There is also the outstanding, yet related, issue with switching sidebands on CW (i.e. CWU to CWL or vice versa) with KD8CEC's code which I had?
previously documented.?
Try this on any commercial rig ....
Properly tune in a CW station and then switch to CWR or whatever the "other" CW sideband is called on your
rig ... you can still hear the station. That is the whole point. Switching back and forth doesn't alter your TX frequency it only changes the BFO/offset
so that you are listening on the other side of true Zero-beat (i.e. the other side of his carrier frequency).? This is a "trick" used by CW operators to avoid QRM as often
you can manage to avoid a loud station QRMing your QSO by just listening to your intended station on the opposite sideband. You should always be able to switch
back and forth without touching the tuning knob, assuming that you have the station tuned in properly.?
Currently when you switch sidebands on CW on the KD8CEC software both your TX and RX frequencies change so not only can you not hear the other
station you were working, he can't hear you anymore either !??
I would be nice if it was possible to submit bug requests again the KD8CEC software within GITHUB itself. GITHUB supports this but it seems that this
option is somehow not enabled for?.?
There seems to be no "official" channels for reporting real bugs against this software so getting things fixed is a bit "hit or miss".?
Not to be totally negative, Ian has done some great stuff and he has responded to many of my suggestions and implemented features and fixes
that I suggested. The problem is that it seems that this list has way too much traffic for any one person to stay on top of everything discussed.?
Cheers
Michael VE3WMB?
|
Gordon. we have people with their extra that can't figure out how to connect the key to their radio (not just bitx radios, commercial too). How do you figure they're able to detect their band edges on USB and LSB? Yeah, it was on the test, but so many people cram for a test and forget everything the second they finish taking it.
Vince - K8ZW.
toggle quoted message
Show quoted text
On 09/03/2018 09:07 AM, Gordon Gibby wrote: 9h1avlaw?
of course you risk outof band transmissions if you aren't at least able
to recognize which WAY your sideband is going, and how close to the band
edge you are.....exactly the same is true of upper side band and lower
sideband voice opeeration.
We expect people with the General class or higher license class to
understand those sideband type pesky issues...in fact, it is a question
or two in the exam packet! and if you were to use FM...or AM....then
you have sidebands on BOTH sides.....so if you're going to be a RADIO
amateur you need to understand just a bit about MODULATION.....
Cheers, my friend!
gordon
------------------------------------------------------------------------
*From:* [email protected] <[email protected]> on behalf of Lawrence Galea
<9h1avlaw@...>
*Sent:* Monday, September 3, 2018 8:57 AM
*To:* [email protected]
*Subject:* Re: [BITX20] CW OPERATION
If you are near the band edge you risk out of band transmissions
On Mon, Sep 3, 2018 at 4:35 AM Gordon Gibby <ggibby@...
<mailto:ggibby@...>> wrote:
You can do it the other way around, with the transmitter upset, but
then you have to be absolutely certain that the user knows that
their transmissions are offset from the dial number.
That¡¯s not terrible, that¡¯s exactly what happens when you¡¯re doing
upper or lower sideband, and certainly when you¡¯re doing pseudo CW
by injecting an pure audio sinewave signal into a single side band
system. FLDIGI will do that, and you can even rig it so your
computer shows your correct transmitting frequency
On Sep 2, 2018, at 22:31, Jim Tibbits <ab7vf1@...
<mailto:ab7vf1@...>> wrote:
Gotta offset, can't hear em on the carrier
On Sun, Sep 2, 2018 at 7:01 PM W2CTX <w2ctx@...
<mailto:w2ctx@...>> wrote:
__
Found this video explaining CW Zero-beating. So based on this
explanation the following is illustrated
for 7.040.000: Dial displays 07.040.000, you transmit on
07.040.000, and the receive is offset by the
sidetone value.
Of course this is based on the video being correct.
<>
rOb
--
Michigan VHF Corp.
|
Hello Allard,
I am a CW-only ham, so your 1.27.7 sketch made me love the BITX40.
Today I tried to upload the 1.28 upgrade but, surprisingly, it does not sense the key and transmit CW any more.
Moreover, the command-driven menus are not working as before.
