Topics

Transmit Output Power (CW) #v5

peter.mccracken@...
 

Thanks Barry, exactly the feedback I was looking for, I'll let you all know how I get on !!

Best regards, Peter.

barry halterman
 

Peter, I had to look at my notes on the two driver transistors as to why I did not change them. It was not because of extra heating it was because I was looking for a constant output on all bands or as close to constant output. Changing them to 11 ohms gave me much more output then what I was aiming for plus more heat on those devices. 
So, yes change the driver and predriver emitter resistors to 11 ohms. You will need to put hats on those transistors as they will get hot...
I have a homebrew amp that I drive with the ubitx and can not exceed 3 watts input. That is the reason I did not change those driver emitter resistors.
Barry


On Wed, Jul 1, 2020, 7:53 PM barry halterman via groups.io <kthreebo=gmail.com@groups.io> wrote:
Peter, I left the 22 ohm resistors in. I did not double up the smd emitter resistors for the two drivers. I changed the predriver emitter to 8.6 ohms. 
Q90, I did not mess with. When I doubled up the emitter resistors for the two drivers, I had more heating on those devices and little gain in output.
Your experience might be different but it is worth the effort, in my opinion, to change out those 3904 transistors. 
Barry


On Wed, Jul 1, 2020, 7:01 PM <peter.mccracken@...> wrote:
Thanks for the response Barry, much appreciated. I order some of ebay uk today, I got 5 for around 12 GBP so not too bad.

This definitely looks like a worthwhile mod on the v6, can you provide any more detail around exactly what you changed along with the removing the 3904 and dropping in the 2n5109. Did you change the resistor values in a similar manner to what was done for the 2n2222 swap ? Did you touch Q90 ?

The basic principal is to remove Q911 and replace Q912 and similarly remove Q92, Q97 and replace Q93, Q96, correct ?

barry halterman
 

Peter, I left the 22 ohm resistors in. I did not double up the smd emitter resistors for the two drivers. I changed the predriver emitter to 8.6 ohms. 
Q90, I did not mess with. When I doubled up the emitter resistors for the two drivers, I had more heating on those devices and little gain in output.
Your experience might be different but it is worth the effort, in my opinion, to change out those 3904 transistors. 
Barry


On Wed, Jul 1, 2020, 7:01 PM <peter.mccracken@...> wrote:
Thanks for the response Barry, much appreciated. I order some of ebay uk today, I got 5 for around 12 GBP so not too bad.

This definitely looks like a worthwhile mod on the v6, can you provide any more detail around exactly what you changed along with the removing the 3904 and dropping in the 2n5109. Did you change the resistor values in a similar manner to what was done for the 2n2222 swap ? Did you touch Q90 ?

The basic principal is to remove Q911 and replace Q912 and similarly remove Q92, Q97 and replace Q93, Q96, correct ?

peter.mccracken@...
 

Thanks for the response Barry, much appreciated. I order some of ebay uk today, I got 5 for around 12 GBP so not too bad.

This definitely looks like a worthwhile mod on the v6, can you provide any more detail around exactly what you changed along with the removing the 3904 and dropping in the 2n5109. Did you change the resistor values in a similar manner to what was done for the 2n2222 swap ? Did you touch Q90 ?

The basic principal is to remove Q911 and replace Q912 and similarly remove Q92, Q97 and replace Q93, Q96, correct ?

barry halterman
 

Peter, yes I did! The 5109 give more power out on the upper bands but not more on 80, 40, 30 or 20. Off the top of my pointed head,  I would say about double the output power vs the stock 3904 devices. One thing I am going to do with my V6 is put a direct dc connection to the final mosfets and run those at 24 volts. 
One thing I noticed from Mouser is in March I bought 5 of the 2N5109 transistors for around $3. Now they are not in stock. So not sure where to buy them from.

Barry. K3bo

On Wed, Jul 1, 2020, 2:42 PM <peter.mccracken@...> wrote:
Barry, did you install the 2n5109's yet ? Interested in this mod for my v6 and would love to know what improvement you see over the 2n2222a's.

peter.mccracken@...
 

