Date   
Re: Trial to control CW power (and reduce harmonics as a result) by unbalancing the 2nd mixer #ubitx

Jerry Gaffke
 

I'm suspicious about the CW-KEY injection level because 
the Bitx40 saw significant variation between rigs when Allard did 
something similar to unbalance the modulator for CW transmissions.
This was solved by going to a fairly high level of injection,
pushing the power amp into non-linear operation.
So it's like all the simple QRP CW transmitters out there with a class C amp.
The Bitx40  transmit LPF seems to work well to remove any harmonics,
and the 40m bandpass filter between the Bitx40's  first mixer
and the power amp removes the spurs.
Neither of these is true of the uBitx, so we can't use the same trick.

Jerry, KE7ER


On Thu, Apr 18, 2019 at 10:29 AM, Jerry Gaffke wrote:
If we are lucky, the mixer at D3,4 will want the same CW-KEY injection level
across all rigs, and we can use fixed resistors instead of a pot.
But that may well not be the case.

Re: next ubitx

Michael Mitchell <mitchellmichaelh@...>
 

I did not mean I was going to design the MAXbitx but maybe the original uBitx guys might do it. I mean most of the design is done just needs to be modulized and made legal.


On Thu, Apr 18, 2019 at 1:26 PM Curt via Groups.Io <wb8yyy=yahoo.com@groups.io> wrote:
Short of doing lots of homebrew, we only get so many of these inside the radio experiences.  Hard to measure whether I spent more time on the K2 or the ubitx.  Of course the ubitx virtue is 'have it your way', while the caution of course is its key limitation. 

Given the challenge of our local builders - some of us doing just fine with transmit drive, others not so - an ALC circuit might indeed be a key addition (if you really sense the need).  Hint - the approach used by the K2 is documented in their manual - as I never 'broke' that part of the rig - I didn't learn about it.  Worth exploring what they did, even if there are unobtainium parts - actually I think they are garden variety. 

We should choose our battles carefully on what to do with the ubitx.  Certainly fix the low band harmonic spurious - very fixable.  I have taken a break from high band mixer spurs (the xtal filter fix wrecks low band CW).  It does mean if I build a clean PA for the lower bands - the combo should be clean, as my ubtix is now good on both CW/SSB up through 17m.  Whether I 'need' a 50 watt rig using ubtix is another story.  For now, enjoying the VK3YE AGC that works wonderfully, I am off buiiding the simple S-meter from an earlier SPRAT that is on the web.  If this rig had EVERY possible addition I don't think I would enjoy it any more.  Nice that many folk around the world can possess the same rig.  Maybe I should build that 40w PA so I can QSO with another ubitx in India when we get our next solar high. 

Don't lament what isn't easy to install -- thrive in the reachable possibilities. 

Curt



--
WM4MM

Re: burst of harmonics during CW key-down?

John (vk2eta)
 

Thanks Adrian.

I understand the logic.

If you make actual measurements please let us know.

All the best,

73, John

Re: vfo cal.

Raymond House
 

Thank you MVS Sarma, a very excellent PDF on calibration, the best I have read so far, I'm keeping this one.Clear and concise step by step! Great. 73


On Thu, Apr 18, 2019 at 11:03 AM MVS Sarma <mvssarma@...> wrote:
https://petetest2017.files.wordpress.com/2019/01/micro-bitx-calibration-instructions.pdf

I got this link from a friend om mahesh vu2iia. It works. Whether stock or lees firmware  procedure is common . In stock you press rotary encoder and in lee firmware yiu use ptt. 

Please study, if it can support yoallthe best

On Thu, 18 Apr 2019, 8:13 pm Adrian Chadd <adrian@... wrote:
hi!

The 30 second overview:


If you can plug in your audio into a computer and run a spectrum analyser (eg fldigi) it's MUCH easier to calibrate the BFO by looking for the right passband with just normal noise from your antenna.

Then after that you can calibrate the VFO - yes it goes into TX mode but it won't transmit a carrier unless you press PTT.


-a


On Thu, 18 Apr 2019 at 07:05, Jack Purdum via Groups.Io <jjpurdum=yahoo.com@groups.io> wrote:
There are likely something like a bazillion posts here about calibrating the µBITX. Have you searched this group? Also, a valuable resource is ubitx.net, too.

