HF Upconverter Guide: When You Need One, When You Don't
HF upconverters used to be mandatory for RTL-SDR users who wanted shortwave. That's no longer true. The RTL-SDR V4's built-in HF has made the category niche — but if you already own a V3, an HF-less SDR, or you want the best HF performance on a budget, an upconverter still has a place.
What an Upconverter Actually Does
An HF upconverter takes signals below about 30 MHz and mixes them up to a higher frequency where your SDR can tune. The most common design uses a 125 MHz local oscillator, so a signal at 7.1 MHz (the 40-meter amateur band) appears at 132.1 MHz inside your SDR. Your software subtracts 125 MHz to display the original frequency.
Why bother? Because most cheap RTL-SDR dongles can't natively tune below about 24 MHz. Direct sampling mods exist, but they're noisy. A quality upconverter uses a proper mixer, front-end filtering, and a stable oscillator — producing cleaner HF reception than direct sampling and extending to VHF-only dongles that couldn't otherwise hear HF at all.
Should You Buy One? Quick Decision
Buy one if...
- You own an RTL-SDR V3 and want better HF than direct sampling
- You own a VHF/UHF-only SDR (Airspy Mini, HackRF One below 30 MHz)
- You want to use the same HF antenna across multiple receivers via a switch
- You're building a dedicated HF monitoring station separate from VHF/UHF
Skip it if...
- You own or are buying the RTL-SDR V4 — it has HF built-in
- You own an SDRplay or Airspy HF+ Discovery — they tune HF natively with better performance
- Your only HF interest is casual AM broadcast listening — any direct-sampling mod is adequate
- You want to minimize the number of boxes in your shack
Why the V4 Usually Makes Upconverters Unnecessary
The RTL-SDR Blog V4 has an internal triplexer that splits incoming signals by frequency. Below ~28 MHz, the signal goes through an onboard upconversion path and lands on the tuner's native VHF range. Above 28 MHz, it bypasses that path and feeds the tuner directly. All of this is automatic — you don't toggle modes, you just tune wherever you want between 500 kHz and 1.766 GHz.
The HF performance isn't as good as an Airspy HF+ Discovery or SDRplay RSPdx, but it's comparable to a Nooelec Ham It Up paired with a V3 — and it's in one box, for less money, with no extra wiring. For 90% of SDR owners, the V4 eliminates the upconverter question entirely.
The one scenario where the V4's built-in HF falls short: if you live next to a 50 kW AM broadcast station and want to hear weak signals nearby. The V4's 8-bit ADC will dynamic-range out before a dedicated HF SDR does. If that's your situation, see our Airspy vs RTL-SDR comparison for the HF+ Discovery.
Nooelec Ham It Up Plus: The Standard Upconverter
Nooelec Ham It Up Plus
If you decide you need an upconverter, this is the one. The Ham It Up Plus uses a 125 MHz oscillator, has a passthrough switch that lets VHF/UHF signals skip the upconversion, includes its own SMA-to-SMA jumpers, and ships with a metal enclosure. Nooelec has iterated this product for years.
- 300 kHz – 65 MHz input range
- 125 MHz local oscillator, TCXO-stabilized
- Passthrough mode for VHF/UHF
- Bias-T pass for LNAs
- USB-powered
- SMA connectors
Software Setup
Using an upconverter is nearly transparent once configured. In your SDR software:
- Open the frequency correction / offset setting
- Enter the negative of your upconverter's LO frequency (−125,000,000 Hz for the Ham It Up)
- Save the preset. When the upconverter is in the signal path, enable the offset; when it's not, disable it.
Most SDR programs save this as a per-source preset, so switching between "HF upconverted" and "VHF direct" is a one-click change. SDR# calls it "Shift Frequency." SDR++ calls it "Offset." GQRX calls it "LNB LO."
When to Add an LNA and Filter
For weak-signal HF (amateur DX, WSPR, FT8 at low power), adding a low-noise amplifier and a band-pass filter ahead of the upconverter helps. Our SDR antennas guide covers the Nooelec LANA SAWbird LNA which is a common pairing. The order in the signal chain is usually: antenna → band-pass filter → LNA → upconverter → SDR.
Be careful with bias-T voltages. The Ham It Up can pass bias-T from the SDR to an external LNA, but only if the SDR generates it correctly. The RTL-SDR V4's software-controlled bias-T is well-behaved for this.
Best Overall / Best Value / Best Budget
Best Overall (No Upconverter Needed)
RTL-SDR Blog V4
$35-45
Built-in HF plus everything the V3 did. Fewer boxes, less wiring.
Check Price →Best Upconverter
Nooelec Ham It Up Plus Upconverter
$60–$80
The default choice if you need one. Reliable, well-documented, passthrough mode.
Check Price →Budget Path (V3 + Direct Sampling)
RTL-SDR Blog V3
$30-40
Only if you already own it. New buyers should spend the extra on the V4.
Check Price →Frequently Asked Questions
Do I need an HF upconverter for an RTL-SDR V4?
No. The V4 has an internal triplexer that routes signals below 28 MHz through a built-in upconverter path automatically. You can plug an HF antenna into the V4's SMA connector and tune down to 500 kHz with no extra hardware. That's the main reason the V4 is worth the upgrade from V3.
What does an HF upconverter do?
It shifts HF signals (500 kHz to ~30 MHz) up to a frequency your VHF/UHF SDR can tune — typically by adding 100 or 125 MHz. So a 7.1 MHz amateur signal becomes 107.1 MHz or 132.1 MHz after upconversion. You set an offset in your SDR software to display the original frequency.
Which upconverter should I buy?
The Nooelec Ham It Up Plus is the mainstream choice. It uses a 125 MHz IF, has a bypass switch for VHF passthrough, includes a built-in bias-T pass, and works with every SDR that tunes 125+ MHz. It's built well and has clear installation instructions.
Is direct sampling on the RTL-SDR V3 good enough for HF?
It works for casual listening to strong stations. For weak-signal work, DX, or crowded bands, a proper upconverter or a V4 is much better. Direct sampling folds image frequencies into your passband and has no front-end filtering, so strong broadcast stations can overwhelm adjacent weak signals.
Can I use an upconverter with SDRplay?
You can but usually shouldn't — SDRplay receivers already tune HF natively with far better performance than an upconverter adds. The exception is if you have a specific antenna setup that only works through the upconverter. For a plain SDRplay RSP1A or RSPdx, skip the upconverter.
How do I set the frequency offset in SDR software?
In SDR#, SDR++, and most programs there's a 'Frequency Correction' or 'Offset' field. For a 125 MHz upconverter, enter -125,000,000 Hz. The software then displays the true HF frequency even though the dongle is actually tuning at 125 MHz + true frequency. Some programs store this per-hardware preset.
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