Date   
Re: boosting the power on 28 MHz #ubitx

Daniel Conklin
 

Allison,
Do you have a schematic of your 6 meter radio available to share?

Re: AGC circuit to try?

Jerry Gaffke
 

That MA4VAT2007-1061T  has a little transformer in there.
Datasheet specs it for 1.7ghz to 2.0ghz.

JerryFri, Jun 1, 2018 at 02:41 pm, Michael Shreeve wrote:

I have picked up some of the MA4VAT2007-1061T MACOM SOIC-8 HMIC PIN DIODE VARIABLE ATTENUATOR  . 
If you look them up, you will see that it is a nice balanced dual pin diode attenuator on a chip. I thought it might work in the IF or just about anywhere . Work in progress, but definitely a very interesting chip. 

Re: AGC circuit to try?

Michael Shreeve
 

Yes, may be a problem for lower freq stuff, but I claims its dc to daylight

Re: AGC circuit to try?

Michael Shreeve
 

They say it will work at those frequencies but don't they say it's capable of a wider response. I'll look.

Re: boosting the power on 28 MHz #ubitx

ajparent1/KB1GMX <kb1gmx@...>
 

David the one published in QQ (QRPQuarterly) back in 2006 and was a 1W design SSB only.
I've done 5 others but those are not published and my notebooks while complete are not a
"here build this".

Doing 6m radios are not not going to use many 3904s save for an IF and audio stuff.  Once
you at 6M RF devices suitable are needed.

Allison

Re: AGC circuit to try?

Michael Shreeve
 

Yes Jerry, very narrow. Oh well, shouldn't work.

Re: AGC circuit to try?

Michael Shreeve
 

I have a Swan SS-200 with a perfectly working broadband amplifier, 10 to 15 watts input.200 watt peak out.  Might do pretty well with uBITX as an exciter. I believe it was built before the Tentec !

Re: AGC circuit to try?

Michael Shreeve
 

And it has a jfet front end, the swan that is. Fairly sensitive, but easy to blow with static in a lighning storm, happened once as a mobile. Even has a socket. Meant as a reply to KB1GMX for his enjoyment. 

Re: ND6T AGC implementation for uBIT-X

William Cullison
 

Kees,

Mine came in today. Nice looking boards thanks. Now all I need is to crack a Merlot to steady my hands. Actually I'm looking forward to the challenge. 

73 Bill WA8VIH/4


On Fri, Jun 1, 2018, 20:12 w1eat via Groups.Io <w1eat=yahoo.com@groups.io> wrote:
My AGC uses 3 simple PIN diode shunt attenuators.  An 0.1 cap connects to the circuit board and an MPN3404 goes to ground.  The attachments points I used are the connections between R27/R105, R47/C30 and R17/C216.  An AGC voltage derived from the audio or a manual "RF gain" voltage derived from RX both work fine.

I don't know what the control range is but it must be 40 db at least.  I can make really loud signals disappear.

Tom W1EAT

Re: ND6T AGC implementation for uBIT-X

Michael Shreeve
 

got a diagram I can look at ?


On Fri, Jun 1, 2018 at 5:12 PM, w1eat via Groups.Io <w1eat@...> wrote:
My AGC uses 3 simple PIN diode shunt attenuators.  An 0.1 cap connects to the circuit board and an MPN3404 goes to ground.  The attachments points I used are the connections between R27/R105, R47/C30 and R17/C216.  An AGC voltage derived from the audio or a manual "RF gain" voltage derived from RX both work fine.

I don't know what the control range is but it must be 40 db at least.  I can make really loud signals disappear.

Tom W1EAT




--
Michael Shreeve N6GRG

Re: RF power chain mods and improvements..

ajparent1/KB1GMX <kb1gmx@...>
 

Here is the problem...

There are a few actually.  Improving the amp leads to acknowledging other issues.

The spurs.

