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Re: Amplifier chain design - best practices

 

IMD can be caused by two things, saturation at high power and
cross-over distortion near idle conditions.

I suspect the high standing current prevents cross-over distortion
which is why you get better IMD performance.

tim ab0wr

On Sun, 23 Sep 2018 14:53:53 +0400
"Ashhar Farhan" <farhanbox@...> wrote:

Allison,
Modelling confirmed to me that fewer active devices (and hence higher
gain per stage), the better is the IMD. From an IMD perspective,
higher gain with high standing current results in better IMD.
That's why it makes sense to use a VHF power device as
driver/pre-driver block. I did a low distortion (less than - 40dbc
IMD) linear chain a few years ago. At 12v, It had to be an RD16HHF1
device biases for close to class A. At 1A of current, it gave 4 watts
of power. The details are on the emrfd group's file section.
- f
Re: Off-topic posts, Amplifier chain design

Jack Purdum
 

Mike:

I think your criteria may be too narrow. Not all of us are EE guys who understand the nuances of amplifier design. To me, most of the topics you're complaining about seem to make sense to me, perhaps because I'm not an EE person. Even something that appears off topic (e.g., K2 and its price) make sense to me since there needs to be a standard against which things are measured. Personally, judging against a well-known product is more insightful than fitting data to an equation from a book.

Often I read posts that I know I probably won't completely understand (like amplifier chain design) because I hope to glean some information from that post. Given that there are thousands of us here and a good chunk are not engineers, "off topic" to some may actually be the post that makes "the penny drop" for others.

Finally, we have a very capable monitor for this group who is unafraid to jump in when he feels the nature of a post or its thread doesn't serve the group's interests. I suggest that we leave the policing of this group to his judgement.

Jack, W8TEE


On Sunday, September 23, 2018, 12:25:42 AM EDT, K5ESS <k5ess.nothdurft@...> wrote:


If there was ever an appropriate comparison, the now overused phrase ¡°like herding cats¡± fits the bill with regard to keeping these group posts on topic.

Mike

K5ESS

?

From: [email protected] [mailto:[email protected]] On Behalf Of ajparent1/KB1GMX
Sent: Saturday, September 22, 2018 2:21 PM
To: [email protected]
Subject: Re: [BITX20] Amplifier chain design - best practices

?

Did a count and nearly 50% of the posts in thsi string have nothing to do with:

amplifier chain design - best practices.

About DBMs,
DBM drive levels
Low pass filters
Spectrum analyzer and probes.
K2 and its price.
SSD
QUCS

I might have forgotten a few.

Someone change the title to "WHATEVER/"

Re: Ubitx evolving fixes updated to wiki? #ubitx #ubitx-help

 

Thanks folks!? I found some good pages on filters to study up on.? Doesn't look too bad.? Think I'll go ahead and build them for the experience points :)
Re: Amplifier chain design - best practices

 

Farhan,

I am very aware that fewer devices are desired for better IMD.? ?The key is using
competent devices at attainable gains.? There are two problems with 3904s in that
role, gain compression at higher operating currents and a distinct problem with
delivering the desired gain at higher frequencies.? ?If they cannot produce the
needed gain any feedback required for?supporting input and output impedance
will be unpredictable producing a cascade of performance degradation.? Its not
what you may have built in some prior time as we have many tested that do not.? ?
Its about how to do it at some production level.

First is we do not ask a device to push above it weight class.? 2n3904 is not going
to deliver more than 12DB power gain at 3-30mhz and less than 1db gain flatness.
The power it can produce is not device dissipation its gain at currents higher than?
its peak current gain (about 10mA for HFE peak and HFE is well down at 100mA).
This shows well of a curve tracer.? We would deire for linear use a prt that has a
more or less flat current gain in the operating range.

By measurement we have insufficient drive and gain at frequencies approaching 8mhz.
As a result of those factors the IMD measured is seriously poor above 2W even on bands
where more power can be delivered.? The key here is power with acceptable IMD from
3 to 30mhz not 3 to maybe 10mhz.? ?We cannot do that with devices that incapable of
that for those first three stages.?

Note this is not an IRF510 issue as the driver has failed to deliver adequate drive and
the prior stages requires overdrive to function at all.? That does not help IMD or spurs.

Also bias of 1A for?RD16HHF is not class A above about 3 to maybe 4W and wanders
into AB1 above that power.? ?A pair of IRF510s at 12V can achieve that at about
250ma though at higher voltages can easily surpass that.? In general the RD16HHF is
about $4.50 more expensive to get maybe 3db better IMD at 12V if everything
around it supports that.? To do that prior stages have to built to do that.? The IK4AUY
amp (IRF510 pp driving IRF510PP) supports the ability of the part to perform.

