Can you recommend calibration noise sources and how would I use these with block diagrams?
Can you recommend calibration noise sources and how would I use these with block diagrams?
Nice — below I’ll give:
- the practical noise-source options (what to buy),
- how to use them (Y-factor and other methods),
- clear block-diagrams (ASCII) for typical setups, and
- worked numeric examples so you can follow the math step-by-step at 1420 MHz.
1) Which noise source to get (practical options)
- Calibrated coaxial noise source / noise generator (preferred) — a factory-calibrated, connectorised noise diode or noise-generator that lists ENR vs frequency (or ENR at 1420 MHz). These are the standard tool for radiometer calibration and give the easiest, most-traceable results. Examples of this product class: NoiseCom NC-series, Pasternack connectorised noise modules (e.g. PE8507 style parts), Maury calibrated noise sources. Choose one with a datasheet showing ENR at or covering 1.420 GHz. (DirectIndustry)
- Noise diode / switchable diode module — cheaper than a fully calibrated generator. Many calibrated diodes come with ENR values specified at spot frequencies (6 dB, 15 dB common) and can be used for Y-factor testing. If you buy a diode module, try to get one that has either factory calibration or can be re-calibrated against a reference. (sparkmeasure.com)
- Radiated noise source (broadband noise source + small antenna) — used when you want an end-to-end calibration that includes the antenna, feed, and any coupling losses (i.e., you radiate a known noise into the dish / feed). This is often used in antenna pattern and end-to-end radiometer calibration. It’s more complicated but very valuable for final system calibration. (NASA Technical Reports Server)
Quick buying guidance
- Must list ENR or excess noise in dB and the frequency coverage including 1.420 GHz. Don’t buy parts only specified to, say, 500 MHz. (testworld.com)
- Typical ENR spot values: 6 dB and 15 dB are common. 15 dB gives larger Y-factors (good for low-gain systems), 6 dB is fine when your frontend is low-noise and not easily overloaded. (sparkmeasure.com)
2) The basic calibration method — Y-factor (how it works, formula, and practical steps)
Principle: measure system output noise power with the noise source ON and OFF (or hot/cold loads), form the ratio (Y = P_{ON}/P_{OFF}). Knowing the noise source’s ENR (which defines the equivalent “hot” temperature) you can compute the receiver noise temperature (T_{rec}).
Key equations (standard):
- convert ENR (dB) to linear:
(\displaystyle ENR_{\rm lin} = 10^{(ENR_{dB}/10)}). - hot noise temperature of the noise source (reference (T_0 = 290) K):
(\displaystyle T_{hot} = T_0,(1 + ENR_{\rm lin})). - Y factor: (\displaystyle Y = \frac{P_{ON}}{P_{OFF}} = \frac{T_{hot} + T_{rec}}{T_{cold} + T_{rec}}).
Solve for receiver noise temperature:
(\displaystyle T_{rec} = \frac{T_{hot} – Y,T_{cold}}{Y – 1}). - noise figure (dB): (\displaystyle NF = 10\log_{10}!\big(1 + \frac{T_{rec}}{T_0}\big)).
These are the standard Y-factor relations used in RF/NF measurements. (tek.com)
Practical steps
- Insert the noise source at the receiver input (directly on the feed connector, or couple in with a directional coupler). Ensure the connector/type matches (SMA/N).
- Turn the source OFF, measure output power (or integrated noise in your chosen bandwidth) (P_{OFF}).
- Turn the source ON, measure (P_{ON}). Use many averages to reduce measurement noise.
