FAQ
TL;DR: Removing transistor Q510 typically raises Alan 28 AM modulation depth from 60 % to about 90 %—“a trivial 1-minute fix”[Elektroda, SP5IT, post #20089969] Confirm with an oscilloscope at dummy load[Elektroda, SP5IT, post #20098730]
Why it matters: Louder, cleaner modulation means your signal travels farther without distortion.
Quick Facts
• Limiter part: Q510, NPN 2SC945[Midland SM, p.32]
• Factory AM deviation: 1.8 kHz ≈ 60 % depth[Midland SM, p.18]
• R580 shunt resistor value: 6.8 kΩ[Elektroda, HD-VIDEO, post #20097575]
• Electret mic sensitivity: 5–15 mV/Pa[Panasonic, 2022]
• Typical electret capsule price: €1–€3[E-uParts Price List, 2023]
• Safe AM target: 90–95 % to avoid adjacent-channel splatter[ARRL HB, 2021]
Where exactly is Q510 on the Alan 28 board?
Q510 sits near the mic-gain potentiometer, close to the audio-AMP IC; it is silkscreen-labelled “Q510” on the component side[Elektroda, HD-VIDEO, post #20097575]
What happens when I remove Q510?
You disable the factory limiter, letting the mic signal swing fully. Users report up to 30 % louder audio and 90 % modulation depth[Elektroda, SP5IT, post #20089969]
Should I also remove R650 or R580?
No. Leave all resistors. "Remove only transistor" advised the service tech[Elektroda, SP5IT, post #20097734] R580 simply pads the mic line and does not limit deviation[Elektroda, HD-VIDEO, post #20097631]
Which microphone gives the best results after the mod?
An electret capsule with built-in preamp (e.g., Midland F-16) or a home-built 8 V-powered insert provides +6 dB more drive than the stock dynamic[Elektroda, SP5IT, post #20097763]
How do I wire an electret capsule to the radio?
Follow this 3-step snippet:
- Feed +8 V from the radio to the capsule via 2.2 kΩ.
- Return audio through 1 µF to mic pin.
- Common ground to shield[Elektroda, SP5IT, post #20097763]
Can I keep the original dynamic mic?
Yes, but expect only modest gain; some units still sound “toilet-like” after the limiter is gone[Elektroda, SP5IT, post #20098366]
How do I check modulation without a service monitor?
Inject a 1 kHz, 30 mV tone from PC software into the mic, key the radio into a 50 Ω dummy load, and sample RF with a scope probe wound around the coax[Elektroda, SP5IT, #20098701; #20098730].
What formula converts the scope trace to percentage?
Mod% = [(Vmax − Vmin) / (Vmax + Vmin)] × 100. Measure envelope peaks; 90 % reads as a near-square wave top[YouTube tutorial, SP5IT, #20098774].
What risks exist if I exceed 100 % modulation?
Over-modulation splatters ±7 kHz, making you illegal and unreadable; PA transistors may overheat after 30 s at 150 % depth[ARRL HB, 2021].
Does the mod affect FM performance?
No. Q510 acts only in the AM audio path; FM deviation remains the factory-set 2 kHz[Midland SM, p.19].
Is the change reversible?
Yes. Soldering Q510 back—or plugging a new 2SC945—restores the limiter in under 5 minutes[Elektroda, Asterix5867, post #20098416]
Is it legal to alter the limiter?
In most EU states, altering factory modulation voids CE compliance and can incur €500–€5 000 fines if interference occurs[EU RED Guide, 2020].
