Jerry,
To help me understand better what is going on, can you confirm that the testing is using CW?? Also, what, if any modifications have you done to the v6.
Thank you,
73
Evan
AC9TU
|
Fascinating... We must build this as a module for others. This stuff is the holy grail for the weak signal buffs.
Through experimentation I've determined that the QRP Labs VFO with a 1pps GPS can be used to provide a reasonably stable and accurate crystal substitute for the uBitx raduino (many thanks to everyone's suggestions on this and other threads). The impetus was to see if I could use the two units together to get decent results for the Eclipse Festival happening today.
?
The 25 MHz crystal is unsoldered from the raduino (using good flux and braid to remove the solder on the two pins), then two ground pads scraped on the backside ground plane to reveal the copper, and a SMA connector soldered.
?
Before soldering the SMA connector to the board, I created an assembly of the connector with a 47 ohm resistor load input (parallel), followed by a 150 pF cap in series for DC blocking. The output of the cap wire goes through the former crystal hole to the si5351 pin 2 (XA) and excess wire cut (and almost forgot to solder it).
?
Experiments with an additional PI (C-L-C) LPF right before the 47 ohm resistor load worked (to reduce harmonics), but proved unnecessary, so I left it out.
?
The QRP Labs VFO is configured to be GPS disciplined (in my case an old Fastrax 1pps GPS).
?
It is then configured to generate 25 MHz out which is also set into the first preset so it runs 25 MHz out on power up.
?
I'm using the CEC firmware with Nextion on my v5 uBitx. I set uBitx calibration to 0 because the VFO is generating 25 MHz exactly (within a couple of hertz). This was confirmed by setting the uBitx VFO to 9.999 Mhz and monitoring the carrier of WWV as a 1kHZ audio output tone and the SpectrumLab software FFT measured it to within a couple of hertz of 1000 Hz. One thing I didn't do is change the BFO but I don't think that is necessary (might have to check that at some point anyway).?
?
The documentation for the VFO recommends a 50 Hz delta (correction threshold) before it resyncs to the GPS time to avoid audible glitches, however, I'm finding that the minimum of 1 Hz seems ideal for my application where I'm not actually listening to the audio but I need the highest possible frequency accuracy due to crystal temperature drifts (not unusual for the 27 MHz crystal to change 20 Hz over the course of a day indoors in the spring.
?
So far the graphs and results look good for such a simple time standard (the Fastrax accuracy is only rated 50 ns RMS in the 1pps output). I do see a 1 or so Hz frequency jumps occasionally when the QRP Labs VFO recalibrates its output 25 Mhz. On the VFO 16x2 LCD I display the output frequency, the 1pps heartbeat, the lock (No/2D/3D), the number of satellites, and the reference frequency (somewhere around 27.005 MHz, as the QRP Labs VFO uses a 27 MHz crystal intended for WSPR applications).
?
I've run into two issues:
1. The power up sequence is manual. I first turn on the VFO and then the uBitx to ensure the raduino's si5351 has oscillator present when it powers up.
2. If the GPS signal deteriorates for whatever reason and the unit goes in and out of lock, the heartbeat "skips" a beat or two and under just the right circumstances VFO's pps detector gets confused (possibly due to a bug or implementation limitation) which then causes the VFO to do a severe recalibration throwing the output frequency off hundreds of hertz until it gets a steady lock again. Must get a better GPS.
?
I still need to build a shielded box for the VFO - I find that the GPS loses signal when the VFO is outputting 25 MHz but is fine when it outputs 5 MHz or less (thereabouts). This is a problem because I have the GPS module next to a window so it only sees half the sky. My temporary solution is to connect the GPS with a 1 meter cable to move it away from the VFO and put a 20 cm x 40 cm ground plane about 5 cm under it (these numbers are arbitrary but seems to increase the number of satellites seen by 1 or 2)
?
Hope this is useful info for those looking for a simple hardware solution.
Roman
|
toggle quoted message
Show quoted text
Farhan,
This the same transistor BFR106 I used when improving the earlier
BITX!
David this transistor work very well!
Raj
At 09/06/2021, you wrote:
It's interesting that the noise
floor has been around -93 dBm, with and without the first mixer post
amplifier.? Will explore this some more.? I wonder if the log
amp is setting the floor now.
