Topics

Strange Transmit Characteristic

wfcaston@...
 

Background information: 
Ver. 1.00G 2019  
The qcx was built by another ham from whom I bought it.
I have only had it for several weeks.
It is attached to a QRP trapped dipole which I constructed for portable use and is only a few feet above the ground.
I keep the unit connected to an antenna or dummy load when transmitting.
It receives signals ok, but not too loudly.   
I have not yet made a qso.
I am now connected to a much better power, Astrton 20 amp power supply.  
***************************************************************************************

Problem:
When I set the automated CQ and listened with my Icom 737 in the shack, the automated CQ message ran together.  it sounded like there was a carrier and no silence between dits and dahs.  I then set the keyer for straight key.  I then tried to send a stacato dit, as short as possible, and there was about a 3/10 second character minimum transmit time.  In other words, that is a minimum time that the unit can transmit, and that time is way too long.  What could be causing this unit to maintain the signal so long, even with a really short key down time?  Maybe a setting?
--   
Anson
WV4C

 

Sounds like it might be a problem with the key shaper circuit comprising Q4, Q6, R41, R42, C31, C32. Perhaps check those valves are correct?

--
Julian, N4JO.

 

Further thoughts:
Note that in order to test this you'll have to remove the display (with power off, of course!) but you can operate the device without it as long as you set up the keyer modes and save the configuration first.
--
Julian, N4JO.

Lee
 

Anson, are you using semi break-in?  If you are, switch to full break-in.  You may be hearing backwave which is not actually transmitted.
 
73 de WA3FIY  Lee
 
 

------ Original Message ------
Sent: 6/4/2020 5:02:38 PM
Subject: [QRPLabs] Strange Transmit Characteristic
 
Background information: 
Ver. 1.00G 2019  
The qcx was built by another ham from whom I bought it.
I have only had it for several weeks.
It is attached to a QRP trapped dipole which I constructed for portable use and is only a few feet above the ground.
I keep the unit connected to an antenna or dummy load when transmitting.
It receives signals ok, but not too loudly.   
I have not yet made a qso.
I am now connected to a much better power, Astrton 20 amp power supply.  
***************************************************************************************

Problem:
When I set the automated CQ and listened with my Icom 737 in the shack, the automated CQ message ran together.  it sounded like there was a carrier and no silence between dits and dahs.  I then set the keyer for straight key.  I then tried to send a stacato dit, as short as possible, and there was about a 3/10 second character minimum transmit time.  In other words, that is a minimum time that the unit can transmit, and that time is way too long.  What could be causing this unit to maintain the signal so long, even with a really short key down time?  Maybe a setting?
--   
Anson
WV4C

ajparent1/KB1GMX
 

>>When I set the automated CQ and listened with my Icom 737 in the shack, the automated CQ message ran together.  it sounded like there was a carrier and no silence between dits and dahs. <<

That is because the VFO (SI5351 runs all the time and the radio next to it can hear the signal.
ON RX, the SI5351 is also running for RX, your station receiver will hear that too.
It is NORMAL.  THe question has been raised many times before.

Weak receive maybe because the radio is not dialed in (check instructions).

Allison
-------------------------------
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Allison,
I was inferring from his description that the envelope shape was long, so one pulse blended with the next, but that it did decay. Maybe that last part is incorrect.
If that were the issue, what would be the difference in what you'd hear on an adjacent receiver?
--
Julian, N4JO.

ajparent1/KB1GMX
 

IT would he hard to tell!

The station rx will easily hear the nearly 5-10mW of the Si5153 under all conditions.
You may hear it at a distance.

Its possible there is keying issues but even if its correct you can hear the "blow by"
as its in the milliwatt or more range.  I have one!

Allison
-------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting

 

Thanks for that, Allison. I don't have any kit other than my QCXs, so I wouldn't have known that gem of information :-)

I do have a little QRP-Guys multi-tune tuner, with an LED indicator which, in tuning mode, glows with increasing SWR. I can clearly see the pulsing of dits on my QCX, and so could easily spot a keyshaper issue.

You don't happen to have such a handy indicator of Tx power, do you, Anson? Alternatively, what does it sound like in full QSK mode? Do you hear the breaks in the QCX receiver then? If you do, then Allison's answer may be spot on (it probably is :-) )
--
Julian, N4JO.

wfcaston@...
 

Lee and Julian:

Thanks for the replies.  Yes, the problem went away when I changed the setting to full break-in!  I think the signal I heard was actually going out on the air.  Now the signal going out was pretty clean.  I noticed when I called CQ for an extended period of time, (no replies yet) the unit heated up quite a bit at the display.  Should I limit the number of CQs so as not to heat the unit, or would you think the QCX is robust with respect to duty cycle?

You guys are helping me not to get frustrated.  Next thing I need to do is get a really high 1/2 wave dipole up in the air.

73 all,
--
Anson
WV4C

 

I'm going to throw out a wild guess that heating at the display means heating at the finals, and coupled with no returns you may easily have an antenna problem - at least high SWR. Be careful with those little finals, they're not very robust.
Do you have something to check SWR with ??
--
Julian, N4JO.

N3MNT
 

Hook up a good dummy load and try the same thing.  If you have a high swr the finals will heat up and could be damaged.

wfcaston@...
 

I do not yet have a QRP method of measuring SWR but I am going to buy a unit to do that.
--
Anson
WV4C

 

If something really simple is all you need, the QRPGuys SWR indicator might fit the bill:
https://qrpguys.com/tuning-indicator
It's the same circuit that's in their antenna tuner (that I have), it's designed for QRP, and at $20 it does the job at a decent price. By very nature of the resistance bridge circuit it guarantees a max SWR of 4:1, so taking out your finals is difficult.
It won't give you a numerical value, of course, but it tells you what you need to know.
Of course, if you need a tuner, the combined version works well too.
--
Julian, N4JO.