I was thinking about running 2 102"s on a roof rack on my truck.
i would mount them on the rail towards the back of the cab and have a space about 4 inches between them 2 on the center.
i was thinking of running 2 radios thats why i would need 2 whips, would the antennas cause interference for each other being that close even if their on different channels?
thanks
2 102"s
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coondog
your SWR no doubt will go through the roof being that close to each other.i can"t even imagine being able to get them tuned in.i believe they say the rule is like 8ft apart.4 inches apart and your going to have problems when they smack each other to.
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'Doc
otter,
That's not the 'best' spacing by any means, for several reasons. Antennas are affected by the 'things' around them. How much they are affected depends on how close the 'things' are, and if another antenna, how 'close' in frequency usage they are. The closer in distance and frequency, the more each is affected. That says nothing about if they should happen to touch, just in how they respond to a signal. With two antennas only something like 4" apart, it's very nearly like hooking one radio feeding directly into another radio. The radio doing the transmitting may/may not be affected at all. But the one doing the receiving is going to get it's pants blistered, it's legs switched, and will probably never be the same again. The 'closeness' of the two antennas for something like that happening isn't limited to inches, or yards for that matter. I have no idea what the minimum 'safe' distance is, but it's not going to be very 'small' with antennas on the same band. That also applies to radios/antennas on different bands to some undetermined point, just not as bad as if on the same band, sort of.
Having said that, it is possible to do, receiver and transmitter on very close frequencies. It's done quite often on VHF/UHF bands. BUT! It ain't simple, and the required equipment -IS- expensive. That required equipment is commonly called a 'duplexer'. For HF, those duplexers are going to be huge! I'm not sure my pickup would even pull one, much less carry one. Of several companies that make those duplexers, I'm sure at least one of them will be willing to custom build one for you. That'll be cash in advance, and no guaranty, by the way
.
Then again, I guess you could hook up some kind of relay system to turn off the non-transmitting radio when you push the other's mic button. You wouldn't be missing anything except hearing it squall anyway.
Not impossible, but I really don't think you wanna do that.
- 'Doc
That's not the 'best' spacing by any means, for several reasons. Antennas are affected by the 'things' around them. How much they are affected depends on how close the 'things' are, and if another antenna, how 'close' in frequency usage they are. The closer in distance and frequency, the more each is affected. That says nothing about if they should happen to touch, just in how they respond to a signal. With two antennas only something like 4" apart, it's very nearly like hooking one radio feeding directly into another radio. The radio doing the transmitting may/may not be affected at all. But the one doing the receiving is going to get it's pants blistered, it's legs switched, and will probably never be the same again. The 'closeness' of the two antennas for something like that happening isn't limited to inches, or yards for that matter. I have no idea what the minimum 'safe' distance is, but it's not going to be very 'small' with antennas on the same band. That also applies to radios/antennas on different bands to some undetermined point, just not as bad as if on the same band, sort of.
Having said that, it is possible to do, receiver and transmitter on very close frequencies. It's done quite often on VHF/UHF bands. BUT! It ain't simple, and the required equipment -IS- expensive. That required equipment is commonly called a 'duplexer'. For HF, those duplexers are going to be huge! I'm not sure my pickup would even pull one, much less carry one. Of several companies that make those duplexers, I'm sure at least one of them will be willing to custom build one for you. That'll be cash in advance, and no guaranty, by the way
.Then again, I guess you could hook up some kind of relay system to turn off the non-transmitting radio when you push the other's mic button. You wouldn't be missing anything except hearing it squall anyway.
Not impossible, but I really don't think you wanna do that.
- 'Doc
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otter
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Foxhunter
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Good answers all. The 1/4 wavelength (9-FT) apart recommendation for co-phased aka dual antennas is mostly true.
I once wrote early-on asking about co-phasing 102 whips also. I did some reading online and some thinking and if you're leaning towards having 2x 102 whips, possibly consider this. To get the requisite spacing and to maximize ground plane you would need to mount each 102 whip on the front and rear bumers (or hitches if you have them). It would look pretty wild and think would work well and be properly spaced as well.
It may be possible to switch over to even a 3rd antenna mounted up on your rack (to be used in conjuction with a coax switch to switch over to) as an alternate third single antenna. Antennas tend to interact with their surroundings (including other antennas) in either a positive or negative way.
At any rate using two 102 whips it would seem could be mounted front & rear on the bumpers or hitches---or---possibly on both side mirrors utilizing "extended side mirror brackets" like people put on to pull horse trailers or campers. Either of these two mounting schemes would seem to be the only possible method of using two 102 whips together and adequately spaced apart. Just some possible suggestions and thoughts.
I once wrote early-on asking about co-phasing 102 whips also. I did some reading online and some thinking and if you're leaning towards having 2x 102 whips, possibly consider this. To get the requisite spacing and to maximize ground plane you would need to mount each 102 whip on the front and rear bumers (or hitches if you have them). It would look pretty wild and think would work well and be properly spaced as well.
It may be possible to switch over to even a 3rd antenna mounted up on your rack (to be used in conjuction with a coax switch to switch over to) as an alternate third single antenna. Antennas tend to interact with their surroundings (including other antennas) in either a positive or negative way.
At any rate using two 102 whips it would seem could be mounted front & rear on the bumpers or hitches---or---possibly on both side mirrors utilizing "extended side mirror brackets" like people put on to pull horse trailers or campers. Either of these two mounting schemes would seem to be the only possible method of using two 102 whips together and adequately spaced apart. Just some possible suggestions and thoughts.
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TheTeZ
i agree. 1 antenna a switch and 2 radios. you will only listen to one, but its an easy switch back and forth.
