Re: Finding an AGC circuit with fast/slow attack
Somewhen in the past there was a version of the SL621 AGC circuit
made with individual transistors.? Try searching the RSGB handbook
or tech topics.
Cheers,
William
On 03/09/2017 08:38 AM, Doug - via
Groups.Io wrote:
toggle quoted message
Show quoted text
Chuck,
? I am very interested in an AGC circuit for the BITX40. I have
already installed a new audio output amp - LM386 - that works
substantially better but on strong signals and a good antenna
there is distortion from some point onboard. Having to ride the
volume is a pain in the you know what. I was looking at my
radio-engineer handbook and one of the AGC circuits they show
uses the Plessy Sl621 AGC chip. I doubt it is still available
but if it was it would make things very simple. Google it, the
PDF data is still out there. This uses audio to establish AGC
that could be applied in some way to probably Q1 on the BITX
board.
|
Added a Wiki Cheat Sheet to help anyone that may want to contribute to the Wiki. Bottom topic on the first page.
James
|
Re: Finding an AGC circuit with fast/slow attack
Chuck, ? I am very interested in an AGC circuit for the BITX40. I have already installed a new audio output amp - LM386 - that works substantially better but on strong signals and a good antenna there is distortion from some point onboard. Having to ride the volume is a pain in the you know what. I was looking at my radio-engineer handbook and one of the AGC circuits they show uses the Plessy Sl621 AGC chip. I doubt it is still available but if it was it would make things very simple. Google it, the PDF data is still out there. This uses audio to establish AGC that could be applied in some way to probably Q1 on the BITX board.
|
|
|
Just curious, what does the serial number tell you?
|
I bought a wall wart, cheep when if first got my BITX40.. from ALLELECTRONICS.COM because-- always a because --it was cheep, had the power connector on it and-----AND--- I also needed to order other items for my build ---and ALLECLECTONICS.COM had them.. Matching knobs both 1/8 and 1/4 diameter for the pots, a speaker, and other odds and ends.. such a 12MHz crystals 4 for a $1....which I will experiment with the BITX40. They have a flat rate shipping so.. The point I am making is that I've been using that wall wart since...you can't but the parts to build one for what I got this.. Besides if I get ambitious, venturing further, a battery based system would be in order..
|
Re: uBITX - A reboot of the old BITX
PDF will be best for home brewing Regards Lawrence
On Tue, Mar 7, 2017 at 1:25 PM, John VA7JBE via Groups.Io <va7jbe@...> wrote: As much as I'd love to see a kit for the uBitX released it may not be feasible in the immediate future.? Instead it might be more realistic to create and release things like PCB gerber files, BOMs, and Kicad project files to make it easier for new homebrewers to tinker with the schematic and layout.? Different files for SMD and through hole components would be relatively simple to do.? There will undoubtedly be people who release their own files, as has happened with the BitX20, but having a foundation to work from would be a great start for those who don't have much experience with these things.
|
Re: uBITX - A reboot of the old BITX
Farhan jee,
Except the first mixer that handles 45MHz with 57MHz carrtier, ?others could be almost compatible. ?you , I suppose , need to give specifics of trafos of 1st mixer only. regards ?sarma ?vu3zmv
On Wed, Mar 8, 2017 at 11:04 AM, Ashhar Farhan <farhanbox@...> wrote: That's about right. Been busy with lamakaan anniversary.. i will post the values after confirming them in the prototype builds.
- f
|
The serial number is difficult to read but looks like 43-228. Randy Hall <listk7age@...> wrote: Hi What is your serial number. It is written on the main board. Randy, K7AGE
On Tue, Mar 7, 2017 at 5:53 PM, km4wii via Groups.Io <km4wii@...> wrote: My bitx40 just arrived. Ordered 2/12 delivered 3/7.? Too bad there's a halfway this weekend. Maybe I'll get some build time Sunday afternoon. Wish me luck!
|
No problem Simon,
Now its good time at Melbourne for a beer or to try another hack on bitx40.
Try this:
1. Power the audio stages directly by connecting 12V line to the junction of R111, R113 and D18.
Now you will hear your own voice during TX and we need to mute it.
2. Take a 2N7000 or similar and connect SOURCE to ground, DRAIN to the top of the volume control (M1/M2).
feed the TX 12V through a 10K or nearby value to the gate.
This should mute the amp during TX.
If this works for you then remove the diode D18!