The BFR106 seems like a good candidate.? The only concern
might be power supply (Vceo is 15-16V and specs are at 8V).? What
voltage have you been using?
I'm mostly a HW guy but an improved user interface would be nice.? I
had thought of changing the pot to an encoder and some other
improvements.? More computing power and a graphic display would be
nice.? I've thought of pairing the Specan with a Rasberry
Pi.
I'll order some BFR106's and let you know how I make out.? Thank you
for helping,
--
David KV4FP
|
Farhan,
This the same transistor BFR106 I used when improving the earlier
BITX!
David this transistor work very well!
Raj
At 09/06/2021, you wrote:
toggle quoted message
Show quoted text
It's interesting that the noise
floor has been around -93 dBm, with and without the first mixer post
amplifier.? Will explore this some more.? I wonder if the log
amp is setting the floor now.
The BFR106 seems like a good candidate.? The only concern
might be power supply (Vceo is 15-16V and specs are at 8V).? What
voltage have you been using?
I'm mostly a HW guy but an improved user interface would be nice.? I
had thought of changing the pot to an encoder and some other
improvements.? More computing power and a graphic display would be
nice.? I've thought of pairing the Specan with a Rasberry
Pi.
I'll order some BFR106's and let you know how I make out.? Thank you
for helping,
--
David KV4FP
|
Through experimentation I've determined that the QRP Labs VFO with a 1pps GPS can be used to provide a reasonably stable and accurate crystal substitute for the uBitx raduino (many thanks to everyone's suggestions on this and other threads). The impetus was to see if I could use the two units together to get decent results for the hamsci.org Eclipse Festival happening today.
?
The 25 MHz crystal is unsoldered from the raduino (using good flux and braid to remove the solder on the two pins), then two ground pads scraped on the backside ground plane to reveal the copper, and a SMA connector soldered.
?
Before soldering the SMA connector to the board, I created an assembly of the connector with a 47 ohm resistor load input (parallel), followed by a 150 pF cap in series for DC blocking. The output of the cap wire goes through the former crystal hole to the si5351 pin 2 (XA) and excess wire cut (and almost forgot to solder it).
?
Experiments with an additional PI (C-L-C) LPF right before the 47 ohm resistor load worked (to reduce harmonics), but proved unnecessary, so I left it out.
?
The QRP Labs VFO is configured to be GPS disciplined (in my case an old Fastrax 1pps GPS).
?
It is then configured to generate 25 MHz out which is also set into the first preset so it runs 25 MHz out on power up.
?
I'm using the CEC firmware with Nextion on my v5 uBitx. I set uBitx calibration to 0 because the VFO is generating 25 MHz exactly (within a couple of hertz). This was confirmed by setting the uBitx VFO to 9.999 Mhz and monitoring the carrier of WWV as a 1kHZ audio output tone and the SpectrumLab software FFT measured it to within a couple of hertz of 1000 Hz. One thing I didn't do is change the BFO but I don't think that is necessary (might have to check that at some point anyway).?
?
The documentation for the VFO recommends a 50 Hz delta (correction threshold) before it resyncs to the GPS time to avoid audible glitches, however, I'm finding that the minimum of 1 Hz seems ideal for my application where I'm not actually listening to the audio but I need the highest possible frequency accuracy due to crystal temperature drifts (not unusual for the 27 MHz crystal to change 20 Hz over the course of a day indoors in the spring.
?
So far the graphs and results look good for such a simple time standard (the Fastrax accuracy is only rated 50 ns RMS in the 1pps output). I do see a 1 or so Hz frequency jumps occasionally when the QRP Labs VFO recalibrates its output 25 Mhz. On the VFO 16x2 LCD I display the output frequency, the 1pps heartbeat, the lock (No/2D/3D), the number of satellites, and the reference frequency (somewhere around 27.005 MHz, as the QRP Labs VFO uses a 27 MHz crystal intended for WSPR applications).
?
I've run into two issues:
1. The power up sequence is manual. I first turn on the VFO and then the uBitx to ensure the raduino's si5351 has oscillator present when it powers up.
