Topics

Issue with high SWR on transmit

Kurt Loken <kurt.loken@...>
 


Hello All,

I have a 20M D4D, and I think I may have a problem with it.  

I have been a bit mystified that I have so far only had 1 contact on this thing even though I've been on the air with in for many hours.  I had been thinking it is due to my use of an indoor experimental magloop antenna and the 1W is just isn't making it out of the house.  Yet...what has bothered me is that I have a WSPRlite that only puts out 0.2W and I get picked up all over the US....here is a picture of my spots I got on 20M today with my setup with 0.2 watts on my antenna.  
Screen Shot 2019-11-17 at 10.00.08 PM.png

I have good FT8 reception on the D4D...so the receiver part of the system is working like a champ.

I am just getting back into working on radios after a long hiatus and I have have an antenna analyzer, but I actually didn't have a normal SWR meter so that could read my transmissions insitu.  Today I got one.  ...and low and behold...I have horrible SWR readings during transmit when I run the D4D.    I have an Elecraft W1 Power Meter and the SWR pegs out when I transmit.  If I transmit into a dummy load, I get perfect SWR and perfect 1W output. 

I am using a mag loop antenna that is tuned to the 14075 (see pic).  The bandwidth shown is around 40kHz....so unless this thing is way off on the transmit freq or noisy as hell, I should not be seeing huge SWR.

IMG_4511.jpg

Any ideas what is going on?  I would be curious what the spectrum my D4D looks like in transmit, but I don't have that test equipment yet.  I'm getting a Red Pitaya very soon...so I will be able to to measure that in the future.  

I don't understand what is going on with the high SWR...any ideas?  

Thanks,

Kurt-AE6UJ

Bryan Brauer
 

Kurt,

I am having almost exactly the same experience; with the 20 meter D4D as well as with the QRPGuys DSB TRXCVR.  I am inclined to believe that double side band is not a good way to go.  I suspect that the signal is just to "dirty" to decode dependably.

I will try a bit more, this time with a resonant dipole. I thought that this radio might be a bit of fun, and I enjoy building kits, but life is to short to muck around with such marginally functioning equipment.  If the dipole does not produce dramatically different results, I will go back to my KX2 for FT8.

Thanks,

Bryan, AI6B

On Sun, Nov 17, 2019 at 8:22 PM Kurt Loken <kurt.loken@...> wrote:

Hello All,

I have a 20M D4D, and I think I may have a problem with it.  

I have been a bit mystified that I have so far only had 1 contact on this thing even though I've been on the air with in for many hours.  I had been thinking it is due to my use of an indoor experimental magloop antenna and the 1W is just isn't making it out of the house.  Yet...what has bothered me is that I have a WSPRlite that only puts out 0.2W and I get picked up all over the US....here is a picture of my spots I got on 20M today with my setup with 0.2 watts on my antenna.  
Screen Shot 2019-11-17 at 10.00.08 PM.png

I have good FT8 reception on the D4D...so the receiver part of the system is working like a champ.

I am just getting back into working on radios after a long hiatus and I have have an antenna analyzer, but I actually didn't have a normal SWR meter so that could read my transmissions insitu.  Today I got one.  ...and low and behold...I have horrible SWR readings during transmit when I run the D4D.    I have an Elecraft W1 Power Meter and the SWR pegs out when I transmit.  If I transmit into a dummy load, I get perfect SWR and perfect 1W output. 

I am using a mag loop antenna that is tuned to the 14075 (see pic).  The bandwidth shown is around 40kHz....so unless this thing is way off on the transmit freq or noisy as hell, I should not be seeing huge SWR.

IMG_4511.jpg

Any ideas what is going on?  I would be curious what the spectrum my D4D looks like in transmit, but I don't have that test equipment yet.  I'm getting a Red Pitaya very soon...so I will be able to to measure that in the future.  

I don't understand what is going on with the high SWR...any ideas?  

Thanks,

Kurt-AE6UJ

Adam Rong
 

Kurt,

I saw the same. Nothing is wrong at your side. I believe the main problem is the wide spectrum caused by IMD. The IMD modification should help, but I will not expect it will be gone.

The D4D is sort of fun kit to test the communication possibilities with such a simple rig. It is not perfect.

Thanks,
Adam

在 2019年11月18日,下午12:22,Kurt Loken <kurt.loken@...> 写道:



Hello All,

I have a 20M D4D, and I think I may have a problem with it.  

I have been a bit mystified that I have so far only had 1 contact on this thing even though I've been on the air with in for many hours.  I had been thinking it is due to my use of an indoor experimental magloop antenna and the 1W is just isn't making it out of the house.  Yet...what has bothered me is that I have a WSPRlite that only puts out 0.2W and I get picked up all over the US....here is a picture of my spots I got on 20M today with my setup with 0.2 watts on my antenna.  
<Screen Shot 2019-11-17 at 10.00.08 PM.png>


I have good FT8 reception on the D4D...so the receiver part of the system is working like a champ.

