Date   
Re: Tracing receive signal for low signal

Dave Space
 

Thanks I missed that.

I do see arrow looks like they have something with that part number
https://www.arrow.com/en/products/b82422a3681k100/epcos-tdk



On Tue, Jan 15, 2019 at 06:47 PM, Evan Hand wrote:
I used the link in this web page:
https://ubitx.net/spectral-purity/

Lead me to this ebay link:
https://www.ebay.com/itm/480pcs-kit-assorted-chip-inductor-coil-1210-1008-24x20pcs-EPCOS-TDK-MURATA-/143001305190?oid=142968653807

Raj did have the following caution:

Raj vu2zap rajendrakumargg@... via groups.io 

Tue, Dec 25, 2018, 5:44 AM
 
 
to BITX20
 
 
 
 
 
I hope you ordered the right ones like in the pic!

They are shielded and have a resistance of 2 ohms. TDK-EPCOS type is what I used
and also some marked S+M !

Raj

Evan
AC9TU

Re: Tracing receive signal for low signal

Evan Hand
 

I used the link in this web page:
https://ubitx.net/spectral-purity/

Lead me to this ebay link:
https://www.ebay.com/itm/480pcs-kit-assorted-chip-inductor-coil-1210-1008-24x20pcs-EPCOS-TDK-MURATA-/143001305190?oid=142968653807

Raj did have the following caution:

Raj vu2zap rajendrakumargg@... via groups.io 

Tue, Dec 25, 2018, 5:44 AM
 
 
to BITX20
 
 
 
 
 
I hope you ordered the right ones like in the pic!

They are shielded and have a resistance of 2 ohms. TDK-EPCOS type is what I used
and also some marked S+M !

Raj

Evan
AC9TU

Re: Tracing receive signal for low signal

Jerry Gaffke
 

Bob,

No, that's not old fashioned thinking.
And nails the primary cause of spurs in the uBitx.
The gain of the 45mhz IF amp is too high for what the 2n3904's can give us,
so we get a 90mhz harmonic of the 45mhz signal going into the mixer at D1,D2.

As Allison has explained, the solution is to reduce the gains in those IF amps,
then add an extra stage to the power amp to bring the transmit signal back up to where it was.

On the other hand, the uBitx is drop dead simple compared to anything else like it.
That's why I have one, it's about the simplest possible analog transceiver, and easy to play with.
But along with simple, there come tradeoffs.

Jerry



On Tue, Jan 15, 2019 at 05:48 PM, Bob Lunsford wrote:
The gain was low on each tube and the idea
was with some techs was that if one tube got low gain due
to age, etc., it was only one of eight and the others would
compensate. It was more than that, though. The tubes
were run far below their saturation point where harmonics
would result.

Re: Tracing receive signal for low signal

Dave Space
 

Does anyone have a link to an arrow part for the L5 and L7 replacement that works?

Re: Tracing receive signal for low signal

Bob Lunsford
 

Thanks Jerry for that discussion. Very useful and on-point.

The only thing I can add is to remind those who want a louder
signal and contemplate adding an amp is that the concept of
old designers is to spread the gain out among a series of
intermediate amps so any distortion and/or unwanted signals
are less apparent. For example, one tube amp I worked on
at an Army Depot electronics shop had an IF strip with eight
(8) tubes...! The gain was low on each tube and the idea
was with some techs was that if one tube got low gain due
to age, etc., it was only one of eight and the others would
compensate. It was more than that, though. The tubes
were run far below their saturation point where harmonics
would result. Some may snicker at that old technology but
don't forget that they won wars.

Now, the same philosophy is carried over with solid state
amps. their gain is greatest at lower current thought the
device (high beta at lower voltage levels) and to run them
too hard only puts them into a non-linear state. It's almost
axiomatic with solid state designers to run them at lower
levels, to not push them too hard.]

With the foregoing, I would think hard about putting an
amp on some stage of the uBitx since it could actually
sound louder on the other end but so could also the
harmonics and other RF devils. Instead of an amp being
added, I would first determine if the stage is operating
at its design level an make sure it's not some related
component that looks good but is not acting "good."

If I added an amp just to be more powerful as a station,
I'd first make sure the radio was working as designed and
then I'd add an amp at the input and output and leave
the rig itself alone as much as possible. Again, make sure
it is not driven beyond a "clean" design level lest you
get some notice sometime that you were heard in some
unexpected place.

This is why amp gain setting instructions often advise to
monitor the output of the amp and raise the drive level
(after making sure the required bias levels is/are met)
and while monitoring the output of the amp, you are
told to raise the drive level slowly and when you see a
max reading, no more gain showing, then back off slowly
to the point where the output begins to drop and stop
there.

Another problem some have is when they pump power
into a dummy load or into an antenna and you adjust
some drive level and see the power go up. Now, the
big question is, how much of that gain is on the desired
frequency? The Dummy Load is not going to tell you
that the indication of an increase in power is not only
on the frequency you s see on dial but on some other
frequency or frequencies.