In either case loading a IRF510 or RD15HHF to 50 ohms Drain to Drain is far too high
a load resistance for more than a few watts.? Reason is MOSFETs are voltage driven
current sources.? ?If you want power from them the load current must swing in the
linear current region without exceeding the available voltage.? So with 50 ohms and
not more voltage say 12V peak 2.88W is about it and we are driving devices to
saturation.? ?We need s a load line what can support a Drain current in the 1-2A region.
for that was need to get to 12.5ohms for a 10W amp without saturating or voltage clipping.
At that point we are running near 1A Peak current and likely with 200-500ma of bias we
are in the linear region for a push pull amp.? Combined with a reasonable feedback for
flatter gain vs frequency the IRF and RD are in the same region.? ?But this will be true
only if the drivers and prior stages are not suspect.

Allison
Re: Amplifier chain design - best practices

 

Allison,
Modelling confirmed to me that fewer active devices (and hence higher gain per stage), the better is the IMD. From an IMD perspective, higher gain with high standing current results in better IMD.
That's why it makes sense to use a VHF power device as driver/pre-driver block. I did a low distortion (less than - 40dbc IMD) linear chain a few years ago. At 12v, It had to be an RD16HHF1 device biases for close to class A. At 1A of current, it gave 4 watts of power. The details are on the emrfd group's file section.?
- f

On Fri, 21 Sep 2018, 21:21 ajparent1/KB1GMX, <kb1gmx@...> wrote:
On Fri, Sep 21, 2018 at 09:19 AM, Jeff Omundson wrote:
1)Keep amplifier intos and outofs away from each other.

This also applies to all RF systems.??

2)Keep amplifier gain stages reasonable.? Add more stages instead of upping gain.

This is a serious and common error, forcing or wishing for gain that is not predictably there.
Conservative design rules insure that.

3)Pick the right device for the desired frequencies.? Obviously 2n3904's don't work for this application.?

First the 2n3904 can if one does not apply wishful thinking and employs it within the devices capability.

***Does picking a part with an fT about 40 times the highest desired frequency a safe bet??
Oddly the answer is yes if the stages has to deliver at least part of the gain desired.? For a?
30mhz amp with a 20db stage gain you will need an Ft of something approaching 3000mhz!
The real question is does it makes sense when two 3904s at 10DB each can also do that?
at 30mhz.??

***Can you pick an FT that is too high (like a npn transistor with and fT of 10 gHz for a 3-30mHz radio)???
The answer is yes and maybe.? IF you using resistive feedback amps (nearly the entire transmitter and both IFs)
the required FT is a product of the gain and the frequency so at some point you really have to ask is that much
gain per stage reasonable and stable.? IT might be prudent to back down the gain and use a more reasonable
transistor.? Also for higher power stages the cost for a supergain high power device might break the bank.

A lot of QRP designs more so older one try to be minimal and get the most out of a very few parts.
If you making one this is ok as you can dial it in and hand pick parts.? For quantity builds this is terrible.
You want every one to be the same as the last.? So care in not trying to get 101% of capability is advised..
This shows more often in transmitter circuits as out of a group most doe the expected watts, a few do
more and a bunch never do that.? Multiband transmitters due to bandwidth, power and layout require
greater attention.

4)Keep RF wires/traces away from each other and from the dc path.
Again this works for RX and TX circuits.? We do not want o induce unwanted signals into the receiver.

From Crystal Sets to Sideband, a very good starting place.? My Favorite are Solid State Design For Radio Amateurs,
and Experimental Methods in RF Design (Both ARRL).? Neither are light bits and do require several reading through
passes to pick up that what was mentioned here is often elaborated and related to things there.

***Makes me wonder how the ft817 does hf, vhf and uhf...?

Lots of tuned filters, careful layout the use of the chassis as cooling, shielding, and mechanical support.

Its worth looking at Elecraft K1 and K2 as the manuals and detail in them is very good as examples.
I'd add KNQ7A? and the KD1JV Sopbucket 20 as a simple monoband, and a few other as well.? Generally
the designers are creative people so watch for solutions to problems not outwardly discussed as its
often not featured but important.? Cooling and layout are often not obvious without analysis.? Same can
be said for component choices.


Allison

Re: Amplifier chain design - best practices

 

¿ªÔÆÌåÓý

If there was ever an appropriate comparison, the now overused phrase ¡°like herding cats¡± fits the bill with regard to keeping these group posts on topic.

Mike

K5ESS

?

