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I'm considering getting an after-market antenna for my new 2 m/70 cm HT and am trying to decide which of the two antennas I should get. My primary reason for considering an alternative antenna is improved RX/TX performance.

Both antennas in their specifications on the manufacturers web-site say following:

Maximum power: 10 W, gain 2.15 dBi, 1/4 wave on 2m, 1/2 wave on 70 cm, both have appropriate connector and impedance, both have specified SWR as less or equal to 1:1.5.

The only difference between them is that one antenna is 19 cm long and the other antenna is 36 cm long.

After doing some research on the internet, I've noticed that a large number of HT antennas have extremely similar technical specifications, with only difference being the antenna length. I've also read very vague and general descriptions saying that longer HT antenna==better HT antenna.

So how do I determine which antenna is better based on provided information?

By the way, I want to keep the question as general as possible, so I didn't mention models until now, but they are Diamond SRH-701S and Diamond SRH-536.

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    $\begingroup$ Where are you getting these specifications? Diamond's product list includes an SRH-701, but no SRH-701S, and doesn't list an SRH-536. Google searches for "SRH-536" turn up a lot of posts about counterfeit products. I suppose the first step of buying a good antenna would be "buy from a reputable vendor". $\endgroup$ – Phil Frost - W8II Jun 21 '14 at 12:02
  • $\begingroup$ @Phil Frost Take a look at Diamond's product list and compare RH536 and SRH36. I bet they just missed 5 when typing SRH36. It appears to be the same antenna as RH536, but with SMA connector. In any case, I found both SRH-701 and SRH-536 in stock at local Icom distributor which has reputation of being pretty reliable, so that, in my mind, justified perhaps incorrect assumption that there's a mistake at Diamond's website. In any case, that's tangential to the question itself, since I could easily write that I'm comparing the SRH36 and SRH701 and nothing significant would change. $\endgroup$ – AndrejaKo Jun 21 '14 at 12:24
  • $\begingroup$ @Phil Frost Just to be clear, I do appreciate the concern! $\endgroup$ – AndrejaKo Jun 21 '14 at 12:26
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    $\begingroup$ I ask because your specifications sound bogus. Two antennas can not both be 1/2 wave long on the same frequency but be different lengths (maybe they can be electrically that long, but the descriptions are ambiguous). The quoted "2.15dBi" is also the gain of a dipole in free space. It sounds like they didn't actually measure antenna performance. So, the answer to your question about "similar catalogue descriptions" is to find a better catalogue. $\endgroup$ – Phil Frost - W8II Jun 21 '14 at 16:06
  • $\begingroup$ @Phil Frost That looks like a good answer. Please post it! $\endgroup$ – AndrejaKo Jun 21 '14 at 20:49
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Catalog descriptions are bogus. What they are describing are characteristics of monopole antennas in general, not either specific model.

Clearly, they can't both be 1/4 wave antennas at the same frequency but also be different lengths. A 1/4 wave at 145 MHz is about 49 cm. Neither one is a 1/4 wave antenna,. What they probably are is electrically a 1/4 wave, made electrically longer than they physically are with a loading coil. The more loading, the shorter the antenna, and everything else being equal, the less efficient the radiator.

They also both quote gain as 2.15 dBi. This is the theoretical gain of a half-wave dipole in free space. An ideal quarter-wave monopole is equivalent to a dipole, and has the same gain. It doesn't sound like they made any actual measurement of either antenna's gain. These antennas have significant deviation from the ideal models: they have loading coils, they are over (lossy) Earth, and they lack a ground plane that's anything close to ideal.

Absent accurate specifications from the manufacturer or vendor, it's true of all antennas that longer is better, up to the point that the antenna is self-resonant. To make it shorter requires the addition of reactive components that don't contribute to radiation and must necessarily introduce additional loss if constructed of real materials.

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    $\begingroup$ ...and antennas made out of Unobtainium are still freakishly expensive, when they can be had at all. $\endgroup$ – a CVn Jun 23 '14 at 7:47
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All other things being equal, a longer HT whip will outperform a shorter whip. The shorter length is probably because of a larger loading coil, which could result in loss.

The gain numbers from most antenna manufacturers should be taken with a grain of salt. They use wild assumptions when calculating it. In most cases HT whips are so cheap, one could buy both (or several) and simply try them all out to find the best performance for the given band/frequency/repeater.

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