QCX 5W CW Transceiver Troubles Part III


Glen Leinweber
 

Andy Brilleaux has a very good idea regarding the speaker/headphone problem.
In direct-conversion receivers like this, there is a very large audio gain.
I'm greatly impressed that Hans has managed to keep this huge gain well-tamed.

But we users can cause problems with wiring the radio up. This involves ground
currents, and how they return to the +12V power source.

Your speaker ground line should likely return to the +12V power source ground,
rather than connect to the QCX circuit board ground.
You can wire the audio "hot" terminal from headphone jack to a speaker, but the
ground return should not be wired to the headphone jack, but return straight
back to the DC power source...awkward, but it may help reduce the disturbing
growl, or kill it entirely.


Martin DK3UW
 

what kind of antenna did you use for the first test ?

Martin


Andy Brilleaux <punkbiscuit@...>
 

On Fri, Dec 6, 2019 at 08:22 PM, <joseph.corbin@...> wrote:
In our original test, when it worked well, we started by using earphones, then we switched to a speaker with an aux cord so that more people could hear it. We only used the earphones when we went to the new location
It's fairly common for some audio amps to be quite fussy about load impedance, and what you descibe is typical of it.

Here's you have probably gone from a se of cheap headphones with an impedance of 32R and gone to a load speaker
of 4-8R.

Try series shunting the load speaker with a 10R or something and see what happens.

Or..

Try a lower audio output setting.

Or..

Consider and external audio amp, and take measures to maintain an approx 32R or more load across
the QCX AF output at all times (and let the external amp do all the work).

That should do for starters.


- Andy -


joseph.corbin@...
 

Bill,

The relative humidity in the original location is about 50% and the new location has a relative humidity of about 30-40%. We weren't wearing wool socks but we were both wearing 100% polyester shirts, if that makes a difference haha.

Skip,

In our original test, when it worked well, we started by using earphones, then we switched to a speaker with an aux cord so that more people could hear it. We only used the earphones when we went to the new location. But other than that, there were no other changes that we can recall. We are currently using a Keithley 2231A-30-3 Triple Channel DC Power Supply at 12 V. We will get our hands on a battery and see if that works. Our QCX was sitting on the standoffs but I'll confirm that there isn't a short underneath.

Jim,

Thanks! We will definitely try a battery and report what happens. Also, I'll be sure to make sure there is nothing metallic nearby when we fire it up again. Although I don't think that is the issue since it worked in the same conditions earlier this morning. But we'll see what happens! If ever you find yourself back in Ottawa, KS during the school year, feel free to stop by and see our set up!

Thank you all for the helpful and quick responses!

Joe 
--

Joseph Corbin

President of the Engineering Club
Ottawa University
Ottawa, KS


Jim Mcilroy
 

Hi Joe

Congrats on getting some action out of your QCX

Before warming up a soldering iron I suggest you make sure it is not sitting on anything metallic nearby.

At my QTH I have taken to using lids from scrap box files which are thick cardboard but you may have a more elegant solution  :)

Use a battery to power the QCX. As long as you don't key it up a simple PP3 9V battery is probably good enough for a short while.

If you have a dummy load connect that to the antenna socket to be on the safe side.

See what you can hear then.

73

Jim

PS I've been to Ottawa Uni for a brief visit in the last century. Went to see one of the profs who was into precision timing. The name escapes me for now. A nice part of the world.

On 06/12/2019 18:25, joseph.corbin@... wrote:
Hello again all from Ottawa University!

The good news is: my partner, Will, and I were able to finally get our little radio to work well. We were able to send and receive signals this morning while testing it.

The bad news is: We attempted to move the radio to a different location in our building without making any other changes to the radio. But, when we powered it up at the new location, we only heard a loud, bee-like noise. We were unable to receive the simple signals being sent to us by our professor from within the same building. We checked and double-checked the settings on the radio itself. But we don't see or understand what the problem is. We then attempted to bring it back to the original location and try again. Unfortunately, we had the same constant, noisy tone that, quite frankly, sounds like a little sweat bee flying right into my ears (we used both headphones and speakers while testing). It's as if the radio is failing to filter out the noise properly. We are now wondering if there is a hardware problem that might be associated with this noisy tone.

Any help would be greatly appreciated! Also, we are still quite new at this so we may need some help understanding the terminology and functionality associated with our little transceiver.

Thanks!

Joe
--

Joseph Corbin

President, Engineering Club
Ottawa University
Ottawa, KS


Skip Davis
 

Other than location what else might have been changed? What kind of power supply are you using? If it is different and is a switching supply it might be your problem. Try a battery to power up the QCX and see if it goes away. Also is your QCX sitting on the standoffs if not you may have set it on something that caused a short under the board.

Skip NC9O


n4qa at_hotmail.com
 

Hi Joe.
Just wondering what is the relative humidity in your building this time of year.
Best of luck & 72 / 73,
Bill, N4QA
ps
Hope you guys weren't transporting the QCX while wearing your wool socks :0)


joseph.corbin@...
 

Hello again all from Ottawa University!

The good news is: my partner, Will, and I were able to finally get our little radio to work well. We were able to send and receive signals this morning while testing it.

The bad news is: We attempted to move the radio to a different location in our building without making any other changes to the radio. But, when we powered it up at the new location, we only heard a loud, bee-like noise. We were unable to receive the simple signals being sent to us by our professor from within the same building. We checked and double-checked the settings on the radio itself. But we don't see or understand what the problem is. We then attempted to bring it back to the original location and try again. Unfortunately, we had the same constant, noisy tone that, quite frankly, sounds like a little sweat bee flying right into my ears (we used both headphones and speakers while testing). It's as if the radio is failing to filter out the noise properly. We are now wondering if there is a hardware problem that might be associated with this noisy tone.

Any help would be greatly appreciated! Also, we are still quite new at this so we may need some help understanding the terminology and functionality associated with our little transceiver.

Thanks!

Joe
--

Joseph Corbin

President, Engineering Club
Ottawa University
Ottawa, KS