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otter
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ya that would be pretty gnarly seeing 3 102"s on my truck but i think that might be some over kill haha. would i gain receive and transmit if i was to run 3??
ya i might just run a single 102", a switch box and 2 radios..
3 would be soo insane haha
ya i might just run a single 102", a switch box and 2 radios..
3 would be soo insane haha
Rabbit 227
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'Doc
Using more than one antenna makes it possible to make the whole thing directional, and thereby hearing better in a couple of directions. It's not exactly 'simple' to do, but certainly not impossible. It's also not very convenient, but that sort of depends on how much trouble you are willing to put up with. If you hear better in a couple of directions, it also means that you will hear worse in a couple of directions. Just depends on what you are after, right?
If you really wanna 'bad-axe' looking system, put a fold-over 40 foot tower in the back of your truck! Fold/unfold as necessary? ... Naaa, **Censored**.
- 'Doc
If you really wanna 'bad-axe' looking system, put a fold-over 40 foot tower in the back of your truck! Fold/unfold as necessary? ... Naaa, **Censored**.
- 'Doc
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otter
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it looks like i'll be sticking to 1 radio in my mobile for awhile now.
i can only get my receive to work on the other radio that i was going to use.
i'm thinking of using it as it is just to receive since it automatically scans through all the channels..
i can only get my receive to work on the other radio that i was going to use.
i'm thinking of using it as it is just to receive since it automatically scans through all the channels..
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Foxhunter
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I was kind of mentioning the possibility of a third antenna as a smaller stick type or something to not interfere with the others too much but really it is a bad idea in general to have antennas in too close proximity to eachother. The spacing is often important and/or critical. Jeez I can't tell you how many big trucks I see with four stick antennas (two on each mirror) only inches apart from eachother! I've even seen them with a fifth and sixth Wislon Cellular Phone antenna right beside all the others totalling six antennas, three on each side. Usually in the end a bad practice.
Still, the two 102-whips on each mirror or front-to-back on both bumpers with adequate spacing would be insane looking and might just perform very well. Hey in the end I still hope you make out with that install and are happy with the results you get Otter. One thing I've found about this field/hobby is that guys are always experimenting around and changing their setups for either improvement or just "to see what happens" and possibly have better results.
Still, the two 102-whips on each mirror or front-to-back on both bumpers with adequate spacing would be insane looking and might just perform very well. Hey in the end I still hope you make out with that install and are happy with the results you get Otter. One thing I've found about this field/hobby is that guys are always experimenting around and changing their setups for either improvement or just "to see what happens" and possibly have better results.
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Alabama_Cajun
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otter,
On my old truck I had two complete setups; each running thru a 102". The big difference between what I had and what you want to do is that I had each Whip mounted in the front Stake holes...one on each side of the truck.
I had a Cobra 29 running to one of the 102's the other was a Pearce-Simson running to the other.
It worked OK on my truck, the only issue I had was the desire to have both on at the same time... as long as I listened on both and NOT transmit, I was OK. I would have one on Ch19, the other on Ch15 listening to traffic. But when I wanted to transmit, I turned one off. Otherwise, I got some major feedback...kinda glad I didn't smoke something the first time I did that
Doc's right on the money with regarding the proximity. Antennas are affected by it's surroundings; hence trying to put them up as high as possible, above the rest of the metal vehicle, using as much of the vehicle as possible as the ground plane.
If you're going to run two setups, I'd spread those 102's a lot further apart... bringing the SWRs down.
~AC
On my old truck I had two complete setups; each running thru a 102". The big difference between what I had and what you want to do is that I had each Whip mounted in the front Stake holes...one on each side of the truck.
I had a Cobra 29 running to one of the 102's the other was a Pearce-Simson running to the other.
It worked OK on my truck, the only issue I had was the desire to have both on at the same time... as long as I listened on both and NOT transmit, I was OK. I would have one on Ch19, the other on Ch15 listening to traffic. But when I wanted to transmit, I turned one off. Otherwise, I got some major feedback...kinda glad I didn't smoke something the first time I did that
Doc's right on the money with regarding the proximity. Antennas are affected by it's surroundings; hence trying to put them up as high as possible, above the rest of the metal vehicle, using as much of the vehicle as possible as the ground plane.
If you're going to run two setups, I'd spread those 102's a lot further apart... bringing the SWRs down.
~AC
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otter
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yah i'm just gonna run 1 102" on the roof rack i'm going to put on.
then i might install a switch box so i can run the 2nd radio just for receive since the transmit on it is broken...
thanks for the feed back guys.
saved me tons of headaches and possibly $$...
Foxhunter: i'll let you know how my install goes on that other set up
then i might install a switch box so i can run the 2nd radio just for receive since the transmit on it is broken...
thanks for the feed back guys.
saved me tons of headaches and possibly $$...
Foxhunter: i'll let you know how my install goes on that other set up
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Roper
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I have several friends who have dual 102's on their trucks but they only have one of them working and the other one is mainly for looks 
2011 Chevrolet Silverado Ext Cab Dually
Cobra 29 LTD Classic 102' SS Whip
Cobra 29 LTD Classic 102' SS Whip
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BearTracker
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If you want to use 2 102s try this:
Fasten both together at the base and rig them as a flat side on some sort of vertical piece that you can turn. This should give you a portable 1/2 wave flat side beam. Great for skip and will handle a lot of wattage. Just make sure you get high enough off your vehicle so you can set your SWRs.
Fasten both together at the base and rig them as a flat side on some sort of vertical piece that you can turn. This should give you a portable 1/2 wave flat side beam. Great for skip and will handle a lot of wattage. Just make sure you get high enough off your vehicle so you can set your SWRs.
