Antenna performance

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W1RRL
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Antenna performance

Post by W1RRL » Tue Oct 31, 2017 6:42 pm

Generally what kind of improvement does one see when comparing a low profile antenna, to a 1/4 wave upwards to a high gain antenna?


http://www.theantennafarm.com/catalog/a ... ennas-211/

http://www.theantennafarm.com/catalog/a ... ennas-207/

http://www.theantennafarm.com/catalog/a ... ennas-208/
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ohiohonda
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Re: Antenna performance

Post by ohiohonda » Tue Oct 31, 2017 10:23 pm

It depends on what application the radio is being used for IMO. The lower profile VHF antenna in your link usually have a small transmit bandwidth window (normally around one MHz). So you can only use that type of antenna with frequencies that are close together. Between the 1/4 wave and 5/8 wave antennas it would depend again on what type of system (if any), the terrain, and environment ( urban or rural ). A lot of times a 1/4 antenna will work better than a gain antenna.
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Notarola
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Re: Antenna performance

Post by Notarola » Wed Nov 01, 2017 3:01 pm

I have found that the low profile antennas dont give the same general performance that a 1/4 does. They work fine in a city environment where the repeaters are close together but out in the country the antennas tend to have only 2/3 to 1/2 the coverage and signal strength compared to a 1/4 whip.

My testing wa done with a 30 watt unit and to a fixed set of repeaters 15-20 and 25 miles out while driving the same route.
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Project25
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Re: Antenna performance

Post by Project25 » Thu Nov 02, 2017 1:00 am

I’ve only really had one run in with VHF lo-pro’s. Couldn’t tell the difference between it on the truck (in a sally port) and it off (aka, an open). Still affiliated without issue.

Now as far as 1/4 wave versus 5/8 on VHF…you’ll never notice a practical difference on a VHF system. It’s only a 3 dB improvement in terms of link budget. Now if all parties are using them on simplex, that’s a 6 dB improvement on the link budget which is (theoretically) double the coverage potential.

Once you get to UHF, I’ve really been fond of the PCTEL wideband knob. No noticeable differences in performance between it and a 1/4 wave (minus the as advertised bandwidth).

Now I have a theory [tinfoilhat] about knob performance on UHF and higher. Typically a UHF and higher 1/4 wave antenna is low enough that it is in the turbulent flow region (aero/fluid dynamics) when the vehicle is under motion. This allows the antenna to independently oscillate from various vibrations and the stiffness of the antenna which can shift the modulated signals off frequency a bit (not a lot) which can put you out of spec of some modulation schemes while a longer whip rides in the laminar flow region of the slip stream (has measurable drag to deaden oscillation is what I’m trying to say). Just a theory though. [/tinfoilhat]

In my professional opinion, every system should be built and tested for 1/4 wave coverage of a roof mount installation (on a sedan). If it is found to not provide adequate coverage under those testing specifications, then the system should be audited and redesigned as necessary (which may not be possible in all situations). If a roof mount can not be used, the a gain antenna shall be fender mounted or trunk mounted.

Now I’m somewhat biased towards 1/4 wave VHF antennas primarily due to the required bandwidth of the P25 system I maintain (band plan channels are 139 MHz, 150 MHz and 161 MHz).


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Notarola
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Re: Antenna performance

Post by Notarola » Thu Nov 02, 2017 4:39 pm

Generally good advice Progect25.
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Re: Antenna performance

Post by RadioRookie » Thu Nov 02, 2017 9:49 pm

I use to buy into the whole "gain antennas are better" principle, just because they're base loaded and taller. Over the years I've come to realize (in my area) a 1/4 waves performance is hard to beat. And so is the price.
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Project25
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Re: Antenna performance

Post by Project25 » Fri Nov 03, 2017 2:21 am

RadioRookie wrote:I use to buy into the whole "gain antennas are better" principle, just because they're base loaded and taller. Over the years I've come to realize (in my area) a 1/4 waves performance is hard to beat. And so is the price.
One of the assumptions I sometimes make, the top 1/4 wave of a gain antenna is a measureable height (relative to the ground) for receive capability but not transmit.
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Re: Antenna performance

Post by Notarola » Fri Nov 03, 2017 3:11 pm

One of the biggest advantages of the 1/4 is the fact the actual whip does not bounce around like a 5/8. this eliminates signal sway introduced by the whip movement. in simulcast systems this has been reported as an issue especially in cut over areas.
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Re: Antenna performance

Post by Falcon » Tue Nov 07, 2017 3:08 am

I pretty much always run a 1/4 on VHF. I can see a enhancement of performance on the fringe but that's about it. Unless it's completely simplex.

I'm also with Project25. UHF and above I'm a huge fan of the knob style antenna. I've done testing with a simulcast 800 system with an open coil style antenna versus my PCTEL knob antenna. I noticed almost the same performance of the two antennas except out on the very fringe where the coil style still maintained affiliation. But, with that said, the radio was still affiliated but I didn't have the ability to get back into the site.
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Re: Antenna performance

Post by Notarola » Tue Nov 07, 2017 5:27 pm

I think you were seeing the slight loss of performance between the knob and the coiled antennas. We all know no 2 antennas will work the same. The trick is to make sure that the target system has good enough mobiles and sites to provide a minimum of 25% or more coverage than is actually needed.
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Re: Antenna performance

Post by Falcon » Thu Nov 09, 2017 5:04 pm

Notarola wrote:I think you were seeing the slight loss of performance between the knob and the coiled antennas. We all know no 2 antennas will work the same. The trick is to make sure that the target system has good enough mobiles and sites to provide a minimum of 25% or more coverage than is actually needed.
Agreed on both accounts.
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Re: Antenna performance

Post by motorola_otaku » Fri Nov 10, 2017 12:56 am

The only serious testing I've done is on 700/800 with low-profile M-branded PCTEL antennas versus new M-branded pigtail (5/8 over 1/2 wave iirc) antennas, both of which ship with APX mobiles as ordered. Both advertise the exact same gain specs, and real-world testing bore that out, but the low-pro puck had a better >2.0 SWR operating bandwith.

Now if you want serious bandwidth, this beast operates as advertised. I swept one with an Anritsu knockoff and the SWR profile looked like an elevation map of California's Central Valley.
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Re: Antenna performance

Post by Notarola » Fri Nov 10, 2017 4:14 pm

Little known fact. The wider the radiator the wider the bandwidth. There are obvious limitations but without going through the math this is true. The loading coil and the general conical shape of the antenna gives the wider bandwidth while maintaining a good swr. The same effect is seen on discone types of antennas.
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Re: Antenna performance

Post by Falcon » Mon Nov 13, 2017 2:56 am

Notarola wrote:Little known fact. The wider the radiator the wider the bandwidth. There are obvious limitations but without going through the math this is true. The loading coil and the general conical shape of the antenna gives the wider bandwidth while maintaining a good swr. The same effect is seen on discone types of antennas.
That's very true. I've always wanted to do a ridiculous HF dipole with some heavy gauge wire for this reason just for the fun of it.
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Re: Antenna performance

Post by Notarola » Mon Nov 13, 2017 5:38 pm

Old military trick use copper plumbing pipe. lots of scrap pipe around. you could use steel pipe too but its not as flexable and a lot heavier.
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