Barry, did you install the 2n5109's yet ? Interested in this mod for my v6 and would love to know what improvement you see over the 2n2222a's.

barry halterman
 

Rob, I have not modified the LPFs on my V4, but I did change the relays. The filter caps on the finals are rated 470uf at 25v, so no need to screw with them. On the harmonics, I did see an increase on 30 meters, but I usually don't operate that band. Other bands were with in spec.
One thing I do, (extra insurance) is run my rig through another low pass filter, external to the ubitx. 
The transmit issue at 7000khz bit me in the butt too, put me in panic mode, it did!!
I do not use a step up converter I just use another power supply that feeds the finals.
I just purchased a bunch of 2N5109 to modify my V6, my V4 has the 2N2222a in so I'm looking forward to see what improvement those will do.
Have fun!! Stay safe.. 
Barry
K3bo


On Mon, Mar 30, 2020, 2:47 PM Rob French (KC4UPR) <kc4upr@...> wrote:
Thanks Barry!

I was hoping initially here to just get the output more consistent across bands.  That said, I have thought about trying to increase the output power overall as well, though I do have a couple of questions:

(1) Did you change the output LPFs at all?  Are they good with the higher power?
(2) Any issues with harmonics at the higher power levels?
(3) Did you change the electrolytics on the final stage?  (I haven't actually checked mine, but I'd heard that they were only like 16V capacitors or something.)
(4) Do you use a step-up converter, or do you actually use a separate power supply?  I was hoping to trying to keep my uBITX running off of 13.8V.

With all of the 2N2222A's, I suspect I will be able to further increase the overall output power... With the same RV1 drive level set that I had in my uBITX stock, I get about 12W now instead of 7W... but I'm not sure at what point it will start distorting.

Thanks!
Rob KC4UPR

Rob French (KC4UPR)
 

Thanks Barry!

I was hoping initially here to just get the output more consistent across bands.  That said, I have thought about trying to increase the output power overall as well, though I do have a couple of questions:

(1) Did you change the output LPFs at all?  Are they good with the higher power?
(2) Any issues with harmonics at the higher power levels?
(3) Did you change the electrolytics on the final stage?  (I haven't actually checked mine, but I'd heard that they were only like 16V capacitors or something.)
(4) Do you use a step-up converter, or do you actually use a separate power supply?  I was hoping to trying to keep my uBITX running off of 13.8V.

With all of the 2N2222A's, I suspect I will be able to further increase the overall output power... With the same RV1 drive level set that I had in my uBITX stock, I get about 12W now instead of 7W... but I'm not sure at what point it will start distorting.

Thanks!
Rob KC4UPR

barry halterman
 

Rob, you might want to try and run the IR510 power transistors from a separate, higher voltage power supply...maybe 18volts or so. I have a V4 that I run the finals at that level and see a big change in output power. I get about 16 watts out on 80, 11w on 40, 16w on 20 and about 7 watts above that. Just a thought :)
Barry
K3bo

On Mon, Mar 30, 2020, 3:24 AM Rob French (KC4UPR) <kc4upr@...> wrote:
Stage 3 - Replaced Q92, Q93, Q96, Q97 with 2N2222A (ended up putting them on the bottom of the board, was easier).  Paralleled R941, R942, R96, and R911 to get 11 ohms each.  Smoke test good!

Definitely see some differences now.  It takes a lot less driver to get the 7.3 W I originally had at 3.5 MHZ.  The output versus frequency is definitely a lot flatter now, though it still goes from ~7W on 80 meters to ~3W on 10 meters.  I am curious about the effects of the output low pass filter characteristics on transmit output power.

