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QCX Mini Distorted tone at low volume

michael.j.bauer@...
 

Hello everyone

Now that I have my EFHW set up, I’ve sent some test messages I’ve saved. I’ve noticed the tone seems distorted or “scratchy” at low volumes. It seems to get cleaner by increasing the volume. I’d there something specific I should check or troubleshoot?


Thanks, 
Michael

--
KD7PTZ
Ronald Taylor
 

Michael, are you talking about the side tone that is present when transmitting? Or the tone of the received signals? If you are talking about the transmitter side tone, then you are most likely getting RF into the audio circuits, which itself is most likely due to common mode current on your feed line, which is an especially noticeable issue when using unbalanced antennas like the EFHW. The cure is to put a choke (line isolator) on the coax near the antenna feed point and provide some coax distance between the antenna and the radio. Try to avoid connecting the EFHW antenna directly to the radio with no coax.

Good luck ... 73 ... Ron

On Wed, Nov 23, 2022 at 12:33 PM <michael.j.bauer@...> wrote:

Hello everyone

Now that I have my EFHW set up, I’ve sent some test messages I’ve saved. I’ve noticed the tone seems distorted or “scratchy” at low volumes. It seems to get cleaner by increasing the volume. I’d there something specific I should check or troubleshoot?


Thanks, 
Michael

--
KD7PTZ
Jack Kibelbek
 

My minis do this also.

The harsh side tone got better when I added ferrite beads (6) to the coax feed line at the transmitter end. But it has not completely disappeared. I have satisfied myself by increasing the gain on the "volume" knob until it sounds acceptable to my ear.

Some bands, different minis, (I've got 4) are worse at this than others. Common mode is a particular problem with portable QRP antennas--EFHW, trapped verticals, and long wires.  Occasionally I can even feel the RF as a tingle (or worse) in my straight key.

I really don't think this is a problem with the transmitted signal. I've made more than a thousand POTA QSOs with my minis and never had a comment or complaint on the other end about the CW tone., The "T" of my RST is invariably a "9".

Good luck.
Donald Kirk
 

Hi Michael,

As others have suggested, I wrap 10 to 14 turns of coax through an FT240-31 toroid core (based on work done by K9YC) and I locate this choke approximately 0.05 wavelengths (on the lowest band) from the feedpoint of the EFHW (based on work done by AA5TB which I also confirmed via modeling).  Doing this does a great job keeping RF off the outside of the coax shield between the choke and the radio.  Also the outside of the shield between the feedpoint and the choke acts as an adequate counterpoise so you don't need to install an additional counterpoise wire.  The choke also helps reduce common mode noise that travels from your shack up to the feedpoint via the outside of the coax shield and this therefore often helps reduce your receive noise floor.  It also makes the SWR much more stable (repeatable) as it eliminates the outside of the shield between the choke and your radio from being another variable (additional counterpoise) that would otherwise alter the SWR depending on how it's coiled up, what its touching, etc.

73,
Don (wd8dsb) 
michael.j.bauer@...
 

Thank you everyone

Ron- yes, just the tones when generating - this does not happen on receive. 

Don - what size toroid are you using in order to get 10-14 turns of coax around it? Do you happen to have a part number? 


Happy Thanksgiving everyone
73
Michael
--
KD7PTZ
Donald Kirk
 

Hi Michael,

I use Fair-Rite part number 2631803802.  They are available at places like Mouser, Digi-Key, Arrow, etc.  I use RG-58 coax which allows me to get 14 turns.  The outside diameter of the core is 2.4 inches, the inside diameter is 1.4 inches, and the height is 0.5 inches.  The Amidon part number for this same part is FT240-31 where the 240 indicates 2.4 inches, and the 31 is the actual grade of the material (you will see the 31 within the Fair-Rite part number too).

73,
Don (wd8dsb) 
Colin Kaminski
 

I have been buying all my ferrite from https://www.kitsandparts.com/  
Fast affordable shipping and a large list of available items. 
--
Colin - K6JTH 
http://tangokeys.com
Bryan Curl
 

Michael,
The choke ideas here work well, but I use a 1:1 unun 1/4 wave from the efhw.

LDG Electronics RU-1:1 Unun RU-1-1

Its a lot more packable. Since my par endfedz for 20m is single band, the 1/4 wave down feed line gives me the high current point where the choke will be most effective. The 1/4 wave also presents as a counterpoise also.
This cured my rf problems whilelst running the 59w amp where my display would lock up and preform odd behaviours in addition to odd tones.

Good luck and happy tapping.

regards,
Bryan, N0LUF
Rob - KC4NYK
 

Donald,

I have built the EFHW shown below and after following the conversation in this thread I'm thinking that I might also need to add the "ugly balun", also shown, that I made for my Yo-Yo-Vee, inverted V dipole.

Also if I understand correctly, I may need to move the balun to the suggested .05 wavelength distance from the feed point for the lowest  band which would be 80 meters even though the antenna is cut for 40 meters (63 ft). does all that cogitation sound right?



Thanks,

Rob
Dave VE3GSO
 

The thing about an “ugly balun” is that the additional coax has some additional loss, both on transmit and receive.

My practice is to slip a few ferrites onto the coax.  They do not add any loss. Usually these were scavenged from old monitors and CGA cables and put on before the connectors are soldered on, but the clip-on ferrites work really well. 

Dave

On Nov 27, 2022, at 14:25, Rob - KC4NYK <rbt@...> wrote:

Donald,

I have built the EFHW shown below and after following the conversation in this thread I'm thinking that I might also need to add the "ugly balun", also shown, that I made for my Yo-Yo-Vee, inverted V dipole.

Also if I understand correctly, I may need to move the balun to the suggested .05 wavelength distance from the feed point for the lowest  band which would be 80 meters even though the antenna is cut for 40 meters (63 ft). does all that cogitation sound right?

<uglyBalun.JPG>
<EFHW_1.jpg>


Thanks,

Rob

bobfox
 

Well, not exactly.

The loss is on the outer braid only, which is intentional, of course.

That’s why it is called RF choke, wave blocker etc.

The inner conductor has less than 0.5 dB, if any.

 

73, Robert OE7OER

 

 

 

Von: QRPLabs@groups.io <QRPLabs@groups.io> Im Auftrag von Dave VE3GSO
Gesendet: Montag, 28. November 2022 00:07
An: QRPLabs@groups.io
Betreff: Re: [QRPLabs] QCX Mini Distorted tone at low volume

 

The thing about an “ugly balun” is that the additional coax has some additional loss, both on transmit and receive.

 

My practice is to slip a few ferrites onto the coax.  They do not add any loss. Usually these were scavenged from old monitors and CGA cables and put on before the connectors are soldered on, but the clip-on ferrites work really well. 

Dave



On Nov 27, 2022, at 14:25, Rob - KC4NYK <rbt@...> wrote:

Donald,

I have built the EFHW shown below and after following the conversation in this thread I'm thinking that I might also need to add the "ugly balun", also shown, that I made for my Yo-Yo-Vee, inverted V dipole.

Also if I understand correctly, I may need to move the balun to the suggested .05 wavelength distance from the feed point for the lowest  band which would be 80 meters even though the antenna is cut for 40 meters (63 ft). does all that cogitation sound right?

<uglyBalun.JPG>

<EFHW_1.jpg>



Thanks,

Rob

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