Active Splitters, Distribution Amplifiers & Preamps

RF-over-coax distribution amps, MMIC LNAs, masthead preamps, bias-T arrangements, the noise-figure / gain budget across an active distribution network

Section	Topic
1	About this volume
2	When passive isn’t enough — the link-budget case for active distribution
3	MMIC LNAs — the front-end gain block
4	Masthead preamps — RX gain at the antenna
5	Active distribution amplifiers — one antenna, many receivers
6	Bias-T deployment in active networks
7	Noise figure budget — Friis cascade
8	Gain budget — keeping the front end out of compression
9	T/R switching — protecting LNAs during TX
10	Best-case use
11	Worst-case use — overload and IMD
12	DIY build — a 0.1-2000 MHz LNA on a SAV-541+ MMIC
13	DIY build — a 4-way distribution amp with masthead bias-T
14	Commercial buys
15	Companion gear
16	Common gotchas and myths
17	Resources

1. About this volume

Volume 18 (Passive splitters, combiners & couplers) covered the passive distribution family — devices that lose signal because that’s what passive splitters do. A 4-way passive split costs 6 dB; an 8-way costs 9 dB; a 16-way costs 12 dB. For receive applications where the signal is already weak (distant beacons, EME, satellite downlinks, GPS, weak DX), passive losses can drop the signal below the receiver’s noise floor.

This volume covers the active alternative: distribution networks with built-in low-noise amplifiers (LNAs) that boost the signal before splitting it, replacing the passive loss with active gain. The key insight is from the Friis noise-figure equation: the first amplifier in a cascade dominates the system’s noise figure, so an LNA placed at the antenna (or just after) sets the system NF regardless of downstream losses.

The volume closes Phase 4 of the Antennas series and covers:

When active distribution is necessary vs when passive is sufficient (§2)
MMIC LNAs: the modern front-end gain block (§3) — Mini-Circuits PSA4-5043+, SAV-541+, Analog Devices ADL5523
Masthead preamps: LNAs at the antenna feedpoint (§4) — the optimal placement for noise figure
Active distribution amplifiers: one antenna feeding multiple receivers (§5) — Stridsberg MCA204, DX Engineering SP4-100
Bias-T arrangements: powering remote LNAs over the coax (§6)
Noise figure budgeting: the Friis cascade equation and its practical implications (§7)
Gain budgeting: keeping the front end out of compression (§8) — the IP3 / IP1dB constraint
T/R switching: protecting LNAs during TX (§9) — sequenced relays, why they matter
DIY builds (§12-13): a SAV-541+ MMIC LNA and a 4-way distribution amp
Commercial market (§14): from $50 Nooelec LANA to $2000 Bonito DA300U

The Phase 4 cluster (Vols 16-19) gives the operator the full matching-network toolkit: fixed-ratio BALUNs (Vol 16), variable matching tuners (Vol 17), passive distribution (Vol 18), and now active distribution. From here, Phase 5 covers physical-deployment topics: grounding (Vol 20), mounting (Vol 21), weatherproofing (Vol 22), and stealth (Vol 23).

2. When passive isn’t enough — the link-budget case for active distribution

2.1 The passive-loss problem

A 4-way passive split costs 6 dB per port (3 dB inherent + 3 dB resistive for Wilkinson, more for resistive). For a 4-radio receive farm (4 SDRs sharing one antenna), each radio receives:

Original signal minus 6 dB passive split loss
The same noise floor (passive split adds no noise)

If the original signal-to-noise ratio (SNR) is 20 dB at the antenna, each receiver sees 14 dB SNR after the split. This is fine for casual operation but problematic for:

Weak-signal modes: FT8 at -20 dB SNR is below the noise floor; another 6 dB of loss makes detection harder
Distant beacon receive: 2 m / 70 cm beacons at -120 dBm need every dB of receive sensitivity
EME: 1.3 GHz EME signals at -150 dBm at the antenna require active amplification before splitting
GPS: satellite signals at -160 dBm at the antenna are below most receivers’ noise floor; mandatory LNA + bias-T

2.2 The active-distribution solution

Instead of splitting first and then losing signal, the active approach:

Amplify the signal at the antenna with a low-noise amplifier (LNA, NF ~0.5-1.5 dB, gain ~15-25 dB)
Split the amplified signal via passive Wilkinson — the per-port loss is still 6 dB, but now applied to a much stronger signal
Each receiver sees: amplified signal minus split loss = roughly the original signal level + (LNA gain - split loss)

For 20 dB LNA gain and 6 dB split loss, each receiver sees signal 14 dB stronger than the unamplified case. The system noise figure is dominated by the LNA’s NF (typically 1.5 dB) instead of the receiver’s NF (typically 8-10 dB).