Here's the table.
Transmit configuration:              
  Replaced Q90 with BFR106, replaced R81 with 2.7k; replaced Q911+Q912 w/ 2N2222A; replaced drivers, resistors            
  RV1 adjusted to match “Baseline” power output on 80 meters            
  BFO=11,055,935            
Power measurement:              
  ATU N7DDC ATU from Russia; configured for 150W          
  DDL Digital Dummy Load; configured for QRP; calibrated against ATU at 5.3W w/ RS-HFIQ          
               
    CW       2-tone SSB  
Frequency SWR Watts-ATU Watts-DDL   Sideband Watts-ATU Watts-DDL
3500000 1.00 6.70 7.20   LSB 4.60 2.26
4000000 1.00 5.40 5.67   LSB 4.40 2.13
5332000 1.01 4.00 3.96   LSB 4.90 2.52
5405000 1.00 4.10 4.10   LSB 5.10 2.64
7001000 1.00 5.80 5.99   LSB 6.00 3.35
7300000 1.00 4.90 4.95   LSB 6.20 3.65
10100000 1.00 4.90 4.95   USB 4.00 3.11
10150000 1.00 4.50 4.51   USB 3.80 2.78
14000000 1.01 6.40 6.75   USB 3.60 2.21
14350000 1.01 5.80 5.97   USB 3.50 2.02
18068000 1.02 4.30 4.22   USB 3.90 2.27
18168000 1.02 4.30 4.18   USB 3.90 2.28
21000000 1.04 5.40 5.37   USB 3.20 1.98
21450000 1.05 7.80 7.70   USB 4.00 2.43
24890000 1.04 3.50 3.17   USB 2.00 1.17
24990000 1.04 3.40 3.05   USB 2.00 1.17
28000000 1.04 3.10 2.74   USB 2.50 1.30
29700000 1.03 3.50 3.13   USB 1.70 0.99

Rob French (KC4UPR)
 

Stage 3 - Replaced Q92, Q93, Q96, Q97 with 2N2222A (ended up putting them on the bottom of the board, was easier).  Paralleled R941, R942, R96, and R911 to get 11 ohms each.  Smoke test good!

Definitely see some differences now.  It takes a lot less driver to get the 7.3 W I originally had at 3.5 MHZ.  The output versus frequency is definitely a lot flatter now, though it still goes from ~7W on 80 meters to ~3W on 10 meters.  I am curious about the effects of the output low pass filter characteristics on transmit output power.

Here's the table.
Transmit configuration:              
  Replaced Q90 with BFR106, replaced R81 with 2.7k; replaced Q911+Q912 w/ 2N2222A; replaced drivers, resistors            
  RV1 adjusted to match “Baseline” power output on 80 meters            
  BFO=11,055,935            
Power measurement:              
  ATU N7DDC ATU from Russia; configured for 150W          
  DDL Digital Dummy Load; configured for QRP; calibrated against ATU at 5.3W w/ RS-HFIQ          
               
    CW       2-tone SSB  
Frequency SWR Watts-ATU Watts-DDL   Sideband Watts-ATU Watts-DDL
3500000 1.00 6.70 7.20   LSB 4.60 2.26
4000000 1.00 5.40 5.67   LSB 4.40 2.13
5332000 1.01 4.00 3.96   LSB 4.90 2.52
5405000 1.00 4.10 4.10   LSB 5.10 2.64
7001000 1.00 5.80 5.99   LSB 6.00 3.35
7300000 1.00 4.90 4.95   LSB 6.20 3.65
10100000 1.00 4.90 4.95   USB 4.00 3.11
10150000 1.00 4.50 4.51   USB 3.80 2.78
14000000 1.01 6.40 6.75   USB 3.60 2.21
14350000 1.01 5.80 5.97   USB 3.50 2.02
18068000 1.02 4.30 4.22   USB 3.90 2.27
18168000 1.02 4.30 4.18   USB 3.90 2.28
21000000 1.04 5.40 5.37   USB 3.20 1.98
21450000 1.05 7.80 7.70   USB 4.00 2.43
24890000 1.04 3.50 3.17   USB 2.00 1.17
24990000 1.04 3.40 3.05   USB 2.00 1.17
28000000 1.04 3.10 2.74   USB 2.50 1.30
29700000 1.03 3.50 3.13   USB 1.70 0.99

Rob French (KC4UPR)
 

Stage 2 - I replaced Q911 and Q912 with metal can 2N2222A's I got from Tayda.  Results are below.  Honestly, didn't seem any better than replacing Q90 with the BFR106.  Actually, "the curve" went down slightly.  But when I graphed it, Stage 1 and Stage 2 basically looked the same, with Stage 2's graph shifted down slightly.  Not what I was hoping for, but I'm kinda committed at this point!

