Andy,
First, I’m just curious why your focus on the 1‑second PPS output. Nearly every GPS module provides a PPS signal, so unless you specifically need a programmable frequency synthesizer, the PPS alone doesn’t justify choosing a Bodnar unit.
I don’t own a Bodnar GPSDO myself, but I’ve done extensive research on them while considering a purchase, and I’ve come across several critiques worth noting.
The primary reason for my hesitation relates to my intended application. The Bodnar units generate only square‑wave synthesized frequency outputs, with no option for sine‑wave output. This immediately rules out direct use as a local oscillator without adding an external smoothing or band‑pass filter to suppress the strong harmonic content inherent to square‑wave signals. For any LO‑sensitive RF work, those harmonics must be removed before the signal can be used cleanly.
The reason for the square wave output is that the LBE‑1421 uses a SiLabs clock‑synthesizer type IC. These chips generate frequency outputs using digital PLLs and fractional dividers, and the output stages are digital drivers, not analog RF stages.
That means:
- The chip cannot produce a sine wave directly.
- The output is a rail‑to‑rail square wave with very fast edges.
- Harmonics are strong and extend well into the GHz region.
This is why the device can cover such a wide frequency range at low cost — but the trade‑off is waveform purity.
The Bodnar GPS disciplined synthesizers have been around for a long time and for their general use they seem to be adequate units. For some users they do seem to have some quirks they reference.
I’d say it’s near essential to have a stable, low noise reference especially where you’re working in sub-Hz bandwidth. Not all GPSDOs are equal. I really don’t like the Leo Bodnar as its short term stability is not good and if it unlocks, its hold-over is awful. It’s probably fine for lower frequencies but for 32GHz and 8GHz, the short term stability is a problem in my opinion.
I was using a Datum/Symmetricom System 2000 rubidium GPSDO. It is excellent all round except there are some close in spurs on the output which can get through and multiply in synths. It doesn’t make any difference if working in sub-Hz but if looking at wider spectra on strong signals the spurs are visible. It is fine if cleaned up by locking another OCXO. I use them for 25 & 40MHz references. Using it as a reference for a signal generator with an internal OCXO which locks to the 10MHz is good. For most purposes, I find an undisciplined rubidium standard is convenient. It maintains a few parts in 10e11 but I calibrate it periodically against the Datum. I’d use the Datum direct if I wanted long integration times and better absolute frequency indication.)
A quick AI search for additional quirks yields this;
LBE‑1421: Model‑Specific Critiques
### 1. **Phase Noise Not Competitive With OCXO/Rubidium References**
Measured phase noise is **good**, but **not in the same class** as high‑end GPSDOs like the Trimble Thunderbolt or Datum LPRO‑101.
This is explicitly noted in user reviews and measurement commentary. [eHam.net](https://www.eham.net/reviews/view-product?id=13068)
– The LBE‑1421 uses a **TCXO disciplined by GNSS**, not an OCXO.
– ASR reviewers note that while the noise floor is respectable, **close‑in phase noise** (1–20 Hz offset) is where OCXO‑based units outperform it. [Audio Science Review (ASR) Forum](https://www.audiosciencereview.com/forum/index.php?threads/leo-bodnar-lbe-1421-review-clock-generator.68062/)
**Implication:**
For ultra‑low‑phase‑noise applications (microwave LO chains, narrowband SETI, maser IF chains), the LBE‑1421 is usable but not best‑in‑class.
—
### 2. **Holdover Stability Is Weaker**
Multiple reviewers note that **holdover accuracy is not as strong** as other GPSDOs. [eHam.net](https://www.eham.net/reviews/view-product?id=13068)
– The TCXO drifts more quickly when GNSS lock is lost.
– The LBE‑1421’s GNSS receiver is very sensitive, so holdover events are rare—but when they occur, drift is noticeable.
**Implication:**
If your GPS antenna has intermittent sky view, expect more drift than OCXO‑based GPSDOs.
—
### 3. **Square‑Wave Output Requires Filtering**
The LBE‑1421 outputs **square waves** up to 1.4 GHz.
– Strong harmonics require **external filtering** for RF purity.
– This is not a flaw, but a design trade‑off: the device is a synthesizer, not a sine‑wave lab reference.
**Implication:**
For mixer LO injection or sensitive RF front‑ends, a bandpass or low‑pass filter is mandatory.
—
### 4. **USB Power Noise Sensitivity**
Users report that phase noise performance is **worse when powered from noisy USB sources**. [eHam.net](https://www.eham.net/reviews/view-product?id=13068)
– A clean linear supply or filtered USB source improves jitter and close‑in noise.
– The LBE‑1421 draws very little current, but is still sensitive to supply noise.
**Implication:**
Bench setups should avoid powering the unit from PC USB ports.
—
### 5. **Software & UX Issues**
ASR reviewers note several quirks:
– Software is functional but **not polished**.
– Multiple configuration utilities exist, causing confusion. [YouTube](https://www.youtube.com/watch?v=GGFK81hF-Qw)
– Documentation is sparse.
– Mini‑USB connector is outdated.
**Implication:**
Configuration is easy once learned, but onboarding is not smooth.
—
### 6. **Sub‑Hz Noise Concerns**
ASR discussion highlights suspicion of **“nasty things going on in the sub‑Hz region”** that are difficult to measure. [Audio Science Review (ASR) Forum](https://www.audiosciencereview.com/forum/index.php?threads/leo-bodnar-lbe-1421-review-clock-generator.68062/page-3)
– REW measurements stop at 2 Hz, so ultra‑low‑frequency jitter behavior is not fully characterized.
– This is a known limitation of TCXO‑based GPSDOs.
**Implication:**
For applications sensitive to <1 Hz phase noise (precision audio clocks, VLBI timing, long‑integration DSP), this is a potential concern.
—
### 7. **Warm Operation**
The LBE‑1421 runs warm due to TCXO temperature stabilization.
This is normal but noted by reviewers. [YouTube](https://www.youtube.com/watch?v=GGFK81hF-Qw)
—
| Category | Critique | Evidence |
|————————–|——————————————-|———————|
| Phase Noise | Good but not OCXO‑class | ASR + ham reviews |
| Holdover | Weaker than OCXO GPSDOs | Ham review |
| Output Purity | Square wave; harmonics strong | General Bodnar design |
| Power Sensitivity | USB noise affects jitter | Ham review |
| Software | Multiple tools; sparse docs | YouTube review |
| Sub‑Hz Noise | Suspected issues <2 Hz | ASR discussion |
| Thermal Behavior | Runs warm | YouTube review |
—
## 🧭 Bottom Line for (microwave LO chains, SETI, maser IF work, precision timing):
– **As a frequency reference:** Excellent stability and GNSS discipline.
– **As a microwave LO source:** Usable with filtering and buffering.
– **For ultra‑low‑phase‑noise applications:** OCXO‑based GPSDOs will outperform it.
– **For multi‑frequency synthesis:** The LBE‑1421 is unmatched at its price.
Adrian