Date   
Re: RD16HHF1 power curve flattening...some

K9HZ <bill@...>
 

Here’s what I found... if you change R85 from 100 to 470 ohms (pre-driver stage bias), change R261 and R262 from 100 to 1K ohm (Although 820 ohms will work too… it’s not that critical), run RV1 wide open (full drive) and then use a compensating capacitor (your 33pf at 14 MHz) across T11 primary with a 1:4 transformer:

 

6M - 48pf

10M - 110pf

20M - 320pf

40M - 680pf

80M - 1,500pf

60M - 4,700pf

 

It shows at least 20 watts out on each band except for 6 meters... where it peaks at 12 watts.  My calculations show that the 3:2 is not optimal for this pair. You might want to have a look at:  http://www.tapr.org/pdf/PennyWhistleManual.pdf

 

 

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

Moderator – North American QRO Yahoo Group.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of John
Sent: Sunday, February 25, 2018 7:59 PM
To: BITX20@groups.io
Subject: [BITX20] RD16HHF1 power curve flattening...some

 

Having read with interest the information provided by Erhard Haertel (DF3FY) on ubitx.net regarding the changes to the finals circuit I decided to try to improve the flatness or lack thereof of the power curve over frequency on my uBitx unit.

 

I therefore performed his proposed changes (final's transformer, cap across drains, feedback resistors) with one exception: the feedback resistors between drain and source of the final was changed from 220 Ohms to 820 Ohms instead of 1K Ohms.

 

I got the following result at 13.8V, with idle current at 250mA per final, RV1 unchanged at approx 60% as before:

 

Freq.      Power     Total Current

 7Mhz        18W         2.8A

14Mhz        16W         2.7A

21Mhz         9W         1.5A

24Mhz        11W         1.9A

28Mhz        11W         2.2A

 

Hmmmm...not bad but still that dip at 21 and not that high on the high frequencies.

 

But the good news was that I would get power improvement all the way to the end of the RV1 pot and it looked like no compression was occurring. Good news as this means that I have spare power for frequency compensation.

 

Using the LTSpice simulation done by Jerry Gaffke (thanks Jerry) with a replacement of the finals with the RD16HHF1 model found on the internet and I got some interesting pointers (reality is always different, but I find this is a good starting point).

 

I simulated capacitors in parallel with the 22 Ohms emitter resistors in the pre-driver and driver stages alternatively. Since I had "free gain" left by turning RV1 this meant that none of the stages were limiting at 60%, therefore I could increase the gain anywhere in the chain, including at RV1 for that matter.


LTSpice gave me a flat curve with caps of 150-200pf in the pre-driver stages, and more importantly a rapid drop in power above 40Mhz which I hope may prevent V-UHF oscillations of the power train (linear amplifier specialists can comment on that point).

 

So I experimented with various caps values across the R87 and R88 resistors and found that I would not get more gain above 330pf.

 

Results as per above conditions (RV1 back at 60%):

 

Freq.      Power     Total Current

 7Mhz        18W         2.8A

14Mhz        16W         3.0A

21Mhz        10W         1.6A

24Mhz        11W         not recorded

28Mhz        14W         1.9A

 

Not perfect but at least now 10W on the high bands, and above 15W at and below 14 megs.

 

One minute key down then "finger heat test": the finals new transformer is a little warm but not much. The filters the same. The finals and the heat-sink (thermally coupled to the metal case) are fine.

 

So the question is: can the filters handle that kind of power over time? Short of doing and LTSpice simulation is there an easier way to calculate the current and therefore the flux density in the filters cores to check if we are getting to saturation or not? 

 

No instability and oscillation detected with a separate radio, but again I don't have a spectrum analyser. 

 

So in summary this is what I have in the circuit now: Finals as RD16HHF1s, feedback resistors R261/R262 as 820 Ohms, Tranformer 2T primary / 3T secondary on BN43-202, 33pF across the output transformer primary and 330pf across R87/R88.

 

I haven't tried capacitors across the driver stage emitter resistors (R941/942/911/96), nor from the high to the middle side of RV1 for the following reasons: I wanted to leave the drivers alone and not modify the way they drive the finals (impedance change), and at RV1 it meant that the capacitor value would need to change with the adjustment of RV1, although this could be the simplest way to correct the power curve. 