I came back to the 1.27.7 version and now all is working as it should.
Did I miss something?
Thank you so much, best 72
Joe, IZ0WIT
|
Gordon and all, ?His software is on our group website in the "Files" section.
Jim, W0EB
? ? ?we do not use github
------ Original Message ------
Sent: 9/3/2018 10:23:01 AM
Subject: Re: [BITX20] CW OPERATION
Ron
Where do I go to look for your group software??
Now that I got my harmonic somewhat more under control, I¡¯m going to want to pick out good software modify it if needed and have it ready for our local group. ?
Thanks!
Gordon
On Sep 3, 2018, at 09:54, W2CTX < w2ctx@...> wrote:
Well maybe no one is paying attention but our software has CAT control, S-meter display, Pass Band Tuning, and
we build "memory manager" into the software so, you do not need a pc to change things. We also have a
companion Remote Control Program that allows control of the uBITX from a PC.? We also include keyboard control and
keyboard CW sending.
We are not in competition with Ian, we are just a few guys trying to make the best uBITX possible.? We make our
efforts available if people want to try them.
rOn
On September 3, 2018 at 9:00 AM MadRadioModder <madradiomodder@...> wrote:
Jim¡ I think you may have missed many of the positive features of the Nextion display¡ and in particular BECAUSE of that editor, anyone can
move those, how did you call it¡ clutter?, things around¡ add and subtract easily to fit their needs without understanding and writing hundreds of lines of code like others implementations?.? That is a real BIG plus.? And¡ if the popularity of the Nextion
keeps up, it will be no time before, feeling left out of the game, the ¡°competition¡± follows suit with their own clone-ish display.? Now Ian¡¯s code isn¡¯t perfect, but it has brought us a lot of positive things¡ decent CAT control, usable ¡°S¡± meter circuitry,
IF shift for attenuation¡ etc.? And the memory manager.? Yeah at some point it makes sense for some real programmers to do a rewrite¡
?
Dumping on Ian isn¡¯t a good sales tactic given his base¡
?
--
¡_. _._
?
|
Ron
Where do I go to look for your group software??
Now that I got my harmonic somewhat more under control, I¡¯m going to want to pick out good software modify it if needed and have it ready for our local group. ?
Thanks!
Gordon
On Sep 3, 2018, at 09:54, W2CTX < w2ctx@...> wrote:
toggle quoted message
Show quoted text
Well maybe no one is paying attention but our software has CAT control, S-meter display, Pass Band Tuning, and
we build "memory manager" into the software so, you do not need a pc to change things. We also have a
companion Remote Control Program that allows control of the uBITX from a PC.? We also include keyboard control and
keyboard CW sending.
We are not in competition with Ian, we are just a few guys trying to make the best uBITX possible.? We make our
efforts available if people want to try them.
rOn
On September 3, 2018 at 9:00 AM MadRadioModder <madradiomodder@...> wrote:
Jim¡ I think you may have missed many of the positive features of the Nextion display¡ and in particular BECAUSE of that editor, anyone can
move those, how did you call it¡ clutter?, things around¡ add and subtract easily to fit their needs without understanding and writing hundreds of lines of code like others implementations?.? That is a real BIG plus.? And¡ if the popularity of the Nextion
keeps up, it will be no time before, feeling left out of the game, the ¡°competition¡± follows suit with their own clone-ish display.? Now Ian¡¯s code isn¡¯t perfect, but it has brought us a lot of positive things¡ decent CAT control, usable ¡°S¡± meter circuitry,
IF shift for attenuation¡ etc.? And the memory manager.? Yeah at some point it makes sense for some real programmers to do a rewrite¡
?
Dumping on Ian isn¡¯t a good sales tactic given his base¡
?
