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Re: Changing out L5 & L7 in UBitX for Spur Fix

 

How big are the spurs at 12Mhz? Transmitting on 20m I could barely see that on my Softrock receiver (which grounds on TX) and a lot less than the fundamental, seems, I would say at least - 50db. The spur exists but seems to me quite low. Has anyone measured it against the fundamental with a reliable spectrum analyzer?


Il 25/dic/2018 13:04, "Evan Hand" <elhandjr@...> ha scritto:
I ordered the kit from the link on spectral purity:?

I am assuming that it will include the correct devices.

Thank-you for your checking!

73
Evan
AC9TU

Re: Tracing receive signal for low signal

 

Thanks will check.? I was thinking about that before and I tried a random cap I had around but didn't seem to make a difference maybe have to try a different one.
Re: Help on parts and or repairs !

Timothy Fidler
 

Chuck,?

there are cases where people have wanted a new Raduino and hfsignals has allegedly sold one of those , independently of other hardware (via an email enquiry to the gmail.com? letterbox ).? That was $25 USD plus shipping last I saw.? Subtract that from what you paid for your board and that will give you an idea of the cost you are up for.? ?(A fair proportion of the original price )
2. Re contacting HF signals - you could get cheeky and sniff around for a recent post/ans by A. Farhan on this wunnerful (sic)? BBS and reply to him about cost and arrangements for getting a new main board.?

3. There is another option (but with greater technical risk)? if you have not put it into a min. size case and if the board works fine on Rx.?? It needs 25 mW to drive it . You will need to ensure you have somewhere on the existing PCB that has this power available.? He does not state the input impedance of the? .... hust ma mouth... look at the input Z measurements by Fred? down the bottom of the referenced page.? BTW others (AN Other) AKA the mad radio modder has allegedly had the modified kit working on 6m SSB and it appears that the Hans 10 W kit is the one to do just that (with other mods on the HF signals board and firmware? too)
Re: Bitx40 No display

 

Thanks to all who responded,
I was checking solder points with a meter... voltage ect and it blinked and blew a fuse( 2A)? ? ?now i get no hiss out of the speaker.... after replacing the fuse....
have good voltage in all points.... speaker checked out OK.

?
Re: Help on parts and or repairs !

Timothy Fidler
 

Basis of? above? rabbit out of the hat statement Drive power? in this case 25 mW =? 10 Wout? x Alog? ( - 26/10)
Re: Help on parts and or repairs !

 

Reviewing this tale of woe, I find no mention of initial bias. It's a common failing that people will 'zero' the pots before power-on, and *before* RTFM! Reading that fine manual will reveal the bias pots to be wired the 'wrong' way, i.e. fully clockwise to zero. Leaving them with factory-setting is recommended until either 'fine-tuning' with meter in *each* FET's supply (difficult, not for the newcomer) or complete 're-do from start'.
Hopefully helpfully - and "Best'v the Festive"!
Dex, ZL2DEX
Re: uBITX Low Power Output

Bret Mills
 

Hi Rod,?
Did you ever get your low power issue resolved?
I have finally gotten around to getting my UBITX V3 board done and on the air and I find the same issue as you have described here on this thread.?
about 3 Watt's is about all I can get out and that is on 20 Meters when driving the Mosfet's to about 125MA Bias.?

--
You can email me back direct?bret.wx7y@...?if you like.
thanks and 73's
Bret
WX7Y
Re: Tracing receive signal for low signal

jim
 

Check (with an ohm-meter) for resistance to ground on generator ...Likely it has 50 ohm to ground ..If you hook that directly across the base of the transistor, you've just mucked up the bias on that transistor ...If you want to random-probe circuits, you need a DC blocking capicitor on the generator lead

Jim


On Wednesday, December 26, 2018, 9:56:42 AM PST, Dave Space <davesspacebar@...> wrote:


Interesting thanks that is a good map to work through will try to trace.

I noticed something interesting maybe it's expected trying to understand why though.? If I input a low signa from generatorl like 10mv 1khz one side of C50 I get a clear tone (the side away from the Q70 base) the other side towards Q70 base I hear nothing unless I increase the power to like 2v or more on the generator? (That could be due to the issue you found with collector voltage I guess... though I see similar behavior on the other transistors inputting to the base Q71, or? (72,73 - I see these in push pull config not sure if that correlates to needing more power at the base).
Re: Volume Limiting and Distortion Reduction for uBITX #ubitx

 

Yes, points connected to volume control are in parallel with existing wiring.? The relay and regulator are new, not the existing uBITX ones.?? Here is a photo of the mod that I made for mine.
Re: Tracing receive signal for low signal

 

Interesting thanks that is a good map to work through will try to trace.