Some of the old ham radio practices may yet be valuable.
Most of them are based on those old radio formulas and
electrical laws and they do not change. Getting into the
[old] basics sometimes provides the answers we need.

Bob — KK5R

--------------------------------------------

On Tue, 1/15/19, Jerry Gaffke via Groups.Io <jgaffke=yahoo.com@groups.io> wrote:

Subject: Re: [BITX20] Tracing receive signal for low signal
To: BITX20@groups.io
Date: Tuesday, January 15, 2019, 11:17 AM

That's a pretty good
summary, here's some minor corrections and
a major dump of nitty-gritty detail:

>  If you can fix the
harmonics, then operation on bands 20m and lower in
frequency 
> should not have the IMD
issue.  You can reduce that with both Ashhar's and
Raj's fixes combined.

Transmitter harmonics occur at integer
multiples of the transmit frequency.
So if
transmitting at 7mhz, you might have harmonics at 14 and
21mhz.
I would be happy enough on the
harmonics  if folks just replaced KT1,KT2,KT3
with proper RF relays such as the Axicom, flat
on the board.

Spurs are
similar to harmonics, except they occur at unexpected
frequencies that are not
multiples of the
transmit frequency, can be due to harmonics in an earlier
stage of the rig.
For example, the 90mhz
harmonic of the 45mhz desired signal in the 45mhz IF
stage
will also mix with the high side clk2
VFO, producing a spur at 2*45mhz - (DialFreq+45mhz)
Or your transmitter output (perhaps 7mhz)
sneaks back into the 45mhz IF, and that mises with the
VFO.
Raj and Farhan have both suggested
fixes that are apparently good enough on the spurs
(replace L5,L7 with special shielded inductors,
and/or add a low pass filter going into
the
mixer at D1,D2 to knock out the harmonic from the 45mhz IF
amp at 90mhz, respectvely).
One or the other
(or both) should bring spurs mostly into spec.  (Might also
want Farhan's 12mhz trap 
to deal with
12mhz crosstalk from clk0 into clk2, creating a 12mhz
spur).
The worst spurs are at 15m, 12m and
10m, though there can be spurs beyond the -43dB spec on
the lower bands too.

IMD (intermodulation distortion) is what
happens when a band of frequencies goes through a non-linear
amp.
Those various components of your signal
interact with each other, creating new close in
frequencies.
For example, you are
transmitting a two tone USB test on 7.2mhz, the tones at
7.2010 and 7.2015 mhz,
The second harmonic
of 7.2015 at 14.4030 mixes with 7.2010 producing a new tone
at 7.2020.
On the uBitx, IMD is mostly due
to having the mike audio higher than it should be, the diode
ring mixers
and the two IF amps get more
signal than they can cleanly deal with and thus become
non-linear.
Also some IMD due to the final
amp.  Fixing IMD would take a major redesign of the uBitx,
redistributing
gain away from those IF amps
and adding more gain to the final power amp, nobody has
given a
step-by-step recipe to do this yet
in the forum.  Fortunately, IMD is considered a lesser sin
than 
spurs and harmonics, the extra cruft
is so very close in with the main signal such that
everything still
pretty much fits into the
bandwidth of a legal AM signal.

An RTL-SDR using one of the DVB-T dongles uses
an 8 bit ADC to digitize the entire world of incoming
signals.
There's generally enough noise
to see only 7 valid bits of data out of such an 8 bit
ADC.
An increase in signal power by 4x is
equivalent to +6dB, and since power into a fixed 50 ohm
load 
is proportional to the square of the
voltage, that same +6dB is a doubling in the signal
voltage. 
Each of those 7 binary data bits
represents a doubling of voltage, so teh RTL-SDR has a range
of 7bits*6dB/bit = 42 dB.
Thus an RTL-SDR
might be able to simultaneously see both your desired signal
and a spur (or harmonic) that is 43dB down,
but you will have to set up your step
attenuator just right for them both to fit into the 7
bits.  Trying to measure a spur that
is 50
dB down with a device using an 8 bit ADC is totally
doomed.  However, an RTL-SDR is good enough to catch
the really bad cases, there have been reports
of uBitx spurs and harmonics that are only 30dB down.

Asking a friend to check for
spurs and harmonics is unlikely to be very thorough.
The emissions will vary with each band you use,
and to some degree as you move across the band.
The spurs can be most anywhere, your friend
would have to scan the entire HF spectrum.
This sort of check is best carried out with a
spectrum analyzer,
using a communications
receiver will be very time consuming if you want to do a
good job of it.