2.3 The net improvement

Comparing the two approaches for a typical 4-receiver setup:

Configuration	SNR at receiver	System NF
4-way passive split (no LNA)	14 dB (from 20 dB original)	~10 dB
4-way active distribution (LNA gain 20 dB, NF 1.5 dB)	28 dB	~2 dB

The active approach delivers 14 dB better SNR and 8 dB lower system NF. For weak-signal applications, this is decisive — the active distribution amp pays for itself in the ability to receive signals that the passive setup couldn’t.

3. MMIC LNAs — the front-end gain block

MMIC (Monolithic Microwave Integrated Circuit) LNAs are the dominant modern front-end gain technology. A single tiny package (typically SOT-89 or SOT-363) contains a complete LNA — input matching network, amplifier transistor, output matching network, and bias circuitry.

3.1 The canonical MMIC LNAs

Part	Frequency	NF	Gain	IP1dB	OIP3	Price (each)
Mini-Circuits PSA4-5043+	50 MHz – 4 GHz	0.4-0.8 dB	20 dB	+18 dBm	+33 dBm	$5
Mini-Circuits SAV-541+	DC – 3 GHz	0.5-0.8 dB	14 dB	+14 dBm	+32 dBm	$4
Analog Devices ADL5523	400 MHz – 4 GHz	0.7 dB	22 dB	+13 dBm	+30 dBm	$8
Mini-Circuits PMA3-83LN+	5-8 GHz	0.7 dB	17 dB	+12 dBm	+30 dBm	$12
Avago MGA-635P8	0.7-3 GHz	0.7 dB	18 dB	+18 dBm	+35 dBm	$5
NXP BFP840F	DC – 6 GHz	0.6 dB	18 dB	+15 dBm	+33 dBm	$6
Skyworks SKY67013-396LF	0.5-4 GHz	0.55 dB	19 dB	+20 dBm	+34 dBm	$7
QORVO TQP3M9009	50 MHz – 4 GHz	0.7 dB	15 dB	+18 dBm	+33 dBm	$5

The Mini-Circuits PSA4-5043+ is the amateur-radio reference part — wide frequency range (50 MHz – 4 GHz), excellent NF (0.4-0.8 dB), reasonable IP1dB, and $5 in single quantity. The amateur SDR community’s de-facto first LNA choice.

3.2 Understanding the LNA spec sheet

The key parameters:

Noise figure (NF): lower = better. 0.5 dB is excellent; 2 dB is mediocre; 5 dB+ is bad
Gain: typically 12-25 dB. Higher gain means more amplification but also more risk of compression and IMD
Input 1 dB compression point (IP1dB): the input signal level where the gain drops by 1 dB (the LNA starts compressing). Higher = better.
Output 1 dB compression point (OP1dB) = IP1dB + Gain. The output level where the LNA can’t deliver more power
Third-order intercept point (OIP3 / IIP3): the theoretical signal level where third-order intermodulation products equal the desired signal. Higher = better immunity to IMD
Input/output return loss: how well-matched the input/output ports are to 50 Ω

For receiver front-end work, NF and IP1dB are the dominant specs. Gain is important but typically secondary (a 25 dB LNA is wasteful if you only need 15 dB for the application).

3.3 The NF vs IP1dB tradeoff

LNA designers trade these two parameters:

Very low NF (0.3 dB): tend to have lower IP1dB (e.g., +8 dBm) and higher distortion under strong signals
High IP1dB (+25 dBm): tend to have higher NF (e.g., 2 dB) — better for handling strong nearby transmitters

The Mini-Circuits PSA4-5043+ is the amateur reference because it has both low NF and decent IP1dB — typically 0.5 dB NF + +18 dBm IP1dB. This is a “no-compromise” choice for most amateur applications.

3.4 LNA building blocks beyond MMIC

Discrete-transistor LNAs (HEMTs, ATFs from Avago) can achieve lower NF (0.2-0.3 dB) than MMICs but require careful matching network design. They dominate in:

EME (earth-moon-earth): 1.3 GHz EME LNAs use HEMTs for absolute best NF
Radio astronomy: ultra-low-noise discrete designs
Satellite ground stations: discrete-transistor designs for ultimate sensitivity

For amateur SDR receive, MMICs are the practical default. Discrete designs are overkill except for the most demanding applications.

A masthead preamp (also called “mast-mount LNA” or “amplifier-at-antenna”) is an LNA installed in a weatherproof enclosure at the antenna feedpoint. The LNA is powered remotely via a bias-T over the coax, eliminating the need for a separate power cable.

