get alot of sites of peoples farms but no real basic pictues or illustrations of how they are constructed.

Such as we have had in this thread.

Thank you al once again.
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  #63 (permalink)  
Old 08-17-2005, 2:33 AM
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Quote:
Originally Posted by MarkEagleUSA
Using the ribbon cable, it should look more like this (no need to "fan"):
You're a much better artist than I am.
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Old 08-17-2005, 6:11 PM
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http://www.ac6v.com has links to tons of antenna web sites.
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Old 08-17-2005, 7:27 PM
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Ok, this dipole design got the best of my curiosity so I decided to build one for myself.

I used a BNC chassis-mount jack and a 3' RG-58A/U patch cable with BNC's at each end. The elements are made from some 18 awg 4-conductor wire I had lying around. I settled on 3 elements sized at 18" (VHF-Hi 156 mHz), 6-1/8" (UHF 459 mHz), and 3-1/4" (859 mHz).

After removing 1 conductor completely, I cut 2 pieces of the remaining 3-conductor to about 20" each. I slit between conductors about 1-1/2" on one end and then stripped each wire at 3/4". Taking the 2 outer wires, I made a double wrap of both around the center wire (which I left straight) and soldered the connection. I then tinned the center wire and trimmed it to about 1/4" in length. Next, I measured from the wrap/solder point to the above lengths for the elements and cut each conductor accordingly. This process was repeated so that I had 2 identical halves for the dipole.

One set of elements was soldered to the center pin of the BNC jack, and the other set to the ground pin. The connector sits perpendicular to the elements. Admittedly a little flimsy, but should sufice for now.

Using some tape, the antenna is currently hanging from the bookshelf above my desk so that the elements are vertical. The patch cable runs to my 246 for now (I can't seem to locate my SMA adapter for the 396 ). So far, is definitely a significant improvement over the standard duck antenna. It alos seems to be the same as, if not a little better than, the Valor PMM3B I'm using as a poor man's base antenna. Where I was getting some staticy reception before, it doesn't seem to be as bad with the dipole.

As soon as I can find my SMA adapter, I'm going to try it on the 396 and see if I notice changes on the signal strength meter. I'd also like to get it outside and a little higher to see what happens.

Having done this for a paltry $6.00 in parts and about 30 minutes of time, and seeing how good it is for the short time it's been connected, I'd say it was worth the effort. I wonder, though, why a simple dipole like this isn't more prominent as a commercial offering as a scanner antenna? Is a $100.00 (or more) discone antenna going to offer anything more than this design?
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Old 08-17-2005, 8:47 PM
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They do, the scantenna is a dipole, but its not as good as everyone has been brainwashed into believing it is. Discones are the same way, no real improvement over a simple dipole, but the discone is more broad banded. the dipole you built was made to fit your needs, so it will work well for what you want to hear, but not too well for other bands you arent intrested in. You can add to that antenna so you can hear more bands as you go along, so later if you want to listen to military air band you can ad the elements for that band or for low band or whatever else you want to do. if you ever get into MURS or GMRS or Amateur radio, you may be able to TX with that antenna as well
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Old 08-17-2005, 9:27 PM
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Quote:
Originally Posted by kf4lne
You can add to that antenna so you can hear more bands as you go along, so later if you want to listen to military air band you can ad the elements for that band or for low band or whatever else you want to do.
So, if a dipole is so versatile, why aren't there a boatload of them available commercially? It would seem to me that a true "all-band", low-cost receiving antenna could possibly be produced with this design.

Now, all this has me thinking why/how is a multi-element dipole different than several dedicated antennas? Based on what I've read in various posts here, a 3-element dipole works as well, if not better than, 3 dedicated antennas connected via a coupler.
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Old 08-17-2005, 9:56 PM
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With several antennas you have loss in the couplers, the antennas can interfere with each other and then coax loss. Not that there is anything wrong with the multi-antenna idea, basically the multiband dipole is really just multiple dipoles shareing a common connection. As for there being a lot of dipoles on the market, there are, they have names like scantenna and such. They are all over the place. the difference between your antenna and the commercially made antennas i that yours was custom made for your needs whereas the commercially made antennas are a comprimise for 25-1300MHz. The commercial stuff works great on some bands and not worth digging out of the trash on others where a multiband dipole cut for the frequencies you want to hear will work much better.
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Old 08-17-2005, 11:24 PM
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Would you mind posting some pics ther MarkEagleUSA?

