Below the Noise Floor — Episode 7: "Before You Transmit: Audio Setup"

Before you key up for the first time there are a handful of things to check and configure - and doing them in the right order saves a lot of frustration. This episode is the pre-transmit checklist: microphone selection and level setting, PTT options in AetherSDR, how to set your power level correctly, and how to verify your audio is clean before you ever put a signal on the air.

Transcript

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The first six episodes of this show were about receiving, listening to the bands, reading the waterfall, understanding what you are hearing. That phase of learning is genuinely useful and it is also comfortable. You cannot cause any harm by listening. No one knows you're there. You're just observing. Transmitting is different. When you key up, you put a signal on a shared resource. Other operators can hear you. If your audio is set up wrong, they will hear that too. If your power is too high or your signal is distorted, you are creating interference for everyone else on that frequency. None of this is catastrophic, and every experienced operator has made beginner mistakes. They remember making them. But a little preparation before the first transmission means your first contact is something to be proud of rather than something to cringe at later. This episode is the pre-transmit checklist. We are going to go through microphone selection, level setting, PTT configuration, and power level one step at a time, in the order that makes sense. By the end, you will have a transmit setup that is ready to go and you will understand what each setting is doing. Let me start with the microphone, because it is where the signal chain begins and getting it wrong affects everything downstream. The microphone options for HF voice operating fall into a few categories. The microphone built into your computer, a laptop webcam mic or an integrated desktop mic, is almost always a poor choice. These are designed for voice calls and video conferencing, which use processing optimized for intelligibility in a noisy office environment. That processing, noise cancellation, automatic gain control, equalization tuned for telephony, works against you in HF radio. You want a clean, unprocessed audio signal going into Ether SDR so that the radio's own processing chain can work with it correctly. A USB headset designed for communications use is a reasonable entry-level option, something in the headset category from a brand that caters to amateur radio or aviation, Heil, Sennheiser, Plantronics, will have flatter frequency response and less automatic processing than a consumer gaming headset. Gaming headsets tend to add bass boost and other coloration that muddies HF voice audio. A dedicated desktop microphone on a stand connected via USB or via an audio interface gives you more flexibility and is often what operators settle on for fixed station use. For mobile or portable operation, a headset with Boom Mic is more practical. Whatever microphone you are using, the first step is to make sure your operating system recognizes it as the correct input device and that Ether SDR is set to use it. In Ether SDR, go to the audio settings and confirm the input device is your microphone, not the system default, not a virtual device, and not a loop back from WSJTX or any other software you may have running. Now level setting, this is the most important step, and it is the one most people rush. The goal is to have your microphone input level high enough that your voice produces a healthy reading on the transmit level meter in Ether SDR, but not so high that it drives the meter into saturation. Saturation, also called clipping, is what happens when the audio level exceeds the maximum the system can handle. The signal distorts. On HFSSB, a distorted transmit signal produces what operators call splatter, audio energy, that spills outside your intended bandwidth and interferes with stations on adjacent frequencies. It also sounds terrible. Experienced operators can immediately identify an over-driven audio signal, and it is one of the things they will tell you about if they hear it. The transmit level meter in Ether SDR responds to your microphone input when you are in transmit mode. The target is to have peaks, the loudest parts of your normal speaking voice, reaching roughly 70 to 80% of the meter's full range without hitting the top. Speaking at a normal conversational level, at a normal distance from the microphone, typically 6 inches to a foot, should put you in that range with the microphone gain set appropriately in Ether SDR's mic gain control. A practical way to set this before your first transmission, put the radio into monitor mode if Ether SDR supports it, or temporarily connect to a dummy load if you have one. Speak at your normal operating level, not louder than you would normally talk, because the temptation when you first sit down at a radio is to project your voice more than necessary. Watch the meter. Adjust the mic gain until peaks are comfortably below the top without being so low the meter barely moves, then stop adjusting. The level you set in this step is the foundation everything else builds on. One thing to be aware of regarding Windows specifically, Windows has its own microphone processing layer that can interfere with radio audio in ways that are not obvious. In the Windows Sound Control Panel, under microphone properties, there is typically an option for microphone boost and another for audio enhancements. The enhancements, noise suppression, echo cancellation, automatic level adjustment, should generally be disabled for radio