Re: Wow... 15 volts in and a bunch out..
Hi Jerry,
I think you omitted 17 meters in that lineup. I am using external filters for CW on those bands and keeping it under 10 watts.
73,
Bill KU8H
toggle quoted message
Show quoted text
On 08/21/2018 01:03 PM, Jerry Gaffke via Groups.Io wrote: An MMIC between Q90 and RV1 is an easy way to add an extra stage.
/g/BITX20/message/51211
Of course, you still have to adjust the other stages to distribute the
gain properly.
Including those IF amps.
And to really clean stuff up, create a new board layout.
Rapidly becomes way more than most of us want to take on.
I think just operating the uBitx on 20,40,80m with an external LPF (or
cleaned up on-board LPF's)
and with mike levels appropriate for 5 to 10 watts out is acceptable.
We may still have IMD issues, a somewhat unsuppressed suppressed
carrier, some low level out-of-band spurs.
But such operation can meet our legal requirements.
I would not operate the uBitx with an external linear amp to boost power.
Not without a benchfull of gear to monitor the result.
Jerry
On Tue, Aug 21, 2018 at 09:06 AM, Gordon Gibby wrote:
Allison, what about adding an additional stage after the last mixer
in the transmitter lineup? Better choice of transistors (replace Q90
and maybe the other 3904¡¯s)... add (insert) a tiny daughter board
with an additional stage, could that allow for operating the
existing stages at more reasonable gain goals with more negative
feedback?
Further Having intercepted the signal it might also give a point
for bandpass filters to be easily inserted¡ª-
You might laugh at it, but even a single or dual-stage preselecter
with variable capacitor(s) tuning a parallel filter, (like what I
had on my heat kits), once marked for the proper positions for each
band, might significantly clean up most of them except for the 21
MHz debacle. ¡ª tune for maximum signal output making sure you¡¯re
near the correct Mark. If too much to ask from one inductor, add
a tap for the higher end
Gordon
--
bark less - wag more
|
Re: boosting the power on 28 MHz
#ubitx
Simple answere is NO .? But there are advantages as per below.
1.The Pinning on RD devices is GSD with device flat on its back. ( that means inter alia the final transformer has be direct wired to the? Drain of the RD - if the wire will stretch.)
2. RD16HH needs slightly? more? measured bias current? on D-S? leg to stay linear.
3. RD16HH is near idiot proof wrt SWR up to 15V (see datasheet)? but above that you are near one third of its? max operating condition and you take the risk of losing them if the output is unterminated. THe qualification voltage for these devices is 12.5V and many homebuilt amps with a pair have provided 16W out,? linear at 14V supply.
4. RD16HH has Source ie zero volts thermal/elec bonded to the tab, so if you provide approp support,? you can rejig existing sink arrangement and have both devices direct mounted on a common massive finned heatsink with NO mica washers under the devices.? Obviously to do that,? you would need a carrier plate that the PCB stands on via hex nut stand off legs, and the heat sink is mounted off that carrier plate.?
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Re: Wow... 15 volts in and a bunch out..
It has all been done before over 20 years back.? LT1252. It has essentially infinite input impedance. In this cct it is providing 5K input Z to the wiper of the potentiometer.? This chip can produce 50-60mW out at these voltages and at this load.? In this specific cct it drove the PA in class C to 4W RF.? There is no reason why the PA cannot be replaced by a 2n3866/4227 or any other "2W"? To39 RF? qualified transistor biased class A to produce 600-700 mW into a Trifiilar wound transformer, ie CT for use in a following class B stage.? This comes from a class of Video amps that will drive a +-5V signal into a 150R approx load given a 12V supply.? You can thank the great Dave Benson (SWL) for this cct but frankly a Chap called Breed used it some years before. again as? driver for a class C PA transistor. I respectfully suggest the OPT needs to be on a FB-61-202 core if you want good performance above 10 Mhz.? ? ?Take care with the component values on the schema. The leading decimal point is often meaningless.
Other devices / Sourcing?
