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Author Topic: Only 13" Height Available for Antenna  (Read 1322 times)
W8JX
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« Reply #15 on: May 04, 2016, 09:59:42 AM »


And while a 3/4 wave on 440 isn't ideal, just try it.  Quarter wave whips are cheap.  If it doesn't work out to your satisfaction you still have an NMO mount on the roof you can use for something else.


A 3/4 wave on 440 is pretty much a negative gain antenna at radiation angles you will see in a mobile. There is a very noticeable difference between it and a 1/4 wave.

Gain is irrelevant when working repeaters, assuming that is what about 99% of mobile operators do especially considering the ones who are willing to make insane compromise for looks and or ability to go in and out of garage without having to move anything. Again Gain, what a marketing term these days, has almost no effect on working through a repeater. I can work a repeater 40 miles away on my 817nd QRP radio at 0.5w if I have line of sight and get full quieting. Wheres the gain in that?

Gain is irrelevant? What are you smoking? There is a big difference with repeater performance between a 1/4 wave and 3/4 wave on 440. The further you are from repeater the worse the 3/4 wave is. I was surprised at difference real world.
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KT4NR
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« Reply #16 on: May 04, 2016, 10:21:50 AM »

Actually, while I would not have phrased it that way I agree with the spirit slightly.

Gain does matter, however, the antenna pattern with the way some antennas achieve higher gain fight mobile operators needs.

I personally have 2 antennas at home. An NMO270 (1/2 wave 3.8 dB gain on VHF and Collinear 5.2 dB gain on UHF) and a Diamond Super Gainer (SG7900 7/8 wave double C-Load radialless 5.0 db gain on VHF and 3x5/8 wave C-load radialless 7.6 db gain on UHF). I have a lot of holes in repeater coverage in my urban environment using the Super Gainer that do not exist with the NMO270. Why? Because of the antenna pattern. Higher gain antennas have a lower takeoff angle. Additionally, antennas that are not 1/4 or 1/2 wave often have weird secondary lobes.

When I cannot hit a local repeater using the Super Gainer I often find no issues hitting a machine 100 miles away. Swap the Super Gainer out and install the NMO270 and the reverse is true. I don't lose the repeater 100 miles away, but I do not hit it reliably. I might also offer that you can make this work to your advantage. If you have a repeater with remotes you might be actually getting into a different remote than you expect because you are stronger there than the main or closer site as a result of the antenna pattern.

So does gain matter? Absolutely. The repeater you want is not always going to be close or be able to hear you. Is gain everything? NO! Experimenting with antennas to find the one that provides the coverage you desire for your environment is. Tinker with antennas and find what works for your operations and you will be happy. More over, the guy/gal in Arizona may not have the same needs as the guy/gal in New York City because repeater distance, density, bands, etc.

Hope this helps.

Good luck!
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K0BG
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« Reply #17 on: May 04, 2016, 01:55:51 PM »

If we're talking about repeater use, in an urban to suburban area, gain is actually a negative quality.

I didn't write this piece (http://www.k0bg.com/images/pdf/mobile_vhf_ant.pdf), albeit it is stored on my web site with the author's permission. There is a similar article on Tom's, W8JI, site.

The whole gist is based around HAAT between the repeater sites and the mobile ones. It isn't magic, or junk science.
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KZ1X
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« Reply #18 on: May 04, 2016, 01:58:41 PM »

You forgot one ...

The Austin Antenna 500C soft-top will work quite well for your needs.

http://www.rfwiz.com/AustinAntenna/AustinAntenna_InfoDat.htm

scroll down to find it ... also sold by Ham Radio Outlet
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W8JX
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« Reply #19 on: May 04, 2016, 02:47:47 PM »

If we're talking about repeater use, in an urban to suburban area, gain is actually a negative quality.

I didn't write this piece (http://www.k0bg.com/images/pdf/mobile_vhf_ant.pdf), albeit it is stored on my web site with the author's permission. There is a similar article on Tom's, W8JI, site.