I'd
recommend at least Raj's fix of replacing L5,L7 with his
specific shielded inductors (easy!)
and
replace the relays at KT1,KT2,KT3 with axicom, no sockets. 
(Tough to remove.)
Alternately, instead of
replacing the relays, could use an external low pass filter
appropriate for each band
in line with the
antenna.   Do not goose the mike gain to get more power
out.
Then the rig is mostly compliant with
the US -43dBc spec

I
haven't heard any reports of any of these rigs
attracting legal attention, even without mods..
But I would not consider using a uBitx with an
external linear amp without an awful lot of work
on the uBitx first.

Jerry, KE7ER



On Tue, Jan
15, 2019 at 06:25 AM, Evan Hand wrote:

I go the relays at Mouser:
https://www.mouser.com/ProductDetail/te-connectivity/v23105a5403a201/?qs=Nk6ydC%2fJI6we9mx5p4DWfg%3d%3d&countrycode=US&currencycode=USD

I believe you can do better on
price if you go through ebay, though the lowest cost may
take awhile in shipment.

I
am not sure that I would trust my RTL-SDR to accurately
measure for the harmonics/spurs.  I got different results
when compared to my RF Explorer WSUB1G+, and the front end
of the RTL-SDR seems to overload easily, giving strange
results.  Again, I am not sure which one to believe.  They
both do agree that there is a 3rd order harmonic at 21mhz
that is higher than the -43db that is required in the US.

I would also read the
following threads:
https://groups.io/g/BITX20/message/61256
https://groups.io/g/BITX20/topic/27001748#61457
https://groups.io/g/BITX20/topic/28049653#61551

There are more and the net of
all of this is that there is not total agreement on the
fixes that are required.

My
interpretation is as follow (please understand that I am NOT
and expert.  I have just read a LOT of the emails related
to the uBitx)
1 - The relay replace is
minimum and may not totally fix the harmonic issues.  The
true fix is an external low pass filter board linked to the
uBitx switching relays, or possible loss in receiver
sensitivity if left in and manually switched when the band
is changed.

2 - If you can
fix the harmonics, then operation on bands 20m and lower in
frequency  should not have the IMD issue.  You can reduce
that with both Ashhar's and Raj's fixes combined.

3 - without the major
modifications that are suggested by the v5 board changes,
the v4 and earlier should NOT be used as the exciter to a
PA, UNLESS you have the equipment and skill to verify the
spurious radiation is under control.

I have been told in this group that in the
"old days" spurious emissions where tested using
another receiver located far enough away to not overload the
front end.  In other words, have a friend that can hear
your signal verify no spurious emissions.  This would
involve scanning for them.  I am sure that was state of the
art then, not sure the FCC would agree now.  We are
responsible for our transmissions.

It has also been pointed out that with the
normal power levels of the uBitx, that as long as you were
close, the spurs would be so far down that it would not
really cause interference or be noticed.  One of the
reasons for me abandoning the PA until I know what to do to
the uBitx.

As always, take
my input with a grain of salt.
73
Evan
AC9TU

Re: Tracing receive signal for low signal

estwing W
 

I just ordered mine from arrow as well. Got the ubitx as a birthday gift from my xyl. Been reading this board for a month now...so much info here to digest. Thanks for all of the info you all have posted.


On Tue, Jan 15, 2019, 8:10 PM Dave Space <davesspacebar@... wrote:
Thanks I ordered from Arrow seems like a good deal, they even had 10% off , free overnight shipping.




On Tue, Jan 15, 2019 at 07:00 AM, Jack Purdum wrote:
 
 Interesting. I checked the one-price for the relay at Digikey, Mouser, Arrow, and Newark and all but Arrow were the identical price, $2.81. Arrow is $2.67. I've been pleased with Arrow in terms of prices, service, and low shipping costs (sometimes, zero).
 
Jack, W8TEE
 
On Tuesday, January 15, 2019, 9:25:48 AM EST, Evan Hand <elhandjr@...> wrote:
 
 
I go the relays at Mouser:
https://www.mouser.com/ProductDetail/te-connectivity/v23105a5403a201/?qs=Nk6ydC%2fJI6we9mx5p4DWfg%3d%3d&countrycode=US&currencycode=USD

I believe you can do better on price if you go through ebay, though the lowest cost may take awhile in shipment.

I am not sure that I would trust my RTL-SDR to accurately measure for the harmonics/spurs.  I got different results when compared to my RF Explorer WSUB1G+, and the front end of the RTL-SDR seems to overload easily, giving strange results.  Again, I am not sure which one to believe.  They both do agree that there is a 3rd order harmonic at 21mhz that is higher than the -43db that is required in the US.

I would also read the following threads:
https://groups.io/g/BITX20/message/61256
https://groups.io/g/BITX20/topic/27001748#61457
https://groups.io/g/BITX20/topic/28049653#61551

There are more and the net of all of this is that there is not total agreement on the fixes that are required.

