Rubber Antenna Evaluations - SHOOT OUT

[Tim]

Hi Folks,

Well, the EMS ladies are tired of having their XTS2500 antennas stick them in the armpit... or wherever, and have requested that I provide them some shorter antennas (like those on the IC-F50V radios that the XTS replaced).

I've gotten several different types that screw into the SMA connector on the radio - the 'original' XTS 'dipole' antenna, a straight long one from an Astro Saber (about the same length), one from a Visar, and one from an e-bay vendor.

So, I set up a signal generator on one side of the room, and a spectrum analyzer on the other and did some comparisons... I put a 1' square aluminum plate under the DUT (device under test), and just a 'plain' BNC type rubber antenna on the spectrum analyzer - with the theory that only the 'transmitting' antenna would change in the equation.

I'm not seeing what I think I 'should'.

How'z about some recommendations on how to do the testing..... I know, bigger is always better, but I need to get some 'real' numbers before I cave in to their demands.

Thanks,

Tim

[Wowbagger]

How big is this room? Do you know if the room is reflecting the RF or absorbing it? IIRC, "near field" is defined as roughly 10 wavelengths or less, so if you are dealing with 460MHz business band you need over 6m of room to work with. What you are doing really needs a proper anechoic RF chamber do to right.

I'd suggest moving outside - set up the siggen at one point in a big parking lot, the spec-an at another, and shoot for as much distance as you can get between the two.

[Will]

Oh, a mini antenna range. BTDT. A good test tool.
Setting up an antenna range, and that is basically what he is doing, there is some sort of calibration needed so you know that the measurements are of use.

Takes me back to JPL in Pasadena, running the antenna range on the mesa. And at ITT Gilfillen.

I would use a 1/4 wave antenna on the "receiver", rubber duck antennas have some of the weirdest patterns, just what you do not need to skew your measurements.

[Tim]

Thanks guys,

I'll take it outside tomorrow. My garage is an 'echo chamber'!

Tim

[Tom in D.C.]

Tim,

I suggest that you save yourself a lot of time, trouble, and aggravation by just going to the VHF
Visar antenna. I have both used and heard tons of positive comments about this antenna over the
past couple of years. I used to get mine from Precision Electronics who I found on eBay.

Regards,

[Tim]

Hi Tom & all...

You know, Inquiring minds want to know.

Here's how it went:

Transmit signal source: IFR1100S Antenna: 1/4 wave vertical on top of truck.

Receiver: HP8924C Spectrum Analyzer with smoothing (x5) on.

Antenna site: 1' square aluminum plate with hole in center that has BNC/SMA.

TX / RX Separation - 120'

Antenna data:

Astro Saber 7.2" length - -75.1dBm
Visar 5.2" length -77.0dBm (-1.9 dB)
XTS 'dipole' 8.4" length -77.3dBm (-2.2 db)
Chinese shorty 5.4" -77.4dBm (-2.3dB)

So, based upon this data (with a near-perfect ground plane), the Saber is 1st & Visar is 2nd. (good call Tom)!

What really surprised me is the lack of performance of the longer XTS style antenna. I checked several of them. I know it's a wide-band antenna, so maybe you sacrifice in gain, but make up in bandwidth? ;-( (hey, it's a vertical, equally poor in all directions)!

Having said that, when going from the XTS antenna to the Visar you can really tell the difference in a weak-signal condition. The data doesn't support this, so there's got to be other factors affecting the antennas.

Played enough... it's 103 outside.

Thanks,

Tim

[Tom in D.C.]

Tim,

Those test results are interesting.

So, as we all are pretty much aware, all VHF rubber antennas stink, and the question comes down to
what one VHF antenna stinks the least (and doesn't stick the user in the armpit), right? The only really
decent performing rubber antennas are the UHF units where you can actually put a true vertical quarter-wave radiator on
top of the HT.

Regards,

[FireCpt809]

I use the Visar VHF on my XTS and have found it to be as good or better in some regards to the standard SMA whip or Wideband.

[Wowbagger]

I'd check the effect of a body near the antenna - it could be the Visar is better at handling the detuning effect of a big bag of dirty water next to it.

[resqguy911]

Good job. Next time you get bored, toss an APX antenna into the mix and see what kind of dummy load that is.

[Tom in D.C.]

It has been implied, but not actually stated, that the APX GPS VHF/UHF antenna is a particularly good dummy load.
That's why I got a dualbander from Comtelco which needs a BNC-to-SMA adapter but performs great. Problem
is I went looking again at Comtelco's listings recently and could no longer find that particular antenna. A phone
call to them would probably get it to "show up."