Jack, W8TEE

On Thursday, April 18, 2019, 6:57:55 AM PDT, Raymond House <raymondh40@...> wrote:


Hello everyone,I'm Ray House, VE2OL, I have just completed assembling an Ubitx V5 with 3.5 in display. I am testing it with the original display and I find the VFO is out a lot, can someone point me towards info for it's calibration, if I go to 10mhz cal it goes into TX mode, is this normal? I have checked the wiki and this forum but found nothing on this, I'm sure it's just that I don't know where to look.Someone mentioned here that a new member should indicate what test gear he has, so, 100mhz storage scope,freq counter, function generator,RMS meter good to 10mhz and assorted VOM's. Any help will be greatly appreciated, thanks. 73

Re: vfo cal.

MVS Sarma
 

The creator of that article deserves the appreciation., 
Thanks Steve

Regards
Sarma vu3zmv

On Fri, 19 Apr 2019, 12:06 am Raymond House <raymondh40@... wrote:
Thank you MVS Sarma, a very excellent PDF on calibration, the best I have read so far, I'm keeping this one.Clear and concise step by step! Great. 73

On Thu, Apr 18, 2019 at 11:03 AM MVS Sarma <mvssarma@...> wrote:
https://petetest2017.files.wordpress.com/2019/01/micro-bitx-calibration-instructions.pdf

I got this link from a friend om mahesh vu2iia. It works. Whether stock or lees firmware  procedure is common . In stock you press rotary encoder and in lee firmware yiu use ptt. 

Please study, if it can support yoallthe best

On Thu, 18 Apr 2019, 8:13 pm Adrian Chadd <adrian@... wrote:
hi!

The 30 second overview:


If you can plug in your audio into a computer and run a spectrum analyser (eg fldigi) it's MUCH easier to calibrate the BFO by looking for the right passband with just normal noise from your antenna.

Then after that you can calibrate the VFO - yes it goes into TX mode but it won't transmit a carrier unless you press PTT.


-a


On Thu, 18 Apr 2019 at 07:05, Jack Purdum via Groups.Io <jjpurdum=yahoo.com@groups.io> wrote:
There are likely something like a bazillion posts here about calibrating the µBITX. Have you searched this group? Also, a valuable resource is ubitx.net, too.

Jack, W8TEE

On Thursday, April 18, 2019, 6:57:55 AM PDT, Raymond House <raymondh40@...> wrote:


Hello everyone,I'm Ray House, VE2OL, I have just completed assembling an Ubitx V5 with 3.5 in display. I am testing it with the original display and I find the VFO is out a lot, can someone point me towards info for it's calibration, if I go to 10mhz cal it goes into TX mode, is this normal? I have checked the wiki and this forum but found nothing on this, I'm sure it's just that I don't know where to look.Someone mentioned here that a new member should indicate what test gear he has, so, 100mhz storage scope,freq counter, function generator,RMS meter good to 10mhz and assorted VOM's. Any help will be greatly appreciated, thanks. 73

Attenuator function in CEC firmware #nextion #ubitx #firmware

Jack Brabham - KZ5A
 

I looked around but haven't found just how the "attenuator" function in the CEC firmware actually works.

I'm curious because I'm interested in the mod that puts a digital attenuator between the pre-drivers and the filters, using it as a varible attenuator on RX and using it to normaiize the output levels between bands on TX.

More to the point, I'm wondering if the Attn function can be utilized to control the digital attenuator on RX instead of whatever it does normally?

73 Jack KZ5A

JackAl Secondary source for download files

Jack, W8TEE
 

All:

Although our site has been restored with new security software, some of you have expressed concern about the site. We understand this completely. On the other hand, many of you want to download the updated files about the JackAl project. To that end, I have copied the relevant doc and source files to the JackAl@groups.io site. Look in the Files section under JackAl Documentation and Code Files.

Jack, W8TEE
Al, AC8GY

Re: Attenuator function in CEC firmware #nextion #ubitx #firmware

Tom, wb6b
 

Some time ago, a clever person on this list developed a method of adjusting the mixer frequencies to place the desired signal on the edge of the 45Mhz filter. That filter being much wider than the signal and having a more gradual drop-off (Than the 12Mhz filter for example) on the edges of the bandpass, could function as a variable gain stage by moving the desired signal progressively into the edge of the bandpass.