My interpretation is as follow (please understand that I am NOT and expert.  I have just read a LOT of the emails related to the uBitx)
1 - The relay replace is minimum and may not totally fix the harmonic issues.  The true fix is an external low pass filter board linked to the uBitx switching relays, or possible loss in receiver sensitivity if left in and manually switched when the band is changed.

2 - If you can fix the harmonics, then operation on bands 20m and lower in frequency  should not have the IMD issue.  You can reduce that with both Ashhar's and Raj's fixes combined.

3 - without the major modifications that are suggested by the v5 board changes, the v4 and earlier should NOT be used as the exciter to a PA, UNLESS you have the equipment and skill to verify the spurious radiation is under control.

I have been told in this group that in the "old days" spurious emissions where tested using another receiver located far enough away to not overload the front end.  In other words, have a friend that can hear your signal verify no spurious emissions.  This would involve scanning for them.  I am sure that was state of the art then, not sure the FCC would agree now.  We are responsible for our transmissions.

It has also been pointed out that with the normal power levels of the uBitx, that as long as you were close, the spurs would be so far down that it would not really cause interference or be noticed.  One of the reasons for me abandoning the PA until I know what to do to the uBitx.

As always, take my input with a grain of salt.
73
Evan
AC9TU

Re: low output only on 40m

jim
 

Ah good ..More eyeballs make for better results

Jim

On Tuesday, January 15, 2019, 5:24:39 PM PST, Curt via Groups.Io <wb8yyy@...> wrote:


Jim

most of my data is CW, as that plot.  all bands but 40m are okay CW output.  using a dummy load after the wattmeter, a TT1202 that is decently designed. 

SSB seems to be doing same, weak on 40m per needle response.  our local build leader did request I take some SSB data -- I need to see if my audio test source has enough drive. 

I cannot fathom what is doing the above.  originally I was getting around 4 or 5 watt CW - weaker than other bands.  I don't see any visual damage on the LPF that serves 40m.  since 80m and 160m do fine -- I can't fathom what is happening here. 

Saturday I hope to take rig to our club building session - for careful evaluation. 

73 Curt

Re: low output only on 40m

Curt
 

Jim

most of my data is CW, as that plot.  all bands but 40m are okay CW output.  using a dummy load after the wattmeter, a TT1202 that is decently designed. 

SSB seems to be doing same, weak on 40m per needle response.  our local build leader did request I take some SSB data -- I need to see if my audio test source has enough drive. 

I cannot fathom what is doing the above.  originally I was getting around 4 or 5 watt CW - weaker than other bands.  I don't see any visual damage on the LPF that serves 40m.  since 80m and 160m do fine -- I can't fathom what is happening here. 

Saturday I hope to take rig to our club building session - for careful evaluation. 

73 Curt

Re: Tracing receive signal for low signal

Dave Space
 

Thanks.  That could be a problem... I think my adapter only supplies 1 amp.

Might need to look for another power supply then perhaps.


On Tue, Jan 15, 2019 at 09:24 AM, jim wrote:
 
Nothing specific ..Just be sure the voltage does not change when going from receive to transmit ..decreasing voltage due to current draw will increase spur/harmonic/cruft generation ..
 
Spur/harmonic measurement ...Back in the old days, hams used a "Grid Dip Meter" with the switch in the "diode" position as an "absorption wavemeter"
 
Jim
 
On Tuesday, January 15, 2019, 4:57:20 AM PST, Dave Space <davesspacebar@...> wrote:
 
 
Only running one supply and it's basically just an old wall wart adapter that can run at 12v.  Supplies help a lot?  Have any suggestions on supplies?

Re: Tracing receive signal for low signal

Dave Space
 

Thanks to both you and Evan nice writeups on the spurs/harmonics summary and my RTL-SDR situation.  My RTL-SDR is definitely showing some bad harmonics on 21 when transmitting on 7 MHZ.

I ordered some relays.  I'll check into Raj's fix as well thanks.



On Tue, Jan 15, 2019 at 08:17 AM, Jerry Gaffke wrote:
That's a pretty good summary, here's some minor corrections and
a major dump of nitty-gritty detail:

>  If you can fix the harmonics, then operation on bands 20m and lower in frequency 
> should not have the IMD issue.  You can reduce that with both Ashhar's and Raj's fixes combined.

Transmitter harmonics occur at integer multiples of the transmit frequency.
So if transmitting at 7mhz, you might have harmonics at 14 and 21mhz.
I would be happy enough on the harmonics  if folks just replaced KT1,KT2,KT3
with proper RF relays such as the Axicom, flat on the board.

