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low output only on 40m

Curt
 

Reporting Success!

First of all, my dip was down to 2-2.5 watts on 40m.  I myself would not worry much about having a less extreme dip.

Asshar gave us the valuable clue that capacitor C81, 470 pF is selected for frequency compensation of the transmit chain. 

I added 330 pF in parallel, and it solving my issue. 

approx CW power before and after this change:

1.8 MHz   8w    7.5w
3.5 MHz   6w    5w
7 MHz      2.5w   5w
10.1     5w     4.5w
14     7w       7w
21      4.8w     4.5w
28      3w        3w

i did not use my best wattmeter, but I trust this TT1202 enough that I am very happy with this change. 

caveat - I do not know how critical this adjustment is for SSB - I have another mod there to be tested. 

Thanks to Jim who brought back this thread, I hope a few hundred pF added to C81 might cure yours also

73 may your BITx efforts rock

Curt wb8yyy

Vic WA4THR
 

I have been following this thread with a little confusion, and I am not sure what the resolution is or if there is one. I have a V4 uBitX and the 40m CW output has always been low. Where I see 3.5w out on 40m CW into a dummy load, I can see 12w when on SSB and "Ahhh"ing into the microphone. I see a similar disparity on 17m. Since the SSB output is reasonable, I haven't worried about it too much and assumed something about the way CW is generated isn't unbalancing the mixer enough or something. Is there a fix?

FWIW, i am using KD8CEC v 1.1 software.

=Vic=

MVS Sarma
 

I meant, the user is happy athat.fter

MVS Sarma
 

in the code of si5351 under ubitx v5.
line 45 reads
uint8_t  si5351bx_drive[3] = {3, 3, 3}; // 0=2ma 1=4ma 2=6ma 3=8ma for CLK 0,1,2
They are set for higher output level.

while in V3 the same I remember is set to 1,1,1

In one case where similar complaint is received , we managed to change to higher current 2 or 3 depending, and the cw Tx power rose from 2 watts to 4 watts, followed by similar increase obviously on ssb.
the use is happy after that.


Curt
 

Jim

so how low are you outputting on 40m CW?  do you have any audio oscillator to check out SSB (I am forgetting what I obtained but it may have been a bit low also)?

I am thinking that 3w CW isn't bad, and I could work this for a long time to get maybe a couple more watts.  yes a single band rig it would be easier to keep working on. 

yes I have a nice signal on 30m so it is strange, and even stranger to make any changes near the 45 MHz mixer port. 

so perhaps you have a nano VNA there or something fancier? either way you seem to have good data. 

Curt

Jim
 

Checked the filter out with the VNA (by soldering coax leads directly to the input and output), and swept it from 6 to 14 MHz.  It has -0.3dB insertion loss at 6MHz, -0.4dB insertion loss across 7-9 MHz, and the -3dB point is at 11.1 MHz.  It looks just like a low pass filter designed to roll off around 11 MHz.  I don't think that this is the culprit.

Curt
 

Fortunately its only a small fraction of the v4 population that have this issue.  I carefully counted turns in the LPF - no issue there.  Also I bypassed the LPF with a wire - still stay issue that 40m power output is a bit low.  I remember my ubitx may have been 4-5 watts on 40m as delivered.  Any attempts to insert added 40m filtering into the 45 MHz transmit path further reduces power.  When 40m CW is used the transmit path seems to experience whatever is attached in the (unused) 45 MHz transmit signal path - I verified this with too much experimenting!  Could it be a faulty core material in those mixer transformers, I don't know I can't think of why it may vary otherwise between rigs. 

Since then I have decided on an added xtal filter of this configuration - retaining the 47 ohm resistor onto the mixer side, then a 0.1 uF blocking cap, a binocular transformer that feeds one side of the xtal filter.  the other side is going straight to the transistor emitter, which should be adequate given its higher impedance there.  Now my 40m CW signal is 'only' dipping to about 3 watts.  I don't possess a spectrum analyzer, but I may get to evaluate later this month.  In summary I am using Gordon's relay board for addressing harmonics (it is fully compliant now here) along with this added filtering - which I hope will improve my 17-10m band mixer spurious (I tried the v5 style LC filter it did not help much).  I do have shielded SMT inductors installed at L5 and L7 - they weren't enough by themselves to remedy this 40m challenge. 