The CEC firmware incorporated this gain control method. This might be the attenuator function you are looking for.  It has been a while since I looked at this so I believe it was used to adjust output power, but I may be wrong. Might be a clever idea to try to measure the received signal and have the firmware adjust the mixer frequencies to act as an AGC. Maybe that is already being done.

Tom, wb6b

Re: Attenuator function in CEC firmware #nextion #ubitx #firmware

Jerry Gaffke
 

The clever person is John, VK2ETA.
Here's where it started:
    https://groups.io/g/BITX20/topic/16737180
    https://groups.io/g/BITX20/topic/17009424

And we have an active thread right now about doing this with CW:
    https://groups.io/g/BITX20/topic/30997272

And a mention of it yesterday here:
    https://groups.io/g/BITX20/message/67982

It works by adjusting the si5351 to move the frequency at which the desired signal
hits the 45mhz crystal filter.  The filter has shoulders gradual enough that this serves
as an effective attenuator.  Works great for transmitting, where you set it once based
on the operating frequency and desired output power.  Using this method to dynamically
shape the receive attenuation would be sort of possible but not very satisifying
since there would be a pop heard every time the si5351 is updated.

There have been a half dozen different schemes for implementing simple AGC schemes
on the uBitx (and Bitx40).  I'd recommend Don's (ND6T) scheme as was kitted up
by Kees (K5BCQ).    http://www.nd6t.com/uBITX/AGC.htm
The kits are no longer available, but would be simple enough to dead bug it.
Others here will have their own favorites.
They pretty much all rectify the recovered audio to determine the amount of attenuation,
applying a DC voltage to some attenuation device.
You could easily control that attenuation from a processor, perhaps using pulse-width-modulation
to determine the amount of attenuation, though better would be an small ADC hanging off the I2C lines.

Jerry, KE7ER

Re: Attenuator function in CEC firmware #nextion #ubitx #firmware

KE2GKB
 

Just to comment here and pass some info on, Don's (ND6T's) AGC is available as a kit from N8DAH and my Self over at https://shop.kit-projects.com We are still working on talking to Don to get him to update his web page. We have his blessing but nothing has been updated yet on his end.

-- Tim Keller - KE2GKB https://shop.kit-projects.com

Re: Attenuator function in CEC firmware #nextion #ubitx #firmware

John (vk2eta)
 

Thanks guys for the qualification, but luck had its place in that exercise.

Jack,

Here is the correct graph and if you follow the thread it shows the logic (the first graph is wrong by a factor of 10 on the horizontal axis): https://groups.io/g/BITX20/message/45700

If you follow the usage of the firstIFShift variable in the implementation below you will see the code that implements a stepped power setting per band so that I have three levels (low=5W, medium=10W and max=open). I simply use a set of 4 values for each levels which represent the shift in KHz at 4 frequencies, then I interpolate for frequencies in-between. Moves up and down a little due to the interpolation but it does the job. You could have one set of value per band if you wanted to be more precise.

There is even some dead code (commented out) in there for an automatic ALC as you find in commercial rigs. But it didn't play well with my ATU so I used a fixed ALC instead.

In the file section: https://groups.io/g/BITX20/files/Variations%20on%20KD8CEC%20Software%20%28by%20VK2ETA%29%20+%20ATU%20sketch

I also use the IF shift in reception to augment the range of my AGC and it does the job. But as Jerry mentioned it makes a small pop when adjusting the shift. Not annoying in my case as I only adjust when the ALC hits the top of its range and step back only when it reaches the bottom of its range. So it normally happens on very strong stations and once at the start and end of an over. Not a major at all, but you will notice it. That code in in there too.

If you have questions on the code please ask.

All the best,

73, John

Re: Attenuator function in CEC firmware #nextion #ubitx #firmware

Jerry Gaffke
 

Good, thanks for the correction.
And good to know the ND6T scheme is still available as a kit.

I think I probably knew that once, but I'm not sure I can remember even that!

Jerry


On Thu, Apr 18, 2019 at 05:10 PM, KE2GKB wrote:

Just to comment here and pass some info on, Don's (ND6T's) AGC is available as a kit from N8DAH and my Self over at https://shop.kit-projects.com We are still working on talking to Don to get him to update his web page. We have his blessing but nothing has been updated yet on his end.

