For those in the Wi-Fi and Helium mining communities, a question we often get asked is how to confirm antenna gain. With many choices and many similar looking antennas with widely varying "dBi" gain, how do you know?
Gain is often mis advertised, and often on purpose.
We encountered a situation of possible gain inflation in an eBay listing last week and reached out to the seller. We were surprised with their shockingly honest answer about why they inflated the gain spec in their advertisement.
Before we get to that, you should know it is true that gain does not correlate exactly to size, and manufacturers can use larger fiberglass casings that increase the antenna length. Our low profile 8 dBi outdoor miner antenna uses shorter fiberglass and is about 26 inches tall, while the RAK antenna is 36 inches. It is also true that for a multi-spectrum antenna, for example gain at 2400 MHz, will be higher than gain at 900 MHz for the same antenna. But if you see a 14" fiberglass 915 MHz antenna advertised as 8 dBi by one seller, while another seller has a 26 or 36" antenna that is also 8 dBi, it is highly likely the short one is not correct.
We encountered this exact scenario on eBay last week and reached out to the seller. The seller wes almost unbelievably honest about their own dishonesty. See this image below- our inquiry is at the bottom and their reply is at the top. 
Basically, because others are doing it, they must do it as well. Crazy, but at least they are honest about their outright dishonesty. We made the decision to redact the sellers name because they are just one in a hundred online marketplace sellers doing the same thing, and we aren't "out to get them" in particular. We did report their listing to eBay for inaccuracy.
So what can you do to protect yourself? Well, you don't have to assume every antenna is mislabeled because it is not the same height as a RAK or Nebra fiberglass- dome-style for example will be shorter and rubber duck indoor antennas of the same gain are usually quite a bit shorter than outdoor ones because they don't have fiberglass. Antennas can also be made low profile. But if you see a huge anomaly- like a 1 foot outdoor dipole being advertised at the same gain as a 2 or 3 foot one, it may be worth asking the seller about how they got the number. Maybe you will get an "honest" answer like we did, or at least learn more about how they came to that spec. We also recommend dealing with companies that specialize in antenna manufacturing, vs general retail marketplace sellers that sell everything from antennas to baby apparel. Chances are the latter is just publishing specs they found elsewhere, and they don't know anything about the actual product itself.
Military and First Responder 