2. If the GPS signal deteriorates for whatever reason and the unit goes in and out of lock, the heartbeat "skips" a beat or two and under just the right circumstances VFO's pps detector gets confused (possibly due to a bug or implementation limitation) which then causes the VFO to do a severe recalibration throwing the output frequency off hundreds of hertz until it gets a steady lock again. Must get a better GPS.
?
I still need to build a shielded box for the VFO - I find that the GPS loses signal when the VFO is outputting 25 MHz but is fine when it outputs 5 MHz or less (thereabouts). This is a problem because I have the GPS module next to a window so it only sees half the sky. My temporary solution is to connect the GPS with a 1 meter cable to move it away from the VFO and put a 20 cm x 40 cm ground plane about 5 cm under it (these numbers are arbitrary but seems to increase the number of satellites seen by 1 or 2)
?
Hope this is useful info for those looking for a simple hardware solution.
Roman
|
n 2021-06-09 19:40, John Cunliffe W7ZQ wrote: From what I have seen with my V6, you will see the 2 spurs with >your good spectrum analyzer also. I installed a HPF since mine showed >up on
21Mhz and up
Was it this bad? See attached picture of tinySA trace.. I just swapped out the TSW Raduino and reinstalled the HFSignals one. No difference. I thought maybe since the si5351 was on that card then... Note that the closest spurs are only 8 & 10 dB below the fundamental. That means that if I'm transmitting 5W on 14 MHz, O I'm also transmitting a full half a watt on 16MHz...which isn't a ham band. Neither is 12 MHz. Share some details about your HPF? Did you put it on the output, or insert it into the circuit? How many poles? For my radio to be legal, a 20M HPF would have to give over 30 dB of attenuation at 2 MHz away from the fundamental. - Jerry John
Links:
------
[1] /g/BITX20/message/89075
[2] /mt/83413015/243852
[3] /g/BITX20/post
[4] /g/BITX20/editsub/243852
[5] /g/BITX20/leave/10189903/243852/952924773/xyzzy
|
From what I have seen with my V6, you will see the 2 spurs with your good spectrum analyzer also. I installed a HPF since mine showed up on 21Mhz and up
John
|
On 2021-06-09 19:06, Ashhar Farhan wrote: Which version of ubitx is this? The versions prior to v5 needed an
extra lpf between the first mixer and the if amp V6 - Jerry On Wed 9 Jun, 2021, 10:31 PM jerry@..., <jerry@...> wrote:
Hi Farhhan,
I'll hook up my other spectrum analyzer today. It's a Texscan
VSM-5D. Only 4MHz-450MHz, but that's plenty for this.
HOWEVER, this test was without any amp. Just the uBITX feeding the
Narda attenuator. And the scope & the tinySA agree - lots of mixing
products. Only on 20M.
Reading the block diagram, I am at a loss as to how such a problem
could
occur. The two biggest spurs are at the fundamental plus about
2.5Mhz,
and also MINUS 2.5Mhz.
Specific to 20M would only be the LPF. And what failure in the LPF
could cause such a cacophony of mixing spurs?
I will also check the outputs of the si5351a - I am using the TSW
Teensy
board, will try popping your display/vfo board back in.
- Jerry KF6VB
On 2021-06-09 08:51, Ashhar Farhan wrote:
The tinysa does not have shielding needed for a decent, spur free
reading, at 40 watts of power it will probably read spurs even without
connecting it up.
On Wed 9 Jun, 2021, 6:41 PM jerry@..., <jerry@...> wrote:
Ashhar,
I would expect the effect - of the scope not being terminated -
to
be minimal, because there was a 30dB Narda attenuator between the
uBITX
and the scope. The Narda is rated for microwave, and is flat as a
board
through
HF & VHF. And the difference at the input - what the uBITX sees
-
between
terminated and not terminated ( at the output of the Narda ) - is
minuscule. Because it's a 30dB attenuator - divides the power by
1000.
So 99.9% of the power put into that attenuator is dissipated by
the
attenuator itself.
The idea was not to use the scope to *measure* the uBITX output
in any
absolute sense, but rather to compare it in a qualitative sense
to
the
output of the uBITX
on other bands.
The tinySA verified massive mixing product spurs on 20. And it
*does*
have an internal termination.