-- Tim Keller - KE2GKB https://shop.kit-projects.com

Re: Attenuator function in CEC firmware #nextion #ubitx #firmware

Jack Brabham - KZ5A
 

Funny you should mention the ND6T AGC, I just got one in the mail today from kit-projects.com.

My uBITX V.5 will be here tomorrow (love the DHL tracking).  Nextion 3.5 has been here for a few days.

The nice Cheval SA case from Bangkok probably won't be here for a month.  Hopefully by then I will have figured out how many and what sized holes it needs where.

I intend to go thru stock operation for a while (probably a short while) before loading the CEC firmware, just so I can better appreciate the differences.

As far as the ATTN goes, I try to follow the wisdom of "If it ain't broke, don't fix it".  I may or may not decide it needs fixin',  as the approach obviously works but seems a little "non-optimal".  I'm not one to fret over increasing the parts count and the digital attn idea is very compelling.  We'll see, I've got a lot of learning curve to wade thru first.

73 Jack KZ5A











On 4/18/2019 5:26 PM, Jerry Gaffke via Groups.Io wrote:
The clever person is John, VK2ETA.
Here's where it started:
    https://groups.io/g/BITX20/topic/16737180
    https://groups.io/g/BITX20/topic/17009424

And we have an active thread right now about doing this with CW:
    https://groups.io/g/BITX20/topic/30997272

And a mention of it yesterday here:
    https://groups.io/g/BITX20/message/67982

It works by adjusting the si5351 to move the frequency at which the desired signal
hits the 45mhz crystal filter.  The filter has shoulders gradual enough that this serves
as an effective attenuator.  Works great for transmitting, where you set it once based
on the operating frequency and desired output power.  Using this method to dynamically
shape the receive attenuation would be sort of possible but not very satisifying
since there would be a pop heard every time the si5351 is updated.

There have been a half dozen different schemes for implementing simple AGC schemes
on the uBitx (and Bitx40).  I'd recommend Don's (ND6T) scheme as was kitted up
by Kees (K5BCQ).    http://www.nd6t.com/uBITX/AGC.htm
The kits are no longer available, but would be simple enough to dead bug it.
Others here will have their own favorites.
They pretty much all rectify the recovered audio to determine the amount of attenuation,
applying a DC voltage to some attenuation device.
You could easily control that attenuation from a processor, perhaps using pulse-width-modulation
to determine the amount of attenuation, though better would be an small ADC hanging off the I2C lines.

Jerry, KE7ER


Re: Trial to control CW power (and reduce harmonics as a result) by unbalancing the 2nd mixer #ubitx

John (vk2eta)
 

Thanks Jerry, all very good points.

I really need to invest in a scope and an SA.

I didn't notice any difference in the CW output power after this mod (but I didn't record the before power).

I will check if there is a difference between SSB and CW power levels. That should give me an indication.

Also please tell me if that statement is correct: since the clock #1 signal passes through the xtal filter this should strip its harmonics to pretty low levels (xtal filter overload excepted as you mentioned above. Not sure at what levels this starts occurring).

All the best,

73, John

Re: Menu Sequence for CEC Firmware v1.200 #ubitx #firmware

John (vk2eta)
 

Hello Dan,

Not tested since I use my own customized version, so just by reading his code therefore that solution could be buggy but should point to what you need to do.

Example swap around the position of toggle VFO and Mode in the menu:

in ubitx_menu.ino change from:

#if FN_VFO_TOGGLE == 1
      case FN_VFO_TOGGLE_IDX :
        menuVfoToggle(btnState);
        break;
#endif       
#if FN_MODE == 1
      case FN_MODE_IDX :
        menuSelectMode(btnState);
        break;
#endif       

To (swap around):

#if FN_MODE == 1
      case FN_MODE_IDX :
        menuSelectMode(btnState);
        break;
#endif       
#if FN_VFO_TOGGLE == 1
      case FN_VFO_TOGGLE_IDX :
        menuVfoToggle(btnState);
        break;
#endif       

AND change from:

  #define FN_VFO_TOGGLE_IDX   (FN_BAND_IDX         + FN_VFO_TOGGLE)
  #define FN_MODE_IDX         (FN_VFO_TOGGLE_IDX  + FN_MODE)
  #define FN_RIT_IDX             (FN_MODE_IDX                  + FN_RIT)

To (re-sequence from menu item position to menu item position):

  #define FN_MODE_IDX                 (FN_BAND_IDX                + FN_MODE)
  #define FN_VFO_TOGGLE_IDX   (FN_MODE_IDX               + FN_VFO_TOGGLE)
  #define FN_RIT_IDX                      (FN_VFO_TOGGLE_IDX  + FN_RIT)

That should do the trick I suspect.

