Date   
Re: uBitx just started transmitting a loud hum #ubitx-help

Skip Davis
 

Dave are you using shielded cable on your mic? It could be RF getting into the mic circuit. If you are using shielded cable try putting decoupling caps across the mic audio line. 

Skip Davis, NC9O

On Apr 11, 2018, at 06:02, davesters@... wrote:

I had the bitx40 that quit transmitting. The electret mic failed. I didn't get the hum just silence. The replacement mic has given the radio increased power, about 10 watts. 

I wondered if humidity from my breath caused the failure. I like the idea of a voltage spike though. Seems more likely.  Am wondering if I should put a choke between voltage source and load resistor.
Dave
K0MBT

Re: AGC circuit to try?

Dexter N Muir
 

Bill N2CQR ('Soldersmoke') has been using 2 FETs in 'series'/cascode as dual-gates. Jxxx numbers. Bog-standard, readily available. AFAIK good NF, gain-bandwidth etc...

73
Dex, ZL2DEX

Re: AGC Added to uBITx

K4LXY
 

Do you mean R253?
Howard 

Re: POP fix

ve7hcw@...
 

Re: AGC circuit to try?

Kees T
 

Wes Hayward, W7ZOI, also has an article on using dual J-FETs in cascode mode for AGC use.

73 Kees K5BCQ 

Audio pop on CW

K4LXY
 

I think I solved the audio pop problem on CW based on the VE1BWV muting circuit (see uBitx.net)

Earlier I tried this muting circuit, which mutes the audio during transmit, but it also muted the sidetone.

The solution was to use his muting circuit but insert the sidetone on the top side of the volume control, after the muting circuit, instead of earlier in the audio circuit as it was originally.
 
The idea was suggested earlier by Philip as part of his AGC solution (though he incorrectly identified the resistor involved as R235 rather than R253).
 
Here is what I did
Removed R253.
To the end of R235 that was also connected to C252, I added in series a 1K resistor and .1 microfarad capacitor, then going to the yellow wire on the volume control (top).
 
There are two things about my setup that make it different than Philip’s but it should work as suggested above.
 
1) I have a Hi-Per-Mite SCAF after the volume control, and it may provide some amplification.
 
2) Earlier I had replaced R250 with a variable resistor so that I could control the sidetone volume, so I have the option of fine-tuning sidetone volume.
 
73 Howard K4LXY

Re: AGC circuit to try?

ajparent1 <kb1gmx@...>
 

It can be done with 2 Jfets, 2 bipolar if the lower input impedance is useful, or 1 of each (HyCas).
IF one wants to be retro a 12AT7!

They all work.  The two J-fets is really old and appear in ths Allied Radioshack AX-190 from
the early 70s.  Two transistors was over 10 years before.  Hycas actually was in the same
time frame.  HyCas was published as a complete IF with RF derived AGC and it works
very well.

I've used all the chips ua703, MC1550, CA3028 and their variants and follow ons
like the 1350/1590.    They work but require care or you get of what you asked for.
All of them where differential mode is used suffer an increase in noise as agc is
increased.  The exception is maybe the CA3028 as it can be used in cascade
mode as well and  will avoid that.  That noise increase degrades signal quality.

Designs like dual Jfet, Dual gate mosfets like the BFR998 tend to be quieter.
They are more difficult in incorporate in some topologies.  I think they are worth
it.  A high dynamic range receiver puts a very high requirement on succeeding
stages.

Like K9HZ I've built enough high performance radios for hobbe and some commercial
and I have one general comment.  AGC can be an aid to a smooth performing radio.
You can calculate and model it to death, then you build it, most importantly test it
and listen to it.  If it sounds good you done all to often it will not.   Many times its 
easier to do it empirically  cut, try and test.  Right wrong and what I want doesn't
matter if it meets your criteria.  

One thing, filter ripple is hard to hear for most people and unless its more than 6DB 
most will not.  Most commercial filters can easily have 3Db of ripple.  I doubt one
made form less than hand picked parts is much better than that.  I've never made
a satisfactory quality filter without hand picking the crystals for both frequency
and Q and same for the parallel caps.  Data can be picky and not like that but
our ears are not the same (we have different preferences) and we are building
to suit the ears.  


Allison

Re: AGC circuit to try?

Kees T
 

Since dual gate BF998 units are apparently older and either not stocked or obsolete, I would assume the BF2040 is acceptable to try (and inexpensive).

73 Kees K5BCQ 

Re: AGC circuit to try?

Lawrence Galea
 

Also used by DL6WD Rudolf Fischer.
See ARRL Single Sideband for the Radio Amateur 1970 p193 et seq.
"An Engineer's Ham-Band Receiver"
Used in the RF amplifier with 0-60dB manual RF gain control
Regards
Lawrence

On Wed, Apr 11, 2018 at 11:45 AM, Dexter N Muir <dexy@...> wrote:

Bill N2CQR ('Soldersmoke') has been using 2 FETs in 'series'/cascode as dual-gates. Jxxx numbers. Bog-standard, readily available. AFAIK good NF, gain-bandwidth etc...