 

Interestingly enough for the units with the IRF510s, LTSpice reports a flat power curve with 800pf caps across these four drivers resistors....it could be just theory...and stability could be an issue as we reduce negative feedback. Is anyone game enough?

 

Happy hacking,

 

73, John (VK2ETA)


Virus-free. www.avg.com

Re: Erratic tuning with my new uBitx

Jerry Gaffke
 

As you rotate the encoder shaft, the enocder alternately grounds ENC_A and then ENC_B.
The timing in how it shorts one and then the other tells the Raduino which direction you are turning the shaft.
So this grounding is not an error.
You should see a regular pattern of 5v and 0v on those pins as you turn the shaft, and the two patterns should look very similar (just slightly shifted in time)


On Sun, Feb 25, 2018 at 07:34 pm, DrZ wrote:
It does seem weird that I would have this problem even with the original sketch.  I'll try the test you suggest.  Are you saying that the occasional short to ground is an error?

Re: Looking for Completely Functional Dual-Band 20/(17/15/10/6) Meter QRP Rig with SSB/PSK #bitx20help

Richard Spohn
 

Yes Mark, just bent -- actually looped back upon itself. Say you need
to shorten each leg by 6 inches. Bend the wire back on itself at the
6-inch mark; you can then twist that 6 inches around the antenna wire
it is bent back onto, but you can just as well simply clip the extra
wire onto the antenna using a wire clip. Either way, the antenna
"ignores" the 6 inches that is bent back onto the antenna leg. - Rich

On 2/25/18, Mark via Groups.Io <mboston72=yahoo.com@groups.io> wrote:
Hi Rich,

Thanks for the suggestion. Yes, I've heard that before. They don't
necessarily need to be clipped. They can just be bent? More information for
my antenna book. Great!

Mark

Re: Looking for Completely Functional Dual-Band 20/(17/15/10/6) Meter QRP Rig with SSB/PSK #bitx20help

Jerry Gaffke
 

There are plenty of threads here I'd just as soon skip over, and often do.
Perhaps you can do the same.
I for one am fine with discussions of antennas (that seems very appropriate) 
and with discussing the pros and cons of the Bitx radios vs others. 

Jerry, KE7ER


On Sun, Feb 25, 2018 at 08:13 pm, Rod Self wrote:
I, for one, am very tired of off-topic general discussions about radios and antennas on the bitx20/ubitx group.

Please let this thread die, or move it to another discussion group.

A good guideline: if it does not involve a bitx or utibx, it probably does not belong here.

Re: Erratic tuning with my new uBitx

Jack Purdum
 

One way to visualize how an encoder works is to think of 20 speed bumps arranged in a circle. Floating above the speed bumps is a wire. Now imagine a contact arm anchored in the center of the circle and a second contact arm 90 degrees out of phase with the first arm. As a shaft turns, the contact hits a speed bump and make contact with the wire above it. Therefore, every 18 degrees (360 / 20 = 18) a contact is made and a pulse chain is form by the two contact arms. By looking at those signals, you can determine if the shaft is rotating CCW or CW. Therefore, you will see a pulse chain of binary values coming from the encoder. A better description can be seen on YouTube:



Jack, W8TEE



From: Jerry Gaffke via Groups.Io <jgaffke@...>
To: BITX20@groups.io
Sent: Sunday, February 25, 2018 11:29 PM
Subject: Re: [BITX20] Erratic tuning with my new uBitx

As you rotate the encoder shaft, the enocder alternately grounds ENC_A and then ENC_B.
The timing in how it shorts one and then the other tells the Raduino which direction you are turning the shaft.
So this grounding is not an error.
You should see a regular pattern of 5v and 0v on those pins as you turn the shaft, and the two patterns should look very similar (just slightly shifted in time)

On Sun, Feb 25, 2018 at 07:34 pm, DrZ wrote:
It does seem weird that I would have this problem even with the original sketch.  I'll try the test you suggest.  Are you saying that the occasional short to ground is an error?


