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

Mark K0ABD
 

Hello All,

Even though I may not be making a uBitx, I have learned a lot over the last couple of days. I copied these most important messages to my HAM text file.

With more study, I can probably answer many of my questions on my own. I have a list of material that is "next up" for me to absorb.

Books & articles are nice. Yet, there is nothing like having access to a community of people who have traversed the path, & are willing to share their experiences.

You have been very kind to me. :)

I don't want to keep distracting you all with these questions & comments that are obviously far below your level of expertise.

I'd rather not tie-up the groups.io/g/BITX2 anymore, that is devoted to BiTx, with basic questions about antennas.

Right now I'm searching groups.io for other amateur radio groups to join, using these key words: amateur radio; HAM; antennas; QRP; etc.

Who knows, maybe I'll be communicating with some of you.

HAMs are a great bunch.

Thanks!

Mark

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

Mark K0ABD
 

Hi Tim,

There most definitely has been. I did not expect such support!

In addition to learning about antennas, it might be a good idea for me to get more familiar with some of these terms. It's like learning a different language.

Mark

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

MVS Sarma
 

Chris,
Any thing couild be used. IMHO, Simopler circuitry bring better stability.
Just for sake of modding we don't have to.
RegaRDS
 SARMA
 VU3ZMV

Regards
MVS Sarma
 

On Mon, Feb 26, 2018 at 5:04 PM, <DF1EA@...> wrote:
Hello,

look here : http://www.qrpproject.de/Media/pdf/Mosquita40.pdf.

The tranceiver use a TCA440 / A244 as audio preamp with gaincontrol. It should be possible to use the audio part in the ubitx.

73 de df1ea, Chris!


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

DF1EA@...
 

Hello,

look here : http://www.qrpproject.de/Media/pdf/Mosquita40.pdf.

The tranceiver use a TCA440 / A244 as audio preamp with gaincontrol. It should be possible to use the audio part in the ubitx.

73 de df1ea, Chris!

Re: Strong carrier on transmit. #bitx40help

Allard PE1NWL
 

Alternatively, install the latest Raduino sketch which eliminates the RF-burst by software:
https://github.com/amunters/bitx40

73 Allard PE1NWL

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

John <passionfruit88@...>
 

Thanks Jerry for that information.

I have a better understanding of the constraints and benefits of IF AGC now.

My personal preference when listening on speakers is for a strong AGC where the volume is pretty constant and the noise is simply "pushed down" on the reception of strong stations.

I agree that for headphone operations a simple limiter is useful and sufficient.

In line with what you say about the location of the AGC in my experiments I did connect the drain of the 2N7000 to the base of Q70 via a resistor and capacitor but I must have had too much gain in the loop and created massive audio feedback, and just dismissed that option.

I also read on the internet that distortion can be reduced if the audio voltage is small, so I definitely need to re-visit that option.

Thanks and 73s, John (VK2ETA)

I want to know when uBITX is coming ? (Invalid address)

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: Bansong Road 177 (205-1104) Hyundai Apartment
Changwon City Seongsan-gu, Gyeongsangnam-do
51425
Republic of Korea.


Please let me know when you arrive.







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) 

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

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: 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: 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: 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: 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)


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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)


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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)

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: 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.


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: 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)


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