An NE592 Will NOT work in such a circuit.? The LT1252 is out of production but still available out of SE Asia.? As Glenn? has pointed out to me the OPA2674 from TI is capable of even MORE and appears to be available on Ebay ex PRC? (but are they white spot chips from out back of the factory bin??).? ?A possible subs for the LT device (ie similar datasheet performance ) is the Max452CPA which Futurlec.com sell.?
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Re: Wow... 15 volts in and a bunch out..
The "bias-t" network shown in fig 2 of the datasheet on page 6 of the BGA616
is just an inductor up to the dc supply resistor plus a series cap to the following stage:
? ??
So exactly the configuration for U2 shown in Farhan's specan.
?
Jerry
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Show quoted text
On Tue, Aug 21, 2018 at 01:20 PM, Jerry Gaffke wrote:
If you want to feed it from 12v, then use a resistor of (12v-4v)/60ma = 133 ohms.
You lose some gain, because that 133 ohms is competing with your 50 ohm load at the output
for the available AC output power.? If that matters, add an inductor in series with the 133 ohms.
If running without the inductor, you are much better off feeding it from 12v than from 6v.
|
Re: Wow... 15 volts in and a bunch out..
Max supply voltage on an MMIC is a function of the supply resistor you choose.
Only the output pin itself is limited to 4.5v absolute max for supply voltage with respect to ground,
and that does not include the AC output signal that might be riding on top of it.?
Look at the top left graph on page 8 of the BGA616 datasheet?
showing device supply current vs supply resistor in ohms.
At zero ohms, the BGA616 looks like a zener diode with a knee around 4.0 volts.
Now look at the test circuit in fig 2 on page 6.
They are powering it from a 6v rail through a series 33 ohm resistor.
So the device is sucking (6v-4v)/33 = 60ma.
Table 3 on page 5 says the total device current is 60ma.
Coincidence?
So just think of it as a zener diode, as far as supply voltage goes.
If you want to feed it from 12v, then use a resistor of (12v-4v)/60ma = 133 ohms.
You lose some gain, because that 133 ohms is competing with your 50 ohm load at the output
for the available AC output power.? If that matters, add an inductor in series with the 133 ohms.
If running without the inductor, you are much better off feeding it from 12v than from 6v.
A string of two or three MMIC"s plus the Hans/Allison design for the BS170+IRF510 push-pull driver and final
could make a very nice power amp for the uBitx.
Downsides?
The MMIC's are not as cheap as the 2n3904's, and are not necessarily efficient with power.
The *Bitx* radios are back to basics, trying to do everything they can with npn transistors,
and an MMIC does not quite fit in.
But they are easy to use, and in a 50 ohm environment there is no need for transformers
Jerry, KE7ER?
?
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On Tue, Aug 21, 2018 at 12:52 PM, MadRadioModder wrote:
WARNING:? Max Vd on that part is 4.5VDC !!!
?
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Re: Wow... 15 volts in and a bunch out..
the temperatures taken with a sensor probe that sits on the heat sink of that transistor inside the enclosure closed up, and I would never take it outside. I do all of my radio stuff in the house.
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Re: Wow... 15 volts in and a bunch out..
If they're similar to MARS MMIC, input and output MUST be 50 ohms.
73
Ken VA3ABN
On Tue, Aug 21, 2018 at 3:52 PM, MadRadioModder <madradiomodder@...> wrote: WARNING:? Max Vd on that part is 4.5VDC !!! ? ? ? So I read the BGA616.? ?$1.50 from Digikey?? ? ? I see you provide a 33 ohm collector load resistor, drive it with 6 volts or less, and it SEEMS to have a 50 ohm input impedance and its own biasing.? ? ? Pretty interesting little amplifier.? ?Supposed to provide a power gain of 20 dB.? ? Seems like more than we really need but extra gain is probably easy to throw away with MORE negative emitter feedback resistance, instead of fighting for every bit we can pull out of 2N-3904 or other transistors.... ? Are there any downsides that you see to adding this after Q90? ? Gordon ?