The Friis noise-figure equation (§7 below) shows that the first amplifier in a cascade dominates the system’s noise figure. Place the LNA at the antenna feedpoint and:

The coax loss between LNA and receiver does not degrade the system NF (only the receiver’s NF does, scaled by the LNA’s gain)
The system NF is approximately equal to the LNA’s NF + coupling losses up to the LNA
For a typical setup (LNA NF 1 dB, receiver NF 10 dB, LNA gain 20 dB), system NF ≈ 1.1 dB

Without the LNA, the coax loss directly subtracts from the system’s signal. A 30 m run of LMR-400 at 432 MHz has 1.5 dB loss; that 1.5 dB is added to the receiver’s NF, giving a system NF of 11.5 dB. With a masthead LNA having 1 dB NF, the system NF is 1.1 dB — a 10 dB improvement.

A typical masthead preamp consists of:

LNA (e.g. PSA4-5043+ + matching components)
Bias-T at the LNA’s input side (separates DC power from RF signal)
Voltage regulator (typically 5V LDO from 12V coax-delivered supply)
Bypass capacitors for power supply decoupling
Weatherproof enclosure (typically die-cast aluminum or polycarbonate)
SO-239 / N input (antenna side) and SO-239 / N output (coax-to-shack side)

The LNA’s gain is typically 15-25 dB, designed to overcome the coax loss + provide margin for the receiver.

4.3 Bias-T integration

The masthead preamp’s input bias-T receives DC power from the coax shield and delivers it to the LNA’s voltage regulator. The bias-T at the shack end injects the DC into the coax. Both bias-Ts must be carefully designed:

DC blocking caps: pass RF, block DC
DC chokes: pass DC, block RF
Voltage regulator: provides clean LNA supply voltage

A simple bias-T uses one capacitor + one inductor at each end (Vol 18 §9). A more sophisticated bias-T includes additional filtering for cleaner power.

Model	Frequency	Gain	NF	Power	Price
Mini-Circuits ZX60-V63+	0.05-6 GHz	21 dB	1.5 dB	12V	$80
Nooelec LANA-HF	0.1-30 MHz	24 dB	1.2 dB	5V	$50
Nooelec SAWBird+ GOES	1685-1695 MHz	30 dB	0.6 dB	5V	$50
Cross-Country Wireless HF Active Antenna	0.1-30 MHz	25 dB	2.0 dB	12V	$200
DX Engineering DX-PRE-1	1.8-30 MHz	25 dB	2.0 dB	12V	$250
Stridsberg MCA-1AT	0.1-3 GHz	18 dB	1.5 dB	12V	$200
Bonito MegActiv (built-in LNA)	9 kHz – 300 MHz	25 dB	2.0 dB	12V	$350

For amateur SDR use, the Nooelec LANA family (LANA-HF, LANA-PA) is the popular budget choice. For VHF/UHF, the Mini-Circuits ZX60-V63+ is the reference part.

5. Active distribution amplifiers — one antenna, many receivers

An active distribution amplifier combines an LNA with an internal splitter, delivering amplified signal to multiple output ports. The configuration is:

   Active distribution amp:
   
   Antenna ●─────●─── LNA ───●─── Wilkinson 4-way splitter ─┬───●  Output 1
                  │           │                              │
                  │           │                              ├───●  Output 2
                  │           │                              │
                  │           │                              ├───●  Output 3
                  │           │                              │
                  │           │                              └───●  Output 4
                  │           │
                  │           Bias-T for masthead LNA
                  │           │
                  │           ●  DC supply input
                  │
                  ●  Internal voltage regulator

5.1 The architecture

A 4-way active distribution amp typically has:

One LNA stage at the input (NF dominates the system NF)
One internal Wilkinson 4-way splitter (each output sees -6 dB from the LNA’s output)
Output port impedance match to 50 Ω
Optional bias-T at each port (for powering downstream LNAs in chain configurations)

5.2 Examples — Stridsberg MCA204

The Stridsberg MCA204 is the canonical 4-way active distribution amplifier:

1.8-2000 MHz frequency range
15 dB gain
1.5 dB NF
4 outputs at 50 Ω
12V DC supply
$200 commercial

The MCA204 is the SDR-radio-farm reference. Feed it from one antenna; it delivers amplified signal to 4 separate SDRs without the 6 dB passive-split penalty.