From: [email protected] [mailto:[email protected]] On Behalf Of ajparent1/KB1GMX
Sent: Saturday, September 22, 2018 2:21 PM
To: [email protected]
Subject: Re: [BITX20] Amplifier chain design - best practices

?

Did a count and nearly 50% of the posts in thsi string have nothing to do with:

amplifier chain design - best practices.

About DBMs,
DBM drive levels
Low pass filters
Spectrum analyzer and probes.
K2 and its price.
SSD
QUCS

I might have forgotten a few.

Someone change the title to "WHATEVER/"

Re: Amplifier chain design best practices

jim
 

Maybe not written stone, but rather silicon ...All diodes need a minimum threshold voltage to "turn on" ie start conducting ...Silicon happens to be about .7 volts, schottky about .3 volts ...Level "7" mixers have one diode per leg in the bridge,? Level "14" have 2 diodes in series per leg ..etc.?? You can build your own out of 1n914's if you wish ...Still gonna take X amount of volts to turn em on...If you don't meet "x" then your problems start ..

Jim

On Saturday, September 22, 2018, 4:46:11 PM PDT, Timothy Fidler <engstr@...> wrote:

st

Amplifier chain design - best practices? WHATEVER.

For whom it may concern : The 7 dBm/50Z? figure comes from a requirement which was common for the Minicircuits series of? DBMs? viz the ADE-01 and SBL-1 which used to be very common in ARRL Imprimatur designs.? It is not written in stone.? Some other? Minicircuits Dbms require other input power to meet the mafr's datasheets.?
Re: Ubitx evolving fixes updated to wiki? #ubitx #ubitx-help

Mark M
 

Low pass filter kits can be had from QRPLabs or you can build your own. The QRPLabs instruction documents have all the values they use...it would be easy to roll your own on a piece of perf board. Or some of the members here offer circuit boards. The components are not expensive or hard to find (altho it might be more cost effective to order them from QRPLabs). Lots of info online or in the ARRL Handbook on design.

Or see the wiki for details on how to hack the existing filters on the uBitX (thanks to Allison, et al.).

See for more info on the kits (disclaimer...I have no financial interest in QRPLAbs, just a customer).

73... Mark AA7TA

On 9/22/18 7:41 PM, ajparent1/KB1GMX wrote:
...
Spurs are less an issue for 20M and below.
External low pass or transmitting band pass filters are responsible way to go.
Re: Ubitx evolving fixes updated to wiki? #ubitx #ubitx-help

 

¿ªÔÆÌåÓý

Dave,

I can only speak with some authority about 20 meters.? I don¡¯t have antennas for the other bands so I haven¡¯t characterized my uBitx on those bands yet. ?I verified that my unmodified uBitx passed muster (by 1.6 dB third harmonic) for harmonics and spurs with my spectrum analyzer.? I¡¯m only doing FT8 not voice.? uBitx is running with about 7watts out on 20.? 298 confirmed QSOs since July which include Australia, New Zealand, Brazil, Alaska and Hawaii.? All with a fantastic dipole in the attic (see my QRZ page).?

Go for it.

Mike

K5ESS

?

From: [email protected] [mailto:[email protected]] On Behalf Of davedt1e@...
Sent: Saturday, September 22, 2018 7:57 PM
To: [email protected]
Subject: Re: [BITX20] Ubitx evolving fixes updated to wiki? #ubitx #ubitx-help

?

Sorry if I'm asking you all to beat a dead horse here, but I need to ask a few questions.

I've just passed my General, and would really like to get on the air.? Very much a neophyte.? ?

The "Simple Spurs Fix"? Looks easy enough for me to handle.? But not entirely clear as to whether this is required for 20 or 40 meter ssb.

For harmonics, would you all consider it responsible to use external filters in the coax?? Seems there's been some debate as to whether that is acceptable.? Are there suitable filters available for those bands? (low pass right?)? ?If not how does one go about building one?

I have read thru all of the posts repeatedly,? but there always seems to be a few things that stump me so sorry if I'm asking questions that have already been answered.

Any input would be much appreciated.

Re: Ubitx evolving fixes updated to wiki? #ubitx #ubitx-help

 

Doc sees horse,
? ? ? ? ? ? ? ? He's dead Jim!

Spurs are less an issue for 20M and below.
External low pass or transmitting band pass filters are responsible way to go.


Allison
Re: Ubitx evolving fixes updated to wiki? #ubitx #ubitx-help

 

Sorry if I'm asking you all to beat a dead horse here, but I need to ask a few questions.

I've just passed my General, and would really like to get on the air.? Very much a neophyte.? ?

