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Re: BITX attenuator

 

Rafel,

See my comments below:

On 17-03-2017 22:35, Rafa? Lichwa?a wrote:
Hi Peter,
Thanks for this forwarded message!
So I noticed my first mistake: crystal filter has ~200 ohms Zin/Zout -
not 50, as I thought before.
Ok, so that means, attenuator has right Zin/Zout, but there is an
impedance mismatch between 1st AMP (just right after LPF) and mixer.
This AMP translates 50 ohms of the LPF to ~200 ohms, but mixer expects
50 ohms. Maybe that's why we can notice much improvement in the way
BITX works, when we remove that 1st AMP completely - then mixer has 50
ohms on all ports.
But I don't understand two things:

Second the terminal impedance of the crystal filter and the various
RF/IF amplifiers were optimized for 200 ohms the mixers are better at
50 ohms and there is no impedance matching to correct for that.
Yes, the lack of matching keeps the circuit simple but you pay the price of less than the best achievable performance from this circuit. In the real world you will need to measure and compare the results of both matched and unmatched circuits to see the performance difference and keep in mind that often what looks good on paper does not translate into a large practical (real world) difference, ie; the improvement may not be worth the added complexity.
Why mixers are better at 50 ohms?
I thought there is not much difference in mixing for different
impedances on mixer ports, but the point is to keep them EQUAL on each
port (nevermind if it is 50 ohm or 200 ohms - mixer will work fine as
long as those impedances are equal on each port). Is that correct?
When I saw this question it caused me to think about how I have been using DBM's for many years now. In truth I have never considered operating them at impedance's other than 50 ohms, all the books and circuits said 50 ohms so thats what I did. However, (I am not into the basic physics of these things) my understanding is that for the DBM to be effective the diodes need to be switched hard on/off as quickly as possible. It seems to me that it is probably easier to achieve this if the DBM is being driven from a low impedance source which ensures maximum current flow through the diodes.
And second thing: why RF/IF are optimized for 200ohms?
You should ask the designer, Farhan is active on this group ask him.

As it was explained by the author of that project, each AMP translates
impedance: 50ohms -> 220ohms and 220ohms -> 50ohms (for resistances
used in the circuit).
So I think there is no mismatch anywhere except this one between 1st
RF AMP and mixer. Is that correct?
That is not my understanding of how the bi-lateral amps work, again talk to Farhan.

Additional question at the end: is that a good idea to use ADE-1 (SMD
level 7 double balanced mixer) instead of those 1n4148 diodes and
"manual" transformers?
This link was posted by a member of our group in the past and compares the performance of various DBM's. I was very happy to see that the homemade 1N4148 DBM's performed so well against the commercial DBM's. Of course you will have to be careful in how you build the homemade DBM, match the diodes and be careful with the transformers but if you do a good job the results can be quite good. See link below:



Regards,
Rafal SP3GO
Best regards,

Peter VK1XP

18/03/2017
Re: Fixing the galloping VFO problem

 

Thanks, that one worked.

Roy
WA0YMH

On Mar 17, 2017 7:31 PM, "Art Olson" <olson339@...> wrote:
Repost of link


Art

Sent from my iPhone

On Mar 17, 2017, at 7:23 PM, Roy Appleton <twelveoclockhigh@...> wrote:

Bad link to YouTube video.

Roy
WA0YMH

On Mar 17, 2017 4:40 PM, "KE0OG" <casler28@...> wrote:

The VFO's "feature" of galloping up or down in 10kHz increments when the Raduino's VFO pot hits the stop is driving me crazy.

I made a fix, picture attached<AD50 dwg small.png>. Also a video at??I may be reinventing the wheel here. Anyway, this goes in the YAM category (yet another mod).

73, Dave, KE?OG,

Re: Fixing the galloping VFO problem

 

¿ªÔÆÌåÓý

Repost of link


Art

Sent from my iPhone

On Mar 17, 2017, at 7:23 PM, Roy Appleton <twelveoclockhigh@...> wrote:

Bad link to YouTube video.

Roy
WA0YMH

On Mar 17, 2017 4:40 PM, "KE0OG" <casler28@...> wrote:

The VFO's "feature" of galloping up or down in 10kHz increments when the Raduino's VFO pot hits the stop is driving me crazy.

I made a fix, picture attached<AD50 dwg small.png>. Also a video at??I may be reinventing the wheel here. Anyway, this goes in the YAM category (yet another mod).

73, Dave, KE?OG,

Re: Rotary Encoder and latest sketch

Graham
 

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Jack,

Thank you posting these two files. I was just starting to work my way down the path of integrating a rotary encoder into my project.

Ashar's use of pot and ADC as a control for frequency is a very good bit of creative lateral thinking. Very simple and sometimes simple is all you need. I will have to spend some time playing with the idea.

However, I think perhaps I would prefer a rotary encoder but perhaps using a pot and ADC to implement a RIT function may work well. Nothing ventured, nothing gained.


cheers, Graham ve3gtc


On 2017-03-17 19:46, Jack Purdum via Groups.Io wrote:

I just uploaded:


and


which are the rotary encoder articles I wrote for QRP Quarterly. Perhaps those will help.