5.3 Examples — DX Engineering SP4-100

The DX Engineering SP4-100 is a similar 4-way distribution amp:

0.5-1500 MHz
17 dB gain
1.8 dB NF
4 outputs
$250

5.4 Cascading active distribution

For 8 or more receivers, cascade two 4-way amps:

   Antenna ●── LNA ── 4-way splitter ──┬── 4-way amp ──┬── Out 1
                                       │               │
                                       │               ├── Out 2
                                       │               │
                                       │               ├── Out 3
                                       │               │
                                       │               └── Out 4
                                       │
                                       ├── 4-way amp ──┬── Out 5
                                       │               │
                                       │               ├── Out 6
                                       │               │
                                       │               ├── Out 7
                                       │               │
                                       │               └── Out 8

The cascade adds another LNA + 4-way split per branch — total loss per port is still manageable (~12 dB inherent + ~25-35 dB total gain from the cascade).

6. Bias-T deployment in active networks

Bias-Ts power masthead amplifiers and remote LNAs by injecting DC power onto the coax shield while passing the RF signal through transparently.

6.1 The bias-T topology

Already covered in Vol 18 §9, summarized here:

RF capacitor in series: passes RF, blocks DC
DC inductor in shunt: passes DC, blocks RF
At the shack end: DC supply → bias-T inductor → coax shield + center
At the antenna end: coax → bias-T capacitor → LNA RF input; coax shield + center → bias-T inductor → LNA voltage regulator → LNA supply

6.2 Voltage drops and current capacity

A typical bias-T setup:

Shack supply: 12V regulated, 0.5-1 A
DC voltage drop on coax shield: 0.1-0.3V (depends on coax length and shield resistance)
LNA voltage: typically regulated down to 5V via a small LDO
Coax shield current: 100-300 mA typical

For longer coax runs (30+ m), the shield resistance can drop ~0.5V at 500 mA. This is acceptable but should be designed for — the shack-side supply should provide enough voltage that the LNA’s regulator can compensate.

6.3 Safety considerations

DC on the coax shield is generally safe but has safety considerations:

Lightning protection: any coax with DC on it must be protected by a polyphaser arrestor at the shack entry that doesn’t short DC to ground (polyphasers with proper DC-blocking are mandatory)
Antenna isolation: the antenna itself should be DC-isolated from the coax shield (to prevent DC from flowing into the antenna and causing unwanted effects)
Multiple bias-Ts: when chaining multiple amps, each junction needs a bias-T or a DC-block

6.4 Built-in bias-Ts in modern equipment

Modern SDR receivers and some commercial radios include built-in bias-T capability:

HackRF One: built-in bias-T option (3.3V, 50 mA — sufficient for small LNAs)
RTL-SDR Blog V4: built-in bias-T (4.5V, 180 mA)
AirSpy HF+ Discovery: built-in bias-T (5V, 200 mA)
SDRplay RSP1A / RSPdx: built-in bias-T (4.7V, 100 mA)
Yaesu FT-991A / Icom IC-7300: no built-in bias-T (separate bias-T needed)

For an amateur SDR setup with the built-in bias-T, no external bias-T is required — just connect the LNA’s output to the SDR’s input.

7. Noise figure budget — Friis cascade

The Friis noise-figure equation governs how individual stages combine to produce the system NF.

7.1 The Friis equation

For a cascade of N stages, each with noise figure F_i (linear, not dB) and gain G_i (linear):

   F_system = F_1 + (F_2 - 1)/G_1 + (F_3 - 1)/(G_1·G_2) + ...

The first stage’s NF (F_1) dominates the system NF when its gain (G_1) is significant. Subsequent stages contribute less and less as the cascade’s accumulated gain grows.

7.2 The “first stage dominates” insight

For a typical 2-stage cascade (LNA + receiver):

LNA: NF = 1 dB (linear F = 1.26), gain = 20 dB (linear G = 100)
Receiver: NF = 10 dB (linear F = 10)

System NF (linear): F_sys = 1.26 + (10 - 1)/100 = 1.26 + 0.09 = 1.35 System NF (dB): 10 × log(1.35) = 1.3 dB

The system NF is dominated by the LNA’s NF (1 dB); the receiver’s NF (10 dB) contributes only 0.3 dB to the total because the LNA’s gain (20 dB) “amplifies” the LNA’s NF while attenuating the receiver’s contribution.

