[ Radio Antennas: Handhelds, Scanners, the Field and Meshtastic ]

Everyone wants to talk about radios, and the radio is the easy part. The
antenna decides how far you hear and how far you get out, and the stock one on
most handhelds is a compromise built to be short and cheap. Swapping it is the
single best thing I've done for any of my radios, and the same goes for almost
any radio you can buy.

What I knew about antennas was scattered across my radio and Meshtastic pages,
so I pulled it into one place and filled in the gaps. Where another page
already goes deeper, I just link to it. There are calculators along the way for
antenna length, range, coax loss and SWR, so you can plug in your own numbers.

If it had to fit on a sticky note: get a longer antenna made for your band,
keep it vertical, get it as high as you can, and use as little coax as you can
get away with. And never transmit through an antenna that wasn't made for it.

A handheld puts out about 5 W, and that's not going to change. The antenna is
where you win or lose most of the rest: a better antenna helps on receive and
transmit at the same time, while more power only helps one direction and drains
the battery doing it.

The antenna that ships with a handheld is short so the radio fits in a pocket.
A short antenna has to be electrically loaded to work at all, and it gives up
efficiency to do it. A longer whip made for the bands you use hears and gets
out noticeably better. On my Baofeng the swap was the biggest single
improvement, and the same goes for the UV-K5.

What I use:

  Baofeng UV-5R Mini   Diamond RH77CA, 15", BNC, through an SMA adapter
  Quansheng UV-K5      ABBREE AR-771 (the GMRS-printed one) to transmit;
                       a Bingfu scanner dipole, 20-1300 MHz, for listening
  Meshtastic nodes     915 MHz antennas, covered in the node build

Antennas are sized to the wavelength they work on. The classic numbers come
from one formula: a quarter wave in feet is 234 divided by the frequency in
MHz, and a half wave is 468 divided by it.

  Band             Quarter wave        Half wave
  2 m (146 MHz)    about 19 1/4"       about 38 1/2"
  70 cm (446 MHz)  about 6 1/4"        about 12 1/2"
  915 MHz          about 3"            about 6"

For any other frequency, type it in:

A dual-band whip like the RH77CA is cut so one length works on both: it's a
quarter wave on 2 m and a half wave on 70 cm, so a 15" whip beats the stub on
both bands, not just one.

Gain isn't extra power. An antenna can't make energy; it can only aim it. More
gain means the radiation pattern is squashed flatter: more toward the horizon,
less up and down. That's great on flat ground and can be a problem on a
mountainside, where the people you want to reach are below you. Gain is quoted
in dBi (against a theoretical point source) or dBd (against a half-wave
dipole), and a dipole is 2.15 dBi, so the same antenna reads 2.15 higher in
dBi. I treat gain numbers on cheap listings with suspicion, especially when
they don't say which one they mean.

Most of the frustration with antennas is connectors. These are the ones you'll
run into:

  SMA, Baofeng style   the radio is SMA-male: a pin in the middle, with
                       the threads inside the jack. The antenna is
                       "SMA-female", a threaded post with a hole, and it
                       screws in. Baofeng and Quansheng both do it this
                       way
  SMA, Yaesu/Kenwood   the reverse: the radio has the threaded post and
                       the hole, and the antenna has the collar and the
                       pin. Same thread, opposite genders, so the two
                       won't mate
  RP-SMA               the Wi-Fi version, with the pin and the hole
                       swapped. Looks almost identical. Skip it for radios
  BNC                  a bayonet that locks in a quarter turn. Common on
                       scanners, test gear and better handheld antennas
  U.FL / IPEX          the tiny snap-on jack on LoRa boards, for a short
                       pigtail out to an SMA bulkhead
  N-type               big and weatherproof, on outdoor and fiberglass
                       antennas
  UHF (PL-259)         the screw-on plug on mobile and base radios, despite
                       its name

The SMA genders trip up everyone, me included. Here's the jack on my UV-5R Mini
with the antenna off, how the two families pair up, and what the right and
wrong adapters look like:

For a Baofeng or a K5, the adapter that lets you use BNC antennas is SMA-female
to BNC-female, often listed "for Baofeng". The first one I bought was the Yaesu
kind and didn't fit; the whole story is in my Baofeng guide. The quick check:
the adapter's SMA end should look like the base of your stock antenna, a
threaded post with a hole in the middle.