Stage 3 will be replacing the drivers Q92, Q93, Q96 and Q97 with 2N2222A's, and decreasing R941, R942, R911, and R96 to 11 ohms each.  And at that point, I'll kinda have what I have...

Regards,
-Rob

Transmit configuration:              
  Replaced Q90 with BFR106, replaced R81 with 2.7k; replaced Q911+Q912 w/ 2N2222A            
  RV1 adjusted to match “Baseline” power output on 80 meters            
  BFO=11,055,935            
Power measurement:              
  ATU N7DDC ATU from Russia; configured for 150W          
  DDL Digital Dummy Load; configured for QRP; calibrated against ATU at 5.3W w/ RS-HFIQ          
               
    CW       2-tone SSB  
Frequency SWR Watts-ATU Watts-DDL   Sideband Watts-ATU Watts-DDL
3500000 1.00 7.20 7.47   LSB 5.10 2.67
4000000 1.00 5.80 6.20   LSB 5.10 2.57
5332000 1.01 4.00 4.06   LSB 4.90 2.65
5405000 1.00 4.20 4.30   LSB 5.00 2.72
7001000 1.00 5.20 5.35   LSB 5.50 3.10
7300000 1.00 4.40 4.46   LSB 5.40 3.31
10100000 1.00 4.40 4.44   USB 3.60 2.56
10150000 1.00 4.10 4.13   USB 3.30 2.35
14000000 1.01 5.10 5.25   USB 3.10 1.83
14350000 1.01 4.60 4.68   USB 3.00 1.71
18068000 1.02 3.50 3.27   USB 3.20 1.85
18168000 1.02 3.40 3.23   USB 3.20 1.83
21000000 1.04 4.00 3.84   USB 2.60 1.56
21450000 1.05 5.40 5.41   USB 3.20 1.97
24890000 1.04 2.80 2.43   USB 1.70 0.99
24990000 1.04 2.80 2.43   USB 1.70 0.98
28000000 1.04 2.50 2.08   USB 1.80 1.08
29700000 1.03 2.60 2.25   USB 1.50 0.87

Rob French (KC4UPR)
 

Stage 1 - Replace Q90 with BFR106, replaced R81 with 2.7k.  Here are the results.  I just did the 2-tone test, because the 300/3000 Hz are tapered down so far by the crystal filter.   I just used those to help me pick a good BFO frequency.  

As an aside, removing that teensy SMD 2N3904 and replacing it with the likewise teensy BFR106, was one of the more tedious things I have done... I could handle not doing that again...

Summary:  Honestly, I don't see tons of change.  I started with RV1 set for minimum drive, and slowly increased it until the 80 meter (3.5 MHz) CW output power on my digital dummy load was equal to the output power that I saw in the baseline configuration.  Then I ran the rest of the numbers.  Power output went up in some cases, down in other cases.  In CW especially, it really didn't look like the output power "flattened out" across the bands.  I will say that in SSB, it does look like there were more power increases than decreases, with the result that the SSB output power level looks "flatter".

Hopefully this is useful to someone??? I'll keep posting as I run through each stage.

