# Radio
Where you learn about radio, and the hardware we use.
# General Knowledge
To share trick on how to maximize your signal
# Antenna knowledge
For information about how antennas work and how to choose one
# Antenna Gain vs Length - Quick Reference
### Antenna Gain vs Length - Quick Reference for 915 MHz Omnis
If you've ever wondered how to ballpark an antenna's gain just by looking at it, here's a cheat sheet:
**2 dBi** → ~120-170 mm
**3 dBi** → ~200-250 mm
**4 dBi** → ~280-350 mm
**5 dBi** → ~400-450 mm
**6 dBi** → ~500-600 mm
**7 dBi** → ~800-900 mm
**8 dBi** → ~1200-1350 mm
**9 dBi** → ~1500-1650 mm
#### Why does this work?
At 915 MHz, one wavelength (λ) is about 328 mm. Omnidirectional collinear antennas get their gain by stacking half-wave elements vertically with phasing stubs between them. More elements = longer antenna = more gain.
\- **2 dB**i is basically a half-wave dipole (λ/2 = 164 mm). This is where most stock LoRa whip antennas land.
\- **3 dBi** gets into 5/8-wave territory (~205 mm plus matching network)
\- **4-5 dBi** covers short collinears and 2-element designs
\- **6 dBi** around 550 mm is a 3-element collinear (~1.68λ)
\- **7 dBi** around 850 mm is a 4-5 element collinear (~2.6λ)
\- **8 dBi** around 1275 mm is pushing 7+ elements (~3.9λ)
\- **9 dBi** around 1600 mm is an 8+ element array (~4.88λ)
The general rule is that doubling your elements gets you about +3 dB of gain. You'll notice the gaps get smaller as you go up because at higher element counts you hit diminishing returns from losses in the phasing network.
#### One caveat
Below 5 dBi, the length-to-gain correlation gets less reliable. Manufacturers use loaded and helical designs to shrink things down, so you'll see "2 dBi" antennas that are only 50-80 mm because they're coiled internally. The eyeball method really shines from 5 dBi and up where you're looking at full-size collinear builds.
#### TL;DR
Under 200 mm? Probably 2-3 dBi. Around 300-450 mm? 4-5 dBi range. Half a metre, ~6 dBi. Approaching a metre, ~7 dBi. Over a metre, ~8 dBi. Pushing 1.5m+, you're in 9 dBi territory. No spec sheet needed, just eyeball it.
#### Choosing the Right dBi and Wave Shape for Your Environment
• **2–3 dBi** (Omni / Rubber Duck)
• Wave Shape: Tall, rounded sphere.
• Best For: Dense urban areas, indoor gateways, mobile nodes (backpacks, cars, or kayaks), or hilly terrain where nodes are located above or below you. A wide vertical beam forgives tilt and varying node elevations.
• **5–6 dBi** (Short Fiberglass)
• Wave Shape: Balanced, medium donut.
• Best For: Suburban environments or mixed terrain. It clears local ground obstructions better than a 3 dBi antenna while maintaining enough vertical beamwidth to reach nodes that aren't on the exact same flat plane.
• **8–9 dBi** (Tall Fiberglass)
• Wave Shape: Thin, flat horizontal disk.
• Best For: Open, flat, rural terrain with clear line-of-sight. Warning: If mounted very high on a tall mast in non-flat terrain, the flat beam will literally shoot straight over nearby nodes, resulting in zero coverage for devices close to the ground.
# Antennas reviews
Learn about antenna models and sweeps
# ✅ Gizont 167mm 915mHz VNA sweep
The Gizont 167mm is a very good narrow band antenna. It is likely a 1/2 wave dipole, **They say it is a 10 dBi but is is more likely a 2-3dBi by lenght**...
Purchase link: [https://www.aliexpress.com/item/1005004607615001.html](https://www.aliexpress.com/item/1005004607615001.html)
Result: -34.2 dB return loss at 910mHz, a perfect result (1.04 VSWR at 32.925230828 cm)
[](https://meshcore.wiki.gd/uploads/images/gallery/2026-10/aty8Az8PsWmDJfke-2026-08-12-gizont-return-loss2.webp)
# ✅Gizont 40cm 915mHz VNA sweep
The Gizont 167mm is a very good (slightly wider band) antenna. This is likely an impedance matched 5/8-wave or a colinear (multi-element). **They say it is a 10 dBi but is is more likely a 5dBi by lenght**...