I leave the adapter on the radio and use BNC antennas. Every swap is a quarter
turn, and the adapter takes the wear instead of the radio's jack. A long
antenna on an adapter is a long lever, though: tighten it by hand, never carry
the radio by the antenna, and take the antenna off before the radio goes in a
bag.

A radio signal keeps the orientation of the antenna that sent it, which is
called polarization. Repeaters, handhelds, mobiles, boats and aircraft all use
vertical antennas, so nearly everything a handheld listens to is vertically
polarized. A vertical antenna hears it best. Turn your antenna sideways and a
lot of the signal goes missing.

In practice:

  - Hold a handheld upright when you talk, not tilted like a phone.
  - Mount a dipole or a scanner antenna with its elements up and down, not
    side to side. There's a diagram of it on my K5 page.
  - A mag-mount on a car goes on the roof, standing straight up.

Your body gets in the way too, especially on UHF. A radio on your hip, with you
between it and the repeater, does a lot worse than the same radio held up at
face height with the antenna clear of your head.

VHF and UHF travel in more or less straight lines, so how far you reach is
mostly about what the antenna can see. On open ground the radio horizon works
out to about 1.41 times the square root of the antenna height in feet, in
miles, with normal bending of the signal by the air included. For two radios,
add the two distances.

  Antenna height               Radio horizon
  5 ft (a handheld)            about 3 miles
  30 ft (a tree or a mast)     nearly 8 miles
  10,000 ft (near Haleakalā)   about 140 miles

That last row is how one repeater up on the mountain can cover Maui, Molokaʻi
and Lānaʻi, while two handhelds on flat ground manage a few miles at best. In
Hawaiʻi the terrain cuts all of these down: ridges, valleys and wet forest
block VHF and UHF, and a handheld down in a gulch might as well be in a drawer.

So the fix is almost always up. Stand on something, walk to the top of the
rise, put the antenna on a pole or up a tree with coax down to the radio, or
use a repeater that somebody already put up high. Doubling a handheld's power
does far less than any of those.

Work out your own, best case over open ground:

Getting the antenna up high usually means coax, and coax loses signal, more the
higher the frequency and the thinner the cable. Approximate loss in dB per 100
feet, from Miklor's cable loss table:

  Cable      144 MHz   450 MHz   915 MHz
  RG-174     10.1      18.1      26.1
  RG-58       5.5      10.0      14.6
  RG-8X       4.2       8.0      12.3
  LMR-240     3.0       5.3       7.6
  LMR-400     1.5       2.7       3.9

Every 3 dB is half your power, both ways. Twenty feet of thin RG-174 on 70 cm
loses about 3.6 dB, more than half the signal, which can undo what you gained
by getting the antenna up there. A few meters of RG-58 for a jungle antenna is
fine. For a long run, especially at 70 cm or 915 MHz, step up to LMR-240 or
LMR-400, and keep the radio close to the antenna when you can. Every adapter
and connector costs a little too, so don't stack them.

Try your own run:

SWR (standing wave ratio) is a measure of how well the antenna matches what the
radio expects, which is 50 ohms. A perfect match is 1:1 and everything the
radio sends goes into the antenna. A mismatch sends some of it back down the
coax into the radio.

  SWR     Reflected   Lost      Rule of thumb
  1.5:1   4%          0.2 dB    great
  2:1     11%         0.5 dB    fine
  3:1     25%         1.2 dB    something's wrong

The signal you lose is smaller than people expect. A 2:1 match only costs about
half a dB, less than the coax often does, so a slightly imperfect match isn't
worth losing sleep over. What you should worry about is the radio. Reflected
power heats the final amplifier, and a bad enough mismatch, or no antenna at
all, can fry it. So never key up without an antenna on, and never transmit
through one that wasn't made for the band.

Receive is different: a mismatch there just costs you a little signal. It's how
a wideband scanner antenna can be great for listening and terrible for
transmitting.

I don't own an SWR meter or a NanoVNA, so I play it safe instead: antennas sold
for the bands I transmit on, from makers that publish specs, and connectors
that are snug and the right kind. If you want numbers, a NanoVNA is cheap, and
a lot of ham clubs have someone with one who'll check an antenna for you.

To see what any SWR reading means:

For listening, I've been using a Bingfu scanner dipole on my UV-K5: the kind
sold for police scanners, rated 20-1300 MHz, with two flexible elements in a T
on a long coax lead that ends in a BNC plug. It goes on through the same
SMA-to-BNC adapter, and for receive it works great. It also fits the Baofeng
the same way.