--
¡_. _._
?
|
Sort of¡ I added a second receiver to my uBITx on VFO B.? It¡¯s great for DXing. I, like you, do like the uBITx receiver.? You can even do some clever things with the audio (stereo channels one for each receiver) and even diversity with a second antenna input. ? ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Michael Babineau
Sent: Monday, September 3, 2018 9:26 AM
To: [email protected]
Subject: Re: [BITX20] uBitx Unfiltered ? W.r.t the current discussions on ubitx transmitter woes ... the route forward that I chose was to order LPFs plus the relay board from QRP Labs. My thoughts were to use a 2nd Arduino Nano clone configured as an I2C slave to allow the Raduino to communicate with the LPF board over I2C. This would require some very minor code changes to send band change info to the new filter board. This solution would give me clean CW TX from 160m through 10m but does nothing to address the spur problem on the higher bands when using SSB nor the more recent concerns about other IMD.? This got me thinking that for another $20?I could just order the QRP Labs 5W PA kit and build a separate 160m to 10m CW TX with raised cosine wave shaping. I do mostly CW anyway so giving up SSB wouldn't be a big loss for me. So now I am considering the option of just using my ubitx as an HF receiver. The RX works quite well so if I just forget the TX, at a little over $100?for my v3 ubitx is was still a great deal IMHO.? Has anyone else thought? of just designing? a separate? TX board? for use with the V3/V4 ubitx? I know that this sounds like giving up ... but in many ways this could be a simpler solution than attempting major surgery on the existing ubitx. I have yet to package my ubitx in a permanent enclosure so for now I am going to put it aside and wait a month or two to see if there is a better option. -- ¡_. _._
|
Dear members you can check:
1. Add parallel to R12 C=470 pF: in my analiser I could see 3 dB gain rising on 30 MHz, 0805 smd resistor over R12;
2. Added two 100 Ohm? to collectotrs Q11 and Q12 (had to cut PCB roads to them). Emitter-follower do not like HF signals and small collector resistor gives light feed back.
3. After this reception has become more sensitive - I had to change my switching Power Supply to transformer analog one.
Best 73s to all George?
|
W.r.t the current discussions on ubitx transmitter woes ... the route forward that I chose was to order LPFs plus the relay board from QRP Labs. My thoughts were to use a 2nd Arduino Nano clone configured as an I2C slave to allow the Raduino to communicate with the LPF board over I2C. This would require some very minor code changes to send band change info to the new filter board.
This solution would give me clean CW TX from 160m through 10m but does nothing to address the spur problem on the higher bands when using SSB nor the more recent concerns about other IMD.?
This got me thinking that for another $20?I could just order the QRP Labs 5W PA kit and build a separate 160m to 10m CW TX with raised cosine wave shaping. I do mostly CW anyway so giving up SSB wouldn't be a big loss for me.
So now I am considering the option of just using my ubitx as an HF receiver. The RX works quite well so if I just forget the TX, at a little over $100?for my v3 ubitx is was still a great deal IMHO.?
Has anyone else thought? of just designing? a separate? TX board? for use with the V3/V4 ubitx? I know that this sounds like giving up ... but in many ways this could be a simpler solution than attempting major surgery on the existing ubitx.
I have yet to package my ubitx in a permanent enclosure so for now I am going to put it aside and wait a month or two to see if there is a better option.
Cheers? Michael VE3WMB?
|
Re: K5BCQ uBITX Relay Switched LPF/BPF board
You can assign the filters to any LPF/BPF you want. Your list looks good to me, maybe combine the 12m/10m LPFs and make the 15m a BPF.
73 Kees K5BCQ
|
Re: K5BCQ uBITX Relay Switched LPF/BPF board
Kees - With 6 filters is the plan as follows?
LPF1 = 80M
LPF2 = 40M and 30M
LPF3 = 20M and 17M
LPF4 = 15M
LPF5 = 12M
LPF6 = 10M
|
Re: K5BCQ uBITX Relay Switched LPF/BPF board
Here is what all 4 uBITX LPFs look like as plug-ins. Note that the 6x LPF board is arranged to where you can cut off 1 or 2 of the LPF/BPF positions with no ill effect. 73 Kees K5BCQ   
|
Re: UBITX TX level diagramme
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
|
Re: K5BCQ uBITX Relay Switched LPF/BPF board
Since most keep talking about the need for BPFs for certain bands, I "guess" the 80m-10m uBITX direction should be a board with 6 filter capability. How about a?basic?dual relay?switched filter board (3-1/4" x 3-7/8") with?up to?6 pluggable filters, all?manually?selected with a 6 position rotary switch --AND-- you can add a small mux board with 2N3904 relay drivers for the filters and a CD4028B mux to go from the 3 Raduino pins to the filters. Start with the existing 111,110,100,000 and add two others when you have the code modified.