Three (and a Half) AGC schemes #ubitx-help

John <passionfruit88@...>
 

I have tried three (and a bit) AGC schemes with the uBitx with the following results:

1. TPA2016 from Adafruit in replacement of the standard audio chain after the potentiometer. Thank you Nik (VK4PLN) for sharing the code.

Like mentioned in another thread recently I also had low volume. To get more signal in I changed R51 to 10K and R50 to 330K. It worked to a point but to get enough "AGC effect" I had to reduce the setgain( ) to close to zero.  This meant lower volume.

I tried multiple combination of parameters, but it felt more like a limiter than an AGC.

I take an FT-817 as a reference, although of course I don't expect to get to the same AGC performance, just to be able to listen to a net without adjusting the volume every time a new station comes on.

The final straw for the TPA2016 was when I discovered hash generated on the 40M band. This meant probably more shielding and filtering although I had it mounted on top of a double sided epoxy circuit board the same size as the uBitx main board and connected to ground in the four corners.

So I moved on the next solution.

2. I tried the 2n7000 AGC circuit as shown in the pre-production uBitx schematic.

I noticed that the gain control would come only on loud signals as there is a significant threshold in the circuit before the MOSFET reaches it conductive state.

I therefore replaced the half wave rectification with a voltage doubler version and changed the 1N4148a to BAT46 (Schotky) but still not enough sensitivity to the trigger the AGC on medium signals.

Since I needed low power to drive the MOSFET I used an 8 Ohms to 500 Ohms 350mW audio transformer with the low impedance side connected to the 2nd output of the TDA2822. This gives plenty of voltage even on low signals to control the MOSFET. The AGC action was good but I had distortion, especially on low signals. 

I tried to decouple the drain of the MOSFET to the Vol-H input but to no avail.

I read on the internet about "adding half of the signal voltage to the gate of the FET to reduce distortion" for these type of AGC schemes, but I am not sure it applies to depletion of enhancement FETs.

So any experience using this "pre-production" AGC circuit in the uBitx would be greatly appreciated.

3. I also tried and I currently have a MAX9814 from Adafruit in place for AGC, connected strait between VOL-H and the top of the volume potentiometer with decoupling capacitors in and out, through an input and output trimmer pot for adjustment.

I also added a 390nF capacitor in parallel to the 100nF at the time constant terminal (TC) to slow the reaction down to about 1ms.

That solution too is not proving that great. The variable gain range seems too small (although the specs says 60dB dynamic range) as it quickly gets overwhelmed by large signals and introduces strong distortion, or, if adjusted lower, only comes into play on very  strong signals.

It is a shame as the TC connection of the MAX9814 give a DC voltage related to the AGC action and could have been used for an S meter input. 

So my questions are:

A. Is the pre-production 2N7000 solution (circuit attached below) producing distortion in your uBitx (where implemented) and if not did you modify the circuit in any way?

B. Any other good proven AGC scheme tested with uBitx?

C. Am I asking too much of an audio AGC circuit?

Thanks for reading.

All the best,

73, John (VK2ETA)

uBITX I want to know when ?

Bae hwangchan
 

Hello

My name is Hwang-Chan  Bae.
We have paid $ 109 to Paypal as a credit card to DEC-21-2019 to purchase uBITX.
But uBITX has not arrived yet.
I want to know when it is coming.
Receipt Number: 5494-5763-6907-3144.
name: Hwang-chan  Bae
Address: Banyan Road 177 (205-1104) Hyundai Apartment
Changwon City Seongsan-gu, Gyeongsangnam-do
51425
Republic of Korea.

Please let me know when you arrive.




Re: Three (and a Half) AGC schemes #ubitx-help

K9HZ <bill@...>
 

Well I guess the question to ask is what is your goal?  Do you want to maintain a constant audio level with varying signal strength, or do you want to maintain a constant RF/IF/Audio gain in your radio.  They are much different… have much different impact on the radio.  Limiting and compression can occur at any stage.  So far you have demonstrated an audio gain level control.  If you want t TRUR and traditional AGC, you need to start at the front end of the radio to prevent it from over-loading with strong signals.