In other news - I have the NESCAF variable bandwidth audio filter integrated inside now - wow nice to have a bandwidth control - it works nicely tuning in signals from the massive CW pileups - as well as providing appropriate selectivity for SSB. I just need to disassemble  front panel and provide the hole for the bandwidth pot. 

73 Curt

MVS Sarma
 

Sorry Jim to have mis spelt tou name. 


On Wed, 5 Feb 2020, 7:43 pm MVS Sarma via Groups.Io, <mvssarma=gmail.com@groups.io> wrote:
Kim, try to trst the cut off point of theclpf and loss at say 40m mid range. 

On Wed, 5 Feb 2020, 7:22 pm Jim, <n0oct@...> wrote:
I removed L17 from the board, and measured it with my nanoVNA -- 745 nH, right about where the schematic says it should be.  The other three inductors have the same number of windings as L17.

MVS Sarma
 

Kim, try to trst the cut off point of theclpf and loss at say 40m mid range. 


On Wed, 5 Feb 2020, 7:22 pm Jim, <n0oct@...> wrote:
I removed L17 from the board, and measured it with my nanoVNA -- 745 nH, right about where the schematic says it should be.  The other three inductors have the same number of windings as L17.

Jim
 

I removed L17 from the board, and measured it with my nanoVNA -- 745 nH, right about where the schematic says it should be.  The other three inductors have the same number of windings as L17.

MVS Sarma
 

Can jim and curt  check the inductorcwinding turns for L17, 18 and 19 thatcwerectentatively used for 40m.

Old boards i remember overwinding thereby blocking 40m 
These coils should have 14 or max 15T

If more , make it 14, 40m improves.

On Wed, 5 Feb 2020, 9:33 am Jim, <n0oct@...> wrote:
Curt,

Did you ever get resolution on this?

Jim
 

Curt,

Did you ever get resolution on this?

M0OOZ
 

Note: I have, like others, injected RF and manually swept the frequency through from 1 to 30 MHz. There is a horrible dip at the lower end i.e. 40 MHz is really low compared to 20 MHz. Yes I realize that this uses different filters. I even made a 'software tool' from modded code. 

The software tool allows me to 'manually' (via arduino serial monitor), change the filter switching, so I can see exactly what is switched in and out, while testing. I did this because at one point I noticed RF appearing on two filters at the same time, which did not seem good, and would have accounted for the apparent attenuation @ 40 Meters. (two filters being connected together would necessarily present a different load and produce characteristics that are non desirable.)

 

I love the idea of the uBITX, but it has actually really dun my head in!

M0OOZ
 

Same horrible problem!
I have good output on all other bands - the best is 20 meters. However, the 40 meter band is really low!

I have shelved this project (as this has dun my head in) for a while until I can face looking at it again as the problem does not seem to have an obvious solution. 

jim
 

Ah good ..More eyeballs make for better results

Jim

On Tuesday, January 15, 2019, 5:24:39 PM PST, Curt via Groups.Io <wb8yyy@...> wrote:


Jim

most of my data is CW, as that plot.  all bands but 40m are okay CW output.  using a dummy load after the wattmeter, a TT1202 that is decently designed. 

SSB seems to be doing same, weak on 40m per needle response.  our local build leader did request I take some SSB data -- I need to see if my audio test source has enough drive. 

I cannot fathom what is doing the above.  originally I was getting around 4 or 5 watt CW - weaker than other bands.  I don't see any visual damage on the LPF that serves 40m.  since 80m and 160m do fine -- I can't fathom what is happening here. 

Saturday I hope to take rig to our club building session - for careful evaluation. 