Caveat: I have not tried it as I am at the coffee farm this week. Itching to get back to my board but it will be Monday next!
While in TX mode some RF might get into the amp stage and be just as annoying.
Then we have to work more on that! A 0.01 across the volume control might fix this if it happens.
Cheers
Raj
toggle quoted message
Show quoted text
At 08/03/2017, you wrote: Raj
It appears I have misunderstood what this mod is trying to achieve from the start.
Thankyou for your explanations.
Regards
Simon VK3ELH
|
Raj
It appears I have misunderstood what this mod is trying to achieve from the start. Thankyou for your explanations.
Regards?
Simon VK3ELH?
|
Simon,
This hack does not address the sound in the BITX40 speaker. This is entirely a different issue.
In my unit the power meter would deflect to more than 500mW when the PTT is pressed. IF I listened to my commercial RX I could hear a
"clonk/tong" sound. After the mod the meter barely moves.
What I am trying to do is not allow the C122 to charge via the diode. C122 BLOCKS the DC from getting to the diode but the cap charge current goes through to the diode when PTT is pressed. You need to put a 1K resistor parallel to C107 to route this current to ground.
If the mic amp had 2 stages and if the second stage is always powered on then there will be no problem.
AFAIK in a 4 diode mixer this wont happen as there are two diodes that will conduct and cancel any carrier leak in the trifilar transformer.
The amp pop would have not been there if it was left powered on but the audio was muted in a stage before it. Farhan has kept BITX40
as simple as possible. We can make it more elaborate in design if we wish.
If the audio pop is to be removed then keep the amp powered on and use a 2n7000 across the volume control and mute it on TX.
toggle quoted message
Show quoted text
At 08/03/2017, you wrote: Raj
I checked the balance using my scope. The balance didnt seem to need any adjustment and the leakage measured the same as without the cap.
The cap was 0.1uf.
While a current burst through the diode unbalancing the mixer makes sense as an explanation for this I still don't understand why a 0.1uf cap in series would block the current flow if c122 wouldn't.
I really would like to find a solution to my ptt pop as I find it to be too unpleasant for headphone use.
Regards
Simon VK3ELH
|
Re: uBITX - A reboot of the old BITX
That's about right. Been busy with lamakaan anniversary.. i will post the values after confirming them in the prototype builds.
- f
On 8 Mar 2017 10:52 a.m., "tdelozie via Groups.Io" <tdelozie= [email protected]> wrote: Nice AndyH. Let me correct myself, playing with shows that the nH and 1.1 uH values are a poor choice for FT 37-43.?
|
Raj I checked the balance using my scope. The balance didnt seem to need any adjustment and the leakage measured the same as without the cap. The cap was 0.1uf. While a current burst through the diode unbalancing the mixer makes sense as an explanation for this I still don't understand why a 0.1uf cap in series would block the current flow if c122 wouldn't.
I really would like to find a solution to my ptt pop as I find it to be too unpleasant for headphone use.
Regards?
Simon VK3ELH?
|
Re: uBITX - A reboot of the old BITX
Nice AndyH. Let me correct myself, playing with www.toroids.info shows that the nH and 1.1 uH values are a poor choice for FT 37-43.?
|
Re: uBITX - A reboot of the old BITX
On Mon, Mar 6, 2017 at 07:02 am, Ashhar Farhan wrote: The inductor values are in the schematic. You can calculate the turns from - f
Ashhar, Here's my first attempt from posts, the schematic, and from your web text. ?Please confirm T1 thru T11 and the choice of 26 AWG. ?Please also provide winding details for T5 and T6, and T10 and T11. Thanks sir!
