FAQ
TL;DR: External antennas can help RCT21 range, but “Antenna with 0 dB gain” plus cheap coax means loss. Use quality parts and short runs, or range may not improve. [Elektroda, max-bit, post #21225030]
Why it matters: This helps Exta Life RCT21 owners fix spotty 868 MHz links without wasting time on ineffective antenna mods.
Quick Facts
- RCT21 setup here operates on the 868 MHz band; match any external antenna to 868 MHz. [Elektroda, kdziadosz209, post #21225147]
- The stock antenna sits on a small daughterboard, soldered by two pins to the main PCB. [Elektroda, kdziadosz209, post #21223811]
- Low-gain (0 dB) whips and cheap cable can add a few dB loss, hurting range. [Elektroda, max-bit, post #21225030]
- A user-added RP‑SMA socket worked with the dedicated antenna and ran stably. [Elektroda, kdziadosz209, post #21253387]
- Real-world case: a 20 m outdoor link with a repeater still saw intermittent dropouts. [Elektroda, kdziadosz209, post #21225167]
Will an external antenna increase range on Zamel Exta Life RCT21?
It can, but only if the antenna and feed add gain, not loss. As one member warns, “This does not guarantee an improvement in range at all.” Long, low‑quality coax and low‑gain whips can make it worse. Keep any feed short and use a tuned antenna. [Elektroda, max-bit, post #21224820]
Where is the RCT21’s stock antenna located?
It sits on a small daughterboard, soldered on two pins and mounted perpendicular to the main board. This affects where you tap the RF feed and how you mount a connector. Plan placement and strain relief accordingly. [Elektroda, kdziadosz209, post #21223811]
Has anyone added an RP‑SMA and confirmed it works?
Yes. A user soldered an RP‑SMA socket to the PCB, connected the system’s dedicated antenna, and reported it works without problems. This shows the hardware accepts an external feed when done carefully. [Elektroda, kdziadosz209, post #21253387]
Which connector should I fit: SMA or RP‑SMA?
RP‑SMA is proven in this thread. The poster fitted an RP‑SMA socket and used the matching antenna with no issues. Match your connector to the antenna you plan to use to avoid adapters. [Elektroda, kdziadosz209, post #21253387]
Is the original Zamel external antenna worth using?
One expert called it “a Chinese product” with “Antenna with 0 dB gain,” plus a cheap cable that causes a few dB of loss. Net performance can be negative if the feed is long. Consider a better 868 MHz antenna and short, quality pigtail. [Elektroda, max-bit, post #21225030]
How long can the antenna cable be before it hurts range?
Avoid “a few metres of poor cable.” That edge case can perform worse than the stock PCB antenna. Keep the pigtail very short and use quality coax only when absolutely needed. Long, lossy runs are a common failure after DIY mods. [Elektroda, max-bit, post #21224820]
My device is 20 m from the house with a repeater and sealed box—why drops?
In the reported setup, the base was indoors, the device 20 m away, and a repeater was used. Despite visibility, links sometimes dropped. Try moving the repeater or enclosure, test with the box open, and keep feeds short. Check antenna orientation and height. [Elektroda, kdziadosz209, post #21225167]
Is repositioning the repeater/base better than adding a long cable?
Often, yes. Shorter RF paths beat long, lossy pigtails. As one member noted, there are “Many questions ... and too many unknowns,” so experiment with placement first to reduce losses and obstructions. [Elektroda, max-bit, post #21225153]
How do I add an RP‑SMA to the RCT21?
- Identify the antenna feed where the daughterboard connects and expose a ground point.
- Solder an RP‑SMA socket or short pigtail to the feed and ground, keeping it very short.
- Attach an 868 MHz antenna and test link quality.
[Elektroda, kdziadosz209, post #21253387]
Do I need to open the receiver, and is there enough space?
Yes. You must open it to inspect and plan a connector. “Take it apart and see what it looks like inside.” Space can be tight with a PCB antenna, so choose the socket location carefully and photograph the internals. [Elektroda, max-bit, post #21222683]
What frequency should the external antenna be tuned to?
Use an antenna tuned for 868 MHz, matching the system’s operating band. Pair it with the same connector type you install on the receiver to avoid mismatch. [Elektroda, kdziadosz209, post #21225147]
What was the result after the RP‑SMA mod in this thread?
After soldering the RP‑SMA and connecting the dedicated antenna, the user reported it “works without any problems.” That indicates the mod can stabilize the link when done correctly. [Elektroda, kdziadosz209, post #21253387]
If my module has no antenna socket, can I still use the optional antenna?
Yes. You can add a socket by soldering to the board. In this case, an RP‑SMA was added and the system’s dedicated antenna was used successfully. Ensure RF ground and mechanical stability. [Elektroda, kdziadosz209, post #21253387]
Where can I get help verifying my mod?
Post clear internal photos. A member advised, “Take photos and we will combine,” after suggesting disassembly. Community review can confirm the feed point and safe routing before you solder. [Elektroda, max-bit, post #21222683]
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