SSB CASE only:
For the case of transmit for 15 and 10 M the biltier used has a cutoff over 30Mhz
so effectively the amp will pass though everything it hears.  If you overdrive
the mixers especially the 45mhz output mixer you get two things. The desired
output say 28Mhz you get a second actually two others one at 11.995mhz about
50 to 60 db down and the other at about 17mhz and if the drive is low its 40+ db
down, push the audio and it can be 25db down from carrier out.  The amplifier
having no filtering below 30mhz will gladly amplify all of them and does!  This
is not an issue for 3-about 18mhz as the output low pass filter that are switched
in helps attenuate the spurs.

The math is:

Output is IF(about 45mhz) + LO (48 to 75mhz)= 3 to 30 mhz
The spur case is IF(45mhz) - Output frequency (42 to 15mhz)  Its going down while the dial frequency is going up.

For up to 18mhz the output lo pass filters and the inside 33mhz low pass filter are at work doing the job.
However for 21 and 28 mhz both filters are roughly 33-35mhz cutoff and the spur is now down around
24 and 17 mhz respectively.  They will be about 40-50db down until the 45mhz mixer overloads and
then the spurs get very much stronger at a frequency well below the cutoff of the low pass filters.
Since power output is low on 10M people will likely push the audio and the spur will get significantly
worse.

The is due to the nature of DBMs, they are three port devices and all three can receive input or deliver outputs.
Also inside the mixer all possible sums and differences for the base frequencies  and their harmonics exist.

This was determined without the amp operating by breaking the circuit at C200 for a spectrum analyzer.
We can't blame the amplifier chain  for this as it would just do its designed duty and amplify everything.

Right now I have no solution.  The usual one commercial radios implement is a switched filter 
at the point were L1 though L4 exist (and C200 to c204) and the filter would be for 15M, 12M and 10M.
I'm looking at and for other ideas.

I've stopped work on the amp (I've had success but the spur took me on a divergent path) till a
solution can be had.

This does not show up in CW mode as the way the radio is keyed there is no 45mhz contribution.

Allison

Re: AGC circuit to try?

Jerry Gaffke
 

Not all that narrow. 
1.7-2.0 GHz means it's 300 mhz wide.
That's plenty.
Unfortunately does not cover 3.5-30 mhz.


On Fri, Jun 1, 2018 at 07:49 pm, Michael Shreeve wrote:
Yes Jerry, very narrow. Oh well, shouldn't work.

Re: AGC circuit to try?

Jerry Gaffke
 

OK,
I didn't see mention of anything below 1.7ghz.
But didn't look very hard.


On Fri, Jun 1, 2018 at 07:41 pm, Michael Shreeve wrote:
Yes, may be a problem for lower freq stuff, but I claims its dc to daylight

FLdigi

Dennis
 

I have wsjt-x working fine, but I can't transmit using FLdigi. Receive works ok. Could someone share their settings with me?

73, Dennis
W7DRW

Re: RF power chain mods and improvements..

Jerry Gaffke
 

Allison, many thanks for looking into that.

The nasty spur is not a problem from 3.5mhz up to 18mhz.
So for operators that never use the 15, 12 and 10 meter bands, this is not of concern.
For many of us, a $129 rig that covers 80-17 meters is still a very good deal.

For those wishing to use the rig above 18mhz, perhaps some sort of external band-pass
or high-pass filter is in order between the uBitx and the antenna.
Some (but not all) antenna tuners might be sufficient.

If the audio from the mike amp is kept reasonable, Allison reports that the spur is 40+ dB down.
I assume it should be 43 dB below our primary signal, so it's marginal at best.
But we might avoid the worst of this problem by somehow monitoring the transmit signal level
at the mixers.  Allison has found that gain with the 2n3904's can vary on the upper bands
depending on your particular device characteristics, so it currently is not sufficient to just
check the level at one point in the chain.  However, if gains can be made more predictable,
perhaps monitoring at the top of RV1 using a diode RF probe is sufficient?
 
The uBitx has a 30mhz low pass filter between the mixers and the power amp at 
As Allison says, most multiband rigs would have switched bandpass filters in that position.
Signals are quite low level, could probably be done with analog switches rather than relays.
So yet another possibility is to add a daughterboard with switched bandpass filters to 
replace the filter at L1,2,3,4.  We only need 3 or 4 filters there and parts can be small and cheap,
so not so bad.