The bigger Gizont 40cm
-24dB of return loss is pretty good
It is much wider band the the 167cm, it is a good one.
Purchase link: [https://www.aliexpress.com/item/1005007121522456.html](https://www.aliexpress.com/item/1005007121522456.html)
Result: -24dB of return loss at 910mHz is pretty good.
(Calibrated for a span of 100MHz, but displays a span of 200MHz, so good enough)
[](https://meshcore.wiki.gd/uploads/images/gallery/2026-10/b9HfjeQRWnuLL1mm-2026-09-10-gizont-40cm-sweep-910mhz-span-200m.webp)
# ❌ ABBREE 40cm 915 mHz VNA sweep
### ❌ DO NOT BUY
This is a sweep of the 40cm ABBREE antenna, the result of -7 dB of return loss is garbage, the antenna does not resonate anywhere from 1hz to 8GHz... Unusable. disappointing. Disgustang!
[](https://meshcore.wiki.gd/uploads/images/gallery/2026-10/hAlDspoBmtZeJBRA-2026-08-31-abbree-40cm-antenna-sweep.webp)
#### This is a bad antenna, do not purchase.
Purchase link just for reference: [https://www.aliexpress.com/item/1005012228888082.html](https://www.aliexpress.com/item/1005012228888082.html)
# ✅Heliumtech 50cm VNA sweep
Heliumtech 5.8 dBi (50cm) 915 MHz Waterproof fiberglass Antenna with Mount Bracket Kit (N Female) from Canadian Wireless Supply on Amazon
Purchase link: [https://www.amazon.ca/dp/B0BSYKSS22](https://www.amazon.ca/dp/B0BSYKSS22)
##### Result: -20.9 dB at 915mHz is good enough
[](https://meshcore.wiki.gd/uploads/images/gallery/2026-10/e8t1dWANMtuLHvwG-2026-07-06-heliumtech-antenna-return-loss.png)
[](https://meshcore.wiki.gd/uploads/images/gallery/2026-10/SXrZkOsI829776nm-2026-07-06-heliumtech-antenna-swr.png)
# ❌ Gorilley (Fake ALFA 5 dbi) VNA sweep
### ❌ DO NOT BUY
This is a sweep of the "5dBi" Gorilley antenna, which looks like an ALFA 5 dbi knockoff, which ended up being a fake.
##### Result: **-6.4 dB** at 915mHz is **BAD**, and it only slightly resonates at 1.2GHz...
[](https://meshcore.wiki.gd/uploads/images/gallery/2026-10/8G2gOR151Ps968gz-amazon915mhzlog.png)
#### This is a bad antenna, do not purchase.
Purchase link just for reference: [https://www.amazon.ca/dp/B0G4CWQMDX](https://www.amazon.ca/dp/B0G4CWQMDX)
# ✅ RF Explorer 8dBi 1300mm VNA sweep
### Fiberglass Antenna Kit For 902-928MHz 8dBi 1300mm
Comes with an antenna pole bracket and a 1m N female to **RP-SMA** male (RP is a weird inversion)
This antenna is the backbone of our core Meshcore network in Ottawa.
It has been proven to allow for long distance links while maintaining omnidirectionality.
Purchase Link: [https://www.seeedstudio.com/RF-Explorer-LoRa-Fiberglass-Antenna-Kit-902-928MHz-8dBi-1300mm-p-5278.html](https://www.seeedstudio.com/RF-Explorer-LoRa-Fiberglass-Antenna-Kit-902-928MHz-8dBi-1300mm-p-5278.html)
#####
##### Result: -26.5 dB of return loss at 910.525MHz is excellent
[](https://meshcore.wiki.gd/uploads/images/gallery/2026-10/l2G16MMNqYBjtFOF-2026-08-27-seeed-8dbi.png)
# Cables
# Filters
To share good special purpose filters
# Cavity Filters
To share sweeps of specific specialized Cavity Filters