Also known as: E4000, Elonics E4000, E4k
E4000 is a wideband CMOS RF tuner chip made by the Scottish company Elonics, and one of the two tuners — alongside the Rafael Micro R820T2 — that defined the early RTL-SDR era.1 A tuner sits between the antenna and the RTL2832U demodulator, mixing the frequency you want down toward baseband; the E4000 was valued for reaching higher in frequency than any other RTL-SDR tuner, at the cost of a gap in its coverage and more noise.
Overview
The E4000 is a zero-IF (direct-conversion) tuner: it mixes the target frequency directly to a complex baseband using an on-chip local oscillator, which the RTL2832U then digitises. Its distinguishing spec is reach — roughly 52 MHz up to about 2200 MHz — noticeably higher than the ~1766 MHz ceiling of the R820T2. That extra top end made E4000 dongles the tool of choice for anyone needing the 1.8–2.2 GHz range (some aeronautical, pager, and early cellular monitoring) that the newer R820T2 simply cannot see.
The coverage gap and the noise trade-off
Two caveats came with the reach. First, the E4000 has a coverage gap — a band roughly 1100–1250 MHz where its frequency synthesizer cannot lock, leaving a dead zone in the middle of its otherwise wide range. Second, across the frequencies most scanning cares about (VHF/UHF), the E4000 is generally noisier and less sensitive than the R820T2, and it has a larger DC spike at the tuning centre typical of direct-conversion designs. So for everyday reception the R820T2 usually wins; the E4000 was the specialist’s choice for its ceiling, not its floor.
Discontinuation
The E4000 became scarce when Elonics ceased trading around 2012, ending production of the chip just as the RTL-SDR hobby was taking off. Existing stock was consumed, prices on the used and stockpiled market rose, and the R820T2 (later re-released as the R860) settled in as the de-facto standard tuner because it was cheaper, more sensitive across the popular bands, and still in production. Today an E4000-based dongle is a premium/legacy item bought specifically for the extended top-end coverage — Nooelec’s NESDR SMArt XTR line is the main way to still get one new.
Relevance to GopherTrunk
To GopherTrunk the tuner is essentially invisible: the RTL2832U presents the same raw-IQ interface regardless of whether an E4000 or an R820T2 sits in front of it, so GopherTrunk drives an E4000 dongle exactly like any other RTL-SDR. The tuner choice matters only for what frequencies you can reach and how cleanly: an E4000 buys coverage above ~1.77 GHz that an R820T2 lacks, but for the VHF/UHF land-mobile trunking GopherTrunk decodes, an R820T2/R860 unit is the more sensitive and more available pick. Mind the ~1100–1250 MHz gap if a target sits there.