- Jerry KF6VB
On 2021-06-08 21:45, Ashhar Farhan wrote:
Jerry,
I would suspect the measuring instruments. If you have an
oscilloscope, then parallel up 20 of 2 watt/50 ohms resistors as
a
dummy load and measure RF voltage (with bandwidth filter on our scope
turned off) across the dummy load (not across the antenna jack).
Once, you are sure of the Rf voltages, then, in parallel to the
50
ohm
resistor bundle, add a 2.2K in series with a 50 ohms, such that the 50
ohms is connected to the ground side. Now, measure the RF
voltage
across the 50 ohms and the square of the ratio of raw to attenuated
voltages is your attenuated power. Crude by accurate.
- f
On Wed, Jun 9, 2021 at 10:02 AM Max via groups.io [1] [1] [1]
<kg4pid@...> wrote:
Do you think this is the cause of the amp failing, or damage caused
by the amp failing and sending some rf back into the radio?
Max KG4PID
On Tuesday, June 8, 2021, 10:27:00 PM CDT, jerry@...
<jerry@...> wrote:
All,
To help me postmortem the Chinese linear,
I was checking the output of the uBITX on various bands. I
used
a
Bird
4410 wattmeter with the 10kW slug ( which can be switched down
to
10W
full scale ), and my trusty Narda attenuator as a load. Here's
what
I
got
3.615 MHz - 4.2W
7.029 MHz - 4.9W
10.115 MHz - 3.7W
14.030 MHz - 17W <======= HUH?
21.03 MHz - 2.5W ( more like it )
28.35M MHz - 3.9W
That 14MHz reading is a doozy - no WAY is the uBITX making
SEVENTEEN
WATTS.
My wattmeter ( a recent Ebay purchase ) must be defective!
Specifically
the slug, where all the RF stuff is.
Let's double check this. I lugged out a scope ( Rigol 1054z ).
Plugged it directly into the output of the 30dB Narda
attenuator.
No
termination feature on the scope inputs, and I was too lazy to
go
get a
tee fitting and a 50ohm mini-load. So the readings of the
scope
would
be 6 dB off. Fine, I could live with that, I was interested in
the
difference, if any, between 20M and the other bands.
40M Hit the mic button - got a reasonable looking sine wave.
Little
fuzzy.
20M Hit the button - wow, what a mess! Looked like multiple
unrelated sine waves at the same time.. Or something. What
was
it?
Let's look at this in the frequency domain...
Got out the tinySA, plugged it into the output of the Narda.
Starting
at 80M, I looked for the 3rd harmonic:
80M - 3rd harmonic -32 dB
40M - 3rd harmonic -18 dB
20M - All heck broke loose. Big mess. Spurs all over, in a
more
or
less symetrical pattern around the fundamental. The two
biggest
ones
were at 11.3 MHz ( -10dB ) and 16.55MHz ( -8 dB ). Looked like
the
unfiltered output of a
mixer.
- Jerry KF6VB Links:
------
[1]
[2] /g/BITX20/message/89054
[3] /mt/83413015/243852
[4] /g/BITX20/post
[5] /g/BITX20/editsub/243852
[6]
/g/BITX20/leave/10189903/243852/952924773/xyzzy
Links:
------
[1]
[2] /g/BITX20/message/89060
[3] /mt/83413015/243852
[4] /g/BITX20/post
[5] /g/BITX20/editsub/243852
[6]
/g/BITX20/leave/10189903/243852/952924773/xyzzy Links:
------
[1]
[2] /g/BITX20/message/89073
[3] /mt/83413015/243852
[4] /g/BITX20/post
[5] /g/BITX20/editsub/243852
[6] /g/BITX20/leave/10189903/243852/952924773/xyzzy
|
Which version of ubitx is this? The versions prior to v5 needed an extra lpf between the first mixer and the if amp?
Hi Farhhan,
I'll hook up my other spectrum analyzer today.? It's a Texscan
VSM-5D.? Only 4MHz-450MHz, but that's plenty for this.
HOWEVER, this test was without any amp.? Just the uBITX feeding the
Narda attenuator.? And the scope & the tinySA agree - lots of mixing
products.? Only on 20M.
Reading the block diagram, I am at a loss as to how such a problem could
occur.? The two biggest spurs are at the fundamental plus about 2.5Mhz,
and also MINUS 2.5Mhz.