73 Kees K5BCQ?
|
K5BCQ uBITX Relay Switched LPF/BPF board
In the interest of avoiding any confusion, I break this out to a separate thread.
73 Kees K5BCQ
|
|
|
I'm not "dumping" on Ian, merely trying to get him to WAKE UP and fix the problems he's kept missing in his software. ?It could be really good for ALL modes if he'd just listen to what a few of us have told him and fix his code. ?It's about time somebody got a bit forceful and tried to wake him up. That's all I'm doing here and we HAVE offered our help to him several times but he chose to ignore it. ?
He claims "open source" but I can't seem to find any reasonably readable code to even help fix these days.
Sorry, but I will continue to remind him until he fixes the problems.
As to the Nextion, ?Take a look at the picture on ?and see what a fully functional, UNCLUTTERED display looks like (it ain't a Nextion) and it's a heck of a lot cheaper.
I rest my case.
Jim - W0EB
------ Original Message ------
Sent: 9/3/2018 8:00:04 AM
Subject: Re: [BITX20] CW OPERATION
Jim¡ I think you may have missed many of the positive features of the Nextion display¡ and in particular BECAUSE of that editor, anyone can move those, how did you call it¡ clutter?, things around¡ add and subtract easily to fit their needs without understanding and writing hundreds of lines of code like others implementations?.? That is a real BIG plus.? And¡ if the popularity of the Nextion keeps up, it will be no time before, feeling left out of the game, the ¡°competition¡± follows suit with their own clone-ish display.? Now Ian¡¯s code isn¡¯t perfect, but it has brought us a lot of positive things¡ decent CAT control, usable ¡°S¡± meter circuitry, IF shift for attenuation¡ etc.? And the memory manager.? Yeah at some point it makes sense for some real programmers to do a rewrite¡ ? Dumping on Ian isn¡¯t a good sales tactic given his base¡ -- ¡_. _._
|
It has to be programmed to work that way, but we do it in all of our recent sketches. There is no reason why it can't be programmed in the other sketches if the programmer choses to do so.
Jim
toggle quoted message
Show quoted text
------ Original Message ------ From: "Joe Milosch" <zzmiloschxx@...> To: [email protected]Sent: 9/3/2018 8:05:15 AM Subject: Re: [BITX20] CW OPERATION On Mon, 03 Sep 2018 12:23:57 +0000
"Jim Sheldon" <w0eb@...> wrote:
Hi, I just want to be sure I understand. The PTT line can
be used for straight CW keying? It seems reasonable,
but I have to ask. Would this be true for any of the sketches?
Thanks,
Joe KN4OND
Thank Jerry, but in all of the software put out by the Triumviratw Skonk
Works from our first public release for the original NANO and ever
since, CW has not only worked properly but the Keyer has too. We
figured out early on that using the voltage divider was NOT and still is
NOT the way to go. Using 2 inputs and learning how to use the available
(timer not pin) interrupts properly works just fine. Our software
(written mostly by Ron, W2CTX) addressed the CW problem early on.
There is no need for me to use Ian's sodftware as it is so full of
work-arounds, not fixes to all the problems that have cropped up that I
refuse to use it. His source code is so convoluted that even the most
experienced programmers on this group have given up trying to fix it for
him.
The Nextion display is getting so cluttered up with extra buttons &
menus that you almost can't read the frequency on it any more. It
started out being a pretty nice addition and now is so cluttered as to
be almost unusable. It's also a "Single Source" display with a GUI
editor that most people can't even figure out how to use. Where's the
utility in that?
What are all of those who spent and are spending LOTS of money just for
the Nextion display alone, trying to make their uBITX $119 or $129 kit
radio look like a $2000 or higher big name radio going to do when that
Chinese company decides to charge hundreds of dollars for the use of
their editor (since it seems to have gotten popular) and raises their
prices astronomically for the Nextion because they are selling to the
hams at such a rate or quits production because the market dries up?
