I’m trying to be less of an appliance operator. To that end, I recently came up with a simple project that I thought I could figure out and build entirely on my own. I was wrong.
My goal was to create a splitter with an attenuator that would allow me to connect the external speaker jack output from my Yaesu FT-8900 to the microphone input on an iPhone in order to record, while simultaneously listening to the live audio via headphones.
I’m doing this because I’d like to record FM satellite QSOs as they occur while I’m outside using a handheld yagi (thankfully, building the antenna was within my skillset!). Currently, I just use an old Olympus DM-10 digital recorder Velcro’d next to the built-in speaker, which is less than optimal.
My problem is I get lost in the calculations for resistor sizes needed to get from the higher voltage output on the FT-8900 speaker jack to the millivolt input on the iPhone, as well as well as how to physically wire everything from the mono TRS plug for the radio side to the stereo TRRS plug for the iPhone side, as well as splitting-off for a headphone jack.
For reference, the specs on the Yaesu output is:
- Maximum AF Output: 2 W @ 8 Ω for 5% THD
- AF Output Impedance: 4-16 Ω
Any help would be greatly appreciated. Thanks in advance.
To answer Chris K8NVH's questions:
As far as headphones always being plugged in: The vast majority of the time, I would be using headphones. However, it would be nice to have the ability to use the device both with and without headphones attached.
As far as line level drop: if the drop is such that it doesn't render the resulting audio unusable, it doesn't really matter to me. I don't mind turning up the volume when playing back if that is the only consequence.
I wanted to go with the iPhone over the Olympus for a number of reasons:
- First and foremost, it is very easy to accidentally hit a button on the Olympus and cancel a recording. This has happened to me in the past. With the iPhone, this would not be a concern.
- I already use the iPhone when I'm working the satellites outdoors to see times, tracks across the sky, etc. Using it over the Olympus would allow me to eliminate one piece of equipment
- The iPhone offers better battery life. Its surprising how fast the Olympus goes through AAA batteries.
But, in the end, simple is probably better. If that means sticking with the Olympus and creating a circuit that is designed to be used only with the headphones plugged in, I can accept that for the time being. I can always try a more involved design later.