use. They are designed for video calls and apply processing that conflicts with the radio's own processing chain. Disable them before you set your levels in Ether SDR, and you will have a much more predictable result. Now PTT, push to talk. PTT is the mechanism that switches the radio from receive to transmit. You have several options in Ether SDR. The simplest is the software PTT button in the Ether SDR interface itself. You click it to transmit and click again to stop. This works and it is perfectly fine for initial setup and testing. For actual operating, it becomes awkward. You need a free hand on the mouse while you are talking, which means you cannot take notes or operate any other controls during a contact. Vox, voice operated transmission, automatically switches to transmit when it detects audio above a threshold and switches back to receive when the audio falls silent. EtherSDR has a Vox function with adjustable sensitivity and hang time. The sensitivity setting controls how loud a sound has to be to trigger transmit. The hangtime controls how long the radio stays in transmit after you stop speaking. This prevents the radio from dropping back to receive in the middle of a sentence during a brief pause. Vox is convenient but has pitfalls. Background noise can trigger it unintentionally. A cough or a loud noise in the room goes out over the air. In a quiet operating environment, Vox works well. In a noisy one, it can be frustrating. A foot switch is the traditional solution for hands-free PTT control. A simple foot pedal wired to a USB interface or to the radio's PTT input keeps your hands free during a contact while giving you precise control over when you are transmitting. This is what most experienced voice operators use for serious operating. For initial setup and occasional contacts, software PTT or Vox is fine. There are also external PTT interfaces, small hardware devices that connect via USB and provide a keying input that give you physical button PTT control. These are inexpensive and widely available from radio accessory suppliers. Whatever PTT method you use, there is one thing to be absolutely clear about before you transmit for the first time. Know which state you are in. Know whether you are transmitting or receiving at any given moment. Ether SDR provides visual indication of transmit state, typically the mocks button lights up or changes color when the radio is transmitting. Glance at it before you speak. Glance at it when you think you have finished. Accidentally leaving the radio and transmit while you are not talking or talking while you think you are still in receive are both common beginner errors and both are immediately obvious to anyone listening on the frequency. Power level is the last piece of the pre-transmit setup. The instinct when you first start transmitting is to run as much power as your radio will allow. More power means stronger signal, stronger signal means better contacts, right? In practice, this is not quite correct, and for a new operator, there are good reasons to start lower. First, any problems in your transmit audio, distortion, improper levels, incorrect mode selection are less damaging to other operators on the band when your signal is weaker. A problem at 5 watts affects fewer people than the same problem at 100. Second, on HF bands with healthy propagation, you often do not need full power. FT8 contacts are routinely made at 5 to 10 watts. SSB voice contacts at 25 to 50 watts are workable under normal conditions. The relationship between power and receive signal strength is logarithmic. Doubling your power increases your signal by only 3 decibels, which is barely perceptible. To make a meaningful difference, you need to multiply power by 10, which takes you from 50 watts to 500 watts, a level most amateur stations do not operate at. Third, lower power is easier on your equipment. Running a transmitter at full power continuously generates heat and stress. Running it at 50 to 70% of rated power for general operating is easier on final amplifier transistors and reduces the chance of thermal issues. For a first transmission, set your power level in Ether SDR to somewhere between 25 and 50 watts if your radio supports it. This is enough to be heard on a local or regional contact and enough to make digital mode contacts under reasonable propagation. You can always increase power later if you find you need it for a specific contact. The checklist, summarized, correct microphone selected in Ether SDR audio settings. Windows audio enhancements disabled if on Windows. Microphone level set so peaks reach 70-80% of the meter without clipping. PTT method, chosen and tested. Power set to 25 to 50 watts to start. Mode set correctly for the band, LSB on 40 and 80 meters, USB on 20 meters and above. One final note. Before your first actual on-air transmission, it is worth checking that your antenna is connected and that the tuner, if you have one, has already found a match on the frequency you plan to use. Transmitting into a badly mismatched antenna or into no antenna at all is hard on the final amplifier. Ether SDR and the Flex Radio will protect themselves to some degree with built-in SWR protection, but it is better not to rely on that protection routinely. The tune function in Ether SDR sends a low power carrier for a moment to let the tuner find a match. Use it before your first voice transmission on any new frequency. Next episode, we put all of this to use. Episode 8 is making your first voice contact. How a QSO works, how to call CQ, what to say when someone comes back, and the standard exchange that gets you from first call to logged contact. This is below the noise floor.