Topics

UBITX TX level diagramme

Henning Weddig
 

All,

in preparing my talk to be held at the "UKW-Tagung" in Weinheim Germany next Saturday about my UBITX I prepared a level diagramme with some assumptions: the maximum powe rlevel at the input of a mixer is in the range of -1 dBm (near the 1 dB compression point?)

The result is intersting: als Allison already stated the gain of the TX stage after the first mixer is 48 dB under these assumptions. My guess is that "normally" a lower level (-10 dBm) will do better in respect of IMD resulting in nearly 60 dB of gain!

Another guess for the resultant spurs observed at higher output frequencies: the bidi amp (45 MHz) is not free of harmonics, i.e. also can and will produce harmonics! If true, these harmonics could be easily removed by introducing a low pass filter between the mixer ("45 MHz port") and the mixer itself. Who can and will try this mod?

Henning Weddig

DK5LV

MadRadioModder
 

Thanks for doing this. The diagram is very informative (need this diagram for the uBITx too). You are correct but a BPF (not LPF) after the mixer is probably better since the mixer is where most of the real nasty harmonics originate...

-----Original Message-----
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Henning Weddig via Groups.Io
Sent: Sunday, September 2, 2018 2:46 PM
To: BITX20@groups.io
Subject: [BITX20] UBITX TX level diagramme

All,

in preparing my talk to be held at the "UKW-Tagung" in Weinheim Germany next Saturday about my UBITX I prepared a level diagramme with some
assumptions: the maximum powe rlevel at the input of a mixer is in the range of -1 dBm (near the 1 dB compression point?)

The result is intersting: als Allison already stated the gain of the TX stage after the first mixer is 48 dB under these assumptions. My guess is that "normally" a lower level (-10 dBm) will do better in respect of IMD resulting in nearly 60 dB of gain!

Another guess for the resultant spurs observed at higher output
frequencies: the bidi amp (45 MHz) is not free of harmonics, i.e. also can and will produce harmonics! If true, these harmonics could be easily removed by introducing a low pass filter between the mixer ("45 MHz
port") and the mixer itself. Who can and will try this mod?

Henning Weddig

DK5LV






---
This email has been checked for viruses by AVG.
https://www.avg.com



--
…_. _._

ajparent1/KB1GMX
 

On Sun, Sep 2, 2018 at 12:45 PM, Henning Weddig wrote:
The result is intersting: als Allison already stated the gain of the TX stage after the first mixer is 48 dB under these assumptions. My guess is that "normally" a lower level (-10 dBm) will do better in respect of IMD resulting in nearly 60 dB of gain!
Doesn't sound at all correct.  Since the mixer output is in the near -20dbm you need 60db of gain to
achieve +40DBm (10W).   I believe I've been saying at least 60db is the target for some time.  What we get is
far less but that an amplifier design issue. FYI most that get maybe 1.7w at 10M are getting far less maybe 48-50db
at 10M.

Most level 7 mixers for "clean" (quoted as they are never pure or clean) output need an input 10db less than
the LO drive minus the insertion loss of the mixer.  So we start at 7dbm (or up to 10 dbM) of LO and that means
input max is -3dbm -another 7db for the mixer loss or minus 10dbm (-10).  Than another 2-4db loss for a
bandpass filter if done right so you at -14.  So you can if lucky get away with 54 db of gain but you need a
tiny bit more for losses and errors.  That is idealized sometimes  you can push the mixer harder, but you
get more unwanted products.

uBitx case is more complicated as you have ground currents inducing signals where they should not be
and a lack of filters to scrub the output.  Now add to that a output low pas filter system that is compromised
by layout.  Now you have a mix of signals that should not be there at all mixing with those that should be
plus excess gain in the IF to overdrive the RF starved ( I measured not more than 3dbm at the mixer) mixer,
output contains a lot of not mathematically predicted outputs because there are inputs not recognized like
a sample of what the power amp is putting out ( coupling though incidental and current loops).

So for a simple 3.5mhz output the mixer may have 45mhx, 48mhz, 3.5mhz, 7mhz, 14mhz, and on
with unpredictable levels and those are the likely inputs the output products are .[...]  many!

Now I did try a 45mhz low pass and it helped a little, less than 6db.  Reason was simple you
have unpredictable paths (ground currents, DC supply lines with RF...) you cannot stop.  But
some are also the nature of the DBM and cannot be filtered with a low pass filter.  An example
of that is the 2IF (90mhz) mixing with the LO (we will use 28Mhz) of 73mhz to get both 28mhz
output and 90-73 or 17mhz.  A low pass cannot prevent the 17mhz if it is to pass 28mhz.  Also
the existing 33mhz low pass reflects sum products back the mixer so figure all the possible
sums returning to the mixer.

