|
Looking at the circuit, I see R1 simply is fed with full RF at the top, but relatively weak RF from the first amplifier in the transmitter. I'll measure the voltage, but its simple, ? the wiper sends however much RF you need on to the rest of the output circuit. If this control could be mounted on the panel of the radio, you would have a transmit power control. But, it might not be good to take it off the board.?
This is done, if you look , right at the output of the first rf amplifier Q90 and RV1 passes the rf along to the input of a couple of dc direct coupled 2n3904s . Some sort of RF attenuator after rv1 would do the trick, and control voltage from a bridge swr detector could control that. I'm guessing the Circuit Don uses, or part of it, the AGC, could be modified To control RF when it detects a lot of voltage from a swr bridge. Then you would have what swan calls a "ALC" !
On Sun, Apr 29, 2018 at 2:44 PM, Arv Evans <arvid.evans@...> wrote: Jerry
Instead of using AD8307 Log Detectors, have you considered just adding a bit of forward
bias to the diode detectors?? Conventional SWR bridges do not do this because they
usually do not have access to DC power, but in this application there is power available
inside the BITX case.
Arv
_._
|
Michael,
The Q90 and RV1 you refer to are definitely in the uBitx schematic.
I'm not finding R1 except in the Tandem Match here:??
Is that the R1 you are referring to??
Probably not, as it is not fed with "weak RF from the first amplifier of the transmitter"
An attenuator around RV1 is certainly a good choice for adjusting output power, effective for both CW and SSB.
For SSB, this attenuator could be most anywhere, all the way back to the mike.?
Perhaps an audio AGC circuit or speech compressor between mike and rig?
Have you found Swan's ALC to be a useful feature?
In what way??
Jerry
toggle quoted message
Show quoted text
On Sun, Apr 29, 2018 at 05:32 pm, Michael Shreeve wrote:
Looking at the circuit, I see R1 simply is fed with full RF at the top, but relatively weak RF from the first amplifier in the transmitter. I'll measure the voltage, but its simple, ? the wiper sends however much RF you need on to the rest of the output circuit. If this control could be mounted on the panel of the radio, you would have a transmit power control. But, it might not be good to take it off the board.?
?
This is done, if you look , right at the output of the first rf amplifier Q90 and RV1 passes the rf along to the input of a couple of dc direct coupled 2n3904s . Some sort of RF attenuator after rv1 would do the trick, and control voltage from a bridge swr detector could control that. I'm guessing the Circuit Don uses, or part of it, the AGC, could be modified To control RF when it detects a lot of voltage from a swr bridge. Then you would have what swan calls a "ALC" !
?
|
Jerry you wrote ¡°Don is well aware how cheap this crowd is.¡± I take offense to this remark. Just because we purchased this rig doesn¡¯t mean we are all cheap. If you have paid much attention to the board offerings many have requested more than one. These are great learning platforms for experimenting with hardware and software without a large investment and if it gets fried or firmware bricked it doesn¡¯t cost a fortune to fix or replace.
Skip Davis, NC9O
toggle quoted message
Show quoted text
On Apr 29, 2018, at 16:41, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Don is well aware how cheap this crowd is.
|
My apologies to anyone who did not find that humorous.
Here's a smiley face? ? ;-)? to show I was not intending to insult.
That post was triggered in part by Kees' kind offer to provide kits
at what looks like might be a ridiculously low price.
|
Low price is the name of the game. ...and I for one, think it's fun.? After all, copper wire was invented by two Dutchmen fighting over a penny .......and I'm Dutch. The AGC board is ready to go for build and Don, ND6T, and I are cleaning up some details on the "RX/TX Click Noise Elimination" board and his "Polite Antenna Tuner" board. I can post a PDF of the AGC board if you want......25mm x 25mm......but I have to figure out how to "step and repeat" the design so I can get 16 on a 100mm x 100mm panel .....and NOT have the component identifiers change.
73 Kees K5BCQ
|
https://jlcpcb.com/ has the option to do multiple PCBs on a 100x100 plate....
I have used them with great success.
73
|
Ah, where you say "R1", you meant to say "RV1".
Still curious how desirable you have found Swan's ALC to be.
toggle quoted message
Show quoted text
On Sun, Apr 29, 2018 at 05:58 pm, Jerry Gaffke wrote:
Michael,
The Q90 and RV1 you refer to are definitely in the uBitx schematic.
I'm not finding R1 except in the Tandem Match here:??
Is that the R1 you are referring to??
Probably not, as it is not fed with "weak RF from the first amplifier of the transmitter"
An attenuator around RV1 is certainly a good choice for adjusting output power, effective for both CW and SSB.
For SSB, this attenuator could be most anywhere, all the way back to the mike.?
Perhaps an audio AGC circuit or speech compressor between mike and rig?
Have you found Swan's ALC to be a useful feature?
In what way??
Jerry
. . .
?