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

Moderator – North American QRO Yahoo Group.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of John
Sent: Sunday, February 25, 2018 11:10 PM
To: BITX20@groups.io
Subject: [BITX20] Three (and a Half) AGC schemes #ubitx-help

 

I have tried three (and a bit) AGC schemes with the uBitx with the following results:

1. TPA2016 from Adafruit in replacement of the standard audio chain after the potentiometer. Thank you Nik (VK4PLN) for sharing the code.

Like mentioned in another thread recently I also had low volume. To get more signal in I changed R51 to 10K and R50 to 330K. It worked to a point but to get enough "AGC effect" I had to reduce the setgain( ) to close to zero.  This meant lower volume.

I tried multiple combination of parameters, but it felt more like a limiter than an AGC.

I take an FT-817 as a reference, although of course I don't expect to get to the same AGC performance, just to be able to listen to a net without adjusting the volume every time a new station comes on.

The final straw for the TPA2016 was when I discovered hash generated on the 40M band. This meant probably more shielding and filtering although I had it mounted on top of a double sided epoxy circuit board the same size as the uBitx main board and connected to ground in the four corners.

So I moved on the next solution.

2. I tried the 2n7000 AGC circuit as shown in the pre-production uBitx schematic.

I noticed that the gain control would come only on loud signals as there is a significant threshold in the circuit before the MOSFET reaches it conductive state.

I therefore replaced the half wave rectification with a voltage doubler version and changed the 1N4148a to BAT46 (Schotky) but still not enough sensitivity to the trigger the AGC on medium signals.

Since I needed low power to drive the MOSFET I used an 8 Ohms to 500 Ohms 350mW audio transformer with the low impedance side connected to the 2nd output of the TDA2822. This gives plenty of voltage even on low signals to control the MOSFET. The AGC action was good but I had distortion, especially on low signals. 

I tried to decouple the drain of the MOSFET to the Vol-H input but to no avail.

I read on the internet about "adding half of the signal voltage to the gate of the FET to reduce distortion" for these type of AGC schemes, but I am not sure it applies to depletion of enhancement FETs.

So any experience using this "pre-production" AGC circuit in the uBitx would be greatly appreciated.

3. I also tried and I currently have a MAX9814 from Adafruit in place for AGC, connected strait between VOL-H and the top of the volume potentiometer with decoupling capacitors in and out, through an input and output trimmer pot for adjustment.

I also added a 390nF capacitor in parallel to the 100nF at the time constant terminal (TC) to slow the reaction down to about 1ms.

That solution too is not proving that great. The variable gain range seems too small (although the specs says 60dB dynamic range) as it quickly gets overwhelmed by large signals and introduces strong distortion, or, if adjusted lower, only comes into play on very  strong signals.

It is a shame as the TC connection of the MAX9814 give a DC voltage related to the AGC action and could have been used for an S meter input. 

So my questions are:

A. Is the pre-production 2N7000 solution (circuit attached below) producing distortion in your uBitx (where implemented) and if not did you modify the circuit in any way?

B. Any other good proven AGC scheme tested with uBitx?

C. Am I asking too much of an audio AGC circuit?

Thanks for reading.

All the best,

73, John (VK2ETA)


Virus-free. www.avg.com

Re: RD16HHF1 power curve flattening...some

John <passionfruit88@...>
 

Thank you Bill.

I was intrigued by the low value of the capacitor value across T11. So that makes more sense.

I find interesting the size of the output transformer on the PennyWhistle compared to the BN43-202. It might explain the warm temperature of the T11 transformer at 18-15 Watts. I will try a BN43-3312 as it should still fit in the space between the finals.

I will definitely try your suggestions.

All the best,

73, John (VK2ETA)

Re: Looking for Completely Functional Dual-Band 20/(17/15/10/6) Meter QRP Rig with SSB/PSK #bitx20help

Arv Evans
 

Might want to check out MIG welding wire.  It is copper coated steel, so
both strong and conductive. 
_._


On Sun, Feb 25, 2018 at 5:37 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Anything that doesn't break in the weather is thick enough, within limits.
Drive 1000 Watts into 28 gauge copper, it may fall out of the sky into little molten puddles on the ground.
And kind of a bummer to have to go out and climb trees to fix broken antenna wire during an ice/wind/rain storm.
Galvanized steel is less conductive than copper,  I doubt you would notice the difference, except it's stronger.
Copper clad steel is available, seems a good idea, I've never used it:  https://thewireman.com/antennap.html
Hard drawn copper is stronger than standard copper wire, often used for antennas.
You may have a local HRO storefront:  https://www.hamradio.com/detail.cfm?pid=H0-002444
they have lots of different antenna products.
Disconnect your equipment if an electrical storm is in the area.