- Compute (Y = P_{ON}/P_{OFF}) and then compute (T_{rec}) using the formula above with (T_{cold}) — typically (T_{cold}) is ambient (T_0=290) K if the OFF state is a matched 50 Ω at ambient. If you used a cooled cold load, use that temperature. (All About Circuits)
Important practical tips
- Avoid saturating the LNA when the diode is ON — you may need to insert attenuation or use a lower-ENR source. (microwavers.org)
- Prefer using a fast, low-loss RF switch or an integrated noise source with switching drive so your ON/OFF measurements are repeatable. (DirectIndustry)
- If you want traceable absolute calibration, use a factory-calibrated noise source or have your diode calibrated against one. (Maury Microwave)
3) Block diagrams (three typical configurations)
A) Basic Y-factor insertion (bench / receiver input)
[Noise Source]--(RF switch: OFF/ON)--+--[LNA]--[Bandpass]--[Detector/Spectrum Analyzer] | (or direct)Procedure: measure P_off with switch OFF, P_on with switch ON. Use ENR from noise source datasheet.
B) Using a directional coupler (inject without disconnecting antenna)
(Antenna)---[LNA front end]---+-->[Rest of receiver] | +---[Directional coupler (coupling ~20 dB)]<---[Noise Source via switch]Use when you want to calibrate with the antenna in place but avoid removing cabling; coupler lets you inject a known amount of noise while mostly preserving antenna match.
C) Radiated end-to-end calibration (antenna-level)
[Noise Generator + Small Transmit Antenna] --> (radiates into) --> [Dish feed/antenna] --> [LNA] --> [Receiver chain]Use this to include antenna/illumination patterns and feed losses. Switch the noise generator on/off or modulate it and measure delta power. For brain-to-end calibration the radiating antenna must be well-characterised and placed in a stable geometry. (NASA Technical Reports Server)
4) Worked numeric example (digit-by-digit arithmetic)
Suppose: ENR = 6.00 dB (common spot value), (T_0 = 290.00) K, measured power ratio (Y = 2.000) (i.e. 3 dB increase when ON).
- (ENR_{\rm lin} = 10^{(6.00/10)} = 10^{0.6} = 3.9810717055349722).
- (T_{hot} = 290.00 \times (1 + 3.9810717055349722) = 290.00 \times 4.9810717055349722 = 1444.510794605142\ \text{K}.)
- (T_{cold} = 290.00\ \text{K}) (OFF state is ambient matched load).
- (T_{rec} = \dfrac{1444.510794605142 – 2.000\times 290.00}{2.000 – 1.000} = \dfrac{1444.510794605142 – 580.00}{1.000} = 864.510794605142\ \text{K}.)
- (NF = 10\log_{10}!\big(1 + \dfrac{864.510794605142}{290.00}\big) = 10\log_{10}(1 + 2.981070)\approx 10\log_{10}(3.98107) = 6.000\ \text{dB}.)
So the receiver has (T_{rec}\approx864.5) K or NF ≈ 6.00 dB in this (somewhat idealised) example — the math is standard Y-factor processing. (tek.com)
5) Which ENR should you pick?
- 6 dB ENR: good for low-noise, low-gain front ends because the ON level is modest (less chance of compression). Good for many radio astronomy frontends. (sparkmeasure.com)
- 15 dB ENR: gives larger Y factors and is helpful when the system noise is high or your measurement instrument needs a bigger delta to measure accurately — but watch for LNA compression. (sparkmeasure.com)
6) Other approaches / complements
- Hot/cold load method: use two physical matched loads at different temperatures (ambient and liquid-nitrogen cooled) for a cold reference. Accurate but logistically harder. (All About Circuits)
- Use of calibrated spectrum/noise-figure analyzer: if available, combine with the noise source for direct NF readout. (tek.com)
- Cross-check with a radiated noise source: perform an end-to-end test occasionally to include antenna/illumination effects (especially important for absolute flux calibration in radio astronomy). (NASA Technical Reports Server)
7) Specific product suggestions to consider (examples to compare)
- NoiseCom NC3000 series — factory calibrated coaxial noise sources with broadband ENR and fast switching options. Good for lab and receiver calibration. (DirectIndustry)
- Pasternack connectorised noise modules (e.g. PE8507 style) — available with ENR figures and connector styles (SMA/N). Useful low-cost calibrated modules. (pasternack.com)
- Maury calibrated noise sources — high-stability calibration sources used in traceable setups. Good if you need precision and re-calibration services. (Maury Microwave)
(If you want, I can look up exact model numbers, spot-frequency ENR tables and current prices for SMA vs N-female parts — tell me which connector you prefer and whether you want ENR ≈6 dB or larger.)