On Sun, Apr 29, 2018 at 05:32 pm, Michael Shreeve wrote:
Looking at the circuit, I see R1 simply is fed with full RF at the top, but relatively weak RF from the first amplifier in the transmitter. I'll measure the voltage, but its simple, ? the wiper sends however much RF you need on to the rest of the output circuit. If this control could be mounted on the panel of the radio, you would have a transmit power control. But, it might not be good to take it off the board.?
?
This is done, if you look , right at the output of the first rf amplifier Q90 and RV1 passes the rf along to the input of a couple of dc direct coupled 2n3904s . Some sort of RF attenuator after rv1 would do the trick, and control voltage from a bridge swr detector could control that. I'm guessing the Circuit Don uses, or part of it, the AGC, could be modified To control RF when it detects a lot of voltage from a swr bridge. Then you would have what swan calls a "ALC" !
?
|
toggle quoted message
Show quoted text
On Sun, Apr 29, 2018, 5:58 PM Jerry Gaffke via Groups.Io <jgaffke= [email protected]> wrote: Michael,
The Q90 and RV1 you refer to are definitely in the uBitx schematic.
I'm not finding R1 except in the Tandem Match here:??
Is that the R1 you are referring to??
Probably not, as it is not fed with "weak RF from the first amplifier of the transmitter"
An attenuator around RV1 is certainly a good choice for adjusting output power, effective for both CW and SSB.
For SSB, this attenuator could be most anywhere, all the way back to the mike.?
Perhaps an audio AGC circuit or speech compressor between mike and rig?
Have you found Swan's ALC to be a useful feature?
In what way??
Jerry
On Sun, Apr 29, 2018 at 05:32 pm, Michael Shreeve wrote:
Looking at the circuit, I see R1 simply is fed with full RF at the top, but relatively weak RF from the first amplifier in the transmitter. I'll measure the voltage, but its simple, ? the wiper sends however much RF you need on to the rest of the output circuit. If this control could be mounted on the panel of the radio, you would have a transmit power control. But, it might not be good to take it off the board.?
?
This is done, if you look , right at the output of the first rf amplifier Q90 and RV1 passes the rf along to the input of a couple of dc direct coupled 2n3904s . Some sort of RF attenuator after rv1 would do the trick, and control voltage from a bridge swr detector could control that. I'm guessing the Circuit Don uses, or part of it, the AGC, could be modified To control RF when it detects a lot of voltage from a swr bridge. Then you would have what swan calls a "ALC" !
?
|
Swan felt the power output should be lowered if the SWR was high in these early solid state transceivers from the 70s.
On Sun, Apr 29, 2018, 8:50 PM Jerry Gaffke via Groups.Io <jgaffke= [email protected]> wrote: Ah, where you say "R1", you meant to say "RV1".
Still curious how desirable you have found Swan's ALC to be.
On Sun, Apr 29, 2018 at 05:58 pm, Jerry Gaffke wrote:
Michael,
The Q90 and RV1 you refer to are definitely in the uBitx schematic.
I'm not finding R1 except in the Tandem Match here:??
Is that the R1 you are referring to??
Probably not, as it is not fed with "weak RF from the first amplifier of the transmitter"
An attenuator around RV1 is certainly a good choice for adjusting output power, effective for both CW and SSB.
For SSB, this attenuator could be most anywhere, all the way back to the mike.?
Perhaps an audio AGC circuit or speech compressor between mike and rig?
Have you found Swan's ALC to be a useful feature?
In what way??
Jerry
. . .
?
On Sun, Apr 29, 2018 at 05:32 pm, Michael Shreeve wrote:
Looking at the circuit, I see R1 simply is fed with full RF at the top, but relatively weak RF from the first amplifier in the transmitter. I'll measure the voltage, but its simple, ? the wiper sends however much RF you need on to the rest of the output circuit. If this control could be mounted on the panel of the radio, you would have a transmit power control. But, it might not be good to take it off the board.?
?
This is done, if you look , right at the output of the first rf amplifier Q90 and RV1 passes the rf along to the input of a couple of dc direct coupled 2n3904s . Some sort of RF attenuator after rv1 would do the trick, and control voltage from a bridge swr detector could control that. I'm guessing the Circuit Don uses, or part of it, the AGC, could be modified To control RF when it detects a lot of voltage from a swr bridge. Then you would have what swan calls a "ALC" !
?
|
Not wishing to stray off topic, but has anyone tried this fix by? DF3FY?? Nigel. 
|
It's an international fact that hams are called a cheap gang, but when you go into their shack you are usually impressed with their vast collection. My memories of constantly repairing equipment for hams and only getting a thank you kinda confirms the title tho. ?So let's just say we always get the biggest bang for our bucks. Bo W4GHV since '54
|
Wonder how much is tied up in this shack (W9EVT)? 