Specific to 20M would only be the LPF.? And what failure in the LPF
could cause such a cacophony of mixing spurs?
I will also check the outputs of the si5351a - I am using the TSW Teensy
board, will try popping your display/vfo board back in.
? ? ? ? ? ? ? ? ? ? ? ? - Jerry KF6VB
On 2021-06-09 08:51, Ashhar Farhan wrote:
> The tinysa does not have shielding needed for a decent, spur free
> reading, at 40 watts of power it will probably read spurs even without
> connecting it up.
>
> On Wed 9 Jun, 2021, 6:41 PM jerry@..., <jerry@...> wrote:
>
>> Ashhar,
>>
>> I would expect the effect - of the scope not being terminated -
>> to
>> be minimal, because there was a 30dB Narda attenuator between the
>> uBITX
>> and the scope.? The Narda is rated for microwave, and is flat as a
>> board
>> through
>> HF & VHF.? And the difference at the input - what the uBITX sees -
>> between
>> terminated and not terminated ( at the output of the Narda ) - is
>> minuscule.? Because it's a 30dB attenuator - divides the power by
>> 1000.
>> So 99.9% of the power put into that attenuator is dissipated by the
>> attenuator itself.
>>
>> The idea was not to use the scope to *measure* the uBITX output
>> in any
>> absolute sense, but rather to compare it in a qualitative sense to
>> the
>> output of the uBITX
>> on other bands.
>>
>> The tinySA verified massive mixing product spurs on 20.? And it
>> *does*
>> have an internal termination.
>>
>> - Jerry KF6VB
>>
>> On 2021-06-08 21:45, Ashhar Farhan wrote:
>>> Jerry,
>>> I would suspect the measuring instruments. If you have an
>>> oscilloscope, then parallel up 20 of 2 watt/50 ohms resistors as a
>>> dummy load and measure RF voltage (with bandwidth filter on our
>> scope
>>> turned off) across the dummy load (not across the antenna jack).
>>> Once, you are sure of the Rf voltages, then, in parallel to the 50
>> ohm
>>> resistor bundle, add a 2.2K in series with a 50 ohms, such that
>> the 50
>>> ohms is connected to the ground side. Now, measure the RF voltage
>>> across the 50 ohms and the square of the ratio of raw to
>> attenuated
>>> voltages is your attenuated power. Crude by accurate.
>>> - f
>>>
>>> On Wed, Jun 9, 2021 at 10:02 AM Max via [1] [1]
>>> <kg4pid=[email protected]> wrote:
>>>
>>>> Do you think this is the cause of the amp failing, or damage
>> caused
>>>> by the amp failing and sending some rf back into the radio?
>>>>
>>>> Max KG4PID
>>>>
>>>> On Tuesday, June 8, 2021, 10:27:00 PM CDT, jerry@...
>>>> <jerry@...> wrote:
>>>>
>>>> All,
>>>>
>>>> To help me postmortem the Chinese linear,
>>>>
>>>> I was checking the output of the uBITX on various bands.? I used
>> a
>>>> Bird
>>>>
>>>> 4410 wattmeter with the 10kW slug ( which can be switched down to
>>>> 10W
>>>>
>>>> full scale ), and my trusty Narda attenuator as a load.? Here's
>> what
>>>> I
>>>>
>>>> got
>>>>
>>>> 3.615? MHz - 4.2W
>>>>
>>>> 7.029? MHz - 4.9W
>>>>
>>>> 10.115 MHz - 3.7W
>>>>
>>>> 14.030 MHz - 17W <======= HUH?
>>>>
>>>> 21.03? MHz - 2.5W ( more like it )
>>>>
>>>> 28.35M MHz - 3.9W
>>>>
>>>> That 14MHz reading is a doozy - no WAY is the uBITX making
>>>> SEVENTEEN
>>>>
>>>> WATTS.
>>>>
>>>> My wattmeter ( a recent Ebay purchase ) must be defective!
>>>> Specifically
>>>>
>>>> the slug, where all the RF stuff is.
>>>>
>>>> Let's double check this.? I lugged out a scope ( Rigol 1054z ).
>>>>
>>>> Plugged it directly into the output of the 30dB Narda attenuator.
