McPhee Aviation

Radio FAQs

Q. What is the difference between the hot mike on the 760 and a vox operated mike? 
A. A hot mike runs all the time when the intercom is turned on, this means that the background noise will be there as well, in quieter cockpits like the Jabiru it normally is quite acceptable, however, in louder noise environments it can be annoying. A vox operated system is one that only activates when you talk, most aftermarket units do this and we recommend them in noisy cockpits. Our new 760SL series will have a vox operated intercom as standard.
The 760 can be wired as a push to talk intercom - [Wiring diagram to come]

Q. Why are some glider microphones dynamic?
A. Most of the German radios have used dynamic microphones over the years, mainly because of a tandem configuration there is less problems with just wiring the two together, unlike electrets. However, the Microair has 2 inputs for electrets so this overcomes that problem. The 760 will only work on an electret mike like the microboom, or an amplified dynamic like the telex. If you have a dynamic mike you can use our amplifier - MD-01 to boost the audio. Our new 760SL series will have an inbuilt dynamic circuit for gliders.

Q. Why do you need relay switching when using two headsets?
A. Most G.A. radios require the pilot and co pilot mikes to be isolated when transmitting, otherwise both mikes are live. In the past a simple relay was used. We sell the RB-02 to do this on our radio. Alternatively you can build up your own using a supplied wiring diagram. [Wiring diagram to come]

Q. Why is SWR so important?
A. SWR ( Standing Wave Ratio ) is a term used for antennas, it relates to the amount of power being transmitted to the antenna and the ratio of reflected power back to the radio. A high SWR can degrade the performance of your transmit range and in some instances it can cause distortion of the transmitted audio and possibly damage to the radio. An SWR on a standard 1/4 wave whip should be around 1:2:1 or better, some can be as high as 2:1. We do not advise using an antenna with an SWR higher than 2:1. To check this you can use an SWR meter ( local avionic guy, ham radio operator etc ) which covers the 118 to 136 Mhz band, a 27 Mhz CB type will not be suitable. Antennas in fibreglass aircraft must have a ground counterpoise or groundplane.

Q. I have excessive ignition noise, what can I do to reduce it?
A. The use of shielded ignition leads helps dramatically. Also grounding is important, make sure the engine has a good ground strap to the battery and frame. In fibreglass it it advisable to keep the ground as direct as possible so as to avoid ground loops that can show up as noise. A common earth bus is needed and avoid multiple routes back to the battery earth. The ignition coils on some brands of ultralight engines have a plastic casing which needs to be shielded as the high energy emitted from these can be a nuisance .

Q. I have heard stories of radios being damaged by electrical systems overcharging, can this be prevented?
A. A good quality regulator is essential. Most engine manufacturers overlook this as they a more concerned about keeping the engine running. However, an electrical breakdown can cause just as much trouble. We recommend the use of an Australian designed regulator ( see links ) that works well. Our 760 will work up to 16 volts, any more and it will be damaged.

Q. Are Microair products Year 2000 compliant? 
A. Yes. Microair products use any time/date related information and are therefore unaffected by any of the Year 2000 issues.

It is the user's responsibility to ensure that any other equipment to which a Microair product may be interfaced is year 2000 compliant.