On Sun, Feb 25, 2018 at 03:59 pm, Mark wrote:
For QRP I'd only need #17?

There's a write-up on this type of wire purchased from tractor supply stores, entitled, Does wire gauge (size) make any difference for vertical antenna radials?, at eHam.net.

They say that some antenna manufactures suggest 14. I guess that is possibly because it is used for base stations with 100 or more watts.

However, for my specific QRP & mobile situation, maybe 17 would be fine. It would also be a bit lighter.

Would reception improve if it were copper? Or, maybe for something like this it wouldn't really matter.


Looking for Completely Functional Dual-Band 20/(17/15/10/6) Meter QRP Rig with SSB/PSK #bitx20help

Tim Young
 

There is a degree of Elmering here that I have been very impressed with since I joined the group. Some threads are way to esoteric or deep for me and others are spot on. The beauty is that I can pick and choose what to move to my mini wiki and what I choose to delete. Given the experimental nature of the Bitx, the Elmering is really appreciated. What a fantastic learning platform.

I hope the bandwidth doesn't get too narrow.

Tim

WB7UVH


On 2018-02-25 21:39, Jerry Gaffke via Groups.Io wrote:

There are plenty of threads here I'd just as soon skip over, and often do.
Perhaps you can do the same.
I for one am fine with discussions of antennas (that seems very appropriate) 
and with discussing the pros and cons of the Bitx radios vs others. 

Jerry, KE7ER


On Sun, Feb 25, 2018 at 08:13 pm, Rod Self wrote:

I, for one, am very tired of off-topic general discussions about radios and antennas on the bitx20/ubitx group.

Please let this thread die, or move it to another discussion group.

A good guideline: if it does not involve a bitx or utibx, it probably does not belong here.


Re: Three (and a Half) AGC schemes #ubitx-help

John <passionfruit88@...>
 

Bill, 

Thanks again for taking the time to read and reply.

I didn't think of this in these terms but that makes sense.

My objective is to maintain a rather constant audio level rather than constant rf/if/audio gain.

My thinking is that since I haven't had conditions where the radio was overloaded (I just had to reduce the volume down quite a lot and the audio was not distorted) I came to the conclusion that (for the moment) I don't need to control the gain upstream of the audio chain.

So my focus (maybe wrongly) is to find an audio AGC scheme with sufficient dynamic range that it can keep the volume within a narrow range avoiding the constant pot adjustment when scanning the band or listening to a net or even to a QSO between two parties, one lower than the other, AKA in a similar manner to the commercial rigs, even if with less effectiveness.

Hope that makes sense.

All the best,

73, John (VK2ETA)

Re: RD16HHF1 power curve flattening...some

K9HZ <bill@...>
 

Yes please publish your results when you update the circuits… as I’ve now gone away from working on that aspect of the radio in favor of designing a good RF-driven AGC, finishing the tuner, and working on a variable pass-band filter that is usable for CW AND SSB that is also cheap!  I already published to control circuit recently for saving the radio due to SWR, over power, etc.  

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

Moderator – North American QRO Yahoo Group.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of John
Sent: Sunday, February 25, 2018 11:47 PM
To: BITX20@groups.io
Subject: Re: [BITX20] RD16HHF1 power curve flattening...some

 

Thank you Bill.

I was intrigued by the low value of the capacitor value across T11. So that makes more sense.

I find interesting the size of the output transformer on the PennyWhistle compared to the BN43-202. It might explain the warm temperature of the T11 transformer at 18-15 Watts. I will try a BN43-3312 as it should still fit in the space between the finals.

I will definitely try your suggestions.