For the same setup with a masthead LNA + 1.5 dB coax loss before the receiver:

LNA at antenna: NF = 1 dB, gain = 20 dB
Coax loss: NF = 1.5 dB (passive losses contribute their loss directly to NF), gain = -1.5 dB
Receiver: NF = 10 dB, gain = (irrelevant for NF calc)

System NF: 1.26 + (1.41 - 1)/100 + (10 - 1)/(100 × 0.708) = 1.26 + 0.004 + 0.127 = 1.39 System NF (dB) = 1.4 dB

The 1.5 dB coax loss contributes only 0.4 dB to the system NF because the LNA’s gain “amplifies through” the coax loss before the receiver sees it.

Same setup, but the LNA moved from masthead to inside the shack (after the coax run):

Coax loss: NF = 1.5 dB (lossy passive — first stage now)
LNA: NF = 1 dB
Receiver: NF = 10 dB

System NF: F = 1.41 + (1.26 - 1)/0.708 + (10 - 1)/(0.708 × 100) = 1.41 + 0.37 + 0.127 = 1.91 System NF (dB) = 2.8 dB

The shack-mounted LNA gives system NF of 2.8 dB; the masthead LNA gives 1.4 dB. The masthead placement is 1.4 dB better — the difference is the gain of the LNA versus the loss of the coax.

For long coax runs and weak-signal applications, masthead placement is the right answer.

8. Gain budget — keeping the front end out of compression

While LNA gain is good for noise figure, too much gain causes the LNA to compress under strong signals, generating intermodulation distortion (IMD) and other artifacts that corrupt the receive chain.

8.1 The IP1dB constraint

The IP1dB (input 1 dB compression point) is the input signal level where the LNA’s gain drops by 1 dB. Above this point:

Output power saturates (no longer linear)
Harmonic distortion increases
Intermodulation products appear
The LNA’s NF degrades

For a PSA4-5043+ with IP1dB = +18 dBm, any incident signal above +18 dBm starts to compress. If your antenna picks up a strong nearby signal (a local AM broadcaster at -10 dBm), the LNA is fine. If your antenna is near a 1 kW commercial broadcaster delivering -3 dBm at the antenna, the LNA will compress and generate IMD.

8.2 The IP3 spec and IMD products

The third-order intercept point (IP3) characterizes how strong the third-order intermodulation products are. For two input signals at frequencies f1 and f2, IMD products appear at frequencies 2f1-f2 and 2f2-f1. These are particularly insidious because they often fall within the receive band.

For an LNA with OIP3 = +30 dBm and two input signals at -20 dBm each, the IMD products are at -90 dBm — well below the receiver’s noise floor. For the same LNA with two input signals at +5 dBm each, the IMD products are at +30-50 = -20 dBm — above many signals of interest.

The OIP3 spec characterizes the LNA’s ability to handle multiple strong signals without generating noise. Higher OIP3 = better IMD performance under crowded-band conditions.

8.3 Filtering before the LNA

For RF-rich environments (urban, near broadcasters), filtering before the LNA is mandatory:

Low-pass filter: rolls off above the band of interest, blocking FM broadcast and strong UHF/VHF signals
High-pass filter: rolls off below the band of interest, blocking AM broadcast and broadcast TV
Bandpass filter: selects only the band of interest

For amateur HF receive:

0.1-30 MHz bandpass filter (or 30 MHz low-pass) before the LNA
Rejects FM broadcast band (88-108 MHz) and VHF/UHF strong signals

For VHF/UHF amateur receive:

Filter to specific band (2 m, 70 cm) before the LNA
Rejects out-of-band cellular, broadcast, and other strong signals

8.4 The gain budget tradeoff

LNA gain	NF improvement	Compression risk	IMD risk
10 dB	-2 to -5 dB	Low	Low
15 dB	-5 to -8 dB	Moderate	Moderate
20 dB	-7 to -10 dB	High	High
25 dB	-9 to -11 dB	Very high	Very high

For most amateur SDR applications, 15-18 dB LNA gain is the sweet spot — enough to overcome coax loss without driving the LNA into compression for typical signal levels.

9. T/R switching — protecting LNAs during TX

LNAs do not survive TX power. A 100 W transmit signal at the antenna’s location couples enough power into the LNA’s input to destroy it. The fix: a sequenced T/R relay that disconnects the LNA before keying the rig and reconnects it after.

9.1 T/R relay sequencing

The proper sequence:

PTT pressed: rig signals “transmit” to the T/R relay
T/R relay flips: RX path disconnected, TX path connected
PTT delay: ~10 ms delay for relay to fully switch
TX enables: rig outputs TX signal
Reverse on release: TX disables → delay → relay flips back to RX

The sequencing matters because if the rig keys before the relay flips, the LNA sees full TX power and burns. If the rig keys after the relay flips, no damage occurs.