73 Curt

Curt
 

Jim

most of my data is CW, as that plot.  all bands but 40m are okay CW output.  using a dummy load after the wattmeter, a TT1202 that is decently designed. 

SSB seems to be doing same, weak on 40m per needle response.  our local build leader did request I take some SSB data -- I need to see if my audio test source has enough drive. 

I cannot fathom what is doing the above.  originally I was getting around 4 or 5 watt CW - weaker than other bands.  I don't see any visual damage on the LPF that serves 40m.  since 80m and 160m do fine -- I can't fathom what is happening here. 

Saturday I hope to take rig to our club building session - for careful evaluation. 

73 Curt

jim
 

Ok thanks ..just trying to get some references to establish some sort of  rational base-band ..High accuracy is not needed,  just something "close"

this one 5 watts from 8 to 10 Mhz on CW ..Previous quoted from you was SSB? right?

Jim


On Tuesday, January 15, 2019, 2:57:13 PM PST, Curt via Groups.Io <wb8yyy@...> wrote:


Okay here is my CW measurement into a power meter - yes broadband.  My rig was measured, I have usual spurs for a stock uBITX - nothing to impact this measurement.  I think my LPF might be shifted up - maybe - not sure what this response is across 40m as a LPF does not do that! 

X axis is frequency and Y axis is power in watts.  sure my instrument isn't high quality but I trust the trend it conveys. 

Curt


Curt
 

Okay here is my CW measurement into a power meter - yes broadband.  My rig was measured, I have usual spurs for a stock uBITX - nothing to impact this measurement.  I think my LPF might be shifted up - maybe - not sure what this response is across 40m as a LPF does not do that! 

X axis is frequency and Y axis is power in watts.  sure my instrument isn't high quality but I trust the trend it conveys. 

Curt


jim
 

Couple 'o questions ...SSB or CW  and How is power being measured?  broadband watt meter ?

If so ..All emissions from the xmitter are being summed together (dc to daylight) ie fundamental + harmonics + spurs + ?

Jim

On Tuesday, January 15, 2019, 9:30:55 AM PST, Bill Cromwell <wrcromwell@...> wrote:


Hi Evan,

Here is a contrary report for you. The forty meter output on my uBitx is
close to the same as 80 amd 30 meters and close to 10 watts. I have the
red and brown power supply wires connected together and run all of my
radios on 12 volt batteries (~13 volts at no-load, full charge). Due to
tolerance stacks among all the various parts used each of these radios
will be at least a little different from all others. If any parts are
out of tolerance that is going to be more so.

Mine is a V3 with the non "WX" audio IC socketed. I am running the CEC
software but that has nothing to do with RF power out. Board version might.

73,

Bill  KU8H

On 1/15/19 12:10 PM, Evan Hand wrote:
> This 40m output is very low compared to others, however ALL reports that
> I have seen always seem to have the 40m output much lower than 20m. 
> Does anyone know the reason for the drop on 40m compared to 20m?  Is it
> related to spurs being measured as part of the power out?
>
> Trying to learn and understand.
>
> Evan
> AC9TU
>

--
bark less - wag more



Bill Cromwell
 

Hi Evan,

Here is a contrary report for you. The forty meter output on my uBitx is close to the same as 80 amd 30 meters and close to 10 watts. I have the red and brown power supply wires connected together and run all of my radios on 12 volt batteries (~13 volts at no-load, full charge). Due to tolerance stacks among all the various parts used each of these radios will be at least a little different from all others. If any parts are out of tolerance that is going to be more so.

Mine is a V3 with the non "WX" audio IC socketed. I am running the CEC software but that has nothing to do with RF power out. Board version might.

73,

Bill KU8H

On 1/15/19 12:10 PM, Evan Hand wrote:
This 40m output is very low compared to others, however ALL reports that I have seen always seem to have the 40m output much lower than 20m. Does anyone know the reason for the drop on 40m compared to 20m?  Is it related to spurs being measured as part of the power out?
Trying to learn and understand.
Evan
AC9TU
--
bark less - wag more