Remember a DBM is both a 4 quadrant multiplier and a chopped sampling system the products
out suggest both as its linear and no linear.  With clean 45mhz you still get diode limited and
squared 45mhz with harmonics circulating internally.

In short you have to map all the possible signals that may exist and their unwanted return
paths and then do the matrix of sums and differences for the fundamentals and their harmonics.

IT made my head hurt and spurtune went nuts listing all of them though the 11th order.

By then levels are no longer an issue.

Allison

ajparent1/KB1GMX
 

MRM,

An example of a DBM radio and oldie is the Atlas180 and friends (210, 215 210x...).
a really simple radio once you cut to the bone.

They use band pass filters for RX and TX pre-power amp and low pass post amp
to take out harmonics.  It was the standard of the day and still is.  

So is the case for bitx20V1, Bitx17, bitx40 and other variations and flavors.
Filter using band pass you get clean, low pass is not adequate filtering save
for harmonics.

Allison

MadRadioModder
 

That’s why I mentioned it.  And yes, most radios do have bandpass filters at intermediate stages for the very reason we are seeing a problem in the uBITx.

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of ajparent1/KB1GMX
Sent: Sunday, September 2, 2018 4:46 PM
To: BITX20@groups.io
Subject: Re: [BITX20] UBITX TX level diagramme

 

MRM,

An example of a DBM radio and oldie is the Atlas180 and friends (210, 215 210x...).
a really simple radio once you cut to the bone.

They use band pass filters for RX and TX pre-power amp and low pass post amp
to take out harmonics.  It was the standard of the day and still is.  

So is the case for bitx20V1, Bitx17, bitx40 and other variations and flavors.
Filter using band pass you get clean, low pass is not adequate filtering save
for harmonics.

Allison


Virus-free. www.avg.com

--

…_. _._

Lawrence Galea
 

Hi Allison
You said that ( I measured not more than 3dbm at the mixer) mixer, which shows not enough rf drive.
Ever thought of adding a small amplifier for more rf drive to the mixer with suitable padding to maintain the required drive and impedance?
Possibly this could cause more spurii and more carrier leakage due to the board layout, but do you think it is worth a try?
Regards
Lawrence


On Sun, Sep 2, 2018 at 11:40 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
On Sun, Sep 2, 2018 at 12:45 PM, Henning Weddig wrote:
The result is intersting: als Allison already stated the gain of the TX stage after the first mixer is 48 dB under these assumptions. My guess is that "normally" a lower level (-10 dBm) will do better in respect of IMD resulting in nearly 60 dB of gain!
Doesn't sound at all correct.  Since the mixer output is in the near -20dbm you need 60db of gain to
achieve +40DBm (10W).   I believe I've been saying at least 60db is the target for some time.  What we get is
far less but that an amplifier design issue. FYI most that get maybe 1.7w at 10M are getting far less maybe 48-50db
at 10M.

Most level 7 mixers for "clean" (quoted as they are never pure or clean) output need an input 10db less than
the LO drive minus the insertion loss of the mixer.  So we start at 7dbm (or up to 10 dbM) of LO and that means
input max is -3dbm -another 7db for the mixer loss or minus 10dbm (-10).  Than another 2-4db loss for a
bandpass filter if done right so you at -14.  So you can if lucky get away with 54 db of gain but you need a
tiny bit more for losses and errors.  That is idealized sometimes  you can push the mixer harder, but you
get more unwanted products.

uBitx case is more complicated as you have ground currents inducing signals where they should not be
and a lack of filters to scrub the output.  Now add to that a output low pas filter system that is compromised
by layout.  Now you have a mix of signals that should not be there at all mixing with those that should be
plus excess gain in the IF to overdrive the RF starved ( I measured not more than 3dbm at the mixer) mixer,
output contains a lot of not mathematically predicted outputs because there are inputs not recognized like
a sample of what the power amp is putting out ( coupling though incidental and current loops).

So for a simple 3.5mhz output the mixer may have 45mhx, 48mhz, 3.5mhz, 7mhz, 14mhz, and on
with unpredictable levels and those are the likely inputs the output products are .[...]  many!

Now I did try a 45mhz low pass and it helped a little, less than 6db.  Reason was simple you
have unpredictable paths (ground currents, DC supply lines with RF...) you cannot stop.  But
some are also the nature of the DBM and cannot be filtered with a low pass filter.  An example
of that is the 2IF (90mhz) mixing with the LO (we will use 28Mhz) of 73mhz to get both 28mhz
output and 90-73 or 17mhz.  A low pass cannot prevent the 17mhz if it is to pass 28mhz.  Also
the existing 33mhz low pass reflects sum products back the mixer so figure all the possible
sums returning to the mixer.

