Performance degradation using stubby antenna?

[robertsdoug]

We are in a sprawling urban area in the desert southwest. Motorola P25 700mhz PII simulcast network. The network is extremely reliable and the portable radios get usually all five bars of signal strength everywhere in the city.

Is there any reason to continue using the large whip antennas? I have been testing some of the stubby antennas and personally I haven’t noticed any difference on 700 or 800 or the GPS receiver performance.

I’m not finding any statistics regarding the antenna gain differences on the two models, but suffice to say, the stubby antenna is a lot more practical than the whip.

 

[K4EET]

Hi @robertsdoug,

I’m afraid I don’t have any statistics to share but I have two thoughts to share.

1. Consider re-running coverage maps with both antennas at waist level if anybody uses a speaker-mic for in-building coverage at worst case. You might be surprised at the results.

2. If you are public safety especially and even everyone else, if someone is using a “stubby” and cannot get into the system when they need to, and if a flexible whip could have accessed the system from the same spot, there may be liability involved.

That’s just for starters. I’m sure you’ll get other comments; pro and con for the stubby. Weigh them carefully for your specific scenarios.

Dave

 

[GTR8000]

Stubby antennas are always going to introduce some degree of diminished signal, but it may not be enough to make any difference. If the system coverage is robust and terrain is favorable, then you will likely never notice the difference between the full length whip and the stubby. Maybe you'll see a loss of 1-2 dBm, which is negligible if the signal is strong enough already.

Besides, are some of the full length whips broken? Do guys fold them over and rubberband them to make them shorter? If the answer is yes, then an intact stubby is going to be a much better option than a broken/compromised full whip.

To put it in real world perspective, a 200 square mile county in the northeast with varied terrain operating on a 12 subsite ASTRO 25 700 MHz TDMA system had a number of law enforcement agencies ditch the original full length whip on their APX 6000s and changed them out with the 700/800/GPS stubby. This was years ago and there have been no complaints since.

 

[robertsdoug]

Stubby antennas are always going to introduce some degree of diminished signal, but it may not be enough to make any difference. If the system coverage is robust and terrain is favorable, then you will likely never notice the difference between the full length whip and the stubby. Maybe you'll see a loss of 1-2 dBm, which is negligible if the signal is strong enough already.

Besides, are some of the full length whips broken? Do guys fold them over and rubberband them to make them shorter? If the answer is yes, then an intact stubby is going to be a much better option than a broken/compromised full whip.

To put it in real world perspective, a 200 square mile county in the northeast with varied terrain operating on a 12 subsite ASTRO 25 700 MHz TDMA system had a number of law enforcement agencies ditch the original full length whip on their APX 6000s and changed them out with the 700/800/GPS stubby. This was years ago and there have been no complaints since.

None of the full length whips are broken, but it does get in the way on a belt, such as when driving or when using a vest

 

[hill]

Using full size antennas you can always wear the radios the way NSA Police do.

They wear their Harris radios in the front pocket of the vest and most use a speaker mic.

For obvious reasons I really can't be taken pictures from the cell phone within NSA.

 

[robertsdoug]

Using full size antennas you can always wear the radios the way NSA Police do.

They wear their Harris radios in the front pocket of the vest and most use a speaker mic.

For obvious reasons I really can't be taken pictures from the cell phone within NSA.

Yeah, but even on the vest having that big antenna stick up does get caught on things and restrict movement. But, some people do use it as a hanger to hang things like handcuffs. 😅

 

[mmckenna]

I run an 800MHz trunked system. I discourage use of the stubby antennas since there is some very slight impact on performance.

But people do it anyway. Very hard to notice the difference, and I don't stop them from using them. Coverage is good enough that it really doesn't impact things unless you get way out on the fringes, and by that point thing get to be touch and go anyway that a dB or two isn't going to make a huge difference.

I think if it's working, they are not complaining, and it makes use of the radio easier, then it's something to let ride.

 

[OrangePelican]

We had some guys switch out their v/u/700-800 antennas to the stubby ones because it “looked cool” or the original was uncomfortable. We have a ton of allied agency VHF and UHF channels in the radios and they lost a lot of performance on those.

The main public safety trunking system in my county is also an oddity with its 700-800 sites and handful of VHF sites. Our state system thats being built is also a mix of VHF and 700-800. I don’t know your situation but I’d check to be sure you don’t use anything that isn’t actually 700-800.

I always recommend keeping the longer antenna but I also don’t care how it looks and have never had a comfort issue with it on my belt or in a vest or harness.