9.2 Commercial T/R relays

Relay	Power	Switching speed	Price
DX Engineering RTR-1A	1 kW	5 ms	$200
Mini-Circuits ZSDR-230+	200 W	1 ms	$500
Tohtsu MAS-1	100 W	50 ms	$100
Sentec RF T/R switches	1 kW	10 ms	$300
Custom relay + driver	varies	50-500 ms	$50

For amateur use, the DX Engineering RTR-1A is the canonical reference part — handles 1 kW SSB, switches in 5 ms (well under the rig’s typical PTT-to-TX-output delay), and is reliable enough for daily operation.

9.3 Bypass during RX-only operations

If the rig is RX-only (a separate TX antenna), no T/R switching is needed — the LNA stays connected continuously. This is the simpler configuration:

Shared antenna (RX-only): no T/R switch, LNA always on
TX-capable antenna with LNA: T/R switch mandatory

9.4 Built-in T/R in modern radios

Some modern HF rigs (Yaesu FTDX-101D, FTDX10) have built-in RX antenna jack that bypasses the rig’s TX final amp during RX. This eliminates the need for an external T/R switch. The rig automatically routes RX through the RX antenna jack and TX through the main antenna.

10. Best-case use

The active distribution family wins when:

Multiple radios on one antenna (SDR farm with 4+ receivers) — passive split would lose 6+ dB; active distribution preserves SNR
Distant weak-signal receive (VHF/UHF beacons, EME, satellite downlinks) — the masthead LNA improves system NF by 5-10 dB
High-band receive (where coax loss is significant) — at 1.3 GHz and up, coax loss is 0.5-2 dB/30m. Masthead LNA recovers this loss
GPS receive (mandatory) — GPS signal level (-160 dBm at antenna) is below all receivers’ threshold; LNA + bias-T is essential
Satellite ground stations (uplink LNAs, downlink preamps) — the noise figure dominates link budgets
Long coax runs to remote antennas (30+ m) — the masthead LNA recovers what the coax loses
Active loops (Vol 15 §8) — built-in LNA at the antenna lifts signals above the local noise

11. Worst-case use — overload and IMD

The active distribution family is the wrong answer for:

Near high-power broadcasters — the LNA compresses; IMD products appear in the receive band. Use heavy filtering before the LNA, or use a passive split with a stronger receiver.
Wideband receivers near multiple strong sources — a 30 MHz – 1 GHz LNA picks up the FM-broadcast band (88-108 MHz, often at -10 dBm) and generates IMD into HF and weak-signal VHF bands. Use band-specific filtering before the LNA.
TX operations through the LNA path — LNAs don’t survive TX. Use T/R switching or separate antennas.
Cost-sensitive amateur use — a $400 active distribution amp + $200 masthead preamp + $200 T/R switch is $800 for a setup that a single $50 passive splitter could partly replace. Use passive when budget is the constraint.
Single-receiver operations — no benefit from active distribution. Use a simple direct connection.

12. DIY build — a 0.1-2000 MHz LNA on a SAV-541+ MMIC

About 4 hours of work plus testing. Total cost ~$25.

12.1 BOM

Part	Specification	Source	Mid-2026 price
SAV-541+ MMIC	Mini-Circuits, SOT-89	DigiKey	$4
0603 SMD bypass caps	100 pF + 0.1 μF	DigiKey	$1
5V LDO regulator	LM7805 or LDO equivalent	DigiKey	$2
FR-4 PCB	Custom layout, ~30 × 20 mm	JLCPCB	$10
2× SMA edge-mount connectors	DigiKey	$6
Hardware (screws, washers)		Local	$2
Total			~$25

12.2 PCB layout

The SAV-541+ has a single signal input, a single signal output, and a single Vcc pin. The PCB layout:

Input SMA → 100 pF DC-block cap → SAV-541+ pin 1 (RF input)
Output SMA → 100 pF DC-block cap → SAV-541+ pin 3 (RF output)
SAV-541+ pin 4 → Vcc (5V from LDO)
SAV-541+ pin 5 → Ground

The LDO regulator converts 12V (from bias-T) to clean 5V for the SAV-541+. Add bypass caps (0.1 μF + 100 pF) at the LDO output and at the SAV-541+ Vcc.

12.3 Construction

Order the PCB. Submit the design to JLCPCB or OSHPark; 5 boards arrive in 1-2 weeks for $10.

Solder the SMA connectors. Mount the two SMA connectors on the PCB edges with the center conductors soldered to the PCB pads.

Solder the MMIC. The SAV-541+ in SOT-89 is small (~3 × 1.5 mm); use a fine-tip iron and tweezers. Verify pin orientation by the package datasheet.

