Perplexing DC voltage

RF modules are very sensitive to power noise. A cheap power adapter or a DIY adapter will have a lot of power noise. Maybe this noise is affecting the RF signals from the module.

Try using an electrolytic capacitor (like 24V and 10uf) across the power rail and see if it works 

Direct current (DC) is the unidirectional flow of an electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current. A term formerly used for this type of current was galvanic current.
The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.

Direct current may be converted from an alternating current supply by use of a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alternating current via an inverter.
Direct current has many uses, from the charging of batteries to large power supplies for electronic systems, motors, and more. Very large quantities of electrical energy provided via direct-current are used in smelting of aluminum and other electrochemical processes.

Direct current (DC) is the unidirectional flow of an electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current. A term formerly used for this type of current was galvanic current.
Direct current has many uses, from the charging of batteries to large power supplies for electronic systems, motors, and more. Very large quantities of electrical energy provided via direct-current are used in smelting of aluminum and other electrochemical processes.

The power source you mentioned, you are using for powering up your radio module is not suitable for the radio modules because of the reason that there contains noise signals in these kind of power adaptors. Try using specified batteries, recommend for radio modules or some power adaptor with lowest noise. But also you can try by adding an electrolytic capacitor in power rail, for that use capacitors if voltage ratings of 16V or 25V. There can be any of the capacitance value just check for the best option to reduce the noise signals. Here I would like to recommend you to connect with the SSLA platform, from where you can get further assistance about your project from their technical support team.

The power source you mentioned, you are using for powering up your radio module is not suitable for the radio modules because of the reason that there contains noise signals in these kind of power adaptors. Try using specified batteries, recommended for radio modules or some power adapter with lowest noise. But also you can try by adding an electrolytic capacitor in the power rail, for that use capacitors with voltage ratings of 16V or 25V. There can be any of the capacitance values, just check for the best option to reduce the noise signals. Here I would like to recommend you to connect with the Sierra Software Ltd. platform, from where you can get further assistance about your project from their technical support team.