Remember a DBM is both a 4 quadrant multiplier and a chopped sampling system the products
out suggest both as its linear and no linear.  With clean 45mhz you still get diode limited and
squared 45mhz with harmonics circulating internally.

In short you have to map all the possible signals that may exist and their unwanted return
paths and then do the matrix of sums and differences for the fundamentals and their harmonics.

IT made my head hurt and spurtune went nuts listing all of them though the 11th order.

By then levels are no longer an issue.

Allison

MVS Sarma
 

Lawrance,
 are you using uBITX  with BAT54S as mixer diodes ?
If you used 1n4148, then your tests could be valid.
regards
sarma
vu3zmv


On Mon, Sep 3, 2018 at 6:59 PM Lawrence Galea <9h1avlaw@...> wrote:
Hi Allison
You said that ( I measured not more than 3dbm at the mixer) mixer, which shows not enough rf drive.
Ever thought of adding a small amplifier for more rf drive to the mixer with suitable padding to maintain the required drive and impedance?
Possibly this could cause more spurii and more carrier leakage due to the board layout, but do you think it is worth a try?
Regards
Lawrence


On Sun, Sep 2, 2018 at 11:40 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
On Sun, Sep 2, 2018 at 12:45 PM, Henning Weddig wrote:
The result is intersting: als Allison already stated the gain of the TX stage after the first mixer is 48 dB under these assumptions. My guess is that "normally" a lower level (-10 dBm) will do better in respect of IMD resulting in nearly 60 dB of gain!
Doesn't sound at all correct.  Since the mixer output is in the near -20dbm you need 60db of gain to
achieve +40DBm (10W).   I believe I've been saying at least 60db is the target for some time.  What we get is
far less but that an amplifier design issue. FYI most that get maybe 1.7w at 10M are getting far less maybe 48-50db
at 10M.

Most level 7 mixers for "clean" (quoted as they are never pure or clean) output need an input 10db less than
the LO drive minus the insertion loss of the mixer.  So we start at 7dbm (or up to 10 dbM) of LO and that means
input max is -3dbm -another 7db for the mixer loss or minus 10dbm (-10).  Than another 2-4db loss for a
bandpass filter if done right so you at -14.  So you can if lucky get away with 54 db of gain but you need a
tiny bit more for losses and errors.  That is idealized sometimes  you can push the mixer harder, but you
get more unwanted products.

uBitx case is more complicated as you have ground currents inducing signals where they should not be
and a lack of filters to scrub the output.  Now add to that a output low pas filter system that is compromised
by layout.  Now you have a mix of signals that should not be there at all mixing with those that should be
plus excess gain in the IF to overdrive the RF starved ( I measured not more than 3dbm at the mixer) mixer,
output contains a lot of not mathematically predicted outputs because there are inputs not recognized like
a sample of what the power amp is putting out ( coupling though incidental and current loops).

So for a simple 3.5mhz output the mixer may have 45mhx, 48mhz, 3.5mhz, 7mhz, 14mhz, and on
with unpredictable levels and those are the likely inputs the output products are .[...]  many!

Now I did try a 45mhz low pass and it helped a little, less than 6db.  Reason was simple you
have unpredictable paths (ground currents, DC supply lines with RF...) you cannot stop.  But
some are also the nature of the DBM and cannot be filtered with a low pass filter.  An example
of that is the 2IF (90mhz) mixing with the LO (we will use 28Mhz) of 73mhz to get both 28mhz
output and 90-73 or 17mhz.  A low pass cannot prevent the 17mhz if it is to pass 28mhz.  Also
the existing 33mhz low pass reflects sum products back the mixer so figure all the possible
sums returning to the mixer.

Remember a DBM is both a 4 quadrant multiplier and a chopped sampling system the products
out suggest both as its linear and no linear.  With clean 45mhz you still get diode limited and
squared 45mhz with harmonics circulating internally.

In short you have to map all the possible signals that may exist and their unwanted return
paths and then do the matrix of sums and differences for the fundamentals and their harmonics.

IT made my head hurt and spurtune went nuts listing all of them though the 11th order.

By then levels are no longer an issue.

Allison

ajparent1/KB1GMX
 

MRM,

The not so funny part Is I've been saying that for over two years and especially the last two months.