The whole gist is based around HAAT between the repeater sites and the mobile ones. It isn't magic, or junk science.

If you think that antennas for mobile operations are not important for reliable coverage you are spreading bad info. A basic 1/4 wave on 2m or 440 can provide fairly good repeater coverage but a 3/4 wave on 440 because of its high radiation angle is little more than a radiating dummy load on 440. (unless you are in a valley and repeater is on a mountain top near by and is in its pattern)
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You can embrace new computing technology and change with it or cling to past and fall further behind everyday....
K0BG
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« Reply #20 on: May 04, 2016, 04:08:11 PM »

John, W8JX, I do not know your technical background. I do not know when you got an Extra license, or how technical the test was. I do not know what vehicle you drive. I do not know for certain what HF or VHF antenna you use. To the best of my knowledge, I've not met you, although I have attended the Dayton Hamvention 9 years running. But one thing I do know, that anyone who doesn't agree with you is incorrect! Any one, including you, who has such a closed mind, is in effect on the losing end of the stick! Rather than criticized everyone whose view you do not share, do yourself a favor. Do a bit of research first! Then if you truly can offer a better solution, then give it, and save the rest of us the malicious palaver!
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KT4NR
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« Reply #21 on: May 04, 2016, 04:59:10 PM »

If we're talking about repeater use, in an urban to suburban area, gain is actually a negative quality.

I didn't write this piece (http://www.k0bg.com/images/pdf/mobile_vhf_ant.pdf), albeit it is stored on my web site with the author's permission. There is a similar article on Tom's, W8JI, site.

The whole gist is based around HAAT between the repeater sites and the mobile ones. It isn't magic, or junk science.


Alan I don't disagree at all and it reiterates my argument. The manner in which the antenna lobes are formed does impact coverage because the shape of those lobes are the measured gain. Hustler spirit antennas are a good example. These repeater antennas are designed with flat or depressed lobes. This does not allow for high gain and DX but does enhance the local coverage footprint. If I were to use an old Comet triband antenna I recently sold it would be less effective. It had significant gain, particularly on 70cm. The gain is a result of how the radiation patterns are manifest. Where there are lobes there are also nulls. That antenna does well on 2 and 220 but lousy on 70cm on simplex.

For a quarter wave the null is at 0 degrees and 180 degrees. For an antenna with gain and designed for a low take off angel the lobes/nulls are varied. They impact how well antennas work. Hence my issue being unable to work a repeater within 20 miles but no issue working one 100 miles away even on a relatively elevated location.

Conversely the repeater 100 miles away, when driving near it (like 15-20 miles) has dead spots that HAAT would offer ought not exist.

this is the field findings from living I this area.
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W8JX
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« Reply #22 on: May 04, 2016, 06:08:33 PM »

John, W8JX, I do not know your technical background. I do not know when you got an Extra license, or how technical the test was. I do not know what vehicle you drive. I do not know for certain what HF or VHF antenna you use. To the best of my knowledge, I've not met you, although I have attended the Dayton Hamvention 9 years running. But one thing I do know, that anyone who doesn't agree with you is incorrect! Any one, including you, who has such a closed mind, is in effect on the losing end of the stick! Rather than criticized everyone whose view you do not share, do yourself a favor. Do a bit of research first! Then if you truly can offer a better solution, then give it, and save the rest of us the malicious palaver!