Frankly, the original LCD was quite adequate for a rig of this caliber
and all of the problems involved in using it should have been addressed
before even thinking of trying something else.
By the Way, the TSW DID that. We went to using the (easily accessible
on the original Raduino) I2C bus to drive the display (added minimal
extra cost and freed up a bunch of digital lines to use for the CW Keyer
and other controls.
Also, now that Ian HAS implemented the 4 wire (power ground, TX & RX)
Nextion interface that leaves 8 digital I/O pins freee on the old
display connector. Why has he not solved the major CW problem by
dropping the voltage divider altogether and using digital inputs for the
paddles dot and dash inputs? Switch the hand key portion of the keyer
over to use the Push To Talk (PTT) line, wire the hand key to use the
mike jack if you don't want to add another dedicated jack. This allows
auto select of hand key or paddles just by hitting the hand key or
pressing the paddles. Ask Ron, it took minimal code to do this. You
don't need PTT in CW operation and you don't normally need the hand key
in SSB operation so the PTT wire is easily co-opted for this.
By the way, this is not meant to be a rant though it may be turning into
one. I've seen many people complaining lately that the keyer doesn't
work properly but nobody has proposed or made a proper fix to the CEC
software. TSW has had the solution almost from the beginning but
everyone has drunk the "Nextion" kool-aid and the programmer for that
has chosen NOT to fix the CW issue. TSW has also tried to provide
readable and understandable PDF files explaining how our programs work
and any (usually minor) hardware changes necessary to make it work.
Jim Sheldon, W0EB
for TSW (Triumvirate Skonk Works)
website: www.w0eb.com
------ Original Message ------
From: "Jerry Gaffke via Groups.Io" <jgaffke@...>
To: [email protected]
Sent: 9/2/2018 11:19:23 PM
Subject: Re: [BITX20] CW OPERATION
Ian's software is the most popular update available for the uBitx.
He has added a lot of functionality to the rig and that is to be
applauded.
It's taken months of free time for him to bring it to this level.
Could well be that Ian doesn't use CW much, and CW is not a priority
for him.
Getting an iambic keyer to feel right is best done by a serious CW
operator.
I'd think Jim Sheldon would be an excellent candidate.
Jerry, KE7ER
On Sun, Sep 2, 2018 at 08:00 PM, Jim Sheldon wrote:
I don't like to be overly critical, but I've been hinting for months
now. I am now openly stating that KD8CEC's software has it wrong and
it's been wrong from the beginning. I call on Ian Lee to clean up his
code and get it right before he adds any more junk to his programs.
Jim, W0EB
|
Well maybe no one is paying attention but our software has CAT control, S-meter display, Pass Band Tuning, and
we build "memory manager" into the software so, you do not need a pc to change things. We also have a
companion Remote Control Program that allows control of the uBITX from a PC.? We also include keyboard control and
keyboard CW sending.
We are not in competition with Ian, we are just a few guys trying to make the best uBITX possible.? We make our
efforts available if people want to try them.
rOn
On September 3, 2018 at 9:00 AM MadRadioModder <madradiomodder@...> wrote:
Jim¡ I think you may have missed many of the positive features of the Nextion display¡ and in particular BECAUSE of that editor, anyone can move those, how did you call it¡ clutter?, things around¡ add and subtract easily to fit their needs without understanding and writing hundreds of lines of code like others implementations?.? That is a real BIG plus.? And¡ if the popularity of the Nextion keeps up, it will be no time before, feeling left out of the game, the ¡°competition¡± follows suit with their own clone-ish display.? Now Ian¡¯s code isn¡¯t perfect, but it has brought us a lot of positive things¡ decent CAT control, usable ¡°S¡± meter circuitry, IF shift for attenuation¡ etc.? And the memory manager.? Yeah at some point it makes sense for some real programmers to do a rewrite¡ ? Dumping on Ian isn¡¯t a good sales tactic given his base¡ ?
--
¡_. _._
?
|
|
|
Re: UBITX TX level diagramme
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
|
Jep
Jim Sheldon
MadRadioModder
George