Tinny sidetone (was Re: Using an external electronic keyer with QCX-mini)


Sean Walberg
 

Been trying more things, leaving me more confused.

My baseline case is the QCX mini plugged into the feed line inside my house. Earbuds, a 12v battery, and a 3d printed paddle. About 50' of coax to a grounded polyphase, 100' to a Carolina Windom up about 60' in the trees. Works great. I key, the sidetone sounds just like it does in practice mode.

However I got this transceiver to operate portable. I have the Pacific Antennas 20/40 dipole (https://www.qrpkits.com/dualbanddipole.html) and put it about 15-20' in the trees. 25' of RG316 into the QCX. When I key, the sidetone is loud and high pitched. I reduced the volume of the side tone in the menu which doesn't change the volume of the sidetone I'm hearing. Same thing if I use 50' of RG58u instead of the RG316.

Pulled out an 160-10 end fed -- 88' of wire, put one end into a tree about 20' with 50' of coax. Same thing. Sometimes instead of the tinny sidetone, I just get clicks. In one case I was getting clicks, but if I grounded the shield of the feedline to the ground rod I'd be back to tinny sidetone.

Replaced the earbuds with some over the ear headphones -- Sennheiser HD280 pro. 64ohm impedance. Works perfectly on the end fed. Haven't tried the dipole.

Something's not adding up though, but figured some more datapoints might help people with suggestions.

Thanks,

Sean KN4ZMA


Daniel Conklin
 

I've experienced the same thing. It doesn't take much RF coming back to the radio to affect the sidetone. A good counterpoise helps. 
--
73, Dan - W2DLC


Sean Walberg
 

(following up to my own post)

Went back to the dipole. Removed all ferrite. I got the desired sidetone using the Sennheiser headset. Replaced it with the Earbuds (Skullcandy something or other) and it got the bad sound.

I'm not married to those earbuds, but the Sennheisers are a bit bulky to be taking camping. Any idea what properties I'm looking for in an alternative, or a way to make those earbuds work?

Thanks,

Sean KN4ZMA


Steve
 

Try winding the earbud cord with a toroid.  try both ends or one or the other.  see what happens.



Glory to God in the highest, and on earth peace, good will toward men. Luke 2:14


On Thursday, June 3, 2021, 09:42:25 AM EDT, Sean Walberg <sean@...> wrote:


(following up to my own post)

Went back to the dipole. Removed all ferrite. I got the desired sidetone using the Sennheiser headset. Replaced it with the Earbuds (Skullcandy something or other) and it got the bad sound.

I'm not married to those earbuds, but the Sennheisers are a bit bulky to be taking camping. Any idea what properties I'm looking for in an alternative, or a way to make those earbuds work?

Thanks,

Sean KN4ZMA


Sean Walberg
 

Thanks. I'd done the plug end, but will try the other.

Sean KN4ZMA


Sean Walberg
 

Tried two sets of earbuds. Even wrapped them in a toroid so much that there wasn't more than a couple of inches on either side. Still the same problem. Argh.

Sean KN4ZMA


Steve
 

The fact that the Sennheiser headset works satisfactorily is encouraging.  I'd look into how it is wired (shielded cable?).  I assume the jack is of the 3 terminal type in all cases?


Glory to God in the highest, and on earth peace, good will toward men. Luke 2:14


On Thursday, June 3, 2021, 11:10:25 AM EDT, Sean Walberg <sean@...> wrote:


Tried two sets of earbuds. Even wrapped them in a toroid so much that there wasn't more than a couple of inches on either side. Still the same problem. Argh.

Sean KN4ZMA


Sean Walberg
 

First set of earbuds had a mic, so it was TRRS. Second set was just a regular stereo TRS connector. Sennheisers are TRS. Can't tell if it's shielded or not.

Tried my son's pair of cheap over the ear headphones. Used an aux cord that's likely not shielded. Those work. 32ohm input impedance.

Sean KN4ZMA


Alan G4ZFQ
 

Those work. 32ohm input impedance.
Sean,

Not sure if this has been mentioned but are there some comments about speaker impedance in the manual?

73 Alan G4ZFQ


Sean Walberg
 

The earphones can be any stereo earphones such as commonly used with audio equipment, mobile phones and so on, with a 3.5mm stereo jack plug. These commonly have a 32-ohm impedance. Some people have noted unstable audio operation when low impedances are connected such as 4 or 8-ohm speakers; this is because the output opamp IC (IC10) is not able to supply the required power output.
Well that might do it, Alan. Pretty sure the earbuds I'm trying have a lower impedance. They're common phone ones, but at least the first one is probably closer to 17 based on current models from the same manufacturer. But no idea why it works fine if it's attached to my house antenna... I'll look around the house for another pair of earphones. I used to be tripping over them, now everything is either Bluetooth or Lightning!

Thanks

Sean KN4ZMA


Ronald Taylor
 

Sean, try adding a capacitor across the headphone connector on the bottom of the board. A 100nF should suffice. Install it from the audio out lead to ground on the bottom of the audio jack. I use 1206 size SMD capacitors for this but a small leaded one will work too if you make sure it has proper clearance to the case. This has solved the problem you are describing on several occasions. Good luck ... 73

Ron


Ronald Taylor
 


Here's a photo of the capacitor in place... Ron

On Thu, Jun 3, 2021 at 9:18 AM Ronald Taylor via groups.io <wa7gil=gmail.com@groups.io> wrote:
Sean, try adding a capacitor across the headphone connector on the bottom of the board. A 100nF should suffice. Install it from the audio out lead to ground on the bottom of the audio jack. I use 1206 size SMD capacitors for this but a small leaded one will work too if you make sure it has proper clearance to the case. This has solved the problem you are describing on several occasions. Good luck ... 73

Ron


Sean Walberg
 

Eureka! Thank you. I moved the cap from the place I had it to where you showed me, and I get a normal sidetone now with the earbuds.

Thanks again!

Sean KN4ZMA


Ronald Taylor
 

Glad it worked Sean. 73 .. Ron


On Thu, Jun 3, 2021 at 9:44 AM Sean Walberg <sean@...> wrote:
Eureka! Thank you. I moved the cap from the place I had it to where you showed me, and I get a normal sidetone now with the earbuds.

Thanks again!

Sean KN4ZMA