>>>> No
>>>>
>>>> termination feature on the scope inputs, and I was too lazy to go
>>>> get a
>>>>
>>>> tee fitting and a 50ohm mini-load.? So the readings of the scope
>>>> would
>>>>
>>>> be 6 dB off.? Fine, I could live with that, I was interested in
>> the
>>>>
>>>> difference, if any, between 20M and the other bands.
>>>>
>>>> 40M Hit the mic button - got a reasonable looking sine wave.
>>>> Little
>>>>
>>>> fuzzy.
>>>>
>>>> 20M? Hit the button - wow, what a mess!? Looked like multiple
>>>>
>>>> unrelated sine waves at the same time..? Or something.? What was
>> it?
>>>>
>>>> Let's look at this in the frequency domain...
>>>>
>>>> Got out the tinySA, plugged it into the output of the Narda.
>>>> Starting
>>>>
>>>> at 80M, I looked for the 3rd harmonic:
>>>>
>>>> 80M - 3rd harmonic -32 dB
>>>>
>>>> 40M? - 3rd harmonic -18 dB
>>>>
>>>> 20M? - All heck broke loose.? Big mess.? Spurs all over, in a
>> more
>>>> or
>>>>
>>>> less symetrical pattern around the fundamental.? The two biggest
>>>> ones
>>>>
>>>> were at 11.3 MHz ( -10dB ) and 16.55MHz ( -8 dB ).? Looked like
>> the
>>>>
>>>> unfiltered output of a
>>>>
>>>> mixer.
>>>>
>>>> - Jerry KF6VB
>>>
>>>
>>>
>>> Links:
>>> ------
>>> [1]
>>> [2] /g/BITX20/message/89054
>>> [3] /mt/83413015/243852
>>> [4] /g/BITX20/post
>>> [5] /g/BITX20/editsub/243852
>>> [6]
>> /g/BITX20/leave/10189903/243852/952924773/xyzzy
>
>
>
> Links:
> ------
> [1]
> [2] /g/BITX20/message/89060
> [3] /mt/83413015/243852
> [4] /g/BITX20/post
> [5] /g/BITX20/editsub/243852
> [6] /g/BITX20/leave/10189903/243852/952924773/xyzzy
|
Re: RF power transistor all gone
John, thank you for the incentive to experiment. Looking forward to see what can be done. K3Bo
On Wed, Jun 9, 2021, 6:29 PM John Cunliffe W7ZQ < n2nep@...> wrote: Gentlemen,
All transistors but the BLV861 are gone.
Thank you all, I will be busy getting them all into the mail this weekend. Happy amplifier building I do hope to see some photos of your adventures? if they are for HF, VHF or UHF,
John
|
Re: Impedance 50 ohm Spectral analyzer HP8558B
CDT,
?
Well a simple answer is that there are two parts to Impedance. One part is the resistance that can be measured by your ohm meter. That is DC resistance. When you apply an ac signal to the device, then if there is some magnetic materials that would create magnetic fields an Inductive component along with the static electric fields (an Inductive component) then you get some components that impede the flow of electricity, hence impedance. The reason that is important is that if impedances are matched then the signal flows through the circuit without much loss (loss due to the dc resistance).? They call that impedance matching.? You can see some of those effects with waves on the water. If the waves hit a barrier then the waves are reflected back. If they don't hit a barrier they just keep going.?
?
fIf you have a rope tied to wall and shake the rope, the wave goes to the wall and is reflected back. But if you have a thin rope tied to a much thicker rope that is then connected to the wall then when you shake the rope, when the wave hits the junction of the thin and the thick rope, some physics magic happens, some of the wave moves into the thick rope but some of the wave is reflected back to the thin rope (as though it kind of hit a wall) this is what is called an Impedance Missmatch.? The original wave will continue on the thick rope until it hits the wall on the thick rope and the wave will reflect back along the thick rope (Impedance mismatch between the thick rope and the wall).
?
So what we see now is a wave traveling back along the thin rope (first reflection from the impedance mismatch between the thick and thin ropes) and we see the original wave starting to travel back from the wall along the thick rope.?
?
When that reflected wave of the original signal on the thick rope that is traveling back from the wall hits the junction with the thin rope, some of that wave will move onto the thin rope and some of that wave will reflect back towards the wall (because of the Impedance mismatch between the two ropes).