Transmit configuration:              
  Replaced Q90 with BFR106, replaced R81 with 2.7k            
  RV1 adjusted to match “Baseline” power output on 80 meters            
  BFO=11,055,935            
Power measurement:              
  ATU N7DDC ATU from Russia; configured for 150W          
  DDL Digital Dummy Load; configured for QRP; calibrated against ATU at 5.3W w/ RS-HFIQ          
               
    CW       2-tone SSB  
Frequency SWR Watts-ATU Watts-DDL   Sideband Watts-ATU Watts-DDL
3500000 1.00 7.30 7.63   LSB 5.10 2.68
4000000 1.00 6.00 6.45   LSB 5.20 2.65
5332000 1.01 4.10 4.15   LSB 4.90 2.54
5405000 1.00 4.30 4.32   LSB 5.00 2.72
7001000 1.00 5.30 5.47   LSB 5.50 3.14
7300000 1.00 4.60 4.62   LSB 5.50 3.31
10100000 1.00 4.50 4.53   USB 3.70 2.67
10150000 1.00 4.10 4.10   USB 3.40 2.42
14000000 1.01 5.40 5.51   USB 3.30 2.02
14350000 1.01 4.90 5.01   USB 3.20 1.90
18068000 1.02 3.80 3.62   USB 3.50 2.09
18168000 1.02 3.60 3.44   USB 3.40 2.00
21000000 1.04 4.30 4.18   USB 2.80 1.75
21450000 1.05 5.80 5.81   USB 3.50 2.27
24890000 1.04 3.10 2.82   USB 2.00 1.24
24990000 1.04 3.10 2.78   USB 1.90 1.23
28000000 1.04 2.80 2.44   USB 2.50 1.37
29700000 1.03 2.90 2.49   USB 1.70 1.06

Richard
 

Now there are some real-world numbers.  These are what I am seeing.

On Saturday, March 28, 2020, 11:51:00 PM CDT, Rob French (KC4UPR) <kc4upr@...> wrote:


Alrighty... I finally got around to a couple of things:

(1) Building myself a "digital dummy load" using my QRP Labs 20W dummy load and an Arduino.  I calibrated it against my ATU's wattmeter, which isn't probably a great source, but I used the output power of my RS-HFIQ, which I feel is pretty accurate at 5W +/- a little.
(2) Reset RV1 to the "stock" configuration, about mid-range.  Also tweaked my BFO setting to make sure I was getting some power out with both 300 Hz and 3000 Hz audio.
(3) Hooked up the mic input to my computer so I could play those 300, 3000, and 700-1900 Hz tone wave files into it.

Here are my results in the "essentially stock" configuration.

Transmit configuration:                      
  Factory (RV1 at center)                    
  BFO=11,055,935                    
Power measurement:                      
  ATU N7DDC ATU from Russia; configured for 150W                  
  DDL Digital Dummy Load; configured for QRP; calibrated against ATU at 5.3W w/ RS-HFIQ                  
                       
    CW       300Hz SSB   3000 Hz SSB   2-tone SSB  
Frequency SWR Watts-ATU Watts-DDL   Sideband Watts-ATU Watts-DDL Watts-ATU Watts-DDL Watts-ATU Watts-DDL
3500000 1.00 7.20 7.35   (LSB) 1.40 1.17 1.00 0.90 5.20 2.64
4000000 1.00 5.30 5.51   (LSB) 1.40 1.14 0.90 0.85 5.40 2.68
5332000 1.01 4.00 3.91   (LSB) 1.60 1.35 1.10 1.01 5.00 2.70
5405000 1.00 4.00 3.96   (LSB) 1.70 1.45 1.20 1.10 5.20 2.71
7001000 1.00 4.80 4.73   (LSB) 2.40 1.82 1.50 1.40 5.80 2.37
7300000 1.00 4.00 3.91   (LSB) 2.60 2.00 1.60 1.59 5.70 3.38
10100000 1.00 5.00 4.99   (USB) 2.80 2.39 2.60 2.30 3.70 2.50
10150000 1.00 4.60 4.50   (USB) 2.60 2.17 2.40 2.13 3.40 2.27
14000000 1.01 4.80 4.70   (USB) 1.50 1.23 1.30 1.21 3.30 1.88
14350000 1.01 4.40 4.32   (USB) 1.40 1.15 1.20 1.12 3.20 1.82
18068000 1.02 4.30 4.13   (USB) 2.40 1.83 1.90 1.83 4.00 2.45
18168000 1.02 4.40 4.18   (USB) 2.40 1.84 1.90 1.85 4.00 2.48
21000000 1.04 5.00 4.70   (USB) 1.40 1.21 1.40 1.20 2.60 1.49
21450000 1.05 6.00 5.85   (USB) 1.60 1.36 1.50 1.35 3.20 1.83
24890000 1.04 2.70 2.27   (USB) 1.00 0.77 0.90 0.74 2.00 1.14
24990000 1.04 2.70 2.28   (USB) 1.00 0.77 0.90 0.75 2.00 1.16
28000000 1.04 3.90 3.44   (USB) 1.30 0.97 1.10 0.97 2.60 1.35
29700000 1.03 2.70 2.22   (USB) 0.60 0.36 0.50 0.35 1.10 0.57