All the best,

73, John

Confused about how AGC works?

digger AB3XU
 

Hello All,

(sorry if this topic has been hashed to death elsewhere, if so I couldn't find it).

As the subject says I'm a bit confused about how AGC, and specifically the ND6T version, works. There must be something I'm missing because it doesn't make sense. Here's a link to the basic circuit and how it works.


To begin with I can follow along with the theory and it does makes sense. Very simply, the signal from Vol-Hi via Q1 is used to control the conduction of Q2 and how much Q3 shunts the IF signal. Ideally RF levels below S9 are left relatively untouched, however if greater than that, the action of Q2 conducting less and Q3 acting as a shunt  results in reducing clamping (reducing) the IF level.

So here's where I get lost.  As the IF level gets attenuated by the action of the AGC doesn't that in turn:
  1. attenuate the level you will see at Vol-HI
  2. which will then decreases the effect of the AGC
  3. leading to an increased IF signal level
  4. and increasing Vol-HI
  5. which then increases the AGC's effect
  6. reducing the IF signal level
  7. resulting in a feedback loop of the IF level going up and down...
Am I describing my confusion/question in a way that makes sense?

73, digger AB3XU

Re: Confused about how AGC works?

Curt
 

check this out - this is a similar version of the same circuit

http://www.nd6t.com/bitx/AGC

the main idea is sampling the audio, feeding the transistor to boost this signal.  the 2 diodes develop a rectified signal based upon the audio, and this is used to bias a MOSFET used as a variable resistor. 

Curt

Re: Trial to control CW power (and reduce harmonics as a result) by unbalancing the 2nd mixer #ubitx

Jerry Gaffke
 

John,

Yes, the 45mhz crystal filter should strip out the harmonics coming out of that mixer,
leaving just a pure 45mhz carrier when transmitting CW

For SSB, both of the level 7 diode ring mixers want an incoming signal that is 10 dB or so below
the 7dBm local oscillator, so about -3 dBm max.  Beyond that it starts to distort. 
The output of the mixer is about 6 dB below the signal coming in.
The 45mhz crystal has a loss of 3 to 5 dB I'd think, the 45mhz IF amp has a gain
somewhere between 10 and 16 dB (the hot transistors on v5 might put that one 
closer to 16 dB).  

Of course, our si5351 can't quite deliver 7dBm, but the uBitx pushes things a bit, driving the mixers
hard because we don't have enough gain in the power amp.
Anyways, the paragraph above should get you in the right ballpark regarding signal levels.

I'm liking the looks of this AD8307 RF probe, very clever how they make use of a cheap digital voltmeter module:
    https://qrpguys.com/qrpguys-digital-field-strength-meter
That thing could be calibrated, you could read dBm from it using a hand calculator.
Better yet would be if the uBitx had pads for an optional AD8307 feeding a Nano analog pin.
There are AD8307 chips at $0.50 each on ebay, and they generally work fine.

Jerry, KE7ER
 


On Thu, Apr 18, 2019 at 05:23 PM, John (vk2eta) wrote:
Also please tell me if that statement is correct: since the clock #1 signal passes through the xtal filter this should strip its harmonics to pretty low levels (xtal filter overload excepted as you mentioned above. Not sure at what levels this starts occurring).

Re: POP!!

Sam Tedesco
 

C97 was bad. Failing under load. PITA!

Re: Menu Sequence for CEC Firmware v1.200 #ubitx #firmware

John (vk2eta)
 

Hello Dan,

After coffee the two and half neurons left seem to start working together..hihi: in fact you should only need to do the second part of the changes since the switch statement does not care about the order of tests. It is only a code optimization issue.

So only the #define FN_xxxx section should need to be adjusted.

73, John