?
So what we see now (depending on the length of the thin rope compared to the thick rope) is a reflection of the original wave from the junction of the two ropes traveling back at you, and a smaller reflection of the original wave traveling back to you that bounced off the wall and crossed the rope junction, and a reflection of that from the rope junction traveling back towards the wall on the thick rope.
?
The space between the two impedance matches will have reflections sloshing back and forth diminishing over time.??
?
Lets say you gave the original signal one sine wave, (one up down back to center flip), and you listened to the rope, you would first see a small reflection back from the rope junction, then a larger (depending on all the impedance mismatches) from the signal that reflected back from the wall, then you would continue to see smaller and smaller signals coming from the ringing in the thick rope that escaped over the rope junction.
There is more technical detail with phase changes and such but that can get in the way of understanding the fundamental effects of Impedance mismatches.
So Impedance matches are important to limit reflections which is another way of saying resistance to your signal getting to the antenna or back from the antenna. The SWR? Standing Wave Ratio is a measure of the transmitted energy to the reflected energy and is a measure of how much of your signal makes it through to the antenna. So devices that have an impedance rating like 50 ohms are geared to connect to other 50 ohm devices and not reflect much energy. So readings should be more accurate because nothing is lost in the connection between devices.
Hope this narrative helps you understand some of those issues on a very coarse level. But good and important information esp. for low power operations like the ubitx and other QRP rigs.?
?
? ?---John AC9UV
On 06/09/2021 2:20 PM Gerard <kabupos@...> wrote:
?
?
Hello,
I am sorry to ask the question here, but I have not yet received a specific answer on the subject on the agilent group.
My question is simple: When we say that an analyzer has a input RF of 50 ohms, what does that mean?
I don¡¯t think it¡¯s so simple.....
I take an ohmeter on the input RF N, what i have to get?? 50 ohms, infinity, or something other?
you may see my topic here:
[email protected] | Hp8558b spectral analyzer (2/2)
I¡¯m stuck on my diagnosis
cdt
|
Re: RF power transistor all gone
Gentlemen,
All transistors but the BLV861 are gone.
Thank you all, I will be busy getting them all into the mail this weekend. Happy amplifier building I do hope to see some photos of your adventures? if they are for HF, VHF or UHF,
John
|
Re: Impedance 50 ohm Spectral analyzer HP8558B
Gerard,
This is a really basic question about electronics. The folks on the Agilent group probably didn't know where to start.
I suggest you do a google search for these three terms:
Resistance.
Reactance.
Impedance.
Resistance is what you get with an ideal resistor.
Reactance is what you get with an ideal capacitor or an ideal inductor.
Impedance is a mixture of resistance and reactance. Whatever
the particular circuit happens to have.
When they say your Keysight has 50 ohms *impedance*, they mean that AT THE FREQUENCIES OF INTEREST, its input looks more or less like a 50 ohm resistor. So if I feed it with an ideal generator with a 50 ohm resistor in series, by voltage divider action, you will see exactly half the generator voltage at the Keysight input. But generators are often specified as "50 ohm output impedance". The ideal generator part is buried inside, and you can't get to it. Generally, in order for the output voltage to be what you asked for on the front panel, you need to terminate the generator's 50 ohm output with a 50 ohm load.
- Jerry KF6VB
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On 2021-06-09 12:20, Gerard wrote: Hello,
I am sorry to ask the question here, but I have not yet received a
specific answer on the subject on the agilent group.
My question is simple: When we say that an analyzer has a input RF of
50 ohms, what does that mean?
I don't think it's so simple.....
I take an ohmeter on the input RF N, what i have to get?? 50 ohms,
infinity, or something other?
you may see my topic here:
[email protected] | Hp8558b spectral analyzer
(2/2) [1]
I'm stuck on my diagnosis
cdt
Links:
------
[1]
/g/HP-Agilent-Keysight-equipment/topic/hp8558b_spectral_analyzer/83405508?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,83405508
[2] /g/BITX20/message/89065
[3] /mt/83428634/243852
[4] /g/BITX20/post
[5] /g/BITX20/editsub/243852
[6] /g/BITX20/leave/10189903/243852/952924773/xyzzy
|
Re: Impedance 50 ohm Spectral analyzer HP8558B
Gerard I don't know if the 50 ohms includes DC (0 Hz) or not, but what it means is that the input of the analyzer appears to be a 50 ohm dummy load for the RF frequencies for which it is supposed to work properly.? ?Thats the normal impedance of coaxial systems, so that's the way it looks.? ?Typically they are NOT allowed to have more than a milliwatt or so of power going into them, however....