|
|
Core |
Color |
|
Turns |
|
|
| T1 |
|
FT 37-43 |
Black |
|
8:8:8 trifilar |
8 turns/inch |
26 AWG |
| T2 |
|
FT 37-43 |
Black |
|
8:8:8 trifilar |
8 turns/inch |
26 AWG |
| T3 |
|
FT 37-43 |
Black |
|
8:8:8 trifilar |
8 turns/inch |
26 AWG |
| T4 |
|
FT 37-43 |
Black |
|
8:8:8 trifilar |
8 turns/inch |
26 AWG |
| T5 |
|
FT 37-43 |
Black |
4:1 |
|
|
|
| T6 |
|
FT 37-43 |
Black |
4:1 |
|
|
|
| T7 |
|
FT 37-43 |
Black |
|
8:8:8 trifilar |
8 turns/inch |
26 AWG |
| T8 |
|
FT 37-43 |
Black |
|
8:8:8 trifilar |
8 turns/inch |
26 AWG |
| T9 |
|
FT 37-43 |
Black |
|
8:8:8 trifilar |
8 turns/inch |
26 AWG |
| T10 |
|
FT 37-43 |
Black |
|
|
? |
|
| T11 |
|
FT 37-43 |
Black |
8T:10T |
|
|
|
|
|
|
|
|
Calculated: toroids.info/T37-6php |
| L1 |
330 nH |
T 37-6 |
Yellow |
|
10.5 |
|
|
| L2 |
390 nH |
T 37-6 |
Yellow |
|
11.4 |
|
|
| L3 |
390 nH |
T 37-6 |
Yellow |
|
11.4 |
|
|
| L4 |
330 nH |
T 37-6 |
Yellow |
|
10.5 |
|
|
|
|
|
|
|
|
|
|
| L5 |
720 nH |
T 37-6 |
Yellow |
|
15.5 |
|
|
| L6 |
720 nH |
T 37-6 |
Yellow |
|
15.5 |
|
|
| L7 |
720 nH |
T 37-6 |
Yellow |
|
15.5 |
|
|
|
|
|
|
|
|
|
|
| L8 |
60 uH |
FT 37-43 |
Black |
|
13.1 |
|
|
| L9 |
60 uH |
FT 37-43 |
Black |
|
13.1 |
|
|
|
|
|
|
|
|
|
|
| L10 |
360 nH |
T 37-6 |
Yellow |
|
11.0 |
|
|
| L11 |
1.1 uH |
T 37-6 |
Yellow |
|
19.1 |
|
|
| L12 |
180 nH |
T 37-6 |
Yellow |
|
7.7 |
|
|
| L13 |
1.0 uH |
T 37-6 |
Yellow |
|
18.3 |
|
|
| L14 |
360 nH |
T 37-6 |
Yellow |
|
11.0 |
|
|
| L15 |
1.1 uH |
T 37-6 |
Yellow |
|
19.1 |
|
|
|
Re: uBITX - A reboot of the old BITX
Craig, Taking a good look at the picture of a built version on??,my eyes tell me that?toroidal cores are used for the inductors and transformers. My understanding is that inductors wound on toroids are superior but more expensive and can also be wound to desired value. Also 43 looks like a good material for the frequencies and powers used in both these cases. If you don't have one already than this could be a good excuse to by one of the neat LCD meters available. http://www.banggood.com/GM328-M328-LCD-Backlight-Digital-Transistor-Tester-p-961337.html
http://www.amidoncorp.com/product_images/specifications/2-03.pdf
|
A question for the UK guys.
What sort of delivery times are you experiencing? I have to be in UK around 23-25 of March. Thinking that might not be enough time if ordered now.
Thanks
Martin, HS0ZED
|
College Professor Simon Thompson
A good power supply always makes a big difference to the way a radio operates; I think the Bitx40 is a great opportunity to build a power supply, with a big capacitor and a line filter and a transformer and everything! I am building one right now out of spare parts from the junk drawer.
toggle quoted message
Show quoted text
On Mar 7, 2017, at 6:40 PM, vk3xl via Groups.Io < vk3xl@...> wrote:
You will prpobably need something that can deliver about 1.5A at 12v well regulated. I dont think a wallwart would be good enough. I have used various power supplies with mine. 12v bench supply, 14.1v LIfe battery, 19.5v laptop power supply and a benchtop supply at 28V. In all cases I have ?a 12v regulator inside the ?case to power the board and raduino and the seperate (high voltage) goes to the final. Effectively I can power my BitX40 form any supply between 12v and 28v and everything works. at 28v I get a bit over 20w output. at 12v I get about 5w output.
--
Mike VK3XL
|
OK Simon,
What I had not mentioned is that the carrier balance pot needs to be re adjusted. Listen to the carrier leak in a near by Rx and adjust for a
minimum or scope the output after removing the mic connector and adjust the 106 for minimum carrier.
Make sure the series cap you put is not more than 0.1uF.
toggle quoted message
Show quoted text
At 08/03/2017, you wrote: Raj
I cut the track beteween the wiper of r106 and r38 and confirmed the break with my multimeter. Then put the cap across that break.
The reference in my earlier post to "path to ground" was refering to the path through the diode and then on through r39, ie the path we are putting the cap in series with.
Regards
Simon VK3ELH
|
Raj vu2zap