Oh, I haven't done it.
Just kibitzing.
It could be another npn gain stage, just that an mmic involves fewer parts,
so easier to patch in ugly-style on the bottom ground plane.
An example might be U2 of Farhan's specan:
? ??
L5 is not totally needed, you just lose a little gain if all you have is a resistor between +12v and the output of U2.
The input and output of U2 must be capacitively coupled to adjoining stages.
The input and output of U2 are fixed at 50 ohms.
So basically a 4 pin IC, a resistor, and two AC coupling caps.
The MAV11 is an older MMIC, though certainly viable the manufacturer doesn't sell them at less than quantity 20:
? ??
Beware of ebay clones, they may or may not work for you.
There are hundreds of MMIC's available, at various power levels, gains, noise figures, frequency ranges, packages,? ...
Choosing one at random, take a look at the datasheet for the BGA616,? Mouser pnum? ?726-BGA616H6327XT
? ??
Jerry, KE7ER
On Tue, Aug 21, 2018 at 10:17 AM, Gordon Gibby wrote: Hi Jerry, can you produce a schematic with parts numbers on exactly how to do that? ? I¡¯ve never used one of those components before.? It should be easy to reduce gain in previous day just by simply changing some resistors to higher values in the emitter circuits.¡ª though I haven¡¯t looked at them
--
¡_. _._
|
Re: Wow... 15 volts in and a bunch out..
WARNING:? Max Vd on that part is 4.5VDC !!! ? ?
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Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Gordon Gibby
Sent: Tuesday, August 21, 2018 2:30 PM
To: [email protected]
Subject: Re: [BITX20] Wow... 15 volts in and a bunch out..? So I read the BGA616.? ?$1.50 from Digikey?? ? ? I see you provide a 33 ohm collector load resistor, drive it with 6 volts or less, and it SEEMS to have a 50 ohm input impedance and its own biasing.? ? ? Pretty interesting little amplifier.? ?Supposed to provide a power gain of 20 dB.? ? Seems like more than we really need but extra gain is probably easy to throw away with MORE negative emitter feedback resistance, instead of fighting for every bit we can pull out of 2N-3904 or other transistors.... ? Are there any downsides that you see to adding this after Q90? ? Gordon ?
Oh, I haven't done it.
Just kibitzing.
It could be another npn gain stage, just that an mmic involves fewer parts,
so easier to patch in ugly-style on the bottom ground plane.
An example might be U2 of Farhan's specan:
? ??
L5 is not totally needed, you just lose a little gain if all you have is a resistor between +12v and the output of U2.
The input and output of U2 must be capacitively coupled to adjoining stages.
The input and output of U2 are fixed at 50 ohms.
So basically a 4 pin IC, a resistor, and two AC coupling caps.
The MAV11 is an older MMIC, though certainly viable the manufacturer doesn't sell them at less than quantity 20:
? ??
Beware of ebay clones, they may or may not work for you.
There are hundreds of MMIC's available, at various power levels, gains, noise figures, frequency ranges, packages,? ...
Choosing one at random, take a look at the datasheet for the BGA616,? Mouser pnum? ?726-BGA616H6327XT
? ??
Jerry, KE7ER
On Tue, Aug 21, 2018 at 10:17 AM, Gordon Gibby wrote: Hi Jerry, can you produce a schematic with parts numbers on exactly how to do that? ? I¡¯ve never used one of those components before.? It should be easy to reduce gain in previous day just by simply changing some resistors to higher values in the emitter circuits.¡ª though I haven¡¯t looked at them
-- ¡_. _._
|
Re: Wow... 15 volts in and a bunch out..
So I read the BGA616.? ?$1.50 from Digikey??
?
I see you provide a 33 ohm collector load resistor, drive it with 6 volts or less, and it SEEMS to have a 50 ohm input impedance and its own biasing.? ?
Pretty interesting little amplifier.? ?Supposed to provide a power gain of 20 dB.? ? Seems like more than we really need but extra gain is probably easy to throw away with MORE negative emitter feedback resistance, instead of fighting for every bit we can
pull out of 2N-3904 or other transistors....