Jack, W8TEE


From: N7PXY <hickspj467@...>
To: [email protected]
Sent: Friday, March 17, 2017 3:11 PM
Subject: [BITX20] Rotary Encoder and latest sketch

I am very confused. I find several sketches and many references to using an encoder for tuning. Is there a set of complete instructions for installing an encoder (where to hook it up to which raduino pins etc.) and can someone point me to the latest sketch that incorporates code to operate the encoder? I am very shaky and inexperienced with Arduino IDE and programming and need some hand holding.

PJH
Re: Fixing the galloping VFO problem

 

Bad link to YouTube video.

Roy
WA0YMH

On Mar 17, 2017 4:40 PM, "KE0OG" <casler28@...> wrote:

The VFO's "feature" of galloping up or down in 10kHz increments when the Raduino's VFO pot hits the stop is driving me crazy.

I made a fix, picture attached. Also a video at??I may be reinventing the wheel here. Anyway, this goes in the YAM category (yet another mod).

73, Dave, KE?OG,

Re: Bad arduino board

 

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I just designed an had PCBs made for tiny (.6x.8") 5351 board.? It has 2 four pin connectors for power and I2C and then

output on the other side.??? I now have 40 oscillator modules?? I only built one, worked the first time.

?

So, you would be SURPRISED on soldering in that little fellow.

Flux and some small solder braid and it went in like a breeze?? You need small tipped iorn and tweezers.

Some of the pins shorted, but you wipe the braid while heating outwardly.

Actually the tiny crystal was a bigger problem.? You have to put VIA holes so you? can solder from the reverse side.

Taking of the 5351 just use braid and iron tip.? Clean it up nice with braid and then alcohol for the replacement?

Give it a try!? Mouser has the parts.

My Bitx40 is on the way!

Mike, WA6ISP

On 3/17/2017 1:50 PM, Brian Lewis wrote:

So Mark and I are having the exact same no receive problem. I've reprogrammed my nano thinking maybe something was amiss but that didn't help. Mark replaced his 5351 board including the nano with a known good part and now his works. Is there any way to replacement for these boards? ?There's no way I can replace the smd 5351 chip which I believe to be the culprit. ? Brian
Re: Changing frequency display

M Garza
 

Simple and elegant solution.? I like how this works.? Seeing it in action, it makes more sense.? Time to get some push button switches.

Marco - KG5PRT?

On Mar 17, 2017 5:04 PM, "Michael Davis" <maddmd818@...> wrote:
This is what I tried to explain. Thanks to Dave Casler KE0OG. See

Sent from Mike's iPad WA1MAD
Re: QRP Labs Low Pass Filters

 

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Steve,

I just entered the L and C values that QRP Labs lists for the 20 meter LPF into AADE filter Design.? The analysis shows only a .03 dB loss at 14.5 MHz and doesn¡¯t exceed 1.5 dB until above 15.5 MHz.? I suspect you¡¯ll have to measure and tweek your toroids to get close to the values that QRP Labs calls out for their 20 meter filter.

Mike

K5ESS

?

From: [email protected] [mailto:[email protected]] On Behalf Of Steve Hunt
Sent: Friday, March 17, 2017 4:51 PM
To: [email protected]
Subject: Re: [BITX20] QRP Labs Low Pass Filters

?

Hans - thanks for that. Maybe I just got unlucky with a combination of capacitor and toroid Al tolerances. I think I've seen the figure of 10% quoted by Micrometals for the Type-6 material.

?

Steve G3TXQ
Re: Changing frequency display

Michael Davis
 

This is what I tried to explain. Thanks to Dave Casler KE0OG. See

Sent from Mike's iPad WA1MAD
Re: QRP Labs Low Pass Filters

 

Hans - thanks for that. Maybe I just got unlucky with a combination of capacitor and toroid Al tolerances. I think I've seen the figure of 10% quoted by Micrometals for the Type-6 material.


Steve G3TXQ
Re: QRP Labs Low Pass Filters

 

Hi Steve

I don't think that there is any design error. Most of the band designs come originally from the G-QRP technical pages, which in turn got the component values from the legendary design by Ed Whetherhold W3NQN. The exception to this are the bands 2200m, 600m, 60m, 4m, 2m and 222MHz which are all added later.?

Over 30,000 of the QRP Labs LPF kits are in use in 69 countries and normally without any issues.?

It's a great and reasonably repeatable design. Sharper filters or filters with fewer poles can be built. But this design can usually be built successfully by people without access to exotic test equipment, just by counting turns and installing the right components in the right places.?

That said - there will always be some variations in component tolerances, and winding style, and even the complete measurement system. If you think the cut-offs are uncomfortably close to the band edges then I suggest just removing a turn or two from each inductor.

73 Hans G0UPL?
?
Fixing the galloping VFO problem

KE0OG
 

The VFO's "feature" of galloping up or down in 10kHz increments when the Raduino's VFO pot hits the stop is driving me crazy.

I made a fix, picture attached. Also a video at??I may be reinventing the wheel here. Anyway, this goes in the YAM category (yet another mod).