Rob French (KC4UPR)
 

Alrighty... I finally got around to a couple of things:

(1) Building myself a "digital dummy load" using my QRP Labs 20W dummy load and an Arduino.  I calibrated it against my ATU's wattmeter, which isn't probably a great source, but I used the output power of my RS-HFIQ, which I feel is pretty accurate at 5W +/- a little.
(2) Reset RV1 to the "stock" configuration, about mid-range.  Also tweaked my BFO setting to make sure I was getting some power out with both 300 Hz and 3000 Hz audio.
(3) Hooked up the mic input to my computer so I could play those 300, 3000, and 700-1900 Hz tone wave files into it.

Here are my results in the "essentially stock" configuration.

Transmit configuration:                      
  Factory (RV1 at center)                    
  BFO=11,055,935                    
Power measurement:                      
  ATU N7DDC ATU from Russia; configured for 150W                  
  DDL Digital Dummy Load; configured for QRP; calibrated against ATU at 5.3W w/ RS-HFIQ                  
                       
    CW       300Hz SSB   3000 Hz SSB   2-tone SSB  
Frequency SWR Watts-ATU Watts-DDL   Sideband Watts-ATU Watts-DDL Watts-ATU Watts-DDL Watts-ATU Watts-DDL
3500000 1.00 7.20 7.35   (LSB) 1.40 1.17 1.00 0.90 5.20 2.64
4000000 1.00 5.30 5.51   (LSB) 1.40 1.14 0.90 0.85 5.40 2.68
5332000 1.01 4.00 3.91   (LSB) 1.60 1.35 1.10 1.01 5.00 2.70
5405000 1.00 4.00 3.96   (LSB) 1.70 1.45 1.20 1.10 5.20 2.71
7001000 1.00 4.80 4.73   (LSB) 2.40 1.82 1.50 1.40 5.80 2.37
7300000 1.00 4.00 3.91   (LSB) 2.60 2.00 1.60 1.59 5.70 3.38
10100000 1.00 5.00 4.99   (USB) 2.80 2.39 2.60 2.30 3.70 2.50
10150000 1.00 4.60 4.50   (USB) 2.60 2.17 2.40 2.13 3.40 2.27
14000000 1.01 4.80 4.70   (USB) 1.50 1.23 1.30 1.21 3.30 1.88
14350000 1.01 4.40 4.32   (USB) 1.40 1.15 1.20 1.12 3.20 1.82
18068000 1.02 4.30 4.13   (USB) 2.40 1.83 1.90 1.83 4.00 2.45
18168000 1.02 4.40 4.18   (USB) 2.40 1.84 1.90 1.85 4.00 2.48
21000000 1.04 5.00 4.70   (USB) 1.40 1.21 1.40 1.20 2.60 1.49
21450000 1.05 6.00 5.85   (USB) 1.60 1.36 1.50 1.35 3.20 1.83
24890000 1.04 2.70 2.27   (USB) 1.00 0.77 0.90 0.74 2.00 1.14
24990000 1.04 2.70 2.28   (USB) 1.00 0.77 0.90 0.75 2.00 1.16
28000000 1.04 3.90 3.44   (USB) 1.30 0.97 1.10 0.97 2.60 1.35
29700000 1.03 2.70 2.22   (USB) 0.60 0.36 0.50 0.35 1.10 0.57

 

Hi Rob,

It would be interesting to see "before" measurements.