Solder bypass caps and LDO. SMD components on the back side of the PCB. Use the appropriate pads in the layout.

Test with NanoVNA. Power the LNA via the bias-T (or apply 12V directly to the LDO input pin). Sweep 100 MHz – 2 GHz on port 1. Expect:

Gain: 14 ± 2 dB across the band
NF: 0.7 dB (theoretical, measurement requires reference noise source)
Input SWR: < 1.5:1

12.4 Verification and improvement

A single-stage SAV-541+ gives 14 dB gain. For higher gain, cascade two stages (~26 dB total) with a small attenuation pad between them to maintain stability.

For commercial-grade noise figure performance, the cascaded design with input matching pad achieves 24 dB / 0.7 dB NF.

About 6 hours of work plus testing. Total cost ~$80.

13.1 BOM

Part	Specification	Mid-2026 price
PSA4-5043+ MMIC	Mini-Circuits	$5
Wilkinson 4-way splitter	DIY (Vol 18 §15)	$25
5V LDO regulator	LM7805	$2
Bias-T components (cap + inductor)	DigiKey	$5
FR-4 PCB	Custom layout, larger than single-stage	$15
5× SMA edge-mount connectors	DigiKey	$15
Hammond 1591-XS enclosure	weatherproof	$10
Hardware		$3
Total		~$80

13.2 Architecture

   Antenna ●─────●─── Bias-T ─── PSA4-5043+ ─── 4-way Wilkinson splitter ─┬── Output 1
                  │                                                        │
                  │                                                        ├── Output 2
                  │                                                        │
                  ●  DC power input (12V)                                  ├── Output 3
                  │                                                        │
                  ●  Voltage regulator (5V to LNA)                         └── Output 4
                  │
                  ●  Cap bypass + ground

13.3 Construction

Build the Wilkinson 4-way splitter per Vol 18 §15. Build the PSA4-5043+ LNA per §12 above. Combine them in the same PCB with a bias-T at the input.

Mount in the weatherproof enclosure with the antenna SMA on one face and 4 output SMAs on the opposite face. The DC power input is via a separate small connector or via the antenna SMA’s coax shield (using the bias-T).

13.4 Specifications

Frequency range: 50 MHz – 2 GHz (limited by PSA4-5043+ and Wilkinson design)
Gain per port: 20 dB - 6 dB = 14 dB (LNA gain minus split loss)
NF: ~0.8 dB (PSA4-5043+‘s NF dominates)
Output ports: 4 (with internal Wilkinson)
Power supply: 12V DC at ~150 mA
Cost: ~$80

This 4-way distribution amp lets one antenna feed 4 SDRs simultaneously without the 6 dB passive-split loss penalty.

14. Commercial buys

Sorted by tier and use case (USD, mid-2026):

Tier	Model	Type	Frequency	Power	Price	Notes
Budget	Nooelec LANA	LNA	0.1-2200 MHz	5V	$50	The amateur SDR reference budget LNA
Budget	Nooelec LANA-HF	LNA (HF)	0.1-30 MHz	5V	$45	HF-specific
Budget	Nooelec SAWBird+ GOES	LNA + SAW filter	1685-1695 MHz	5V	$50	GOES satellite reception
Budget	RTL-SDR Blog LNA	LNA	50 MHz – 6 GHz	5V	$25	Cheap, decent
Budget	Uputronics LNA-1	LNA	1-25 MHz	12V	$80	HF-specific
Mid	Mini-Circuits ZX60-V63+	LNA module	0.05-6 GHz	12V	$80	Mini-Circuits reference
Mid	Mini-Circuits ZFL-1000+	LNA module	0.1-1000 MHz	15V	$150	Higher-power
Mid	Mini-Circuits ZHL-3010+	Distribution amp	50-1000 MHz	28V	$200	4-way amplifier
Mid	Stridsberg MCA204	4-way active dist	1.8-2000 MHz	12V	$200	The SDR-farm reference
Mid	DX Engineering SP4-100	4-way active dist	0.5-1500 MHz	12V	$250	DX Engineering version
Mid	Cross-Country Wireless preselectors	Filter + LNA	1.8-30 MHz	12V	$200-400	HF specialty
Premium	Bonito DA300U	Distribution amp + features	9 kHz – 300 MHz	12V	$480	Premium, with preselector
Premium	Stridsberg MCA1208	8-way active dist	0.5-2 GHz	12V	$400	8-way distribution
Premium	MFJ-1026	Noise canceller + distribution	0.1-30 MHz	12V	$250	RX noise canceller
Premium	DX Engineering RPA-1	Preamp	1.8-30 MHz	12V	$400	Premium HF preamp
Premium	DX Engineering NCC-2	Active noise canceller	1.8-30 MHz	12V	$400	RX-only premium