The whole idea of minimally filter 3-30 mhz radio is wishful thinking.  When I first said that
it was "you need to think outside the old box", when I mentioned it will not behave well I was told 
"you don't know what your talking about".  So I shut up for a while and waited for the stuff to
hit the fan.  

I for one would like the concept to work save for over 50 years of radio engineering... it never does.


Allison

ajparent1/KB1GMX
 

Lawrence G.,

I tried a few things along that path.  made matters worse and that was also tried with
external level 7 mixer and level 17 external mixers.   It was then a rock fell on me
and I realized the output of the 45mhz amp with the TX producing power was filthy.
Add a filter module it got better but by then I had so many outboard modules
its was almost a breadboard radio.  Everything is talking to everything by sneak
paths.  

Allison
We need only one magik part.

ajparent1/KB1GMX
 

Henning,

There are errors in the diagram and the levels are really different than shown.

Looked at your diagram and its assumptions are wrong.  If the final mixer can accept -1dbm without
producing spurs then why start with -16dbm at the very first (balanced modulator)?

The input to the balanced modulator would be around -10dbm(audio) an that bumps up the levels 6db.
The problem with the pad at the output is that and the filter (about 8db total) reduce the carrier to signal
ratio by that amount (not allowing for bad layout causing blow by).  Excess gain makes it worse.

Having input to the final mixer  of more than -10dbm causes great amounts of distortion and spurs.
So at that point you are showing about 9db of excess gain.  Also the assumption is the mixers have
enough drive.  When I tested the 5351 was set to 1,1,1 or 4ma (factory code) and at 3,3,3 or 8ma I
did get the stated 13dbm but exceeded to the total current for three outputs if I understand the spec. 
That is only part of that story, for the moment.

So we are both under driving one and over driving mixers and hoping for a good result.  
The output of the last mixer should be around -17dbm (+-2db) for a 7dbm input, about
7db loss and a -10 dbm input.

the two TIA amps the 12mhz nearly hits the 20db mark (actual on 2 were 19) and at
45mhz not even close maybe 14db mine measured 13db.  Good thing too or the
over drive would be worse.

I The filter is before Q90! that means Q90 is part of the power amp chain.  Than means
there is a gain block before the pre-driver and driver missing in the drawing.

Also the design gain of the amp is 3 stages (Q90 through q97) of 16++ db per stage and
1 stage of  about 13db my match says that is 61db and most seem  to do that at 3.5 and
maybe 7mhz.  After that the gain falls by easily 11db to 10M.  So the diagram does not
match the actual.

FYI the second bidirectional amp is not shown (post 45mhz fitler and before last mixer)

The line up should be 45mhz fitler, 45mhz bidirectional amp, mixer, 33mhz low pass fitler, then Q90 tx preamp.

Allison
Being PDF I cannot edit the drawing it does have errors.

Lawrence Galea
 

Thanks Allison
Regards

On Mon, Sep 3, 2018 at 7:41 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
Lawrence G.,

I tried a few things along that path.  made matters worse and that was also tried with
external level 7 mixer and level 17 external mixers.   It was then a rock fell on me
and I realized the output of the 45mhz amp with the TX producing power was filthy.
Add a filter module it got better but by then I had so many outboard modules
its was almost a breadboard radio.  Everything is talking to everything by sneak
paths.  

Allison
We need only one magik part.

Glenn
 

Allison, is this the drawing (pdf) referred to?   Attached .BMP copy could be amended with MS Paint.



glenn

ajparent1/KB1GMX
 

To low res to blow it up to 200% and at the current size its really poor (fuzzy) to read.

I'll sketch it on paper and shoot a picture if I get time.  Either that or start all over in Impress.


Allison

Giancarlo
 

Hi Glenn,

I have not been following 100% the group. Is n RX Level Diagram available?

Thanks and 73

Gian
I7SWX

Henning Weddig
 

All,
 
as I have problems to upload the pdf files  into Groups io I send them directly to the Group as an attachment. So let´s hope they will come throug!
 
Henning
DK5LV
 
-----Ursprüngliche Mitteilung-----
Von: Giancarlo via Groups.Io <i7swx@...>
An: BITX20 <BITX20@groups.io>
Verschickt: Di, 4. Sept 2018 13:11
Betreff: Re: [BITX20] UBITX TX level diagramme

McAfee-Webkontrolle – Warnung
Diese E-Mail-Nachricht enthält potenziell unsichere Links zu den folgenden Sites:
http://ubitx.net/- weitere Informationen...
Hi Glenn,

I have not been following 100% the group. Is n RX Level Diagram available?

Thanks and 73

Gian
I7SWX