A wideband antenna like that covers far more than a handheld can hear, which
doesn't hurt, and the long lead lets the antenna sit up high or by a window
while the radio stays with you. Mount it vertical, elements up and down.

Never transmit through it. It's made for scanners, which only receive, and
nothing about it says it's matched for 2 m or 70 cm or can handle 5 W. Keying
up into a bad match sends power back into the radio's final amplifier, which is
an easy way to fry it. The ham antenna goes back on before I transmit. There's
a hookup diagram on both radio pages (K5, Baofeng), and the off-grid page
lists what's worth listening to in an emergency.

When the repeaters are down or out of reach, an antenna you can build or carry
is worth more than any radio upgrade. The classic is the jungle antenna: the
Army's field-expedient quarter-wave ground plane, one vertical wire and a few
drooping radials, hung in a tree with coax down to the radio. For 2 m it's
about 19 1/4" per wire. The full build, with the numbers for 70 cm, is on my
off-grid page.

Where you put it matters more than which antenna it is. A simple wire 30 feet
up a tree beats a fancy whip in your hand, and paracord over a branch does the
lifting. Keep the coax short and decent: a few meters of RG-58 is fine, but
long thin runs eat the gain (see coax). With a BNC adapter on each radio, one
coax with a BNC end plugs into either of mine. A car works as a mast too: a
mag-mount whip in the middle of a metal roof gets the antenna above the cabin
and uses the roof as its ground plane.

And look up before you throw a line into a tree. Never put an antenna anywhere
near power lines, and don't hold the antenna while you transmit.

Meshtastic nodes play by the same rules, only more so, because 915 MHz is less
forgiving than 2 m. My node build guide goes through it in detail; the short
list:

  - Never power a LoRa board without its antenna. The transmit energy
    has nowhere to go but back into the radio.
  - Match the connector. SMA and RP-SMA look the same and don't mate.
  - Match the band. In the US that's a 915 MHz antenna, not 868 or 433.
  - Gain is a trade. A high-gain antenna on a hilltop can shoot right
    over the valley below it.
  - Keep the coax short. At 915 MHz even a short run of thin cable costs
    several dB. Put the node up high, not just the antenna.

For a node on the move, the mobile network guide covers handheld and car
mounting, and RF coverage planning shows how to model where a node will
actually reach.

What's the best antenna upgrade for a Baofeng or a UV-K5?
A longer dual-band whip made for 2 m and 70 cm, in place of the stock stub. I
use a Diamond RH77CA on my Baofeng through an SMA-female to BNC-female adapter,
and an ABBREE AR-771 on my UV-K5. Either one hears and gets out noticeably
better than the stock antenna.

How long should a 2 m antenna be?
A quarter wave on 2 m is about 19 1/4 inches and a half wave about 38 1/2
inches. The formula is 234 divided by the frequency in MHz for a quarter wave
in feet, and 468 divided by it for a half wave.

What's the difference between SMA and RP-SMA?
RP-SMA is the Wi-Fi version of SMA with the pin and the hole swapped. They look
almost identical and don't mate. Radios like Baofeng and Quansheng use SMA,
with the pin on the radio's jack.

Does it matter which way I mount an antenna?
Yes. Repeaters, handhelds, mobiles, boats and aircraft use vertical antennas,
so their signals are vertically polarized. Mount your antenna vertical,
elements up and down, and hold a handheld upright.

How far can a handheld radio reach?
On open ground, the radio horizon is about 1.41 times the square root of the
antenna height in feet, in miles: about 3 miles for a handheld at 5 feet. Two
handhelds add their distances, so a few miles on flat ground. Terrain cuts that
down, and a repeater up high stretches it a long way.

What SWR is good enough?
Under 1.5:1 is great and under 2:1 is fine; a 2:1 match only loses about half a
dB. Over 3:1 means something's wrong, and transmitting into a bad mismatch can
damage the radio's final amplifier.

Can I transmit through a scanner antenna?
No. Scanner antennas are made to receive, and nothing says they're matched for
the ham bands or can handle transmit power. Use one for listening, and put the
ham antenna back on before you transmit.

Which coax should I use for a handheld antenna up high?
A few meters of RG-58 is fine. For longer runs, especially on 70 cm or 915 MHz,
use LMR-240 or LMR-400. Thin RG-174 loses about 18 dB per 100 feet at 450 MHz.