73
Dex, ZL2DEX


Re: AGC circuit to try?

Jerry Gaffke
 

You can tell the BF998 is an older part because the datasheet identifies it as a "tetrode".
    https://www.mouser.com/datasheet/2/196/bf998series-59603.pdf
Would be very cool to be able to say I have a tetrode front end in my uBitx.


On Wed, Apr 11, 2018 at 12:27 pm, Sandy T wrote:
Since dual gate BF998 units are apparently older and either not stocked or obsolete, I would assume the BF2040 is acceptable to try (and inexpensive).

Re: uBitx just started transmitting a loud hum #ubitx-help

James
 

Skip,
The mic cable was shielded.
I was using the electret that came with the ubitx, and the momentary switch in a custom 3d printed housing (no shielding in the housing) but the longest run of un shielded mic cable is approx 4cm from the audio plug to my jack on the front panel of the case.

As I said, I think the actual electret element failed, as the hum has gone completely when I de-soldered the element and just left bare wires instead.
I'll pick up another electret hopefully in the next 24 hours and see if that solves the problem when transmitting.

Cheers,
James

Re: uBITX shipping time

Paul k9mv
 

Ordered:  Feb. 22, 2018
Shipped:  Apr. 7, 2018
Received:  April 11, 2018  (7 weeks)

Board 0523/4 came with a Youwang UTC2822M audio amp chip.

-Paul  K9MV



Re: AGC circuit to try?

cove37
 

Would this work, changing the matching circuits to the Ubitx IF freq?  (Taken from Texas Instruments AN32 FET Applications)

Re: Audio pop on CW

Bill Carpenter <nz0tham@...>
 

Good work!  I hope that a step by step procedure could be posted for those of us who are schematic/theory challenged.  I can follow step by step instructions ala Heathkit/Elecraft but I totally suck at looking at a schematic and producing a working mod from it.  I love my uBITX but as a CW op that audio pop is a real problem.

73, Bill NZ0T

Re: VK4PLN's Radrino replacement boards

Nick VK4PP
 

HI all.
My apologies, I dont have a complete schematic. I am on holidays now for 2 weeks so should get to doing one up. But the gist is follow the original raduino.
Then follow the BS170 PTT pop fix for that section.
And then there is a simple voltage divider on A6.
A7 is connected to the optional AD8307 meter on the back, 
Ill do up schematics and create a new blog page with all the relevant links and such....

73.
Nick

Re: uBitx just started transmitting a loud hum #ubitx-help

Skip Davis
 

Yes James I read one of your other post where you removed the electret element and the hum went away. Before I read that I was going to suggest that you measure from the element housing (metal part of element) to ground for continuity, but a new electret element should solve you hum problem.

Good luck & let us know how it works,
Skip Davis, NC9O 

On Apr 11, 2018, at 16:47, James <james.manion@...> wrote:

Skip,
The mic cable was shielded.
I was using the electret that came with the ubitx, and the momentary switch in a custom 3d printed housing (no shielding in the housing) but the longest run of un shielded mic cable is approx 4cm from the audio plug to my jack on the front panel of the case.

As I said, I think the actual electret element failed, as the hum has gone completely when I de-soldered the element and just left bare wires instead.
I'll pick up another electret hopefully in the next 24 hours and see if that solves the problem when transmitting.

Cheers,
James

Re: Audio pop on CW

K4LXY
 

Bill
The muting circuit, with photos, is on the uBitx.net site.  I could probably send you photos of my addition.  The schematic is only partially helpful because of the gaps.
If you are interested, take a look at the muting description on uBitx.net, then let me know what more would be helpful.
Howard

Ian Lee KD8CEC integration of SDR demo #ubitx

John <passionfruit88@...>
 

What Ian is working on in his new V1.07 firmware:

https://youtu.be/BlMm4yE4Xaw

73, John (VK2ETA)

Re: AGC circuit to try?

Tim Gorman
 

Any chance you could take a picture of the agc part of that article and
post it?

I gave away both my copies of that book to the local library when I
thought I wouldn't need them any longer!

tim ab0wr

On Wed, 11 Apr 2018 21:38:49 +0200
"Lawrence Galea" <9h1avlaw@...> wrote:

Also used by DL6WD Rudolf Fischer.
See ARRL Single Sideband for the Radio Amateur 1970 p193 et seq.
"An Engineer's Ham-Band Receiver"
Used in the RF amplifier with 0-60dB manual RF gain control
Regards
Lawrence

On Wed, Apr 11, 2018 at 11:45 AM, Dexter N Muir <dexy@...>
wrote:

Bill N2CQR ('Soldersmoke') has been using 2 FETs in
'series'/cascode as dual-gates. Jxxx numbers. Bog-standard, readily
available. AFAIK good NF, gain-bandwidth etc...

73
Dex, ZL2DEX



Re: Audio pop on CW

Bill Carpenter <nz0tham@...>
 

Hi Howard,

Please send me photos of your work.  I have a pretty good idea of what to do but another perspective would help a lot!  My email is nz0tham@....

73, Bill NZ0T