All the best,

73, John (VK2ETA)


Virus-free. www.avg.com

Re: Three (and a Half) AGC schemes #ubitx-help

K9HZ <bill@...>
 

“My objective is to maintain a rather constant audio level rather than constant rf/if/audio gain”

 

Excellent…!   I think you are well onto the correct track then with what you have tried.  If you search the internet for AGC… most of the circuits shown are for audio gain circuits (I suspect most were developed for the music industry so can be very good).  I’m sure you will land on something that works well with the plethora of information available!

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

Moderator – North American QRO Yahoo Group.

 

email:  bill@...

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of John
Sent: Monday, February 26, 2018 12:03 AM
To: BITX20@groups.io
Subject: Re: [BITX20] Three (and a Half) AGC schemes #ubitx-help

 

Bill, 

Thanks again for taking the time to read and reply.

I didn't think of this in these terms but that makes sense.

My objective is to maintain a rather constant audio level rather than constant rf/if/audio gain.

My thinking is that since I haven't had conditions where the radio was overloaded (I just had to reduce the volume down quite a lot and the audio was not distorted) I came to the conclusion that (for the moment) I don't need to control the gain upstream of the audio chain.

So my focus (maybe wrongly) is to find an audio AGC scheme with sufficient dynamic range that it can keep the volume within a narrow range avoiding the constant pot adjustment when scanning the band or listening to a net or even to a QSO between two parties, one lower than the other, AKA in a similar manner to the commercial rigs, even if with less effectiveness.

Hope that makes sense.

All the best,

73, John (VK2ETA)


Virus-free. www.avg.com

Re: uBITX I want to know when ?

Ed Kelley
 

The date of your order is in line with units that are being
shipped now. They are so far behind on orders. You should
receive a shipping notice from PayPal giving you the date
your uBitx is being shipped. Be patient, the wait is worth
it. I was fortunate to get mine in the first batch and I
received mine before you ordered yours. It has worked
perfectly and a lot of enjoyment to use.
Ed W0OIC, Dubuque Iowa, USA

On 2/25/2018 11:32 PM, Bae hwangchan wrote:

Hello

My name is Hwang-Chan  Bae.
We have paid $ 109 to Paypal as a credit card to DEC-21-2019 to purchase uBITX.
But uBITX has not arrived yet.
I want to know when it is coming.
Receipt Number: 5494-5763-6907-3144.
name: Hwang-chan  Bae
Address: Banyan Road 177 (205-1104) Hyundai Apartment
Changwon City Seongsan-gu, Gyeongsangnam-do
51425
Republic of Korea.

Please let me know when you arrive.





Re: Strong carrier on transmit. #bitx40help

Dale Brooks KG7SSB <kg7ssb@...>
 

Hi Bob,
We can certainly talk on the phone. Go to QRZ.com and look up my call sign KG7SSB and my email address is listed. Send me your phone number and I will call you when I get a chance to be in the shop where I can follow along with your troubleshooting. I will tell you; there will be a small amount of carrier that will leak through but if at normal levels it should be fine. On a spectrum analyzer(looking at the output) with no modulation you will see a reduced carrier at the transmit frequency. When you modulate the carrier frequency, the carrier level will go down and the lower sideband signal will go up. So with a good receiver in the room and no modulation there will be a relatively strong carrier heard on the receiver. Now if the balanced modulator circuit is faulty then there will be a constant carrier at higher levels but still partially attenuated because it has traveled through the crystal filter network. Talk to Raj about getting rid of the rf burst when keying up. I just live with it because I don't use a headset and the noise doesn't bother me that much. On my new scratch built rig I had trouble with the VFO leaking through but I haven't seen much in the way of the carrier. By the time the signal travels through the BPF stage most of these signals should be down more than 40 dbm except for the 7mhz band. A one volt or less signal on the antenna could just be noise getting picked up in the different parts of the radio and getting through to the final where it is amplified. 
Send me your information and i will try to help you by phone to analyze the different parts or circuits that should be looked at. By the way my BITX receiver audio is very week and I need to start troubleshooting it also. Remember this is just part of the fun! 73's Bob, Dale

On Sun, Feb 25, 2018 at 8:20 PM, Raj vu2zap <rajendrakumargg@...> wrote:
I have described how to reduce or eliminate PTT carrier burst in BITX40. Please search!

