Bluetooth headset on KX2?


Bluetooth cuts the wire and offers hands free, therefore I’m wondering if there is any experience with setting up Bluetooth headset with a transceiver, especially with KX2.
Generally, I’m wondering why the modern transceiver like IC-7300 does not have this feature anyway.
Being SOTA newcomer I’d very appreciate any advice and tips helping in preparations to the new mountain season.

Christoph, dj0vk

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Hi Christoph,

I have not seen bluetooth adaptors for KX series, but are some advertised for ft817 series, I don’t know but would think they are readily adaptable to kx. One matter to be aware of is the dc voltage that is usually provided to the standard kx series microphone as bias for the electret element in the mike. This voltage is configurable in the kx radio to be on or off, depending on the type of element in the mike.

In general I have not been attracted to using bluetooth for mike and headphones. I have always used cables, with no extra RF floating around the radio and my head. However right next to me is my mobile phone with bluetooth enabled. Every extra bit of RF around the radio can cause issues and with my KX3 I have noticed the high gain audio stages can be very susceptible to the 3G/4G signals from the phone, which creates some unpleasant noises in the headphones, so I try to keep the phone away from the radio or any cables leading to the radio.

The other issue is the battery required in the bluetooth enabled headphones and microphone. They don’t last forever so they are yet another battery to be recharged prior to activating. If they are your only headphones or microphone you are dependent on them for the operation of your radio. Ie. another point of possible failure, which we try to minimise.

As for preparations, I think the best advice is to activate in the company of other experienced SOTA activators. We all learn something from others and in any case, activating in groups is safer and more fun.

Hope this helps… 73 Andrew VK1DA/VK2UH


My Icom 705 can link with a Bluetooth headset although I haven’t tried it yet.

I did use a Bluetooth headset linked to my phone when I was learning Morse (CW) but discovered it seemed to mask or distort the first dit or dash. I suspect the device goes to sleep to save battery power but wakes up when it gets a signal - which won’t be a problem with music but was with CW - although in the real world the background noise should keep it awake.

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I find I get lip-sync delay if I use Bluetooth headphones to watch a film [although I believe some streaming services had a compensation feature]. Wouldn’t the sidetone delay via the BT link cause you to stutter on voice or mis-key on CW?

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Hi Andrew, the Bluetooth adapters for the FT-817 are usually for the serial CAT commands so that the rig can be controlled from a smartphone, rather than audio/PTT Bluetooth.

There are some generic BT (Audio out) adapters available that simply plug into the 3.5mm audio socket and I used one for some time with my IC-7300 to use a Bluetooth headset. It was a pain that the minuscule batteries inside the BT transmitter or the headphones kept running down though and in the end, I went back to the cabled headset and added a coily extension.

There are also BT adapters for a full headset with PTT made for the Chinese HTs - these may be possible to be adapted to fit an HF portable rig.

73 Ed.

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Exactly the problem for stop/start audio but not an issue for streaming. When I was working on BT chip design, battery life was considered the most important design consideration. Everything possible was done to save power.

I’ve had two BT serial dongles that have worked fine for a few weeks then died. They last just long enough so you can’t claim on eBay/Paypal warranties. Cables seem much better after that.

Thanks Ed,
I looked again at the ones I had seen on Aliexpress and found they were for the CAT connector so not suitable for audio in/out. Thanks for reminding me, I should have come back here and clarified that.
73 Andrew VK1DA/VK2UH

There are many Bluetooth adaptors with a 3.5mm input, just check on-line.

My experience is that the ones I tried are not usable for CW due to the lag of the side-tone: it is extremely difficult to send proper CW when there is the slightest delay between your action on the paddles and what you hear, unless you use the side-tone of an external keyer if you can hear it with the headset on your ears.

Back from 2008:

73 Ed.

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As pointed out above, the complication of bluetooth is the delay, introduced by the bluetooth A-D conversion at the encoder end and the D-A converter at the receiver/headphone end.

The application does not really require extremely high frequency range as the receiver bandwidth is only 3khz and bluetooth audio is designed for much more.

So another encoder and decoder that could be used is an fm modulator/transmitter. Simple fm transmitters can operate at 1mw and headphones with fm receivers built-in are readily available.

The other instant remote listening method that I use is an audio to sound pressure transducer that most radios have built in. The sound pressure to audio converters are found on each side of the head. :wink:

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The FM transmitter idea is interesting but would only provide audio out from the TRX to the headphones and has no path back for speech to the TRX. Some (but not all) BT solutions provide two way communications.

I believe the IC-705 has an option of a two-way BT speaker microphone so that the rig can be operated while still in the backpack. Hopefully, the microphone also has a 3.5mm jack for an earpiece to mute the speaker to stop annoying others nearby.

In my opinion, at the end of the day, however, a cabled solution (if weight and size are of concern, based on a smartphone cabled mic/earpiece) will be the simplest option.

73 Ed.

Hi all,
I have no issues with my Bluetooth headphone and mic with the IC705.
Yes I need to charge the batteries before a day in the field but it’s great for log keeping and looking at SW3. I can even get up and walk around. No problems out to 10 or 15 m.

Not all Bluetooth headsets work as well. I selected mine on the basis of that’s what a couple of happy ops were using. Cost $40 from memory. If any 705 owner wants more details please ask. It was debated at length on the 705 forum.


Hi Ron,
That’s good. But you don’t mention CW, have you used the BT system while using a paddle on CW? I would expect some delays which could create confusion in the liveware while sending.
73 Andrew VK1DA/VK2UH

Hi all,

as I can see there is no proper Bluetooth solution for CW due to a delay.
My dream was to have iPads in the ears, KX2 on the lap, no wire in-between and hoped with modern Bluetooth 5.xx it will be feasible similarly to the solution by K7AGE in 2008 and presented here by DD5LP.
BTW, years ago I’ve tried Nokia AD-42W Bluetooth transceiver together with different headsets (incl. Nokia BH-503) but as I can remember there was a permanent noise in ears (especially in the left one) at higher level than the floor noise of tested receivers.
The wired vs. Bluetooth headsets on TRX appears like operation of FT7B vs. KX2 - the first one is intuitive the latter needs 80-pages-isch manual and days of training :wink:

vy 73!

Hi Andrew,

“…is to activate in the company of other experienced SOTA activators. We all learn something from others and in any case, activating in groups is safer and more fun.”

That’s very right!
The only challenge is to find a soul in the Munich area…

I mentioned above my IC-705 has Bluetooth but I hadn’t tried it. I’ve now done a quick trial and initial impressions are this could work for CW but I’m a CW beginner so what worked for me at 15 wpm might not for more experienced operators. The only thing which I didn’t like was the tone in the BT headset was very harsh. I have another BT headset somewhere and I’ll try that and see if it is the same. I’ll also see if there is someway of videoing the results. The 705 has a waterfall so you can see the dots and dashes on the screen and hopefully I could record the sound as well.


Interesting tests John.

I’m not a CW Op but from a technical viewpoint I would have thought to operate CW over BT there would need to be a Bluetooth profile supported by the devices at both ends or are you just using an audio connection and somehow creating a tone from the key? Perhaps a BT serial connection would give you the option of using a key.

Technically very interesting in any case.

Good luck.

73 Ed.

I was just listening to the audio. Having read the 705 instructions again :slight_smile: there is an option to connect a BT device and maintain sound to the sets own speaker. I had it so the system speaker was turned off. If I try again with the speaker enabled it might be possible to hear if there is a delay on the sound coming from the BT device…