Relacart EZ.B8 bodypack transmitter with 3.5 mm external microphone input
A bodypack transmitter is the component that turns a lavalier, headset or instrument cable into a radio link. It is also the part of a wireless microphone system that a presenter actually wears, which makes its size, connector and battery life a daily operational concern rather than a datasheet detail.
This guide sets out the decisions that matter when specifying a bodypack, using the published specifications of Relacart’s EZ.B8, EZD.B8 and UR-D1B transmitters as worked examples. Every figure quoted below comes from those specifications.
What a Bodypack Transmitter Actually Does
A bodypack transmitter takes the low-level signal from a wired microphone capsule, encodes it and radiates it over UHF to a paired receiver. Because the microphone is connected by a short cable, the bodypack has to supply the capsule, encode the audio and transmit — all from a position close to the human body, which absorbs and reflects radio energy far more than open air does.
Three specifications follow directly from that job: the RF output power the transmitter can run at, the connector it uses to accept a microphone, and how long it runs on a set of batteries. Everything else on the datasheet is secondary to those three.
The Four Decisions That Matter
- Microphone connector — The connector decides which capsules you can use. The EZ.B8 and EZD.B8 use a 3.5 mm external microphone input that accepts Relacart LM-P01 lavalier and HM-P06 headset microphones; the UR-D1B uses a 4-pin mini XLR, the standard termination for professional lavalier and headset capsules.
- Battery life — Two AA cells are typical. Relacart quotes 10 hours or more for the EZ.B8, 8–10 hours for the EZD.B8, and around 8 hours on alkaline cells for the UR-D1B.
- RF output power — The UR-D1B offers high, medium and low settings. Lower power reduces current draw and, in multi-channel systems, the intermodulation products the transmitter contributes.
- Frequency band — Relacart bodypacks work across the 470–936.85 MHz range depending on the model, but the usable portion of that range is set by local radio regulations, not by the transmitter.
Matching the Bodypack to the Scenario
Relacart UR-D1B true digital bodypack transmitter with 4-pin mini XLR audio input
Table 1 — Relacart bodypack transmitters by use case
| Scenario | Bodypack | What the specification supports |
|---|
| Schools, corporate AV, single presenter | EZ.B8 | 3.5 mm microphone input plus a separate 3.5 mm monitor output; 10 hours or more on two AA cells; 60–80 m working distance as a system |
| Multi-purpose venues on the EZD.MI platform | EZD.B8 | 3.5 mm input for the LM-P01 lavalier or HM-P06 headset; 8–10 hours on two AA cells |
| Stage, broadcast and high-channel-count work | UR-D1B | 4-pin mini XLR input; single-channel 64 MHz bandwidth; 470–936 MHz carrier range; selectable RF power |
| Confidential meetings on the UR-D platform | UR-D1B with a UR-D2 receiver | The system carries AES-256 and SM4.0 encryption at the link level |
3.5 mm Jack or 4-Pin Mini XLR?
A 3.5 mm jack keeps the transmitter small and the price down, and it is the connector used across Relacart’s compact EZ.B8 and EZD.B8 bodypacks. A 4-pin mini XLR locks in place, resists pull-out on a moving presenter and is the termination used by most professional lavalier and headset capsules — which is why the UR-D1B uses it.
Table 2 — Connector comparison
| Aspect | 3.5 mm mini jack | 4-pin mini XLR |
|---|
| Relacart bodypack | EZ.B8, EZD.B8 | UR-D1B |
| Locking connector | No | Yes |
| Capsule options | Compact lavalier and headset microphones | Professional lavalier and headset range |
| Extra feature | EZ.B8 adds a separate 3.5 mm monitor output | Volume trim from +15 to −5 dB in 1 dB steps (UR-D1B) |
Common Mistakes
- Choosing the bodypack before the microphone. The connector determines which capsules you can use — if the application depends on a specific lavalier, start there.
- Running every transmitter at maximum RF power. Where power is selectable, as on the UR-D1B, short-range channels can run lower, which saves battery and reduces intermodulation in crowded installations.
- Quoting battery life without naming the cell type. The UR-D1B figure of around 8 hours is specified for alkaline AA cells; rechargeable cells behave differently.
- Treating working distance as a transmitter property. The 60–80 m figure Relacart quotes for the EZ.B8 system is a system figure under ideal conditions.
- Mixing platforms. A bodypack pairs only with receivers from the same series: EZ.B8 with EZ.Mi receivers, EZD.B8 with EZD.MI, UR-D1B with UR-D series.
Selection Checklist
- Confirm the microphone you plan to use and its connector termination.
- Check the usable carrier range against local radio regulations before specifying a band.
- Decide whether you need a monitor output at the bodypack — the EZ.B8 provides one.
- Estimate battery life from the number of cells and the rated hours, then add a margin.
- Count the channels that will run simultaneously and plan frequencies for them.
- Verify RF power options so short-range channels can run at reduced power.
- Confirm the bodypack belongs to the same series as the receiver you already own.
- Order spare cables for the connector type you choose.
Frequently Asked Questions
What is the difference between a bodypack transmitter and a handheld transmitter?
A bodypack transmits audio from a wired lavalier, headset or instrument cable and is worn on the body. A handheld transmitter has the capsule built into its housing. Both connect to the same receivers within a series.
How long do bodypack transmitter batteries last?
It depends on the model and the cell type. Relacart rates the EZ.B8 at 10 hours or more on two AA 1.5 V cells, the EZD.B8 at 8–10 hours, and the UR-D1B at about 8 hours on alkaline AA cells.
Can I use any lavalier microphone with a bodypack?
No. The connector and the capsule wiring have to match. Relacart bodypacks use either a 3.5 mm external microphone input (EZ.B8, EZD.B8) or a 4-pin mini XLR input (UR-D1B).
Does a bodypack transmitter work with any receiver?
It works with receivers on the same platform and in the same band. The EZ.B8 pairs with EZ.Mi series receivers, the EZD.B8 with EZD.MI, and the UR-D1B with UR-D series receivers.
What is the working distance of a bodypack system?
Relacart quotes an effective working distance of approximately 60–80 m for the EZ.B8 and EZ.Mi systems under ideal conditions.