Are there any downsides that you see to adding this after Q90?
Gordon
toggle quoted message
Show quoted text
Oh, I haven't done it.
Just kibitzing.
It could be another npn gain stage, just that an mmic involves fewer parts,
so easier to patch in ugly-style on the bottom ground plane.
An example might be U2 of Farhan's specan:
? ??
L5 is not totally needed, you just lose a little gain if all you have is a resistor between +12v and the output of U2.
The input and output of U2 must be capacitively coupled to adjoining stages.
The input and output of U2 are fixed at 50 ohms.
So basically a 4 pin IC, a resistor, and two AC coupling caps.
The MAV11 is an older MMIC, though certainly viable the manufacturer doesn't sell them at less than quantity 20:
? ??https://www.minicircuits.com/WebStore/dashboard.html?model=MAV-11SM%2B
Beware of ebay clones, they may or may not work for you.
There are hundreds of MMIC's available, at various power levels, gains, noise figures, frequency ranges, packages,? ...
Choosing one at random, take a look at the datasheet for the BGA616,? Mouser pnum? ? 726-BGA616H6327XT
? ??
Jerry, KE7ER
On Tue, Aug 21, 2018 at 10:17 AM, Gordon Gibby wrote:
Hi Jerry, can you produce a schematic with parts numbers on exactly how to do that? ? I¡¯ve never used one of those components before.?
?
It should be easy to reduce gain in previous day just by simply changing some resistors to higher values in the emitter circuits.¡ª though I haven¡¯t looked at them
?
Gordon
|
Re: Wow... 15 volts in and a bunch out..
Oh, I haven't done it.
Just kibitzing.
It could be another npn gain stage, just that an mmic involves fewer parts,
so easier to patch in ugly-style on the bottom ground plane.
An example might be U2 of Farhan's specan:
? ??
L5 is not totally needed, you just lose a little gain if all you have is a resistor between +12v and the output of U2.
The input and output of U2 must be capacitively coupled to adjoining stages.
The input and output of U2 are fixed at 50 ohms.
So basically a 4 pin IC, a resistor, and two AC coupling caps.
The MAV11 is an older MMIC, though certainly viable the manufacturer doesn't sell them at less than quantity 20:
? ??https://www.minicircuits.com/WebStore/dashboard.html?model=MAV-11SM%2B
Beware of ebay clones, they may or may not work for you.
There are hundreds of MMIC's available, at various power levels, gains, noise figures, frequency ranges, packages,? ...
Choosing one at random, take a look at the datasheet for the BGA616,? Mouser pnum? ?726-BGA616H6327XT
? ??
Jerry, KE7ER
toggle quoted message
Show quoted text
On Tue, Aug 21, 2018 at 10:17 AM, Gordon Gibby wrote:
Hi Jerry, can you produce a schematic with parts numbers on exactly how to do that? ? I¡¯ve never used one of those components before.?
?
It should be easy to reduce gain in previous day just by simply changing some resistors to higher values in the emitter circuits.¡ª though I haven¡¯t looked at them
?
Gordon
|
Re: boosting the power on 28 MHz
#ubitx
Can the RD16HHF1 be used as a drop in replacement for the 510 or will these mods have to be made? Just looking to get my uBitx back on the air. Seems like a good idea to place these in the finals to get ready to make the mods, or would you recommend replacing the 510s and then do the mods all at once?
--
72 and God bless
KD4EPG
|
Re: Wow... 15 volts in and a bunch out..
Hi Jerry, can you produce a schematic with parts numbers on exactly how to do that? ? I¡¯ve never used one of those components before.?
It should be easy to reduce gain in previous day just by simply changing some resistors to higher values in the emitter circuits.¡ª though I haven¡¯t looked at them
Gordon
On Aug 21, 2018, at 13:03, Jerry Gaffke via Groups.Io < jgaffke@...> wrote:
toggle quoted message
Show quoted text
An MMIC between Q90 and RV1 is an easy way to add an extra stage.