Spurs are similar to harmonics, except they occur at unexpected frequencies that are not
multiples of the transmit frequency, can be due to harmonics in an earlier stage of the rig.
For example, the 90mhz harmonic of the 45mhz desired signal in the 45mhz IF stage
will also mix with the high side clk2 VFO, producing a spur at 2*45mhz - (DialFreq+45mhz)
Or your transmitter output (perhaps 7mhz) sneaks back into the 45mhz IF, and that mises with the VFO.
Raj and Farhan have both suggested fixes that are apparently good enough on the spurs
(replace L5,L7 with special shielded inductors, and/or add a low pass filter going into
the mixer at D1,D2 to knock out the harmonic from the 45mhz IF amp at 90mhz, respectvely).
One or the other (or both) should bring spurs mostly into spec.  (Might also want Farhan's 12mhz trap 
to deal with 12mhz crosstalk from clk0 into clk2, creating a 12mhz spur).
The worst spurs are at 15m, 12m and 10m, though there can be spurs beyond the -43dB spec on
the lower bands too.

IMD (intermodulation distortion) is what happens when a band of frequencies goes through a non-linear amp.
Those various components of your signal interact with each other, creating new close in frequencies.
For example, you are transmitting a two tone USB test on 7.2mhz, the tones at 7.2010 and 7.2015 mhz,
The second harmonic of 7.2015 at 14.4030 mixes with 7.2010 producing a new tone at 7.2020.
On the uBitx, IMD is mostly due to having the mike audio higher than it should be, the diode ring mixers
and the two IF amps get more signal than they can cleanly deal with and thus become non-linear.
Also some IMD due to the final amp.  Fixing IMD would take a major redesign of the uBitx, redistributing
gain away from those IF amps and adding more gain to the final power amp, nobody has given a
step-by-step recipe to do this yet in the forum.  Fortunately, IMD is considered a lesser sin than 
spurs and harmonics, the extra cruft is so very close in with the main signal such that everything still
pretty much fits into the bandwidth of a legal AM signal.

An RTL-SDR using one of the DVB-T dongles uses an 8 bit ADC to digitize the entire world of incoming signals.
There's generally enough noise to see only 7 valid bits of data out of such an 8 bit ADC.
An increase in signal power by 4x is equivalent to +6dB, and since power into a fixed 50 ohm load 
is proportional to the square of the voltage, that same +6dB is a doubling in the signal voltage. 
Each of those 7 binary data bits represents a doubling of voltage, so teh RTL-SDR has a range of 7bits*6dB/bit = 42 dB.
Thus an RTL-SDR might be able to simultaneously see both your desired signal and a spur (or harmonic) that is 43dB down,
but you will have to set up your step attenuator just right for them both to fit into the 7 bits.  Trying to measure a spur that
is 50 dB down with a device using an 8 bit ADC is totally doomed.  However, an RTL-SDR is good enough to catch
the really bad cases, there have been reports of uBitx spurs and harmonics that are only 30dB down.

Asking a friend to check for spurs and harmonics is unlikely to be very thorough.
The emissions will vary with each band you use, and to some degree as you move across the band.
The spurs can be most anywhere, your friend would have to scan the entire HF spectrum.
This sort of check is best carried out with a spectrum analyzer,
using a communications receiver will be very time consuming if you want to do a good job of it.

I'd recommend at least Raj's fix of replacing L5,L7 with his specific shielded inductors (easy!)
and replace the relays at KT1,KT2,KT3 with axicom, no sockets.  (Tough to remove.)
Alternately, instead of replacing the relays, could use an external low pass filter appropriate for each band
in line with the antenna.   Do not goose the mike gain to get more power out.
Then the rig is mostly compliant with the US -43dBc spec

I haven't heard any reports of any of these rigs attracting legal attention, even without mods..
But I would not consider using a uBitx with an external linear amp without an awful lot of work
on the uBitx first.

Jerry, KE7ER



On Tue, Jan 15, 2019 at 06:25 AM, Evan Hand wrote:
I go the relays at Mouser:
https://www.mouser.com/ProductDetail/te-connectivity/v23105a5403a201/?qs=Nk6ydC%2fJI6we9mx5p4DWfg%3d%3d&countrycode=US&currencycode=USD

I believe you can do better on price if you go through ebay, though the lowest cost may take awhile in shipment.

I am not sure that I would trust my RTL-SDR to accurately measure for the harmonics/spurs.  I got different results when compared to my RF Explorer WSUB1G+, and the front end of the RTL-SDR seems to overload easily, giving strange results.  Again, I am not sure which one to believe.  They both do agree that there is a 3rd order harmonic at 21mhz that is higher than the -43db that is required in the US.

I would also read the following threads:
https://groups.io/g/BITX20/message/61256
https://groups.io/g/BITX20/topic/27001748#61457
https://groups.io/g/BITX20/topic/28049653#61551

There are more and the net of all of this is that there is not total agreement on the fixes that are required.

My interpretation is as follow (please understand that I am NOT and expert.  I have just read a LOT of the emails related to the uBitx)
1 - The relay replace is minimum and may not totally fix the harmonic issues.  The true fix is an external low pass filter board linked to the uBitx switching relays, or possible loss in receiver sensitivity if left in and manually switched when the band is changed.