Would be interesting to see yours and then mine come this weekend.
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Old 08-18-2005, 10:08 AM
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Quote:
Originally Posted by flyingwolf
Would you mind posting some pics ther MarkEagleUSA?
I'll try to take some tonight when I get home.
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Last edited by MarkEagleUSA; 08-18-2005 at 5:18 PM..
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Old 08-19-2005, 7:24 AM
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Ok, I know I've beaten this topic to death but I have another question. In my infinite wisdom (ha ha) I was measuring antennas on the ambulances at my one station last night and they were all 5.5" exactly. Is there a reason these are smaller than the 6.06" I mean, yes I understand that they're only .5" off but why exactly are the 5.5"? Not one was any longer, they were all 5.5" and rather thin antenna wire with a little ball on the end of the antenna. Any ideas? Should I shorten my antenna length on my roof to by 5.5"? or what?
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Old 08-19-2005, 9:01 AM
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Quote:
Originally Posted by SlipNutz15
were all 5.5" exactly... smaller than the 6.06"
Just a guess, but they're probably optimized for transmitting (SWR, etc) on the designated frequency. I don't think reception needs to be that precise.
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Old 08-19-2005, 10:51 AM
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Slip, those are the standard Motorola 1/4 wave antennas. Did you measure from the top of the chrome base of from the top of the rubber? I measured mine and it is 6 inches from the top of the chrome ring to the tip. They are versital little antennas and will take a lot of abuse too. They arent tunable either unless you cut the ball off the top. Mine works on 70cm with a SWR of 1.6:1 on 430.000 and 1.3:1 at 450.000, and at GMRS frequencies it gets back up near 1.5:1 but thats near the top of the 450-470 band at 467MHz. Very reliable antennas too, its nothing more than a peice of stiff wire with a loop bent in it in the base of the antenna to hold it in the rubber and the chrome ring just clamps the rubber between the ring and the mount. here are some pics of that antenna:
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Old 08-19-2005, 11:46 AM
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Motorola offers 3 standard 1/4 Wave antennas for the UHF band.

403-430 - HAE4002A - $17.00
450-470 - HAE4003A - $17.00
470-512 - HAE4004A - $17.00

MOL does not state the actual lengths, but I can vouch for the 403-430 and the 450-470 models. They are 6.5" for the 430-430 and 6" for the 450-470 from the top of the base to the top of the ball.

Calculating the antenna height, I'd imagine that the model you have is the 470-512.
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Old 08-19-2005, 12:31 PM
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Yeah, I measured from the rubber to the tip, I'm pretty sure that if I measure from the base to the tip it would be 6.06". The frequencies they trasnmit on are from 460.600 - 467.950
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Old 08-19-2005, 12:52 PM
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Those are still great little antennas. I know where to get them for $12.50 for the antenna AND the cable kit. Doesn't include the connector or the mounting bracket tho
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Old 08-19-2005, 12:55 PM
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Yeah, I don't have any issues with them at all. They work very well and I can't remember a time county couldn't hear me and I couldn't hear county with one.
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Old 08-19-2005, 1:05 PM
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They arent all that for simplex. I have a 1/2 over 1/4 wave antenna for UHF simplex, In comparison testing using the same mount on my car my gain antenna for UHF was better when working simplex, but there was no noticable difference when working through a repeater. I have had mine for about 7 years and the only bad thing that has happened to it is the ball came off the top and it got bent. That happened while loading stuff in the trunk, so to keep from getting stabbed by the whip i put a rubber cap back on top of it, it still works great tho, but with an antenna that simple it usually takes more effort to screw up than to get it right.
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Old 08-19-2005, 1:25 PM
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I'm confused by the "simplex" statement.

They Rx/Tx respectively on
460.600/460.600 F1
460.625/460.625 F2
465.600/465.600 F3
465.625/465.625 F4
460.550/460.550 F5
465.550/465.550 F6
463.175/468.175 MED8
462.950/467.950 MED9
462.950/462.950 MED9 T/A
462.975/467.975 MED10
463.850/463.850 Private

So what am I missing about simplex and repeaters and whatnot?
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Old 08-19-2005, 2:01 PM
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some of those frequencies you have listed are repeater pairs, the others are simplex. You TX on one freq and RX on another. You arent actually transmitting directly to the county, you are transmitting to the repeater site, usually on top of a mountain ot tall building or somewhere really high up overlooking teh area you service, the repeater transmits on the frequency you are listening on. the radio automatically switches when you transmit. Simplex operation is when you use only one frequency, TX and RX on teh same one. Simplex would be if you transmit on one of the F channels, you TX and RX both on the 460MHz channel, that is point to point so there is no repeater involved. So basicaly, Simplex is point to point, your ambo radio to teh county radio, repeater(duplex) is you TX to teh repeater site and it retransmits back to teh county, it gives you much better range. I am guessing you monitor one of the Med channels to talk to county


Easy examples of Simplex and Duplex:

Aircraft radio is typically simplex, Airplane transmits to the control tower and control tower to the airplane with nothing handling the signal in between. Most police, fire and med radios are duplex, where they have a repeater site on top of something tall like a building or a mountain where the hand helds, mobiles and base stations all transmit a signal to the repeater and the repeater retransmits it out on the other frequency in the ppair (ex: your med channels) the repeater site is the transmitter that uses the receive frequency in your radio and it listens on your transmit frequency. The repeater takes the recived signal and retransmits it out exactly as it came in with no delay. Thats why some of your channels are 5 MHz apart on the TX/RX settings because UHF uses a 5MHz offset(450-470 is 5MHz and 470-512 is 3Mhz) and what that means is your radio transmits its signal 5MHz off from where it is listening when using the repeater, but it TX and RX on teh same frequency in simplex mode
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