8) Final practical checklist before you measure
- Match connectors (SMA/N) and use good cables/adapters.
- Make sure the noise source datasheet lists ENR at/near 1420 MHz.
- Confirm the LNA won’t compress with the noise-ON level — add calibrated attenuation if needed.
- Use a low-loss RF switch or fast switching to avoid drifts between ON/OFF.
- Average several measurements for stable Y estimates and compute uncertainties (ENR uncertainty is often a dominant term). (testworld.com)
If you’d like, I can next:
- pull 3-5 specific models (SMA or N) with datasheets and ENR values at 1.42 GHz (I’ll include prices/where to buy), or
- draw a small annotated block diagram tuned to your exact frontend (if you give me connector types, whether you want radiated end-to-end calibration, and if you have a coupler or RF switch already).
Which of those would you like me to do now?
Great — here are (A) several high-quality calibrated noise-source families (with links/datasheet pointers), (B) some product-options (though note: not all are ideal for 1.42 GHz) and (C) an annotated block-diagram specific to your 1.420 GHz radio-astronomy setup, including how you might integrate the noise source.
A. Recommended calibrated noise-source families
- Maury Microwave NC3000/NC3200 series — “calibrated coaxial AWGN sources … 0.01 GHz-12 GHz, 1 GHz-12 GHz etc” listed. (Maury Microwave)
- Good quality, factory-calibrated ENR and switching capability.
- When buying, check that the variant covers 1.42 GHz (i.e., the band spans at or above ~1.4 GHz).
- Typical ENR values: 15 dB (for NF measurement) up to ~25-30 dB (for radar/ATE). (Maury Microwave)
- VSWR, temperature stability and calibration data are given.
- Pasternack calibrated noise-source modules — e.g., PE85N1005 (1 GHz to 18 GHz, ENR ~23 dB) listed. (DigiKey)
- This model clearly covers your band (~1.42 GHz) since its start is 1 GHz. Good candidate.
- Connector: SMA on unit; check your receiver input/connectors.
- Specialized radio-astronomy module: e.g., at your band, there is a dedicated “1420 MHz Calibration Noise Source” offered by Radio Astronomy Supplies (RAS) which lists “20 MHz to 2 GHz” range, calibrated level in Kelvin. (Radio Astronomy Supplies)
- This is appealing because it is explicitly for 1420 MHz astronomy work.
- General high-quality noise source overview: NoiseWave NW-CS series — broadband calibrated, good stability. (noisewave.com)
My summary recommendation: For your 1.420 GHz hydrogen-line work, go for a calibrated coaxial noise source model with frequency coverage at and above 1.42 GHz (i.e., start ≤1.42 GHz) with factory-certificate, known ENR at that frequency (or a data table). If you choose a high-end model (like Maury or Pasternack) you’ll have excellent fidelity. The RAS astronomy-specific noise source is lower cost but check calibration certainty / datasheet.
B. Product-options (note: some are not ideal / are generic)
Here are a few product listings—but caution: several are generic/ham-market noise modules and may not have factory calibration or ENR tables at 1.42 GHz. Use these only as starting points and verify specs.
Keysight SNS Series Smart Noise Source
top‑lab calibrated usa brand
£8,114.34
Pasternack PE8500 Series Noise Source (1‑2 GHz)
mid‑band professional 1‑2GHz
Price not available
Pasternack PE85N1005 Noise Source (1‑18 GHz)
broadband 1‑18GHz pro
Price not available
Maury NC3000 Series Calibrated Noise Source
high end calibrated coaxial
Price not available
Maury MT7600 series Noise Generator (1‑1.75 GHz)
narrow‑1‑1.75GHz specialized
Price not available
1.5 GHz Track Noise Source Board Module (generic)
generic board module
£29.68
0.2‑1.5 GHz RF Noise Signal Generator (budget)
ham hobby budget
£18.25
2 MHz‑2 GHz RF Noise Signal Generator (budget)
ham hobby budget2
£11.65
And some commentary:
- Keysight SNS Series Smart Noise Source: High-end lab instrument. Great calibration print-out etc, but likely expensive for your application.