One trick on viewing SMD parts is to take a good picture with a smartphone or digital camera and then zoom in to view the fine print.  SMD parts typically don't have real names on them like "2n3904" but have codes.  There are code lists on the web to help translate them though.

To check power at lower power levels (like the ubitx) you can use a diode RF probe.  Easy to make from scratch or as a kit.  Some QRP dummy loads have them built in (e.g. Elecraft, QRPGuys, QRP-Labs all have them).

If I remember correctly, I think changing Q90 and its biasing makes the biggest different in evening the output.

73,


Mark

Rob French (KC4UPR)
 

I do have a V5 board.  To be clear, I have not yet made any modifications to the transmit chain... the only thing I have done is adjust RV1 to increase the output power on 80M to about 12W.  Before I did that, the pot was set at about half way, so it would be easy enough to turn RV1 back to a half-turn, and it should pretty much be what it was from the factory, +/- a few tenths of a watt.  I could then take reasonable "before" measurements.

I can't tell by looking what Q90 is (tiny little thing...), but based on the official V5 schematic, it should be an SMD 2N3904.  The rest of the pre-driver/driver transistors (6 of them) are all 2N3904, by the looks of them.

My power meter is built into an automatic antenna tuner designed for up to 150W.  So I'm sure it's not super accurate.

Thanks for all the feedback!
-Rob KC4UPR

jim
 

Well ...anything you've got is better than nothing ...back in the old days, folks used a wave-meter (gdo in diode position) to check for spurs/harmonics ..was hoping for some before/after measurements...ah well

thanks, Jim

On Friday, March 13, 2020, 1:59:53 AM UTC, Rob French (KC4UPR) <kc4upr@...> wrote:


Jim, no, I don't really have a way to check for that.  I suppose I could use my SDR dongle as a poor man's spectrum analyzer??? See what other spikes I get in the spectrum when I transmit?

I will note that, at the low end of 80 meters, prior to turning up RV1, I was only getting ~6.5W, so I'm wondering if my uBITX wasn't quite adjusted right from the factory... I wasn't getting 8 W anywhere.  Although, that probably also gets to Dave's point about different power meters, different measurements.

_Dave_ AD0B
 


If you have a decent amp meter you can adjust RV2 and RV3. Don't try and set them by ear. Review. the procedure on line. All three RV adjusters adjust the final power out be it ditties or voice.  I got one unit that was weak on transmit and turning up RV1 brought it up to spec.

I have a spread sheet that has the approximate RF voltage at each transmitter stage as collected by my 30 year old scope. You would want an oscope to compare. Basically you see that each transformer decreases the voltage substantially but the 3 transistor array more than makes up and by the time it is to the next  transformer it is stronger than it was when it entered the prior stage. 

Personally I would not want to do a two tone test at this point. 
If you have done any modifications you are not in a position to see what if any difference they are making. Best return to stock to make that as good as possible. 

If yours is a v5 it should have the improved transistors in it. No? You should verify. 

I looked through this post and was not sure of the model version. 


--
73
Dave
ADOB
Raduino bracket and Ham_Made_Keys

 

Hi Rob,

Well, what is the power meter you are using?  If it's a 100-200W maximum meter, certainly it will not have much accuracy down below 10W.

Do you have, or could you get, an oscilloscope?  That is a good method for setting SSB power out (using a 2-tone test signal).

73,


Mark

Rob French (KC4UPR)
 

Jim, no, I don't really have a way to check for that.  I suppose I could use my SDR dongle as a poor man's spectrum analyzer??? See what other spikes I get in the spectrum when I transmit?

I will note that, at the low end of 80 meters, prior to turning up RV1, I was only getting ~6.5W, so I'm wondering if my uBITX wasn't quite adjusted right from the factory... I wasn't getting 8 W anywhere.  Although, that probably also gets to Dave's point about different power meters, different measurements.