2 - If you can fix the harmonics, then operation on bands 20m and lower in frequency  should not have the IMD issue.  You can reduce that with both Ashhar's and Raj's fixes combined.

3 - without the major modifications that are suggested by the v5 board changes, the v4 and earlier should NOT be used as the exciter to a PA, UNLESS you have the equipment and skill to verify the spurious radiation is under control.

I have been told in this group that in the "old days" spurious emissions where tested using another receiver located far enough away to not overload the front end.  In other words, have a friend that can hear your signal verify no spurious emissions.  This would involve scanning for them.  I am sure that was state of the art then, not sure the FCC would agree now.  We are responsible for our transmissions.

It has also been pointed out that with the normal power levels of the uBitx, that as long as you were close, the spurs would be so far down that it would not really cause interference or be noticed.  One of the reasons for me abandoning the PA until I know what to do to the uBitx.

As always, take my input with a grain of salt.
73
Evan
AC9TU

Re: Tracing receive signal for low signal

jim
 

More and better test equipment is ALWAYS worth the investment ...However, If the RTL-SDR has some of shielded input, a step attenuator could be used in front of it to 'sorta' calibrate it ...Several many kits are around for those without $$$ qrp-guys has one for $35 or a pile of resistors and 5 or 6 switches ..Elecraft had one at one time too

Jim

On Tuesday, January 15, 2019, 5:05:02 PM PST, Dave Space <davesspacebar@...> wrote:

 
Thanks... interesting.  I'll presume the RTL-SDR is at least accurate in representing there are spurs given all the threads about the ubitx having them :)   Now how big they are I guess we'll see how it compares after some mods I guess.  I think I will start with the relays.  How do you like the RF Explorer ?  Is it worth it or stick with the RTL-SDR or probably just better to find an old signal analyzer and spend the money?

Re: Tracing receive signal for low signal

Dave Space
 

Thanks I ordered from Arrow seems like a good deal, they even had 10% off , free overnight shipping.




On Tue, Jan 15, 2019 at 07:00 AM, Jack Purdum wrote:
 
 Interesting. I checked the one-price for the relay at Digikey, Mouser, Arrow, and Newark and all but Arrow were the identical price, $2.81. Arrow is $2.67. I've been pleased with Arrow in terms of prices, service, and low shipping costs (sometimes, zero).
 
Jack, W8TEE
 
On Tuesday, January 15, 2019, 9:25:48 AM EST, Evan Hand <elhandjr@...> wrote:
 
 
I go the relays at Mouser:
https://www.mouser.com/ProductDetail/te-connectivity/v23105a5403a201/?qs=Nk6ydC%2fJI6we9mx5p4DWfg%3d%3d&countrycode=US&currencycode=USD

I believe you can do better on price if you go through ebay, though the lowest cost may take awhile in shipment.

I am not sure that I would trust my RTL-SDR to accurately measure for the harmonics/spurs.  I got different results when compared to my RF Explorer WSUB1G+, and the front end of the RTL-SDR seems to overload easily, giving strange results.  Again, I am not sure which one to believe.  They both do agree that there is a 3rd order harmonic at 21mhz that is higher than the -43db that is required in the US.

I would also read the following threads:
https://groups.io/g/BITX20/message/61256
https://groups.io/g/BITX20/topic/27001748#61457
https://groups.io/g/BITX20/topic/28049653#61551

There are more and the net of all of this is that there is not total agreement on the fixes that are required.

My interpretation is as follow (please understand that I am NOT and expert.  I have just read a LOT of the emails related to the uBitx)
1 - The relay replace is minimum and may not totally fix the harmonic issues.  The true fix is an external low pass filter board linked to the uBitx switching relays, or possible loss in receiver sensitivity if left in and manually switched when the band is changed.

2 - If you can fix the harmonics, then operation on bands 20m and lower in frequency  should not have the IMD issue.  You can reduce that with both Ashhar's and Raj's fixes combined.

3 - without the major modifications that are suggested by the v5 board changes, the v4 and earlier should NOT be used as the exciter to a PA, UNLESS you have the equipment and skill to verify the spurious radiation is under control.

I have been told in this group that in the "old days" spurious emissions where tested using another receiver located far enough away to not overload the front end.  In other words, have a friend that can hear your signal verify no spurious emissions.  This would involve scanning for them.  I am sure that was state of the art then, not sure the FCC would agree now.  We are responsible for our transmissions.

It has also been pointed out that with the normal power levels of the uBitx, that as long as you were close, the spurs would be so far down that it would not really cause interference or be noticed.  One of the reasons for me abandoning the PA until I know what to do to the uBitx.

As always, take my input with a grain of salt.
73
Evan
AC9TU

Re: Tracing receive signal for low signal

Dave Space
 

On Tue, Jan 15, 2019 at 06:25 AM, Evan Hand wrote:
I go the relays at Mouser:
https://www.mouser.com/ProductDetail/te-connectivity/v23105a5403a201/?qs=Nk6ydC%2fJI6we9mx5p4DWfg%3d%3d&countrycode=US&currencycode=USD

I believe you can do better on price if you go through ebay, though the lowest cost may take awhile in shipment.