I noticed something interesting maybe it's expected trying to understand why though.? If I input a low signa from generatorl like 10mv 1khz one side of C50 I get a clear tone (the side away from the Q70 base) the other side towards Q70 base I hear nothing unless I increase the power to like 2v or more on the generator? (That could be due to the issue you found with collector voltage I guess... though I see similar behavior on the other transistors inputting to the base Q71, or? (72,73 - I see these in push pull config not sure if that correlates to needing more power at the base).
Re: Volume Limiting and Distortion Reduction for uBITX #ubitx

Jack Purdum
 

There are pros and cons to each approach, which is why JackAl has both RF and audio AGC. Indeed, the AGC section takes up a good portion of the JackAl's nanoacres. BTW, we just received the assembled Jack boards which has the SMD parts in place and looks like this:

Inline image

This is what QRP Guys will be selling after we spend a little more time testing everything. After adding the off-board parts (less than $13), the board looks like this:

Inline image

All of the yellow pins are test points to encourage experimentation. You also have about a dozen free I/O pins to experiment with.

Jack, W8TEE

On Wednesday, December 26, 2018, 11:26:29 AM EST, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:


There have been dozens of threads in this forum about adding AGC to the Bitx40 and uBitx.
Most get hacked in (both detection and attenuation) after the rx audio preamp,
to prevent ear damage on a sudden strong signal.
Then perhaps add a manual RF gain pot at the antenna port to avoid audio preamp overload.

Some used PIN diodes to attenuate the signal at RF (or IF) frequencies,
and thus get around the dynamic range limitations of that 2n3904 audio pre-amp stage.
Here's the earliest thread to identify the dynamic range issue of that Bitx/uBitx audio pre-amp stage:
:? ??/g/BITX20/topic/5945215#32066

Kees (K5BCQ) sold nearly 1000 kits of an AGC design from Don (ND6T).
This was audio detection with RF attenuation at the antenna port using 2n7002 FETs.
Nik (VK4PLN) was planning to sell a kit with audio detection and attenuation
after the audio preamp, I don't know what came of that.
? ?
?

Sensing signal levels is probably best done after conversion to audio.
Must sense after the 12mhz crystal filter, or strong signals elsewhere in the band
will bring on the AGC action.? But if we sense between that 12mhz crystal filter
and the demodulator, then we will likely be seeing mostly the unshielded 12mhz bfo.

Attenuation could be anywhere between the antenna port and the input to the audio preamp.
Putting attenuation at the antenna port avoids overloading the mixers and IF amps,
but they generally have enough dynamic range that it doesn't really matter where we pot it.
Putting attenuation after the audio preamp works, but does not fix the dynamic range
issue of that preamp.

Various ways to implement attenuation at RF, here's a good one that?
tries to maintain a 50 ohm impedance match, and is quite cheap:
? ??
Allison recommends using a 1n4007 as a pin diode to set the gain in one (or both)
of the bidi IF amps, many of us have a 1n4007 in the junk box:
??/g/BITX20/message/45984

Jerry, KE7ER

Re: Volume Limiting and Distortion Reduction for uBITX #ubitx

 

There have been dozens of threads in this forum about adding AGC to the Bitx40 and uBitx.
Most get hacked in (both detection and attenuation) after the rx audio preamp,
to prevent ear damage on a sudden strong signal.
Then perhaps add a manual RF gain pot at the antenna port to avoid audio preamp overload.

Some used PIN diodes to attenuate the signal at RF (or IF) frequencies,
and thus get around the dynamic range limitations of that 2n3904 audio pre-amp stage.
Here's the earliest thread to identify the dynamic range issue of that Bitx/uBitx audio pre-amp stage:
:? ??/g/BITX20/topic/5945215#32066

Kees (K5BCQ) sold nearly 1000 kits of an AGC design from Don (ND6T).
This was audio detection with RF attenuation at the antenna port using 2n7002 FETs.
Nik (VK4PLN) was planning to sell a kit with audio detection and attenuation
after the audio preamp, I don't know what came of that.
? ?
?

Sensing signal levels is probably best done after conversion to audio.
Must sense after the 12mhz crystal filter, or strong signals elsewhere in the band
will bring on the AGC action.? But if we sense between that 12mhz crystal filter
and the demodulator, then we will likely be seeing mostly the unshielded 12mhz bfo.

Attenuation could be anywhere between the antenna port and the input to the audio preamp.
Putting attenuation at the antenna port avoids overloading the mixers and IF amps,
but they generally have enough dynamic range that it doesn't really matter where we pot it.
Putting attenuation after the audio preamp works, but does not fix the dynamic range
issue of that preamp.

Various ways to implement attenuation at RF, here's a good one that?
tries to maintain a 50 ohm impedance match, and is quite cheap:
? ??
Allison recommends using a 1n4007 as a pin diode to set the gain in one (or both)
of the bidi IF amps, many of us have a 1n4007 in the junk box:
??/g/BITX20/message/45984

Jerry, KE7ER
Re: Ubitx microphony

 

I had microphony that turned out to be coming from a poor fitting 8 pin audio cable.
Re: Help on parts and or repairs !