[FireCpt809]

Ive also had good results with a VHF antenna for an XPR. Its a little shorter than a standard VHF and the top is rounded overall the visar works for me.

[Astro Spectra]

While a shootout on one frequency is pretty interesting – I wonder if you want to compare with a 1/4 wave to see how much is lost?

I've used a Diamond ham 1/4 wave with an SMA connector that fits the XTS radios and works rather well (but a bit long for the OP's application). You might also consider as Wowbagger mentions that you can't check the antenna in the middle of an ideal metallic ground plane as in use it's attached to the top of a small radio loosely coupled to a poorly conducting human – both are poor substitutes for a groundplane extending at least a 1/4 wave in each direction!

You also need to consider the bandwidth of the antenna as some users need to operate with assignments in several bands including low and high VHF, marine, etc.

The Tait TP9100 P25 radio for example has three helical antennas to cover the entire VHF range, TPA-AN-002, TPA-AN-003, and TPA-AN-004. These are 136 to 151 MHz, 150 to 162 MHz, and 162 to 174 MHz. You can tell them apart by how long they are 170mm vs 154mm vs 147mm. And Tait offer them as a kit of three if you're keen to cover the entire range.

Icom offer for the F50 and other radios the FA-S59v to cover 150MHz to 174MHz with a red ring at the tip of the antenna while the FA-S24v covers 136MHz to 150MHz and has a blue ring at the tip of the antenna.

It seems that only Motorola offer a single portable antenna to cover the whole 136 to 174 MHz range and in my experience they work pretty well across all three bands. If you only need coverage over a few megs then a helical may work better – but make certain you have the right frequency range one.

This post of mine from a while back is a useful reference for Moto portable antennas:
http://batboard.batlabs.com/viewtopic.p ... 60&start=0

[Will]

It has been implied, but not actually stated, that the APX GPS VHF/UHF antenna is a particularly good dummy load.
That's why I got a dualbander from Comtelco which needs a BNC-to-SMA adapter but performs great. Problem
is I went looking again at Comtelco's listings recently and could no longer find that particular antenna. A phone
call to them would probably get it to "show up."

Comtelco is not selling portable antennas anymore since Centurion got bought out.

You could try PcTel but I doubt the quality of their antennas.

[mab]

I just did a very quick test of VHF portable antenna performance on one frequency, with all the antennas that were within reach.

All I did was set up a Rohde & Schwarz PR100 portable measurement receiver, and measured the signal strength of my local NOAA weather station (162.4750), with the antennas stuck directly in the PR100 jack (via a whatever-to-N adapter). I didn't touch the receiver during the measurement, so there was no human to act as a ground plane as there would be on an actual portable. Your mileage (and signal strength) may vary.

Here are the results (in dBuV):

31.8 Icom FAS6270D multiband amateur ducky
36.0 Diamond RH519 multiband amateur flexwhip
37.0 KATHREIN 510375 (cut for 70MHz)
49.0 Moto 8505241U03 800MHz whip
50.3 Icom FA-B02RE VHF amateur ducky
53.1 Moto APX UHF/800/GPS
55.4 Moto 8505644V03 7 inch *
55.5 Moto 8504834W03 5 inch *
56.4 Moto 8505518V01 wideband *
59.1 Moto APX VHF/UHF/GPS *
61.2 Diamond RH537 17 inch multiband amateur flexwhip

Some of the antennas are advertised to cover 162.475 and others weren't. The ones marked with a * are supposed to cover 162.475.

The APX multband antenna doesn''t seem to be so bad on VHF.

Take this for whatever it's worth.

[Tom in D.C.]

Will wrote above:

Comtelco is not selling portable antennas anymore since Centurion got bought out.

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Comtelco is still listing a whole batch of rubber and similar antennas, but for some reason the
V/U dualband unit is missing, which leads me to think that they may have dropped that one.

Question: Who bought out Centurion?

[NodrogCop]

Question: Who bought out Centurion?

I thought I read somewhere that Centurion is now a part of Laird?

Gordon

[Tom in D.C.]

It looks as if Centurion is now part of Laird, so I went through the entire Laird portable antenna line, but no dualband antennas were listed. I'll call Comtelco and find out what's going on.

[Will]

The later Laird branded portable radio antennas are not of the same quality any more.

[n3eg]

I once did a similar comparison on the MX mount antennas, and found that the short VHF HT750 antennas were a good dummy load (outperformed by a standard stubby 3" VHF by 3db!) and the new NAD6579 "gain" long ducky indeed has as much gain as one of those half-helical half-whip armpit pokers from Laird and formerly from Larsen.