I am not sure that I would trust my RTL-SDR to accurately measure for the harmonics/spurs.  I got different results when compared to my RF Explorer WSUB1G+, and the front end of the RTL-SDR seems to overload easily, giving strange results.  Again, I am not sure which one to believe.  They both do agree that there is a 3rd order harmonic at 21mhz that is higher than the -43db that is required in the US.

I would also read the following threads:
https://groups.io/g/BITX20/message/61256
https://groups.io/g/BITX20/topic/27001748#61457
https://groups.io/g/BITX20/topic/28049653#61551

There are more and the net of all of this is that there is not total agreement on the fixes that are required.

My interpretation is as follow (please understand that I am NOT and expert.  I have just read a LOT of the emails related to the uBitx)
1 - The relay replace is minimum and may not totally fix the harmonic issues.  The true fix is an external low pass filter board linked to the uBitx switching relays, or possible loss in receiver sensitivity if left in and manually switched when the band is changed.

2 - If you can fix the harmonics, then operation on bands 20m and lower in frequency  should not have the IMD issue.  You can reduce that with both Ashhar's and Raj's fixes combined.

3 - without the major modifications that are suggested by the v5 board changes, the v4 and earlier should NOT be used as the exciter to a PA, UNLESS you have the equipment and skill to verify the spurious radiation is under control.

I have been told in this group that in the "old days" spurious emissions where tested using another receiver located far enough away to not overload the front end.  In other words, have a friend that can hear your signal verify no spurious emissions.  This would involve scanning for them.  I am sure that was state of the art then, not sure the FCC would agree now.  We are responsible for our transmissions.

It has also been pointed out that with the normal power levels of the uBitx, that as long as you were close, the spurs would be so far down that it would not really cause interference or be noticed.  One of the reasons for me abandoning the PA until I know what to do to the uBitx.

As always, take my input with a grain of salt.
73
Evan
AC9TU
Thanks... interesting.  I'll presume the RTL-SDR is at least accurate in representing there are spurs given all the threads about the ubitx having them :)   Now how big they are I guess we'll see how it compares after some mods I guess.  I think I will start with the relays.  How do you like the RF Explorer ?  Is it worth it or stick with the RTL-SDR or probably just better to find an old signal analyzer and spend the money?

Re: low output only on 40m

jim
 

Ok thanks ..just trying to get some references to establish some sort of  rational base-band ..High accuracy is not needed,  just something "close"

this one 5 watts from 8 to 10 Mhz on CW ..Previous quoted from you was SSB? right?

Jim


On Tuesday, January 15, 2019, 2:57:13 PM PST, Curt via Groups.Io <wb8yyy@...> wrote:


Okay here is my CW measurement into a power meter - yes broadband.  My rig was measured, I have usual spurs for a stock uBITX - nothing to impact this measurement.  I think my LPF might be shifted up - maybe - not sure what this response is across 40m as a LPF does not do that! 

X axis is frequency and Y axis is power in watts.  sure my instrument isn't high quality but I trust the trend it conveys. 

Curt


Re: Tracing receive signal for low signal

Bob Lunsford
 

It's easy to convert a computer power supply and come up
with 12V. Only need to remove all the external wires except
for the ones that put out 12V and put a 10 Ohm 10W resistor
across the 5V line ... this starts the power supply and makes
it reliable. (some use a brakelight lamp for this)

There are websites that have a step-by-step walk-through to
do this. Simple. Just provide the connector. A simple way to
do this is to use the wire-to-wire screw type connector where
you put in a wire in both sides and tighten the screws.

Or, you can get an MFJ power supply with the front panel
voltage selection but they are for more than 20A, typically, and
all you need is a couple of amps and woe to someone who
forgets to turn down the voltage when firing up the uBitx.

Hamfests are good sources. It's easy to buy a 5-10A supply
for about $10-$15 but they need to be one that can be turned
down to 12V. Some are not easy to do this as it should seem.

You can also put a simple regulator to cut down the voltage.
All you need is a 2N2055, a 12.6V Zener, a resistor and two
electrolytic caps and two disc ceramics wired in an emitter
follower circuit. Put it in a minibox so the box is the heat sink
and it's good because you are only talking about one amp.
Use insulation on the transistor. 2N2055s are at an almost
giveaway price.

A 12V power supply designed to run a 2-10W two meter rig
but most of them are not adjustable. Wall Warts are bad news
because if they are not linear/solid state, they are usually rated
at the current rating in a strange way and could blow up the
radio. If, for example, they say 12V 2A, this means that at 2A
they are 12V but if you are running only 300 MA, the voltage
could be as high as 18V or more. This could smoke a radio
that is limited to only 15/16V.

