I often get asked how I get the quality audio sound out of my radios, and how one goes about getting this studio quality audio into their rig. The task is not too difficult, but there are some things to keep in mind. If you are going to run a studio condenser mic, you will need a separate device capable of powering the microphone with Phantom Power (48v). NOTE: If you want the best results, you should consider radios that are able to transmit wide enough to really give you a broadcast quality sound. Using any radio will work, but the results will depend on the capability of the unit, below are the best of the best if you want ESSB type audio.
STOCK eSSB READY TRANCEIVERS
Flex Radio SDR 1000, SDR 5000
You must use a mic preamp or a device capable of powering up the microphone if your going to use a condenser type microphone. If you decide to use a dynamic type of microphone (SM57, SM58, etc..), you do not necessarily need a mic preamp, however unless your radio has a very good mic gain control, you will have difficulty getting your gain up high enough to sound good, so a preamp is highly recommended for both microphone types. Obviously, the better the mic preamp and microphone, the better success you will have with your audio setup at least on paper, however buying more expensive gear may not produce enough audible perception through your rig to warrant the extra costs. Keep in mind however, that most CB class radios will not sound as good as a higher end HAM rigs due to bandwidth limitations on CB radios. However, you can achieve a much better transmit audio on nearly any radio using the methods described here. Some radios may be a little wider than others in their bandpass, so they may sound a little better than others, but rest assure any radio you setup like this will be a major improvement over the default stock mic, and even better than other power mics, and some rigs can be modified for improved bandpass response as well.
Tech Note: One relevant thing to consider is how the other end (Receiver) perceives your audio. Most amateur or CB type radios don’t receive over 2.8 Kilohertz wide (some quite a bit less), so producing big audio is not going to be perceived on the receiving end unless the receiver has filters that listen out wider in their frequency response. For this reason some operators feel the need to do ESSB is not worth the trouble. I’ve been running ESSB for years and I can tell you in my experience it is still is worth the trouble, because external processing can yield noticeable improvements over a stock mic even at a lower frequency responses. Getting the most out of ESSB and external processing will have the best results when both the transmitting and receiving stations have good bandpass filters for both transmit and receive.
There are hundreds of mic preamps on the market, so choose what you can afford and choose wisely. If you are on a budget, you may want to start with something like an ART Studio tube preamp, they cost somewhere in the the neighborhood of $30.00 to $60.00.
(I would suggest a low or mid-level Mic-Preamp with built-in compressor and equalization. PreSonus Studio Channel, Eureka, and Art Pro MPA II are all good mid line pre-amps)
Microphones: There are too many microphones on the market to list, so just pick one and give it a shot. Keep in mind that there will be a difference in the quality of audio you get depending on the brand/type of mike you get, so going the cheap route will not yield quiet as good results as higher end mics. You could just start off with any cheap mic, then work your way up later should you decide to. A pop screen and shock mount would be recommended if your going to use a condenser mic, you will have some sensitivity to sound pressure into the microphone, as well as vibrations picked up by many other things. Your room will play a major part in how your audio sounds due to reflectivity and room acoustics. If possible, try to pick a room that is acoustically silent or add some foam padding to your walls to dampen any echo’s in the room. Both Cardioid and Condenser mics use balanced XLR cables that are designed to shield out external noise such as RF and other interference. The radio your hooking up to is an unbalanced connection so you will need to modify the output XLR cable to make it unbalanced unless you use an external line isolater. (NOTE: I have used balance to unbalanced connection from the XLR cable and it has worked okay for me).
Putting it All Together : Using the diagrams and drawings on the right, you will get a picture on how to hook all of this up. There are many ways to put this together, but one way to do this is to take an existing good microphone and remove the outer shell to where you have nothing but the mic cord, PTT switch, and the speaker connect to the PTT switch (The other option would be to buy a double pole momentary switch and some 5 conductor shielded wire and follow the same instructions). Following the diagrams below, you would remove the existing mic element by desoldering it, and this will only leave you two wires to connect to the PTT switch. You will need to make or cut up an XLR cord for wiring to the PTT switch shown on the right. You will need to modify the XLR cable by putting a jumper between pins 1 and 3 shown below.
Click image to Enlarge
Overcoming Challenges: Over the course of my experience with pro/audio equipment I have found the following issues challenging to over come. Here is a list of things you may run into and how to remedy them. Balanced/Unbalanced line issues Vocal mics (both Dynamic and Condenser) typically use XLR or TRS type cables to carry voice, these lines are typically using balanced wires consisting of a total of 3 wires. HF radio’s typically used Unbalanced lines, which use two wires. This balanced to unbalanced junction can cause many problems, most notably common mode currents, and ground loops along the wire. The best method would be to use an “Ibox“, ISO box, or something similar, which uses line isolation transformation and attenuates the signal before feeding into the radio. For monitoring your audio settings you may want to consider the popular “W2IHY“, which is an excellent in-line audio tool. Keep in mind, using a W2IHY or in line audio hardware will only produce the audio before your XMIT signal. If you want to hear the audio that the radio is actually transmitting, you will need a wideband receiver or another radio capable of listening wide enough to hear the audio. If you decide to go the cheap route in an attempt to squelch common mode, then grounding all of your equipment is a method that can work. I have had great success with Radial Engineering Pro ISO as shown here. http://www.radialeng.com/jisoproiso.php See next.
Grounding Common mode currents are a huge problem for radio operators whether your using pro audio or not. Many problems can be overcome by grounding your radio equipment to a common earth ground. You will need to purchase a 9 foot ground rod, and hammer it into your ground near your house. Make sure you get at least 8 feet into the ground if you can’t go all of the way. Use a heavy gauge copper wire to connect from the ground rod, to a copper bus bar or similar connection in your shack. When grounding your equipment, you must use a separate copper ground wire for each piece of equipment your are grounding to the ground rod. This is the method I use successfully.
HF Amplifiers HF Amplifiers (Linears) running near audio gear is a bad thing, even if properly grounded. Make sure you keep your Amplifier as far away from your Audio equipment as possible. This is a challenge but will yield positive results. Also, the amplifier must be grounded to your copper bus bar, which also helps tremendously. If your using an HR2510, President Lincoln, or HR2600 you are going to find it particularly challenging. These radios are great radios, but they do not like amplifiers and audio gear very well.
Summary Running ESSB/Pro Audio on radio is an awesome experience one you overcome some of the challenges that come with it. For those of you who love a challenge with exciting results, this will be fun. Sometimes you just get lucky and everything just works fine, but usually at some point you will have to confront at least one of the issues above. Enjoy! You can contact me at the following address: dlambeth@osdevices