Extremely well built!
"Extremely well-built 40M coil. I already have one and bought a second one so that I can make a 40M dipole using 2 Chameleon 25’ whips in the field! Great product!!!"
CHA M25-COIL · 40-meter loading coil for the BV / SS25 configuration
Add 40-meter operation to the CHA BV when it is configured with the CHA SS25 telescoping whip.
Why operators make room for it
Bring your SS25 Basic Vertical onto 40 meters
The CHA SS25 gives a portable vertical more radiator to work with, but the documented 40-meter BV configuration still needs the right loading coil. CHA M25-COIL is that purpose-built addition: it installs between the CHA BLANK feed assembly and the SS25 to create the base-loaded 40-meter vertical described in the CHA BV guide.
For the operator who already owns a BV and SS25, the benefit is a targeted expansion rather than another complete antenna. Set up the required mount, radials and feed line, add M25-COIL for 40 meters, then adjust the whip and check resonance at your operating site.
When you move to 30 through 6 meters, a short jumper between the two bypass sockets lets the coil stay in the stack while its winding is electrically bypassed. The jumper is not included. Adjust the SS25 for the selected band using the guide; bypass does not provide simultaneous coverage or automatic tuning.
Loaded on 40 meters, bypassed for the higher bands
- 40 meters: no bypass jumper. Assemble the BV / SS25 with M25-COIL in the base-loading position and use the guide starting dimensions before checking resonance.
- 30 through 6 meters: disconnect the transmitter, safely access the coil and join its two 4 mm sockets with a short jumper, or remove the coil as the guide permits. Adjust the SS25 and radial lengths for the selected band.
- Never fit or remove the jumper while transmitting. Check the jumper connections and remeasure SWR after every configuration change.
Quick product reference
Key Specifications
- Component type
- Fixed base-loading coil for the documented CHA BV / SS25 40-meter vertical
- Threaded interfaces
- 3/8-24 threaded connections for the documented radiator and mounting assembly
- Documented radiator
- CHA SS25 25-foot telescoping whip in the CHA BV configuration
- Loaded band
- 40 meters with M25-COIL in circuit; leave the bypass sockets unbridged
- Higher-band transition
- 30 through 6 meters with the coil removed or electrically bypassed; retune the SS25 for each selected band
- Bypass connections
- Two 4 mm banana sockets at the top and bottom edges of the coil
- Bypass jumper
- Short operator-supplied jumper; not included
- Identification
- Red covering distinguishes M25-COIL from M-COIL; the coils have different winding counts and applications
- SSB power limit
- 200 W SSB; never exceed the lower rating of another component in the completed antenna
- CW power limit
- 100 W CW; the completed antenna may impose a lower limit
- Digital and high-duty operation
- Do not treat the CW rating as a digital-mode rating. Confirm the applicable mode and duty-cycle limit before transmitting
- 40-meter starting setting
- BV guide: SS25 length 24 ft 1 in and four 12 ft 6 in radials; final tuning is site-dependent
- RF connection
- Coax connects to CHA BLANK; the loading coil connects through the threaded radiator path
- Included equipment
- One CHA M25-COIL; whip, feed assembly, mount, radials, coax and bypass jumper are not included
Build the complete BV / SS25 antenna
M25-COIL is an add-on component, not the complete antenna. Use it with the CHA SS25, the BV CHA BLANK feed assembly, the documented support, radial system and coax with choke. Follow the BV guide for component order and band-specific settings.
Do not replace M-COIL with M25-COIL in an SS17 or V-DIPOLE configuration. Their similar size and shared thread do not make their loading interchangeable.
Official product documents
CHA M25-COIL Flysheet and Quick Start
CHA BV User Guide: SS25 configuration, bypass, radial settings and tuning
Tune the antenna, not just the radio
Start with the dimensions in the complete-system guide and measure resonance with an antenna analyzer or at low transmitter power. Adjust the radiator for the intended frequency; ground conditions, radial layout, height and nearby objects can shift the result.
Disconnect the transmitter before installing, removing or bypassing the coil. Hand-tighten threaded joints without using the whip or coil body as a wrench. Stop for abnormal heating, arcing, loose connections or unstable SWR. Keep the antenna clear of power lines and people.