Gordon
On Wed, Jun 9, 2021 at 3:20 PM Gerard < kabupos@...> wrote: Hello,
I am sorry to ask the question here, but I have not yet received a specific answer on the subject on the agilent group.
My question is simple: When we say that an analyzer has a input RF of 50 ohms, what does that mean?
I don¡¯t think it¡¯s so simple.....
I take an ohmeter on the input RF N, what i have to get?? 50 ohms, infinity, or something other?
you may see my topic here:
[email protected] | Hp8558b spectral analyzer (2/2)
I¡¯m stuck on my diagnosis
cdt
|
Re: Impedance 50 ohm Spectral analyzer HP8558B
If the input is AC coupled you get infinity
If the input is DC coupled you should get 50 ohms if the analyzer is wide band. If it is an analyzer is DC grounded you should see 0 ohms
That said, my 8591E measures an open, it is specified for a maximum of 25V DC in and my
R3465 measures a short it is specified for 0V DC input.
Now,
If you look at the service manual of the 85xx series analyzers on page 386 you will see that the input of the analyzer goes to the attenuator and that the attenuator input is blocked by a 0.047uF 25V capacitor. So you should see an open with a DC voltmeter.
I hope this helps.
John
|
Re: Impedance 50 ohm Spectral analyzer HP8558B
It is RF Impedance.? Only loosely related to DC impedance.
Arv _-_
On Wed, Jun 9, 2021, 1:21 PM Gerard < kabupos@...> wrote: Hello,
I am sorry to ask the question here, but I have not yet received a specific answer on the subject on the agilent group.
My question is simple: When we say that an analyzer has a input RF of 50 ohms, what does that mean?
I don¡¯t think it¡¯s so simple.....
I take an ohmeter on the input RF N, what i have to get?? 50 ohms, infinity, or something other?
you may see my topic here:
[email protected] | Hp8558b spectral analyzer (2/2)
I¡¯m stuck on my diagnosis
cdt
|
Impedance 50 ohm Spectral analyzer HP8558B
Hello, I am sorry to ask the question here, but I have not yet received a specific answer on the subject on the agilent group. My question is simple: When we say that an analyzer has a input RF of 50 ohms, what does that mean?
I don¡¯t think it¡¯s so simple.....I take an ohmeter on the input RF N, what i have to get?? 50 ohms, infinity, or something other?
you may see my topic here: [email protected] | Hp8558b spectral analyzer (2/2)I¡¯m stuck on my diagnosis cdt
|
If I were doing it all over again, I would use an Si5351. That way, both the oscillators (plus the tracking generator too) would be taken care of. The low noise figure could be due to low gain in the front-end More gain in the later stages just amplifies the noise of the front-end along with?the signal. - f
On Wed, Jun 9, 2021 at 10:58 PM David Cooper KV4FP < coopers04@...> wrote: By the way, did I buy the proper version of the Si570?? I ordered the?XTAL OSC XO 100.0000MHZ LVDS SMD.? Output drive seems low.
Thanks,
--
David KV4FP
|
By the way, did I buy the proper version of the Si570?? I ordered the?XTAL OSC XO 100.0000MHZ LVDS SMD.? Output drive seems low.
Thanks,
--
David KV4FP
|
It's interesting that the noise floor has been around -93 dBm, with and without the first mixer post amplifier.? Will explore this some more.? I wonder if the log amp is setting the floor now.
The BFR106 seems like a good candidate.? The only concern might be power supply (Vceo is 15-16V and specs are at 8V).? What voltage have you been using?
I'm mostly a HW guy but an improved user interface would be nice.? I had thought of changing the pot to an encoder and some other improvements.? More computing power and a graphic display would be nice.? I've thought of pairing the Specan with a Rasberry Pi.
I'll order some BFR106's and let you know how I make out.? Thank you for helping,
--
David KV4FP
|
Raj vu2zap
Gerard