I am just getting back into working on radios after a long hiatus and I have have an antenna analyzer, but I actually didn't have a normal SWR meter so that could read my transmissions insitu.  Today I got one.  ...and low and behold...I have horrible SWR readings during transmit when I run the D4D.    I have an Elecraft W1 Power Meter and the SWR pegs out when I transmit.  If I transmit into a dummy load, I get perfect SWR and perfect 1W output. 

I am using a mag loop antenna that is tuned to the 14075 (see pic).  The bandwidth shown is around 40kHz....so unless this thing is way off on the transmit freq or noisy as hell, I should not be seeing huge SWR.

<IMG_4511.jpg>


Any ideas what is going on?  I would be curious what the spectrum my D4D looks like in transmit, but I don't have that test equipment yet.  I'm getting a Red Pitaya very soon...so I will be able to to measure that in the future.  

I don't understand what is going on with the high SWR...any ideas?  

Thanks,

Kurt-AE6UJ

Fuqua, Bill L
 

Can you receive 20 Meter signals on the D4D?
If not it is possible that the crystal is oscillating at the 3 overtone.
This could produce a VHF signal that would be way off frequency and produce a high
SWR.  If you can copy 20M signals then it is possible that the TX amplifier is oscillating
off frequency producing output power but again off frequency which again would produce
a high SWR with the loop antenna.

73
Bill wa4lav



From: crkits@groups.io <crkits@groups.io> on behalf of Kurt Loken via Groups.Io <kurt.loken@...>
Sent: Sunday, November 17, 2019 11:22 PM
To: crkits@groups.io <crkits@groups.io>
Subject: [crkits] Issue with high SWR on transmit
 

Hello All,

I have a 20M D4D, and I think I may have a problem with it.  

I have been a bit mystified that I have so far only had 1 contact on this thing even though I've been on the air with in for many hours.  I had been thinking it is due to my use of an indoor experimental magloop antenna and the 1W is just isn't making it out of the house.  Yet...what has bothered me is that I have a WSPRlite that only puts out 0.2W and I get picked up all over the US....here is a picture of my spots I got on 20M today with my setup with 0.2 watts on my antenna.  
Screen Shot 2019-11-17 at 10.00.08 PM.png

I have good FT8 reception on the D4D...so the receiver part of the system is working like a champ.

I am just getting back into working on radios after a long hiatus and I have have an antenna analyzer, but I actually didn't have a normal SWR meter so that could read my transmissions insitu.  Today I got one.  ...and low and behold...I have horrible SWR readings during transmit when I run the D4D.    I have an Elecraft W1 Power Meter and the SWR pegs out when I transmit.  If I transmit into a dummy load, I get perfect SWR and perfect 1W output. 

I am using a mag loop antenna that is tuned to the 14075 (see pic).  The bandwidth shown is around 40kHz....so unless this thing is way off on the transmit freq or noisy as hell, I should not be seeing huge SWR.

IMG_4511.jpg

Any ideas what is going on?  I would be curious what the spectrum my D4D looks like in transmit, but I don't have that test equipment yet.  I'm getting a Red Pitaya very soon...so I will be able to to measure that in the future.  

I don't understand what is going on with the high SWR...any ideas?  

Thanks,

Kurt-AE6UJ

Adam Rong
 

Bill,

The crystal is not overtone type. Also the LPF should do the job to filter the 3rd harmonic products if any.

Thanks,
Adam

在 2019年11月18日,下午2:06,Fuqua, Bill L <Wlfuqu00@...> 写道:


Can you receive 20 Meter signals on the D4D?
If not it is possible that the crystal is oscillating at the 3 overtone.
This could produce a VHF signal that would be way off frequency and produce a high
SWR.  If you can copy 20M signals then it is possible that the TX amplifier is oscillating
off frequency producing output power but again off frequency which again would produce
a high SWR with the loop antenna.

73
Bill wa4lav



From: crkits@groups.io <crkits@groups.io> on behalf of Kurt Loken via Groups.Io <kurt.loken@...>
Sent: Sunday, November 17, 2019 11:22 PM
To: crkits@groups.io <crkits@groups.io>
Subject: [crkits] Issue with high SWR on transmit
 

Hello All,

I have a 20M D4D, and I think I may have a problem with it.  

I have been a bit mystified that I have so far only had 1 contact on this thing even though I've been on the air with in for many hours.  I had been thinking it is due to my use of an indoor experimental magloop antenna and the 1W is just isn't making it out of the house.  Yet...what has bothered me is that I have a WSPRlite that only puts out 0.2W and I get picked up all over the US....here is a picture of my spots I got on 20M today with my setup with 0.2 watts on my antenna.  
<Screen Shot 2019-11-17 at 10.00.08 PM.png>


I have good FT8 reception on the D4D...so the receiver part of the system is working like a champ.

I am just getting back into working on radios after a long hiatus and I have have an antenna analyzer, but I actually didn't have a normal SWR meter so that could read my transmissions insitu.  Today I got one.  ...and low and behold...I have horrible SWR readings during transmit when I run the D4D.    I have an Elecraft W1 Power Meter and the SWR pegs out when I transmit.  If I transmit into a dummy load, I get perfect SWR and perfect 1W output. 

