The Sinclair ST421R-SF2SNF is a low profile, radome enclosed mobile antenna for 806 to 870 MHz. It provides unity gain (0 dBd, 2.1 dBi) with an omnidirectional pattern, handles 200 W, and terminates in an N female connector. At 2.1 in. tall, it is designed for rail, transit, and heavy transport vehicles where antenna height is restricted.
- Frequency: 806 to 870 MHz (64 MHz bandwidth)
- Gain: 0 dBd (2.1 dBi), omnidirectional, vertical polarization
- Power: 200 W average, maximum
- Connector: N female, 50 ohms
- Size: 7.4 x 3.7 x 2.1 in. (188 x 94 x 53 mm)
- Ground plane: 10 x 10 in. minimum
- Protection: IP65, DC grounded
- Manufacturer part number: ST421R-SF2SNF
What is the Sinclair ST421R-SF2SNF used for?
Sinclair Technologies built the ST421R series for rail and heavy transport, where a roof antenna has to stay inside a tight height envelope. The ST421R-SF2SNF is the 806 to 870 MHz model in that series. Its radiating element is sealed inside a grey fiberglass radome with a polyurethane coating, and the aerodynamic shape reduces wind loading.
The antenna is DC grounded. Sinclair specifies this as its lightning protection.
What frequencies does the ST421R-SF2SNF cover?
The ST421R-SF2SNF covers 806 to 870 MHz continuously, a 64 MHz bandwidth, at a maximum input VSWR of 1.5:1. That span includes both halves of the US 800 MHz land mobile band: 806-824 MHz (mobile transmit) and 851-869 MHz (base transmit). One antenna covers both the transmit and receive side of an 800 MHz mobile radio.
It does not cover 700 MHz or 900 MHz. Those bands use different ST421R models, listed in the comparison table below.
ST421R-SF2SNF specifications
| Electrical | |
|---|---|
| Frequency range | 806 to 870 MHz |
| Bandwidth | 64 MHz |
| Gain (nominal) | 0 dBd (2.1 dBi), unity |
| Input VSWR (max) | 1.5:1 |
| Pattern | Omnidirectional |
| Vertical beamwidth | 60 degrees |
| Polarization | Vertical |
| Impedance | 50 ohms |
| Average input power (max) | 200 W |
| Lightning protection | DC ground |
| Mechanical | |
| Connector | N female (socket) |
| Length | 7.4 in. (188 mm) |
| Width | 3.7 in. (94 mm) |
| Height | 2.1 in. (53 mm) |
| Antenna weight | 0.8 lb |
| Radome | Grey fiberglass, polyurethane coated |
| Minimum ground plane | 10 x 10 in. (254 x 254 mm) |
| Mounting hardware | M6 x 25 bolt, A2 stainless steel |
| Ingress protection | IP65 |
| Environmental | |
| Operating temperature | -30 to +60 C (-22 to +140 F) |
Which ST421R model do I need?
The ST421R series is split by frequency. Pick the model that matches your system band. All four are 0 dBd, 200 W, DC grounded antennas in the same low profile radome style.
| Model | Frequency range | Bandwidth | RF connection |
|---|---|---|---|
| ST421R-SF1SNF | 764 to 806 MHz | 42 MHz | N female |
| ST421R-SF2SNF (this antenna) | 806 to 870 MHz | 64 MHz | N female |
| ST421R-SF2SNF(C01) | 806 to 870 MHz | 64 MHz | 1 ft pigtail, N female |
| ST421R-SF3SNF | 870 to 960 MHz | 90 MHz | N female |
What do I need to install the ST421R-SF2SNF?
- A metal ground plane of at least 10 x 10 in. (254 x 254 mm). Sinclair specifies this as the minimum for proper operation. A fiberglass or composite roof needs a metal ground plane added under the antenna.
- M6 mounting. Sinclair specifies M6 x 25 bolts in A2 stainless steel. Check the hole pattern against the Sinclair spec sheet drawing before drilling.
- A 50 ohm feedline with an N male connector to mate with the N female port on the antenna.
- 2.1 in. (53 mm) of clearance above the mounting surface.
What should I know before ordering?
- It is a unity gain antenna. The ST421R-SF2SNF trades gain for a 2.1 in. profile. If you have the height for a taller antenna and need gain, this is not the right part.
- It is single band. Rated range is 806 to 870 MHz only. A 700/800 MHz dual band radio will be outside this antenna's rated range on its 700 MHz channels.
- It is rated for -30 to +60 C. For colder service, Sinclair lists the ST421R-SF2SNF(C01) pigtail version at -40 to +70 C.
ST421R-SF2SNF frequently asked questions
What frequency range does the Sinclair ST421R-SF2SNF cover?
The ST421R-SF2SNF covers 806 to 870 MHz, a 64 MHz bandwidth, with a maximum input VSWR of 1.5:1. That range includes both halves of the US 800 MHz land mobile band: 806-824 MHz and 851-869 MHz.
Is 0 dBd the same as 2.1 dBi?
Yes. Sinclair rates the ST421R-SF2SNF at unity gain, which is 0 dBd referenced to a dipole or 2.1 dBi referenced to an isotropic radiator. Both numbers describe the same antenna.
Does the ST421R-SF2SNF need a ground plane?
Yes. Sinclair specifies a minimum ground plane of 10 x 10 in. (254 x 254 mm) for proper operation. On a fiberglass or composite roof, a metal ground plane has to be added under the antenna.
What connector does the ST421R-SF2SNF use?
It has an N female connector at 50 ohms. The feedline needs an N male connector to mate with it. If you want a factory lead instead, the ST421R-SF2SNF(C01) version has a 1 ft pigtail ending in an N female connector.
Can the ST421R-SF2SNF be used on 700 MHz?
No. This model is rated for 806 to 870 MHz only. The 764-806 MHz version is the ST421R-SF1SNF, and the 870-960 MHz version is the ST421R-SF3SNF.
How much power can the ST421R-SF2SNF handle?
The maximum average input power is 200 W.
Is the ST421R-SF2SNF weatherproof?
It carries an IP65 ingress protection rating, which means it is dust tight and protected against water jets. The radome is grey fiberglass with a polyurethane coating, and the rated operating temperature is -30 to +60 C (-22 to +140 F).
How tall is the ST421R-SF2SNF?
It stands 2.1 in. (53 mm) above the mounting surface. The radome is 7.4 in. (188 mm) long and 3.7 in. (94 mm) wide.
Specifications are taken from Sinclair Technologies product data for the ST421R-SF2SNF. Sinclair may change specifications without notice. Last verified by radioparts.com: October 2026.
Not sure this is the right band or connector for your vehicle? Contact radioparts.com with your radio model and system frequencies before you drill.