I have seen good power supplies at as low as 9.6V that were
used with some older models of printer. Most of them today,
the cheapies sold at Walmart, are designed for 18/19V and
only about 1/2A.

Someone here may have an extra. I have an old power supply
for the Heathkit HW 2036 but it is not adjustable. It could be
modified but getting into such things is a grand distraction from
operating. I also have a 13.6V 5A Regency power supply that
could run higher amperage if not constant and can be tuned
down in voltage but it's value to someone for a larger radio is
more appropriate.

Hope I gave you a few ideas.

Bob — KK5R

--------------------------------------------

On Tue, 1/15/19, Dave Space <davesspacebar@...> wrote:

Subject: Re: [BITX20] Tracing receive signal for low signal
To: BITX20@groups.io
Date: Tuesday, January 15, 2019, 7:57 AM

Only running one supply
and it's basically just an old wall wart adapter that
can run at 12v.  Supplies help a lot?  Have any
suggestions on supplies?

Re: low output only on 40m

Curt
 

Okay here is my CW measurement into a power meter - yes broadband.  My rig was measured, I have usual spurs for a stock uBITX - nothing to impact this measurement.  I think my LPF might be shifted up - maybe - not sure what this response is across 40m as a LPF does not do that! 

X axis is frequency and Y axis is power in watts.  sure my instrument isn't high quality but I trust the trend it conveys. 

Curt


Re: Mic connection

VE3MIC
 

Hi Kevin,

The "stock"(included) mic is an electric condenser mic.  Although some have modified their BITX to use a dynamic mic.

Here are my "go to" links. I'm sure that you'll find your answer in one of them.
73 de Mike

https://groups.io/g/BITX20
http://www.kit-projects.com/Bitx40.htm
http://kv4qb.blogspot.com/2016/11/bitx-40p-building-part-1.html
http://bitxhacks.blogspot.com/2016/



On Tuesday, January 15, 2019, 4:46:09 p.m. EST, k8su <k8su@...> wrote:


Just received a build BitX20.

I keyed the PTT and appear to have proper current.

Has the small 1/8 inch connector on front but not sure how to properly connect a mic and the type of mic.

I see three wires going to the switch.  2 coming from the mic connector on the board and one from the PTT.

I am not sure if the mic needs voltage to operate.

Any help appreciated.  I read several threads but still confused.

Appreciate the help.  I was trying to use an inexpensive computer mic.  Has the right type of connector on it.

Thanks In advance


Kevin


Sent from IPhone.  Sent from iphone without editing for Typos

Mic connection

k8su@...
 

Just received a build BitX20.

I keyed the PTT and appear to have proper current.

Has the small 1/8 inch connector on front but not sure how to properly connect a mic and the type of mic.

I see three wires going to the switch. 2 coming from the mic connector on the board and one from the PTT.

I am not sure if the mic needs voltage to operate.

Any help appreciated. I read several threads but still confused.

Appreciate the help. I was trying to use an inexpensive computer mic. Has the right type of connector on it.

Thanks In advance


Kevin


Sent from IPhone. Sent from iphone without editing for Typos

Re: Simple vfo sketch

Laurence Oberman
 

Don
You will have to change the pin mappings to match the raduino config.
I have a spare raduiino and this weekend will check the circuit
diagram and clean up the sketch for you.

On Tue, Jan 15, 2019 at 3:29 PM Laurence Oberman via Groups.Io
<oberman.l=gmail.com@groups.io> wrote:

I have a signal Generator using the same DDS chip and Arduino setup I
built from ideas from Jacks book.
I use it all the time.
This is my sketch

On Tue, Jan 15, 2019 at 12:14 AM MVS Sarma <mvssarma@...> wrote:

Hi,
Farhan already published his antenna analyser (ANTUINO), where there is a free running osc on one of the clocks of his ANTUINO.
All the best
Sarma vu3zmv

On Tue, 15 Jan 2019, 5:40 am Don Richards <ve3ids.don@... wrote:

I have built this version of the raduino,

http://arrl-nfl.org/wp-content/uploads/2018/05/KX4ZDDSApplicationNote.pdf

It works quite well with my HW 101 in receive. It needs a little more amplitude to drive the transmitter properly, that mod is in progress.

My question to the group is, has anyone written a sketch for the raduino that is a simple RF generator that could be used as a signal generator or for a simple vfo for an old crystal transmitter, ie, one that simply generates the actual frequency that it displays on the LCD and still uses the tuning pot rather than an encoder?

I don't know nearly enough to create this, hoping that some of the talent that frequents this group has done this and can share.

Thanks and 73
Don ve3ids

Re: Need a replacement Raduino.

Billy Shepherd <dis60cd@...>
 

Very good thank you. I'll check with HF Signals and get back with you. I might just order the pre-soldered kit from you....checking your stuff now.