?
Of course, you still have to adjust the other stages to distribute the gain properly.
Including those IF amps.
And to really clean stuff up, create a new board layout.
Rapidly becomes way more than most of us want to take on.
I think just operating the uBitx on 20,40,80m with an external LPF (or cleaned up on-board LPF's)
and with mike levels appropriate for 5 to 10 watts out is acceptable.
We may still have IMD issues, a somewhat unsuppressed suppressed carrier, some low level out-of-band spurs.
But such operation can meet our legal requirements.
I would not operate the uBitx with an external linear amp to boost power.
Not without a benchfull of gear to monitor the result.
Jerry
?
On Tue, Aug 21, 2018 at 09:06 AM, Gordon Gibby wrote:
Allison, what about adding an additional stage after the last mixer in the transmitter lineup? Better choice of transistors (replace Q90 and maybe the other 3904¡¯s)... add (insert) a tiny daughter board with an additional stage, could that allow
for operating the existing stages at more reasonable gain goals with more negative feedback? ??
?
Further ?Having intercepted the signal it might also give a point for bandpass filters to be easily inserted¡ª-
?
You might laugh at it, but even a single or dual-stage preselecter with variable capacitor(s) tuning a parallel filter, (like what I had on my heat kits),?once marked for the proper positions for each band, might significantly clean up most of them except
for the 21 MHz debacle. ?¡ª tune for maximum signal output making sure you¡¯re near the correct Mark. ?? If too much to ask from one inductor, add a tap for the higher end?
?
?Gordon
|
Re: New Group Specifically for "Homebrew Test Equipment"
My 2-cents worth, homebrewtestequipment, homebrew test equipment, or?DIYtestequipment? My first choice when using a search engine is the four words home brew test equipment or three words if you combine homebrew. Terry - KB8AMZ Brimfield Twp, OH USA EN91hd Linux User# 412308, Ubuntu User# 34905,?PCARS#78, NAQCC#6668, QRP-ARCI#8855, SKCC#14195
Hello
A few days ago I mentioned an idea for starting a separate discussion group for
home-brew ham radio test equipment.? The idea still seems interesting but I seem
to be struggling with what to call the group.? It needs to be short enough to type in
easily, and still definitive enough to not be confused with equipment for testing
pigs or homemade beer,? Some possible options that come to mind: - ??? (probably too long)
- ? (Home Brew Test Equipment)
- or....?
There are probably a myriad of better names.? Any ideas? My Linux NFS File Server has a Test Equipment directory that already has several ideas which could be used as a start for this new discussion group. I am sure that others have similar card files or computer files which would be
interesting to the rest of us who like building our own test equipment.? This
does raise questions about how to differentiate hardware test equipment
projects from combination hardware and software based test equipment?
On a slightly different direction........
In the past there have been a few complaints about the amount of software
discussion here on the BITX20 forum.? That raises the question of possibly
starting a separate discussion group specifically for software that is relative
to BITX based equipment.? Again, if such a forum were established, what
In the case of Homebrew Test Equipment and a possible new BITX-Software
group we would need a couple of volunteer moderators for each group.
We already have spawned an Antenna discussion group at
which is working quite well.? The moderators are doing a good job and some
interesting discussion has started.
I can start new discussion groups, but it is possible that someone else could do the same.? The process involves logging into the " create a group" page and filling out the form.? The process is quite easy and straightforward.
It will not hurt my feelings if you want to start one of the above groups, or another
group.? If you have ever envisioned yourself as being the Lord and King of a
discussion group...Go For It !
Arv? K7HKL
_._
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Re: Wow... 15 volts in and a bunch out..