Jack, W8TEE
On Monday, April 30, 2018, 8:59:02 AM EDT, Bo Barry <wn4ghv@...> wrote:
It's an international fact that hams are called a cheap gang, but when you go into their shack you are usually impressed with their vast collection. My memories of constantly repairing equipment for hams and only getting a thank you kinda confirms the title tho. ?So let's just say we always get the biggest bang for our bucks. Bo W4GHV since '54
|
Cheapskate only has one chair! ? I have two.
|
toggle quoted message
Show quoted text
On Thu, Apr 26, 2018 at 9:32 PM, Kees T <windy10605@...> wrote: Got the "OK" from Don and Ion so let me see what I can come up with and the schematics and board layout look fine to me. The only thing I would change is make C7 a 1uF cap. This will be a SMT board
73 Kees K5BCQ
|
Haven't tried it, but here's a few things I see from an inspection of the schematic:
1)?
Like most other AGC schemes here, the attenuation occurs after the audio pre-amp at Q70.?
The audio pre-amp will distort at high signal levels, reducing the dynamic range available.?
The ND6T hack avoids this by putting the attenuation up front at incoming RF.
2)
He adds a 200 ohm resistor to prevent power supply noise from getting into the TDA2822, worth trying.
3)
He adds a 1nF cap across pins IN+ and IN-? of the TDA2822,?the attenuation increases
as the 2n7002 turns off and allows the IN- pin to float away from AC ground.
That's much different than other schemes we have seen.?
I'm not sure of any advantages or disadvantages.
4)
There's an "R up to 1k for gain and hiss reduction of TDA2822", which likewise allows the IN- pin
to float away?from AC ground.? This would determine the maximum gain, about the same as limiting
how far you could turn the volume control.
5)
He's driving the speaker directly from the CW sidetone generator rather than applying that
sidetone to the input of the TDA2822.? This would drastically reduce the sidetone audio level.
Jerry, KE7ER
toggle quoted message
Show quoted text
On Mon, Apr 30, 2018 at 05:48 am, Nigel G4ZAL wrote:
Not wishing to stray off topic, but has anyone tried this fix by?DF3FY??
|
....? ?and he's too cheap to add a Bitx to the collection.
(that was humorous)
toggle quoted message
Show quoted text
On Mon, Apr 30, 2018 at 06:21 am, Bo Barry wrote:
Cheapskate only has one chair! ? I have two.
|
Nigel, the diagram to showed of DF3FY¡¯s circuit is a thump/ pop fix and not an AGC circuit. Also on the original schematic posted by Farhan R253 was 1K and has been changed to a 220K resistor to reduce the side tone level. If you were to build this circuit into your¡¯s you would need to adjust the value of R253 for sidetone level if CW interests you.
toggle quoted message
Show quoted text
On Apr 30, 2018, at 11:38, Jerry Gaffke via Groups.Io < jgaffke@...> wrote: ....? ?and he's too cheap to add a Bitx to the collection. (that was humorous) On Mon, Apr 30, 2018 at 06:21 am, Bo Barry wrote:
Cheapskate only has one chair! ? I have two.
|
On Sun, Apr 29, 2018 at 08:15 pm, Nick VK4PLN wrote:
Thanks for the input, Nick. That is the outfit I've been using .....EasyEDA. It's the same company as Jlcpcb. Can you give me some instructions (offline) on where to look. 73 Kees K5BCQ K5BCQ@...
|
Ah, you are correct.
That's T/R feeding it, not audio.
And the title "rx-tx pop fix" should have been a clue for me.
However, it should be possible to simultaneously use something like that as both AGC and pop fix.
Jerry
toggle quoted message
Show quoted text
On Mon, Apr 30, 2018 at 08:52 am, Skip Davis wrote:
Nigel, the diagram to showed of DF3FY¡¯s circuit is a thump/ pop fix and not an AGC circuit. Also on the original schematic posted by Farhan R253 was 1K and has been changed to a 220K resistor to reduce the side tone level. If you were to build this circuit into your¡¯s you would need to adjust the value of R253 for sidetone level if CW interests you.
|
I like ND6T's approach. For the moment
I built the audio attenuation version changing the design to work
with the parts I have on hand, and to add an analog S meter
output. My audio amp failed (this was my fault, not the bad part
problem, I have the V3 board with the socket). Not having a
replacement IC, I used the LM380 I have here. I made a short
jumper cable to go between the IC socket and the AGC board. I am
planning to add a tuned preamp in front of the uBitx later, and
will probably incorporate a version of the RF agc control with
that. I attached the schematic for my version. The second opamp is
a log amplifier to drive the S meter.
Howard
On 4/30/2018 12:16 PM, Jerry Gaffke via Groups.Io wrote:
toggle quoted message
Show quoted text
Ah, you are
correct.
That's T/R feeding it, not audio.
And the title "rx-tx pop fix" should have been a clue for me.
However, it should be possible to simultaneously use something
like that as both AGC and pop fix.
Jerry
On Mon, Apr 30, 2018 at 08:52 am, Skip Davis wrote:
Nigel, the diagram to showed of DF3FY¡¯s circuit is a
thump/ pop fix and not an AGC circuit. Also on the original
schematic posted by Farhan R253 was 1K and has been changed to a
220K resistor to reduce the side tone level. If you were to
build this circuit into your¡¯s you would need to adjust the
value of R253 for sidetone level if CW interests you.
|
Michael Shreeve
Skip Davis
Nick VK4PP