 

[robertsdoug]

We had some guys switch out their v/u/700-800 antennas to the stubby ones because it “looked cool” or the original was uncomfortable. We have a ton of allied agency VHF and UHF channels in the radios and they lost a lot of performance on those.

The main public safety trunking system in my county is also an oddity with its 700-800 sites and handful of VHF sites. Our state system thats being built is also a mix of VHF and 700-800. I don’t know your situation but I’d check to be sure you don’t use anything that isn’t actually 700-800.

I always recommend keeping the longer antenna but I also don’t care how it looks and have never had a comfort issue with it on my belt or in a vest or harness.

Yeah, we are 100% 700 MHz and there are some 800 MHz interoperability channels programmed into the radios, but they are never used.

 

[RFI-EMI-GUY]

Did someone ask for "statistics"? I have data. This is a pretty old document. There is a significant difference going to a stubby antenna, about 4 dB worse. I have compared on older radios (STX). It is worse, creates fringe conditions where none existed with large coaxial dipole. I doubt the new antennas are any better, probably worse if you try to incorporate multi-band and/or GPS into same.

 

[robertsdoug]

This is a pretty old document. There is a significant difference going to a stubby antenna, about 4 dB worse. I have compared on older radios (STX). It is worse, creates fringe conditions where none existed with large coaxial dipole. I doubt the new antennas are any better, probably worse if you try to incorporate multi-band and/or GPS into same.

Very good information, thank you

 

[Golay]

I think during cold weather a stubby can be a better choice. Like McKenna says, out in the open a full length will outperform a stubby. However, I've seen where during the winter, the radio is under multiple layers and the antenna is being pressed against the body, thereby attenuating the signal. Because a stubby don't bend, I think there is still a bit of an airgap between the body and the antenna when under a coat.

 

[lamarrsy]

Just to remark that, the receive may continue to be useable to good -or even very good- with a stubby-duck on a radio used on a good coverage system, but it’s when the same user tries to *transmit* with that radio that the real difference may start to appear.

 

[RFI-EMI-GUY]

I think during cold weather a stubby can be a better choice. Like McKenna says, out in the open a full length will outperform a stubby. However, I've seen where during the winter, the radio is under multiple layers and the antenna is being pressed against the body, thereby attenuating the signal. Because a stubby don't bend, I think there is still a bit of an airgap between the body and the antenna when under a coat.

Well maybe if the foliage has fallen back. So is it still fashionable to use the big stick after labor day?

 

[MississippiPI]

I have APX 900 with the longer antenna, I was told by the radio shop the short antenna doesn’t work as well. So, I stayed with longer one.


Be safe

 

[GTR8000]

Instead of relying on a 30+ year old study and anecdotal evidence, I would do some extensive testing on your own before signing off on anything. Pay particular attention to any difference in in-building coverage, as well as inbound coverage. I believe someone already noted that just because the subscriber receives the control channel well doesn't always mean that the subscriber is getting into the system equally well.

 

[KevinC]

From my experience, system design, testing and acceptance is usually not with a "stubby" antenna, so use at your own risk.

Semi related...an issue I worked on was caused by officers replacing the supplied antenna with stubby ones. Officers were having major issues and the police union even went as far as doing commercials with little kids saying "Company X is trying to kill my daddy". Once it was discovered the antennas were the issue no apology was issued by the union and "Company X" put out a press release saying something "We worked together with City Y to resolve the issue", completely disregarding the fact it was caused by them.

 

[MTS2000des]

Our Astro 25 system was spec'ed to perform with 5/8 wave antennas, body worn with approved belt clip/holster and standard RSM, and provide the rated performance as specified in the RFP response. The Voyager test kit was setup to emulate this. A stubby antenna may work, but when one's life depends on it, does one want to accept the performance loss?

What does the system design call for to get the rated coverage? That is what one should use.

 

[ElroyJetson]

As a general rule of thumb, portable radio antennas are 3 dB apart in performance.

Stubby is lowest, short whip is 3 dB better, 5/8 wave long whip is 3 dB better yet.

I've found via the radio's internal RSSI meter and a few antennas under test that this has been a pretty accurate general rule of thumb.

Nothing is more annoying than users who insist on stubby antennas and then complain about reduced radio range and performance.

 

[mmckenna]

Nothing is more annoying than users who insist on stubby antennas and then complain about reduced radio range and performance.

This type of user is exactly the reason I discourage it.

If they want to do it, fine, I won't stop them, but they don't get to come *****ing to me later.