An MMIC between Q90 and RV1 is an easy way to add an extra stage. ? /g/BITX20/message/51211Of course, you still have to adjust the other stages to distribute the gain properly. Including those IF amps. And to really clean stuff up, create a new board layout. Rapidly becomes way more than most of us want to take on. I think just operating the uBitx on 20,40,80m with an external LPF (or cleaned up on-board LPF's) and with mike levels appropriate for 5 to 10 watts out is acceptable. We may still have IMD issues, a somewhat unsuppressed suppressed carrier, some low level out-of-band spurs. But such operation can meet our legal requirements. I would not operate the uBitx with an external linear amp to boost power. Not without a benchfull of gear to monitor the result. Jerry ?
On Tue, Aug 21, 2018 at 09:06 AM, Gordon Gibby wrote:
Allison, what about adding an additional stage after the last mixer in the transmitter lineup? Better choice of transistors (replace Q90 and maybe the other 3904¡¯s)... add (insert) a tiny daughter board with an additional stage, could that allow for operating the existing stages at more reasonable gain goals with more negative feedback? ??
?
Further ?Having intercepted the signal it might also give a point for bandpass filters to be easily inserted¡ª-
?
You might laugh at it, but even a single or dual-stage preselecter with variable capacitor(s) tuning a parallel filter, (like what I had on my heat kits),?once marked for the proper positions for each band, might significantly clean up most of them except for the 21 MHz debacle. ?¡ª tune for maximum signal output making sure you¡¯re near the correct Mark. ?? If too much to ask from one inductor, add a tap for the higher end?
?
?Gordon
|
Re: Nextion 3.2 for CEC 1.097
#ubitx
Thanks Darren - works great.
73, Bill
|
Re: Wow... 15 volts in and a bunch out..
Allison, what about adding an additional stage after the last mixer in the transmitter lineup? Better choice of transistors (replace Q90 and maybe the other 3904¡¯s)... add (insert) a tiny daughter board with an additional stage, could that allow for operating
the existing stages at more reasonable gain goals with more negative feedback? ??
Further ?Having intercepted the signal it might also give a point for bandpass filters to be easily inserted¡ª-
You might laugh at it, but even a single or dual-stage preselecter with variable capacitor(s) tuning a parallel filter, (like what I had on my heat kits),?once marked for the proper positions for each band, might significantly clean up most of them except
for the 21 MHz debacle. ?¡ª tune for maximum signal output making sure you¡¯re near the correct Mark. ?? If too much to ask from one inductor, add a tap for the higher end?
?Gordon
On Aug 21, 2018, at 11:51, ajparent1/KB1GMX < kb1gmx@...> wrote:
toggle quoted message
Show quoted text
Tom,
Back when I was resorting to the full bag of tricks the goal was not more power!
The goal was even power from 80 through 10 and improved distortion levels.
Alas, the were other issues found that superseded that work.??
For the moment it was and is possible to improve the amp.? The problem is?
All the spurious product presented to the amp would be amplified as well.
That and the basic modulator/filter/if had issues as well.? The result was a
good amp would be largely wasted.? Then a collective bunch of us noted
other things like compromised output filters that allowed all that excess to
escape.? I like Warren reached the point that salvage was not possible.
I did literally cut the board up to investigate root cause issues and the
conclusions are harsh.
The amp is a disaster.? The radio is 80-10 the amp never made it to 20m.
The choice of devices and layout were big issues and the IRF510 was
blamed?for most of it and it was already a mess before we got to them.?
Plain english, the 2n3904 was a weak choice and poorly implemented
as asking it for more than 10DB at at 30mhz was impossible.? ?Layout
made for further issues with stability.
Output filters due to layout.? Again layout at HF still counts.
Lack of band pass filters before the amp.? I'll repeat what I've said?
garbage in nets garbage out, minimal filtering is wishful thinking.
IF gain issues.? Asking for 18db from 2n3904s is not engineering its wishful.
There are a few that will and many that will not.? IF one asked for 10db it
would not be an issue.? On that same boat , the high gain of the transmit
path leads to spurious signal creation.? To go from the modulator to the last
mixer no more than 16db of gain is needed across the 12 and 45 mhz if
for transmit.? We have on average 32 to 28db of gain.? Too much gain
causes problems those include poor carrier to signal and overload.