73, Dave, KE?OG, youtube.com/davidcasler
QRP Labs Low Pass Filters

 

I wonder if anyone in the group has experience with QRP Labs Low Pass Filter kits? I recently built 10 of them - one for each band 160m thru 10m - and found that on some bands the "knee" of the filter response is very close to the upper band edge. It's particularly bad on 20m and 12m where the tops of the bands are at a point 1.5dB down the filter slope.


I've checked and double-checked the capacitor values and the number of turns on the inductors; I've also spaced the turns on the toroids carefully so as to minimize the inductance. But -1.5dB is the best I can achieve at the 20m and 12m upper band edges. Measurements were made using a 2-port VNA and checked with a TG/SA.


I guess I can reduce the number of turns on the inductors, but wondered if anyone else has experienced the same thing, and if it is a design error?

Steve G3TXQ
Re: Bad arduino board

Mark Underkofler
 

Brian,

I'm going to replace the 25mHz crystal on the SI5351 board and see if that's the culprit. ?If so, I'll let you know. ?I had to order 5 of them so if it works I'll send you one to try.

Mark W5MCU
Bad arduino board

Brian Lewis
 

So Mark and I are having the exact same no receive problem. I've reprogrammed my nano thinking maybe something was amiss but that didn't help. Mark replaced his 5351 board including the nano with a known good part and now his works. Is there any way to replacement for these boards? ?There's no way I can replace the smd 5351 chip which I believe to be the culprit. ? Brian
Re: Changing frequency display

Michael Davis
 

Thanks Dr Fred. I have never messed with the raduino. Changing a sketch scares me. I do need to learn more about how to read the file/sketch save the file and modify the file.
Maybe I didn't explain my simple method very well. Part 1. A 25-50 ohm resistors in series with each outer potentiometer tab to green and another resistor in series to yellow. That would prevent the fast frequency change from engaging (I assume), since the center/violet would never "see" a direct (low or 0 ohms resistance) connection to either yellow or green raduino point. Part 2. A momentary push button switch from the center/purple pot tab to the raduino yellow wire and another to the raduino green wire. This would replicate the full turn, 0 ohms, of the pot CW or CCW. No ground to any of these connections (on purpose anyway) Simple? Work? I hope so. Part 3. A 3 turn or 10 turn pot? We'll see, stay tuned.

Sent from Mike's iPad WA1MAD
Re: Bias Setting?

 

You might look here: ??/g/BITX20/message/22764

and maybe here: ??/g/BITX20/message/21027

Others have posted DC voltages, such as this file ? /g/BITX20/files/K7AGE/BITX40%20Voltage%20Measurments.pdf? from this post ?/g/BITX20/message/23583?

LTSpice is a very cool tool when figuring out this stuff, and is free to download. ?I haven't figured out how to get it to work properly for time domain plots of high Q circuits using quartz crystals yet.

Jerry, KE7ER

On Fri, Mar 17, 2017 at 01:28 pm, Nathern Priddy wrote:

I used a 100 MHz scope to measure the peak voltage across a 50W Bird dummy load.? The peak voltage is about 10 volts which equates to about 1 W of output power.? I had a friend listen to my signal and he said it was clear but very weak.

Any suggestions about where to look?

?
Bias Setting?

[email protected]
 

I just completed my BIT40X and can only get about 1 Watt of RF out.? I turned the bias adjust pot fully clockwise and read a current of about 200 ma from the power supply.? The instructions say it shoud be near zero ma and increase as you turn the pot counterclockwise.

I used a 100 MHz scope to measure the peak voltage across a 50W Bird dummy load.? The peak voltage is about 10 volts which equates to about 1 W of output power.? I had a friend listen to my signal and he said it was clear but very weak.

Any suggestions about where to look?

The receiver portion works just fine on 40 meters.? Having no AGC will take a little getting used to.? Hi Hi

Barry - K5VIP
Re: Rotary Encoder and latest sketch

Jack Purdum
 

I just uploaded:


and


which are the rotary encoder articles I wrote for QRP Quarterly. Perhaps those will help.

Jack, W8TEE


From: N7PXY <hickspj467@...>
To: [email protected]
Sent: Friday, March 17, 2017 3:11 PM
Subject: [BITX20] Rotary Encoder and latest sketch

I am very confused. I find several sketches and many references to using an encoder for tuning. Is there a set of complete instructions for installing an encoder (where to hook it up to which raduino pins etc.) and can someone point me to the latest sketch that incorporates code to operate the encoder? I am very shaky and inexperienced with Arduino IDE and programming and need some hand holding.

PJH
New file uploaded to [email protected]

[email protected] Notification
 

Hello,

This email message is a notification to let you know that a file has been uploaded to the Files area of the [email protected] group.

File: PurdumRotaryEncodersRevisited.doc

Uploaded By: Jack Purdum

Description:
The second rotary encoder article that features Fast Tune for frequency changes.

You can access this file at the URL:
/g/BITX20/files/PurdumRotaryEncodersRevisited.doc

Cheers,
The Groups.io Team
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