Ham Radio Power Supplies: Linear vs Switching and What Your Radio Needs

Every ham radio transceiver needs 13.8 VDC. How you supply those volts matters more than most hams realize. The wrong power supply can introduce noise across your receive passband, generate RFI that affects your neighbors, or simply fail to deliver the current your radio demands during transmit.

Here's how to choose the right supply and avoid the problems.

What Your Radio Actually Needs

Voltage

13.8 VDC ± 15%. This is the universal standard for amateur mobile/base equipment. It matches a car's charging system voltage (running engine with alternator). Your radio is designed around this voltage.

• Below 11.7V: Most radios reduce output power or shut down
• 12.0-13.0V: Works but doesn't deliver full rated power
• 13.8V: Nominal design center. Full rated power.
• Above 15.8V: Risk of damage to some radios (check your manual)

Current

The power supply must deliver enough current for your radio's peak transmit demand:

Radio RX Current TX Current (100W) IC-7300 1.0A 21A FT-991A 1.5A 23A IC-7610 2.5A 23A TS-890S 2.5A 23A FT-710 1.3A 22A IC-705 (10W) 0.5A 2.5A FT-891 (100W) 0.9A 20A

Rule of thumb: A 100W HF radio needs at least a 25A power supply. This provides headroom above the peak demand. Running a supply at its absolute maximum rating continuously reduces lifespan and may cause voltage sag during transmit peaks.

For amplifiers: A solid-state amplifier at 500W output draws approximately 45A at 50V (they use separate supply), or if powered from 13.8V (unusual for high power), enormous current. Most kW amps use their own built-in power supply.

Linear Power Supplies

A linear supply uses a transformer to step down AC voltage, rectifies it to DC, then uses a pass transistor (or multiple) to regulate the output voltage. The excess energy is dissipated as heat.

How They Work

1. AC mains → heavy transformer → lower AC voltage
2. Bridge rectifier → pulsating DC
3. Large filter capacitors → smoother DC (still has ripple)
4. Series pass transistor(s) → regulates to exactly 13.8V, absorbing voltage difference as heat
5. Output filtering → clean 13.8V DC

Strengths

Electrically quiet: No high-frequency switching noise. The transformer operates at 50/60 Hz — far below any amateur band. Ripple is at 100/120 Hz (also far below). A well-designed linear supply has essentially zero RF noise output.

Simple: Fewer components, straightforward design, easy to repair.

Proven: Decades of service in ham shacks. An Astron RS-35M from 1990 still works perfectly.

No RFI: Won't interfere with your receiver or your neighbor's equipment.

Weaknesses

Heavy: The transformer is iron core, wound with copper. A 25A linear supply weighs 20-30 lbs.

Inefficient: The pass transistor dissipates the voltage difference as heat. Efficiency is typically 40-50%. A 25A supply generates 100-150W of heat continuously during transmit.

Large: The transformer and heat sinks take space.

Expensive per amp: Quality linear supplies cost $150-300 for 25-35A.

Popular Linear Supplies

Astron RS-35M: The classic. 35A continuous, 50A surge. Metered (voltmeter + ammeter). Built in California, legendary reliability. $250-280. Heavy (30 lbs).

Astron RS-50M: For stations needing more current (multiple radios, accessories). 50A continuous. $350+.

Alinco DM-340MV: Japanese alternative. 35A, metered. Similar performance to Astron. $200-250.

Switching Power Supplies

A switching supply converts AC to DC at high frequency (50-200 kHz) using power MOSFETs and a small ferrite transformer. Much more efficient and lighter.

How They Work

1. AC mains → rectifier → DC bus (170V or 340V DC)
2. High-frequency switching transistors chop DC at 50-200 kHz
3. Small ferrite transformer steps down to desired voltage
4. Output rectifier and filter → 13.8V DC
5. PWM controller adjusts switching duty cycle to regulate voltage

Strengths

Lightweight: No heavy iron-core transformer. A 30A switching supply weighs 3-6 lbs (vs 25-30 lbs linear).

Efficient: 80-90% efficiency. Less heat generated, smaller heat sinks needed.

Compact: Fraction of the size of equivalent linear supply.

Cheaper: Modern manufacturing makes them less expensive ($80-150 for 30A).

Better voltage regulation: Switching regulation responds faster to load changes.