On top of that? The "12mhz" IF and filter layout made it susceptible to
the 11.997mhz carrier further reducing the carrier to modulation.?
Board layout is the major issue not circuit failure.
The above applies to transmit only but echos of that are in the
receiver as birdies and spurious responses.
The whole 12V thing was a result of the TDA2822.? My board I put in a
regulated voltage?for the TDA and end of issue. By doing that 13.8 was
the standard.? However that does not fix all the broken.? We or at least
I was not?tied to 12V.? If you think fixing that by running 20V or more?
is a solution its clearly a CB solution.
The bottom line is mod like mad for power?and your amping up a
lot of spurious trash and putting it on the band.
Allison
|
Re: Wow... 15 volts in and a bunch out..
Tom,
As a follow up I've built my own amp and also worked with Hands on his and?
as a result I have two different amps that can do 3-30mhz with nearly flat
power and very linear.? That's at 12V (not 12V is really 13.8 noninal).
It I take both of those to 20V I get 20+ watts of clean for the effort
but consider that the design was for 10W with headroom so that
10W isn't full up distorted.
As to using a boot converter...? Hope the switching noise doesn't show up.
The relays will tolerate 16V all day.? The rest should be regulated anyway.
Allison
|
Re: Wow... 15 volts in and a bunch out..
Tom,
Back when I was resorting to the full bag of tricks the goal was not more power!
The goal was even power from 80 through 10 and improved distortion levels.
Alas, the were other issues found that superseded that work.??
For the moment it was and is possible to improve the amp.? The problem is?
All the spurious product presented to the amp would be amplified as well.
That and the basic modulator/filter/if had issues as well.? The result was a
good amp would be largely wasted.? Then a collective bunch of us noted
other things like compromised output filters that allowed all that excess to
escape.? I like Warren reached the point that salvage was not possible.
I did literally cut the board up to investigate root cause issues and the
conclusions are harsh.
The amp is a disaster.? The radio is 80-10 the amp never made it to 20m.
The choice of devices and layout were big issues and the IRF510 was
blamed?for most of it and it was already a mess before we got to them.?
Plain english, the 2n3904 was a weak choice and poorly implemented
as asking it for more than 10DB at at 30mhz was impossible.? ?Layout
made for further issues with stability.
Output filters due to layout.? Again layout at HF still counts.
Lack of band pass filters before the amp.? I'll repeat what I've said?
garbage in nets garbage out, minimal filtering is wishful thinking.
IF gain issues.? Asking for 18db from 2n3904s is not engineering its wishful.
There are a few that will and many that will not.? IF one asked for 10db it
would not be an issue.? On that same boat , the high gain of the transmit
path leads to spurious signal creation.? To go from the modulator to the last
mixer no more than 16db of gain is needed across the 12 and 45 mhz if
for transmit.? We have on average 32 to 28db of gain.? Too much gain
causes problems those include poor carrier to signal and overload.
On top of that? The "12mhz" IF and filter layout made it susceptible to
the 11.997mhz carrier further reducing the carrier to modulation.?
Board layout is the major issue not circuit failure.
The above applies to transmit only but echos of that are in the
receiver as birdies and spurious responses.
The whole 12V thing was a result of the TDA2822.? My board I put in a
regulated voltage?for the TDA and end of issue. By doing that 13.8 was
the standard.? However that does not fix all the broken.? We or at least
I was not?tied to 12V.? If you think fixing that by running 20V or more?
is a solution its clearly a CB solution.
The bottom line is mod like mad for power?and your amping up a
lot of spurious trash and putting it on the band.
Allison
|
Re: Intermodulation Performance
On Tuesday, August 21, 2018, 3:35:46 AM PDT, Warren Allgyer <allgyer@...> wrote:
I am finished. This is simply not worth the effort. When it stops being fun, its time to quit \
Jim
|
Re: QRP SWR meter recommendation?
#ubitx
Jack,
Very interesting. Thanks.
Tom, wb6b
|
MadRadioModder
Terry Morris