Alan, there is a lot you are wrong on. You know some things but are wrong on a lot of others. I comment on things I have done and tested real world not theory or your guesstimates. BTW I worked in Aircraft Mod/Flight test for many years and have a engineering background. I worked with a lot of cutting edge electronics "stuff" (nav, com, radar, threat detection etc) that had to be tested before it could be fielded. I was involved with modifying the F4 aircraft in 1980 that were used as chase planes in the cruise missile fly off to determine how would get contract. (I could tell you stories about those planes) I even worked on Navstar project in early 80's (they started it in late 70"s) Navstar laid ground work for GPS and I knew how and why it worked long before there were hand helds or car nav units or it was a house hold name. (I have personally been using hand held GPS units off road since early 90's) There is many many more projects I worked on over they years that I could tell a lot of stories about that are all true but you would never believe. When I first tried a 3/4 wave on 440 I had very high hopes because in "theory" it should not be too bad but in practice I was amazed how bad it really was. Your theories on power systems in cars and extra batteries are another example of how off base you are sometimes. Alan knows it all on that subject too and Detroit is stupid. Get real. Your comment that states that antenna gain/radiation pattern is not important in repeater work shows how little you really know on that subject and you are not even my league in many areas. If you want to stay closed minded with your way or highway have at it. I merely add a point of view based on ACTUAL experience not theory. BTW Alan been driving electric car for 2 years how long have you and you a expert on them too?  
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You can embrace new computing technology and change with it or cling to past and fall further behind everyday....
AH7I
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« Reply #23 on: May 04, 2016, 07:45:51 PM »

Larson NMO. If you don't like it, you've got plenty of other NMO mount antenna to choose from. screw one off. Screw the new one on.
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ND8M
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« Reply #24 on: Yesterday at 05:13:36 AM »

I have a Larsen 5/8 wave 2m on my truck, with about the same clearance to my garage overhead.  Larsen makes a spring that installs directly on to the base which allows the antenna to fold flat against the roof with no issues. The antenna makes a ton of noise dragging across everything but it works just fine.

Here's a similar spring to what I'm using: http://www.theantennafarm.com/catalog/larsen-spring-3877.html

I know they make them in black as well, as that's what I'm using.
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N0TZU
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Posts: 16




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« Reply #25 on: Yesterday at 07:18:54 AM »

I have a Larsen 5/8 wave 2m on my truck, with about the same clearance to my garage overhead.  Larsen makes a spring that installs directly on to the base which allows the antenna to fold flat against the roof with no issues. The antenna makes a ton of noise dragging across everything but it works just fine.

Here's a similar spring to what I'm using: http://www.theantennafarm.com/catalog/larsen-spring-3877.html

I know they make them in black as well, as that's what I'm using.
Thanks. I didn't realize that the springs were available separately and could be added. Now I see them in the catalog.

Is the spring stiff enough to keep the antenna from waving around excessively and possibly making noise at highway speeds (around here the limits are up to 80MPH)?
« Last Edit: Yesterday at 07:21:25 AM by N0TZU » Logged
ND8M
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« Reply #26 on: Yesterday at 08:01:22 AM »

The spring is stiff enough to not flex at highway speeds, at least with my 5/8 whip.  While my antenna is longer than the 2/70, the 2/70 does have the coil in the middle of the whip so it probably has more wind resistance, so YMMV.  My antenna whistles pretty good at highway speed, and adding the spring didn't change that at all.  I did shorten the whip by the length of the spring to maintain swr.  Not sure if it was necessary or not, but I did it since the instructions I got with the spring called for it. 

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KF7CG
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« Reply #27 on: Yesterday at 11:17:21 AM »

I can't provide a source to purchase, but for many years I used an Untenna brand ddrr type antenna for both 2 meters and 70 centimeters. It is a very strange looking antenna but does work well. The antenna use to be available from Com-Rad Devices. the last time I saw it available was from a vendor of antennas for emergency vehicles. Though the antenna is not designed to dual band, I have never had any problems with that.

The antenna is only about 6 inches tall, but gave me equivalent performance to a Larson 5/8 wave on 2 meters. These were side by side tests so I trust my results. This antenna looks like a flat coil with a capacitor plate at the end. They are often placed under radomes for use on emergency vehicles. Don't look like they should work but they do.

KF7CG
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K0BG
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« Reply #28 on: Yesterday at 12:15:27 PM »

I'm sorry John, but if anyone is closed minded it is you. Carry on.
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