I am using a mag loop antenna that is tuned to the 14075 (see pic).  The bandwidth shown is around 40kHz....so unless this thing is way off on the transmit freq or noisy as hell, I should not be seeing huge SWR.

<IMG_4511.jpg>


Any ideas what is going on?  I would be curious what the spectrum my D4D looks like in transmit, but I don't have that test equipment yet.  I'm getting a Red Pitaya very soon...so I will be able to to measure that in the future.  

I don't understand what is going on with the high SWR...any ideas?  

Thanks,

Kurt-AE6UJ

Fuqua, Bill L
 

Any crystal will oscillate in overtone mode. All crystals can oscillate in series and parallel resonance modes at
fundamental and overtones. The only way the swr would be high with the D4D and not with another source is
that an significant output frequency signal is not what the resonate load expects.
In fact crystals have spurious modes as well, if there is a flaw in it could actually oscillate in an unrelated
frequency. I have seen crystal oscillators jump between modes that are only kHz apart.
   But, you are correct about the low pass filter attenuating an output at the 3rd overtone. I just noticed that the  two
capacitors , C20 and C23, in the filter that are intended to produce notch frequencies in the filter are not in the circuit.
     I think somehow another frequency is being produced that is unintended. And it could be transmitting on the correct frequency and the unintended frequency both.
   Several  other possibilities:
  1. There could be a high frequency applied to the balanced modulator via the audio input. Thus producing a signal way off resonance of the loop antenna.
  2. Q8 may not be shorting the path from the antenna relay into the balanced modulator. Which could offer a significantly high gain feedback path from the output of the balanced modulator thru the RF power amplifier back into the balanced modulator's input.
 A broad spectrum analyzer would be nice. If you have one of these inexpensive nanoVNA's, they can be used as a crude spectrum analyzer. https://groups.io/g/nanovna-users/topic/34079496?20,0,0,0::,,,0,0,0,34079496

This could be useful in seeing what is going on. Just attach a small piece of wire to the input of the nanoVNA as an antenna.

73
Bill wa4lav
Hello again Eric and other possible readers. I received my nanoVNA a couple of weeks ago and I have been doing many tests with it. First I must say my unit came without shields and I added them, but there was no considerable improvement in the base noise level.
groups.io


From: crkits@groups.io <crkits@groups.io> on behalf of Adam Rong via Groups.Io <rongxh@...>
Sent: Monday, November 18, 2019 3:08 AM
To: crkits@groups.io <crkits@groups.io>
Subject: Re: [crkits] Issue with high SWR on transmit
 
Bill,

The crystal is not overtone type. Also the LPF should do the job to filter the 3rd harmonic products if any.

Thanks,
Adam

在 2019年11月18日,下午2:06,Fuqua, Bill L <Wlfuqu00@...> 写道:


Can you receive 20 Meter signals on the D4D?
If not it is possible that the crystal is oscillating at the 3 overtone.
This could produce a VHF signal that would be way off frequency and produce a high
SWR.  If you can copy 20M signals then it is possible that the TX amplifier is oscillating
off frequency producing output power but again off frequency which again would produce
a high SWR with the loop antenna.

73
Bill wa4lav



From: crkits@groups.io <crkits@groups.io> on behalf of Kurt Loken via Groups.Io <kurt.loken@...>
Sent: Sunday, November 17, 2019 11:22 PM
To: crkits@groups.io <crkits@groups.io>
Subject: [crkits] Issue with high SWR on transmit
 

Hello All,

I have a 20M D4D, and I think I may have a problem with it.  

I have been a bit mystified that I have so far only had 1 contact on this thing even though I've been on the air with in for many hours.  I had been thinking it is due to my use of an indoor experimental magloop antenna and the 1W is just isn't making it out of the house.  Yet...what has bothered me is that I have a WSPRlite that only puts out 0.2W and I get picked up all over the US....here is a picture of my spots I got on 20M today with my setup with 0.2 watts on my antenna.  
<Screen Shot 2019-11-17 at 10.00.08 PM.png>


I have good FT8 reception on the D4D...so the receiver part of the system is working like a champ.

I am just getting back into working on radios after a long hiatus and I have have an antenna analyzer, but I actually didn't have a normal SWR meter so that could read my transmissions insitu.  Today I got one.  ...and low and behold...I have horrible SWR readings during transmit when I run the D4D.    I have an Elecraft W1 Power Meter and the SWR pegs out when I transmit.  If I transmit into a dummy load, I get perfect SWR and perfect 1W output. 

I am using a mag loop antenna that is tuned to the 14075 (see pic).  The bandwidth shown is around 40kHz....so unless this thing is way off on the transmit freq or noisy as hell, I should not be seeing huge SWR.

<IMG_4511.jpg>


Any ideas what is going on?  I would be curious what the spectrum my D4D looks like in transmit, but I don't have that test equipment yet.  I'm getting a Red Pitaya very soon...so I will be able to to measure that in the future.  

I don't understand what is going on with the high SWR...any ideas?  

Thanks,

Kurt-AE6UJ