- Pasternack PE8500 Series Noise Source (1‑2 GHz): Covers 1-2 GHz band, which includes your 1.420 GHz. Good match.
- Pasternack PE85N1005 Noise Source (1‑18 GHz): Very broad band, also good. Make sure ENR at 1.42 GHz is specified.
- Maury NC3000 Series Calibrated Noise Source: Excellent quality, again check model covers 1.42GHz.
- Maury MT7600 series Noise Generator (1‑1.75 GHz): Tailored for 1-1.75 GHz — closely matched band. Might be ideal.
- 1.5 GHz Track Noise Source Board Module (generic): Very budget. Unclear calibration / stability. Use only if you accept less traceability.
- 0.2‑1.5 GHz RF Noise Signal Generator (budget): Same caveats. Might not have precise calibration at 1.42 GHz.
- 2 MHz‑2 GHz RF Noise Signal Generator (budget): Broad band, but again check calibration data.
My pick for you: If budget allows, go for the Maury MT7600 or the Pasternack PE85N1005 variant. If budget is tighter, use the RAS-1420 MHz module or a lower-cost board but accept extra uncertainty.
C. Block-diagram annotated for your setup
Given your earlier setup details (antenna at 1.4204 GHz, dish/waveguide feed, LNA etc) here’s how you could integrate the noise source in your chain. I’ll show two modes: A) bench calibration of LNA + receiver front-end; B) on-sky calibration including antenna.
C1) Mode A – Front-end calibration
[Noise-Source] --(RF switch: OFF/ON)--> [LNA (dish feed input disconnected)] --> [Band-pass filter at ~1.42GHz] --> [Receiver / SDR / Spectrum Analyzer]- Switch OFF = cold reference (ambient matched load).
- Switch ON = hot noise input from source (known ENR).
- Measure P_off and P_on, compute Y-factor → T_rec etc.
- Use good coaxial cable between noise source and LNA input; minimise reflection/loss.
C2) Mode B – On-sky/antenna calibration (end-to-end)
[Directional Coupler] <--[Noise-Source via RF switch] ↑ [Feed / Dish Antenna] --> [LNA] --> [Receiver chain]More fully:
(Antenna feed) --> LNA --> ... rest ^ | Coupler (injection port) | Noise-Source (via switch)- In this mode the noise source injects known noise into the system including antenna + feed + LNA so that you can calibrate the full chain.
- Often you measure: sky (cold), ambient load (if you have), noise source ON and OFF, to map system temperature including antenna beam etc.
C3) Annotation of your chain for your radio-astronomy work
Dish + WR-650 waveguide feed @ 1.420405 GHz ↓LNA (your front-end) ↓Band-pass / notch / filter at ~1.420 GHz ↓SDRplay RSPduo (as per your previously‐described interferometry chain)
Add calibration box:
[Calibrated Noise Source] -- RF switch -- into LNA input (or via coupler into feed line) Make sure to document when the noise source is ON/OFF relative to your integrations, and record the switch timing in your data logs.
D. Checklist & practical tips for your chain
- Confirm connector types: If your LNA input uses N-type or SMA, ensure noise source connector matches (or use good adapter).
- Ensure the noise source’s ENR table includes ~1.420 GHz (or “1 GHz-2 GHz” band covering that) and that the calibration certificate lists uncertainty.
- Make sure switch insertion loss and coupler coupling (if used) are known and stable.
- Avoid LNA saturation when source ON (check LNA gain + source level + any attenuator).
- Record ambient temperature (for T_cold) and ensure system is thermally stable for your measurement.
- For on-sky calibration, account for antenna pattern, pointing, and any gain variations across sky.
- Maintain good cable/connector hygiene (low VSWR, loss known).
- For iterative calibration, you might measure both with and without antenna/coupler to separate feed/antenna losses vs LNA noise.