Weaknesses

Switching noise: The fundamental switching frequency (50-200 kHz) and its harmonics can appear in your receiver as birdies (unwanted signals) or elevated noise floor. Quality supplies suppress this; cheap ones don't.

RFI potential: Conducted and radiated emissions require filtering. Without adequate EMI filtering, the supply can create interference on HF bands.

Complexity: More components, harder to repair. Failed switching supplies are often replaced rather than repaired.

Reliability varies wildly by manufacturer: A quality Samlex or Meanwell switching supply is reliable. A generic Chinese supply from Amazon might fail in months or generate terrible RFI.

Popular Switching Supplies

Samlex SEC-1235: 30A continuous, 35A surge. Well-filtered, very low noise. $130-160. The gold standard for switching supplies in ham radio.

Samlex SEC-1223: 23A version of the above. $100-120. Adequate for single 100W radio.

MFJ-4230MV: 30A switching supply with meters. Budget option. Some reports of noise, but acceptable for many stations. $100-130.

Powerwerx SS-30DV: 30A, well-reviewed, integrated Anderson Powerpole outputs. $130.

Meanwell RSP-500-13.5: Industrial supply, 36A. Very well-made but requires adding output connectors and sometimes RFI filtering for ham use. $80-100.

The Noise Question: Does It Really Matter?

When Switching Supply Noise Is a Problem

• You're a weak-signal operator (CW, FT8, EME) and every dB of noise floor matters
• The supply generates birdies (discrete spurs) that land on amateur frequencies
• Conducted emissions travel down the DC cable and radiate from your antenna
• You operate on 160m or 80m where switching harmonics are most problematic

When It's NOT a Problem

• You operate with a local noise floor already elevated (urban environment)
• You're running digital modes where a slightly elevated noise floor doesn't affect decoding
• The supply is well-designed with adequate filtering (Samlex, quality Meanwell)
• You operate VHF/UHF primarily (switching harmonics are usually below 30 MHz)

How to Test

1. Connect your radio to the switching supply
2. Tune across all bands with antenna disconnected (use a dummy load or just receiver)
3. Listen for birdies (carriers/tones that shouldn't be there)
4. Compare noise floor to battery operation (battery = zero supply noise)
5. If noise floor rises more than 1-2 S-units, the supply is problematic

Fixing Switching Supply Noise

• Ferrite chokes on DC output cable: 4-6 turns through a Mix 31 toroid
• Ferrite choke on AC input cable: Snap-on clamp
• Short DC cables: Shorter = less radiation
• Shielded DC cable: Some operators use shielded cable for the DC run
• Bypass capacitors at radio end: 0.1μF ceramic + 100μF electrolytic across DC input at the radio
• Distance: Move the supply away from the radio and antenna feedlines

Sizing Your Supply

For one 100W HF radio: Minimum 25A, recommended 30A. This gives 30-50% headroom.

For radio + accessories (tuner, rotor, accessories): 35A supply. The accessories add 2-5A total.

For two radios (SO2R contesting): 50A or two separate supplies.

For QRP/portable: 5-10A is sufficient. Small, lightweight switching supply works perfectly.

Anderson Powerpole Connectors

The amateur radio standard for DC power distribution is the Anderson Powerpole connector (PP15, PP30, or PP45 sized for current). Benefits:

• Genderless (no male/female — all connectors mate with each other)
• Color-coded (red positive, black negative)
• ARES/EMCOMM standard (interoperability in emergencies)
• Easy to assemble (crimp tool required)
• Rated for the current they carry

Most modern ham power supplies include Powerpole outputs alongside traditional binding posts.

My Recommendation

For the typical home HF station: A quality switching supply (Samlex SEC-1235 or Powerwerx SS-30DV) is the right choice. They're lighter, cheaper, smaller, and the noise performance of quality units is excellent. Add ferrite chokes on the DC leads as insurance.

For the serious low-band DXer or EME operator: A linear supply (Astron RS-35M) eliminates any possibility of supply-generated noise. The weight and size penalty is worth it when you're chasing signals at the noise floor.

For portable/field: Switching supply every time. You're not carrying 30 lbs of linear supply to a POTA activation. A small 10-15A switcher powers your portable radio perfectly.

For budget: A Meanwell industrial switching supply ($80) with Powerpole connectors added and ferrite filtering works great. Just test it for noise before committing to it as your primary supply.