What to avoid:

Random eBay “LNA modules” without published NF — many are commodity amps with NF > 5 dB and provide no benefit over a passive split
“20 dB gain” LNAs without IP1dB spec — these often have IP1dB < 0 dBm, meaning they compress with any strong local signal
“Wideband amps” with no filtering — these will compress on any strong nearby signal, generating IMD throughout the receive band
Generic Chinese “RF amplifier” boards without datasheets — usually low-quality, with unpredictable NF and frequency response

15. Companion gear

Bias-T (or built-in to distribution amp) — for powering masthead LNA
Preselector or bandpass filter (Vol 18) — mandatory before LNA in RF-rich environments
T/R relay for TX-side protection — DX Engineering RTR-1A, Tohtsu MAS-1
Reference noise source — for measuring LNA NF (NoiseCom RNS-1000, Pacific Microwave NS-100)
Spectrum analyzer — for detecting IMD products in the LNA output
DC power supply — clean 12V supply for the LNA (linear regulator preferred over switching)
Lightning protection (Vol 20 §5) — DC-passing polyphaser if bias-T powered

16. Common gotchas and myths

“More gain = better” — false. Gain past the point of overcoming coax loss just creates IMD risk. For amateur HF receive, 15-20 dB LNA gain is the sweet spot.
“All LNAs are equal” — false. NF varies from 0.4 dB (premium GaAs) to 5+ dB (commodity NPN). IP1dB varies from -5 dBm to +25 dBm. These are 5-30 dB differences in real performance.
“Active loop doesn’t need a bias-T” — usually has one built in; check the spec sheet. Some commercial active loops (Wellbrook ALA1530) include the bias-T internally; others require an external one.
“LNAs are immune to RF damage” — false. A 100 W TX signal at the LNA’s input destroys it almost instantly. T/R switching is mandatory for TX-capable systems.
“My LNA has 25 dB gain, so my receiver is 25 dB more sensitive” — partly true; the SNR improvement is only ~10-15 dB (the LNA’s NF + system noise floor sets the ultimate sensitivity). The 25 dB gain is partially absorbed by the system’s noise floor.
“The Friis equation doesn’t apply to passive losses” — false. Passive losses contribute to NF directly: a 3 dB attenuator has NF = 3 dB and gain = -3 dB. Any passive component in the cascade follows the Friis equation.
“Active distribution is always better than passive” — false. Active distribution is better for noise figure but worse for IMD (active components compress and generate IMD; passive splitters don’t). The right choice depends on the application.
“My LNA is broken; it shows 5 dB more loss than spec” — possibly damaged. The most-common LNA failure modes are: input ESD damage (gain drops), output transistor blow-out (gain disappears), and bias-supply leak (LNA bypassed). Measure DC supply current and signal levels to diagnose.
“More distribution amps = more receivers” — true, but the noise figure budget gets worse with each cascade stage. Eight cascaded LNAs accumulate ~3 dB of NF compared to one optimal LNA at the source.
“I can use any LNA for any band” — false. LNAs are band-specific (or at least frequency-range-specific). Using an HF LNA for 2 m operation gives degraded NF and gain.
“OIP3 doesn’t matter for amateur use” — false. In urban environments with multiple strong nearby signals, OIP3 directly determines how much IMD appears in the receive band. Higher OIP3 = cleaner reception.

17. Resources

Mini-Circuits MMIC datasheets and app notes — published specifications and application notes for PSA4-5043+, SAV-541+, and the broader MMIC family.
Razavi, RF Microelectronics (Ch. 5 — LNA design) — the academic reference for LNA design.
Pozar, Microwave Engineering (Ch. 7 — Active components) — covers MMIC and discrete amplifier design.
ARRL Antenna Book Ch. 13 (preamps and receive systems) — amateur-focused coverage.
Stridsberg, Bonito, DX Engineering product datasheets — commercial active distribution references.
W2DU’s Reflections (3rd ed.) — covers the cascade noise-figure equation and its implications.
AA5TB LNA design articles — community-published amateur LNA design.
Avago / Mini-Circuits LNA application notes — manufacturer-published LNA selection and design tutorials.
AMSAT preamp specifications — published amateur satellite receive preamp standards.
NIST noise figure measurement standards — for laboratory-quality NF measurement.
Pasternack catalog (active devices section) — premium commercial LNAs and distribution amps.

Contents