The "Simple Spurs Fix"? Looks easy enough for me to handle.? But not entirely clear as to whether this is required for 20 or 40 meter ssb.

For harmonics, would you all consider it responsible to use external filters in the coax?? Seems there's been some debate as to whether that is acceptable.? Are there suitable filters available for those bands? (low pass right?)? ?If not how does one go about building one?

I have read thru all of the posts repeatedly,? but there always seems to be a few things that stump me so sorry if I'm asking questions that have already been answered.

Any input would be much appreciated.
Re: Ubitx - using Amateurradiokits.in AGC #ubitx

 

Sunil says to wire it just like the instructions for a Bitx20.? Still a little sketchy for me.? I need a schematic !!????

--
John
NQ3RP
Re: I find This Shorted Circuit on Raduino, here the pics..plz Help? #ubitx-help

 

Hi Skip,

yes I know that the v3 schematic is wrong an it was corrected in v4. Just wanted to show Fabian that the connection between these two pins is OK and has nothing to do with his reception problem, and he could concentrate on the alignment process.

I think your more detailed description will help Fabian.?

Armin, DJ2AG
Re: Amplifier chain design - best practices

Timothy Fidler
 

Amplifier chain design - best practices? WHATEVER.

For whom it may concern : The 7 dBm/50Z? figure comes from a requirement which was common for the Minicircuits series of? DBMs? viz the ADE-01 and SBL-1 which used to be very common in ARRL Imprimatur designs.? It is not written in stone.? Some other? Minicircuits Dbms require other input power to meet the mafr's datasheets.?
Re: I find This Shorted Circuit on Raduino, here the pics..plz Help? #ubitx-help

 

¿ªÔÆÌåÓý

Armin, both those are connected under that solder there is a tiny bridge connecting them. The schematic of the Raduino board showed pins 15 and 16 connected (on connector P3) which the clearly are if you measure the board removed from the UBitx. The connector Conn_01X16 on the UBITX schematic first of all has the pin numbers reversed, pin 1 should be pin 16. Also if you look carefully at that pin 16 you will see that it is floating and not connected to anything not ground like the schematic. Unplug the Raduino board and turn the board over and measure between pin 15 and 16 you will measure open circuit and measuring from 16 to ground should be the same. If now you plug-in the Raduino and measure between 15 and 16 you should read zero ohms or a short.?

Skip Davis, NC9O

On Sep 22, 2018, at 15:41, DJ2AG <ya_duck@...> wrote:

Hi Fabian,

sure I used my multi-meter to test connectivity before I sent my message and I also have? the FCI chip.

Please have a look onto attached picture, which shows my Raduino board. You can clearly see that both pins are connected (under solder mask). As far as I remember this was also the case with the first Raduino for BITX40. It may be confusing, but for sure it has nothing to do with your problem.

Are you using Memory Manager?

Regards
Armin
<2018_09_22_Shorted_Pins.jpg>
Re: si5351 crosstalk #radiuno

 

Lyn
Just to clarify. My uBITX still has the original Raduino in it. The DIY pcb I made was fitted to a VK4PLN Raduino just fopr testing? but is not in the rig itself.

The new 'buffer' board will fit directly onto the main uBITX board as shown? further down this thread. Once i actually make it.

glenn
Re: si5351 crosstalk #radiuno

 

Hi Lyn,
Not had time to make up the PCB for it, as yet.? Hopefully in coming week.

glenn
vk3pe


On Sat, Sep 22, 2018 at 07:43 PM, <lynatmts@...> wrote:
Hey Glenn, So what were the results of adding the buffer stages??
Thanks

Lyn
--
"You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat."
Re: Ubitx - using Amateurradiokits.in AGC #ubitx

 

Thanks, Richie.? The mystery is part of the fun, and frustration.

Eddie
Re: BCI Filter

Joe Puma
 

¿ªÔÆÌåÓý

I don¡¯t have your reference at my disposal. Do we need a BCI to transmit through? The BCI mid for the ubitx puts a BCI filter in the RX path only. So my question was is will the one I provided work from a tech spec point of view.?


W3NQN has some nice filters. ?RX only and TX. A bit pricey though. ?

Joe




On Sep 22, 2018, at 5:40 PM, ohwenzelph via Groups.Io <Ohwenzelph@...> wrote:

QST Feb ¡®78 p22 BC-Band Energy ¡ª A Rejection Filter W3NQN
does this look one could transmit thru it?

Re: BCI Filter

 

QST Feb ¡®78 p22 BC-Band Energy ¡ª A Rejection Filter W3NQN
does this look one could transmit thru it?
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