The spur is at the first IF frequency of 45mhz minus the operating frequency.
If the first IF is raised from 45mhz to 70mhz or more, that should remove the spur for all
frequencies from 3.5 to 30mhz.  Will definitely require something better than the 2n3904's
within that 70mhz IF strip.

Anybody see any other possible solutions?

Jerry, KE7ER



On Fri, Jun 1, 2018 at 08:18 pm, ajparent1/KB1GMX wrote:
Here is the problem...

There are a few actually.  Improving the amp leads to acknowledging other issues.

The spurs.

SSB CASE only:
For the case of transmit for 15 and 10 M the biltier used has a cutoff over 30Mhz
so effectively the amp will pass though everything it hears.  If you overdrive
the mixers especially the 45mhz output mixer you get two things. The desired
output say 28Mhz you get a second actually two others one at 11.995mhz about
50 to 60 db down and the other at about 17mhz and if the drive is low its 40+ db
down, push the audio and it can be 25db down from carrier out.  The amplifier
having no filtering below 30mhz will gladly amplify all of them and does!  This
is not an issue for 3-about 18mhz as the output low pass filter that are switched
in helps attenuate the spurs.

The math is:

Output is IF(about 45mhz) + LO (48 to 75mhz)= 3 to 30 mhz
The spur case is IF(45mhz) - Output frequency (42 to 15mhz)  Its going down while the dial frequency is going up.

For up to 18mhz the output lo pass filters and the inside 33mhz low pass filter are at work doing the job.
However for 21 and 28 mhz both filters are roughly 33-35mhz cutoff and the spur is now down around
24 and 17 mhz respectively.  They will be about 40-50db down until the 45mhz mixer overloads and
then the spurs get very much stronger at a frequency well below the cutoff of the low pass filters.
Since power output is low on 10M people will likely push the audio and the spur will get significantly
worse.

The is due to the nature of DBMs, they are three port devices and all three can receive input or deliver outputs.
Also inside the mixer all possible sums and differences for the base frequencies  and their harmonics exist.

This was determined without the amp operating by breaking the circuit at C200 for a spectrum analyzer.
We can't blame the amplifier chain  for this as it would just do its designed duty and amplify everything.

Right now I have no solution.  The usual one commercial radios implement is a switched filter 
at the point were L1 though L4 exist (and C200 to c204) and the filter would be for 15M, 12M and 10M.
I'm looking at and for other ideas.

I've stopped work on the amp (I've had success but the spur took me on a divergent path) till a
solution can be had.

This does not show up in CW mode as the way the radio is keyed there is no 45mhz contribution.

Allison

Re: FLdigi

Ashhar Farhan
 

which firmware are you using? 
- f

On Sat, Jun 2, 2018 at 10:41 AM, Dennis <dennis@...> wrote:
I have wsjt-x working fine, but I can't transmit using FLdigi. Receive works ok. Could someone share their settings with me?

73, Dennis
W7DRW


Re: RF power chain mods and improvements..

Kelly Jack
 

Not a solution but if the uppermost lpf is not going to be used could it be rengineered for 160m?

Re: RF power chain mods and improvements..

Gordon Gibby <ggibby@...>
 

A lot of people use a T- type tuner to connect to their feedline; these might provide a bit of filtering of the lower undesired frequency.


On Jun 2, 2018, at 01:38, Kelly Jack <kellyjack1968@...> wrote:

Not a solution but if the uppermost lpf is not going to be used could it be rengineered for 160m?

Re: RF power chain mods and improvements..

Jerry Gaffke
 

Move to a high side VFO.
Can be done by just switching to USB mode.

I believe all firmware to date uses a low side vfo, at 45mhz - OperatingFrequency.
when in LSB mode.
This was done so that the BFO was low side, to avoid interference with Nano oscillators.
If that's an issue, I think it is easily tamed.

Jerry

µBITX Disable TC (use for CW training)

Hans Stoll
 

Hi,

I would like to use the keyer in µBITX to for some CW excercises with a paddle but I don't want to transmit (or use a dummy load) so is it possible to disable TX while using CW and just listen to the side tone?

73