Raj

At 26/02/2018, you wrote:
>Hi Dale, I disconnected D20 from the input of the attenuation pad going into the tx amp and the carrier was reduced but still there. I was wondering if the 12 MHz oscillator output could be leaking into the tx amp. I also get a large burst of of RF when the ptt is pressed. I read in earlier posts that they never found a solution to the ptt RF burst problem. I also read that with the diodes and the pot that it was normal to get a 1vpp output at the antenna with no audio input. Would you mind you mind discussing this problem on the land line.  Thank You Bob WB2TFG ex





Re: Three (and a Half) AGC schemes #ubitx-help

Jerry Gaffke
 

One reason to have an AGC system is to prevent a sudden high level signal from being painfully loud.
A pair of back-to-back diodes in the appropriate spot might be sufficient
The diodes will cause the loud signal to distort until the gain knob is twiddled,
but no need to rip off the headphones first.  That may be all we need here.

These radios are very good at receiving sensitive signals, as good as some of the
relatively expensive commercial gear.  But tuning in a strong signal can then
overload it.  One solution to this is an RF gain control, perhaps just a pot in line with the 
antenna signal prior to the first RF amp.  Don Cantrell has described an even easier
alternative on the Bitx40, where he cuts power to the first RF amp:
http://bitxhacks.blogspot.com/2017/01/nd6ts-rf-gain-control-with-tombstoning.html
May not work so well on the uBitx, as the BiDi amps are quite different.

As Henning notes in post https://groups.io/g/BITX20/message/32043
it is the AF preamp (Q16 on the Bitx40, Q70 on the uBitx) with its gain of 46dB that
limits the dynamic range of the receiver. 
So reducing gain in the presence of strong signals should occur before the AF preamp.
Most AGC schemes presented in this forum attenuate after the AF preamp.

The really good AGC schemes detect the signal level back in the RF part of the rig
so they can respond very quickly, before the signal is felt in the audio sections.
This RF detection would have to occur after the 12mhz filter on the Bitx rigs, otherwise
signals you couldn't hear anyway would cause the gain to be reduced.  But if you detect
after the 12mhz filter without careful shielding, you will mostly be detecting the BFO.
For this reason any simple to implement scheme on the Bitx rigs should probably 
be detecting audio and not attempt to detect RF.

So, an adequate solution for many might be back-to back diodes to prevent ear damage,
plus some sort of manual RF gain control to throttle back any strong signals we wish to hear.
Many users might prefer this, as you hear the band as it really is rather than the artificial
compression introduced by AGC.

If AGC is implemented, I think a good compromise on the Bitx rigs would be to detect
after the audio preamp stage, then use that result to attenuate somewhere prior to the audio preamp. 
 
Jerry, KE7ER


On Sun, Feb 25, 2018 at 09:33 pm, K9HZ wrote:

Well I guess the question to ask is what is your goal?  Do you want to maintain a constant audio level with varying signal strength, or do you want to maintain a constant RF/IF/Audio gain in your radio.  They are much different… have much different impact on the radio.  Limiting and compression can occur at any stage.  So far you have demonstrated an audio gain level control.  If you want t TRUR and traditional AGC, you need to start at the front end of the radio to prevent it from over-loading with strong signals.

Re: RD16HHF1 power curve flattening...some

Kelly Jack
 

Bill,

Does this mean that a different compensating capacitor is required for each band   ie. To get the 20w on each band?

Regards

Simon
VK3ELH

Re: Strong carrier on transmit. #bitx40help

 

Bob,

The carrier burst occurs because the c122 is charging up on TX through D15, causing the mixer to unbalance momentarily.

Solution is simple:

Cut the track from D15 and D16 common that goes to R38 and 39 and scrape the green paint off the cut track ends and solder a
0.1uF capacitor. Additionally add a 1K across C107 to provide a DC path.

Raj

Re: RD16HHF1 power curve flattening...some

John <passionfruit88@...>
 

Hello Simon,

My understanding is that the value of the capacitor gives the peak of the very broad resonance. Therefore you choose where to increase the gain the most and select the capacitor accordingly.

73, John (VK2ETA)