Performing the Ameritron AL-811 MARS Mod is simple with a little knowledge and basic tools. The AL811 amplifier is limited to traditional ham radio bands before the modification.
For those involved in the Military Auxiliary Radio System (MARS) or who want or need to operate on 10 & 12 meters, as well as frequencies outside standard amateur bands.
Why You Need the Ameritron AL-811 MARS Mod
The MARS mod expands the frequency range of the AL-811, and AL-811H enabling transmission on 2 ham bands, and including frequencies not typically allowed under standard amateur licensing.
This is particularly useful for MARS members who support emergency communication efforts by providing backup communication channels for the U.S. Department of Defense. Additionally, radio operators involved in disaster response or those who hold special permits may also benefit from this mod.
High-power amplifiers like the Palstar LA-1K are part of a larger category of RF amplification equipment used to increase transmitted signal strength across the amateur bands. Operators comparing different amplifier designs, technologies, and power levels may want to explore the
Complete Guide to Ham Radio Amplifiers, which explains how solid-state and tube amplifiers work, how to choose the right amplifier for a station, and what factors affect real-world performance.
What the MARS Mod Does
When you perform the MARS mod, you effectively remove the factory-imposed restrictions on the AL-811. As a result, the amplifier can now transmit across a broader spectrum, including MARS and other authorized frequencies.
Importantly, this modification does not increase the output power of the amplifier; instead, it simply unlocks additional frequency ranges. Therefore, operators must still adhere to all licensing and regulatory requirements when using the expanded capabilities.
Why the AL-811 Is Factory-Restricted
Like most amateur radio amplifiers, the AL-811 and AL-811H are designed to operate only within the standard amateur radio HF bands. Manufacturers intentionally limit transmit capability so the amplifier cannot easily operate on frequencies assigned to other radio services.
These restrictions help manufacturers comply with regulatory requirements and prevent accidental transmission on services such as aviation, marine, or government communication frequencies.
In the AL-811 design, this restriction is implemented through a simple internal jumper that disables the tuning circuit outside amateur band segments. The MARS modification removes this restriction so the amplifier can tune across a slightly wider portion of the HF spectrum.
Even after the modification, operators are still responsible for ensuring they only transmit on frequencies they are legally authorized to use.
What the MARS Mod Adds
Beyond expanded frequency access, the MARS mod enhances the versatility of your radio setup. For example, it allows seamless integration with transceivers that already support wideband operation. Moreover, with more frequencies at your disposal, you gain the flexibility to participate in a wider variety of communication nets, emergency exercises, and inter-agency communications.
Operating Outside Amateur Bands After the Modification
After the MARS modification is completed, the amplifier becomes capable of transmitting on frequencies outside the normal amateur band allocations. However, the amplifier’s tuning system and tank circuit were originally optimized for amateur HF bands.
Because of this, operators should expect tuning controls to fall outside the normal dial markings when operating on expanded frequencies.
Proper tuning practices become especially important when operating near the edges of the amplifier’s designed frequency range. Operators should always:
• Begin tuning with minimal drive power
• Carefully adjust Plate and Load controls
• Monitor plate current and grid current
• Avoid excessive drive power
Following proper tuning procedures helps prevent tube stress and ensures stable amplifier operation.
Disclaimer: Modifying your AL-811 amplifier may void the warranty and could potentially violate regulations if not performed properly. Always ensure you have the appropriate authorization before proceeding. This mod does not open 11 meters!
How to Perform the MARS Mod
Tools Needed:
- Screwdriver set
- Wire cutters
- Anti-static wrist strap (recommended)
Step-by-Step Instructions:
- Power Down and Unplug: Before opening the amplifier, turn it off and disconnect it from all power sources. This step is critical for safety.
2. Remove the Cover: Using a screwdriver, carefully remove the screws securing the amplifier’s cover. Then remove to small access panel on the rear of the amplifier.
3. Locate the Jumper: Inside the amplifier, find the frequency-limiting Green jumper cable. This jumper grounds the tuning pot making it inactive.
4. Modify the Circuit: Depending on the amplifier version, cut the specific green wire.. Some versions require soldering, so proceed carefully.
Reassemble and Test: Once the modification is complete, reattach the covers and securely fasten all screws. Then, reconnect the amplifier and test it with a transceiver to ensure the expanded frequency range is accessible.
Conclusion
The Ameritron AL-811 MARS Mod is a valuable upgrade for radio operators needing more frequency flexibility. By expanding your amplifier’s range, you can operate 10 & 12 meters, as well as support critical communications during emergencies and broaden your participation in various radio activities.
As long as you follow legal guidelines and perform the mod correctly, this enhancement can significantly boost the versatility of your amateur radio setup.
Troubleshooting the AL-811 After the MARS Modification
If the amplifier does not appear to operate correctly after performing the MARS modification, several common issues may be responsible.
Amplifier still limited to amateur bands
The restriction jumper may not have been fully disconnected. Inspect the modification area and confirm the wire is completely cut or removed.
No RF output
Verify the amplifier is properly tuned and the transceiver is providing sufficient drive power.
High plate current during tuning
Excessive plate current usually indicates improper tuning. Reduce drive power and carefully retune the Plate and Load controls.
Reduced output power
Weak tubes, incorrect tuning, or insufficient drive power can all reduce amplifier output.
If problems persist, compare the amplifier wiring against the manufacturer schematic or consult an experienced amplifier technician.
Common Mistakes When Performing the AL-811 MARS Mod
Although the modification itself is simple, several common mistakes can occur during the process.
One of the most frequent issues is cutting the wrong jumper wire. Internal wiring colors can vary slightly between production runs, so operators should confirm the correct wire location before making any modifications.
Another mistake is failing to completely disconnect the jumper. If the wire remains partially connected, the amplifier may still behave as if the restriction is present.
Operators should also ensure that no clipped wire fragments remain inside the amplifier chassis before reassembly. Loose metal pieces can create short circuits or interfere with proper amplifier operation.
Careful inspection before closing the amplifier helps prevent unnecessary troubleshooting later.
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