 

I could only find link to complete kit, is their a link to just the parts
ie: main board as it comes in a kit ?

I did send an email a couple of weeks back to hfsignals but have heard
nothing back... Thanks
Re: Volume Limiting and Distortion Reduction for uBITX #ubitx

 

Wow clever adjusting the bias on the pin diode. I assume that the points connected to the volume control are added in parallel to existing wiring? Where do a1 b1 a2 b2 c1 and c2 go? Is that the existing k1 and 7805? up in the corner by the antenna input on the main board?

Thank you
Re: Ubitx microphony

 

Ok Bill, I think that solution may be temporary but it does not end with the problem.
I have to continue investigating where the microfonics arises and how to solve it, because this effect is a failure of something that I have not yet located.
No circuit / componet must modulate the original signal by mechanical vibrations as it is in the case of the microfonismo that drives me crazy.
I also have to try to replace the electrolytic coupling ceramic capacitors to avoid the piezoelectric effect.
I will continue in the matter.
Thanks for your observations.
Re: Tracing receive signal for low signal

jim
 

Possible, but unlikely ...As a first step tie the wire loop you wound thru the core to the input of your scope..measure the signal from tp2 to the scope across the bandwth you can sweep with your generator..look for any peaking/dropouts across the bandwidth ..

when I didn't have the SA/TG I now have, I made 2 identical RF probes ...Hooked one to one channel of scope, and one to the other ...Used one to monitor the input of a circuit and the other to monitor the output ...Sweep manually the frequency and looked for peaking/dropping/changes and why those occurred ...

I also constructed 2 identical RF attenuator boxes ..3db,6db,10db,20db,20db. with bnc connectors on each end (still use them)
to set levels and verify overload/distortion issues ..

Took HOURS to sweep/characterize circuit ..

Now it takes longer to hook up ths SA/TG than it takes to measure a circuit ..but its still doing the same thing

Its best to start at the "back end" of the circuit and work towards the front ..fixing one problem at a time

Virtually all the "gain" in this receiver is in the audio stages ...

Stage by stage ...Input low-pass ....Probably -3db loss
??????????????????????????? T1/T2 Mixer? .....Minimum 6db loss (probably more)
??????????????????????????? Q10/12 amp??????? 15 Db gain Maybe ..
??????????????????????????? 45 Mhz BPF?????? minimum 6 db loss (probably more)
??????????????????????????? T3/T4 Mixer ....Minimum 6db loss (probably more)
??????????????????????????? Q30/32 amp?????? 15 Db gain Maybe
??????????????????????????? 12 Mhz BPF??? minimum 3db loss (Probably more)
??????????????????????????? T7 mixer .....Minimum 6db loss (probably more)

Add all those up ....Losses Minimum 30 Db ///Gains ...Maximum 30 Db ....

To get from 1 uV (microvolt) to 1 V (volt) you need 120 Db gain ..

All that has to happen somewhere between Q70 and whatever you are using for a speaker

Fix the audio?? then (probably) most of these other issues will solve themselves

Jim

On Tuesday, December 25, 2018, 12:39:31 PM PST, Dave Space <davesspacebar@...> wrote:




Gave it a try same results 1900uv estimated at tp2 to get to .1p-p

9000uv estimated at tp1 to get .1p-p? (I think I reported my signal generator's input in my message last time and mentioned uv when it was really mv 900mv through a -40b attenuator so estimated at 9000 uv.)

with the wire wrapped through about 5 times (it was about as many as I could fit and it's even thinner magnet wire than they used on T2 itself.)

So perhaps that means its not matching that is the issue?

Re: Bitx40 No display

 

Sorry. Did it again. Did not read the title.?
Re: Help on parts and or repairs !

 

On Tue, December 25, 2018 8:14 pm, Curt via Groups.Io wrote:
Chuck


A new board can be ordered from hfsignals.com

I could only find link to complete kit, is their a link to just the parts
ie: main board as it comes in a kir ?

I did send an email a couple of weeks back to hfsignals but have heard
nothing back... Thanks






I am mystified by the finals, I wonder if you have a shorted pot or just
too much current.

I suggest getting it working in stock form before any mods, including
adding kd8cec firmware. Take small steps in your build.

Curt
Re: Bitx40 No display

 

This is a BITX40 board!

At 26-12-18, you wrote:
I would start with the simple and then go to more complex.
Verify that you have the Raduino board plugged in correctly. I noted on my board that the socket on the Mac n board looks like the last pin connector has half of the plug left from when it was cut from the source strip.

Next verify the 12v to the input of the 7805 regulator on the Radoino board.

Fnally verify the tegulator output

the way the7805 is mounted in the Raduino board with the input closest to the main board, and output furthest away.

Evan
AC9TU
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