Re: 2N2222A vs 2N3904 sourcing
I forgot to add that the original analogy was based on the BITX40 only using 3 stages to produce approximately the same power of the uBITX with 4 stages. With 4 stages there should be more gain to work with.?
Tom, wb6b
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Re: 2N2222A vs 2N3904 sourcing
Hi Allison,
That is a handy summation of the gains needed. If switching the pre-driver to a mosfet (or better bipolar transistors, if they provide the same gain advantage) could provide enough additional gain to relax the gain needed in the previous stages, then there would be room to tailor the gain (lower it at the lower frequencies). Before the design change of passing the TX signal through an additional 45Mhz filter that may have been possible. With the additional filter and the newly discovered IMD issues, more gain headroom may be needed than the gain than can be had by improving the pre-driver.?
Tom, wb6b
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Warren,
I understand it will fix getting a cleaner source and levels out of the IF.
You still can drive the mixers harder than compression at which things
get nasty with spurs and all.
Hows that going to fix the power amp gain fade of 10-11 db from 3 to 30Mhz?
The power amp is still tepid at best and suffers badly.
Allison
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Re: 2N2222A vs 2N3904 sourcing
all future will be told see wiki.
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That is not quite correct Iz. My plan is to replace the entire three transistor amplifier, taking the current input from C20 and delivering the MMIC output to C22. The MMIC I tested and published earlier in this thread is rated at +4 dBm out with 23 dB of gain and it produced excellent IMD with a little over 4 watts out. The MMICs on order are rated at +13.5 dBm out and the same 23 dB of gain. If they live up to specifications they will have more than enough output to drive the PA chain. Only testing will tell for sure.
WA8TOD
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Re: 2N2222A vs 2N3904 sourcing
Tom,
The PA is not the issue.? I have three designs using the IRF510 to as high as 50mhz
all wideband.? One even uses 8 of the in 4x4 push-pull for 225W at 6M.? with 6W in?
225 out is not what I'd call weak.
The ubitx has what I call a weak design using devices at gains unattainable at
higher frequencies like 20M and higher.? The problem is simple you need 47db
of gain from three stages to drive the finals.? The 3904s can maybe make
33db of gain at 10M and easily 50db of gain at 80m.? If you design the gain for
what they can do for flat 3 to 30 you get maybe 33db.? So you need more gain.
That means more stages and the ubitx has a shortage then.
Basically to get 10W from a IRF510 you need about 350mw at 80m and maybe 450 at 10M.
Put that in to a competent design you get 10 to 14W from IRF510s at 13V.? Do that at 24V
and put in about 800mw and 25-35W happens.??
But you need an amp that has the same gain at 80m and can produce that gain at 10M.
People make snide comments about the IRF510 being a switch and the 2n3904 is exactly?
the same thing, a cheap low current switch.
Since we have three stages and need 47db of gain that means the average gain
is 16db (round number is 48).? For that you need a device with a FT of not less
than 1200mhz (certainly not 3904s at 300FT).? TheDrive stange needs to do
1W for comfort. a pair of decent parts like 2n3866 or 2n5109(and others)
can do that easily.? That's not 4 but two.? But gain at high power is harder
so at best we can get 13db from them.? So the prior two stages need to produce
about 35db.? Best again is a single 5109 for the pre-driver and we get more
gain at lower power say 15db.? That leave the q90 stage needed to produce?
a few milliwatts and 20db of gain.? A 2n5179, BFR106, MAR6, and others
easily can do that.? Of course all the transformers need to be redone and
the output feed and transformer is pretty poor.? The board layout complicates
matters being much too tight.
allison
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I was thinking whether a MMIC up to 10dbm and an RD06HHF as driver like in the 10w qrp-pa-2008 might make sense
Il 16/set/2018 00:51, "iz oos" < and2oosiz2@...> ha scritto: Allison,
I know that in general MMICs (Mav, Ina, Era, Gali whatever) are eager of drawing current. If I understand Warren, he wants to change the first one or two 2n3904 in the chain just to clean the IMD. Then the one watt or more RF power transistor would be used.
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MRM,?
Roger that.? Pete has been doing it for a while and differing ways.? Experimenter he is.
We talk/write from time to time.
Multi-band is not terribly hard but requires attention and filtering and?
maybe layout tricks.
I've considered doing the ubitx dead bug again only dumping the Bidi used for?
something that doesn't make a 3904 vendor rich for quantity.? ?That Plessy bidi
I've used before for a very compact 6M radio and has good return loss and?
scalable gain.? Take out the dozen 3904 and replace with 3904 and two 3906
dial back the 45mhz gain to 10-11db.? Maybe loose a few attenuators and use
SBL1 or MD108s.? That should fit in much less space and in a nice straight line.
that alone will minimize crud pick up.
Allison
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Yes, as a matter of fact I have looked at the schematic.
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Tom,?
Have you ever even looked at the schematic or the web site???
That called bi-directional.? ?Thats the general? ways its done.
The Plessy is exactly the same only one is upside down for fewer parts as they
share the same 1k bias and feedback resistor.? The right to left is the NPN amp
and the left to right is the PNP.
If you mean the same device for either way there is a good one using a fet and a
pound of diodes and chokes in EMRFD.??
Allison
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Hi Terry,
I quickly tried the modifications to the sketch as I suggested earlier
today, and they seem to work OK.
I tested this on my own BitX40 and I could tune through the entire
80m band. Also the scan mode worked OK, and I could set the upper and
lower scan limits via the Function Button.
Of course, my BitX40 does not have the 80m filters, so I could'nt hear
much. But when I transmit a strong signal on 80m using a nearby
transceiver I can receive it on the BitX.
Good luck on 80m!
73 Allard PE1NWL
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Allison,
I know that in general MMICs (Mav, Ina, Era, Gali whatever) are eager of drawing current. If I understand Warren, he wants to change the first one or two 2n3904 in the chain just to clean the IMD. Then the one watt or more RF power transistor would be used.
Il 15/set/2018 22:25, "ajparent1/KB1GMX" < kb1gmx@...> ha scritto: Iz oos,
The big problem with MMICS is power...? The devices we are talking about eat 50-60ma each
and prefer to be run from a fixed voltage.? For a say 8V source that on the order of 400mW
each for receive or transmit.? Not friendly for battery powered systems.
The other price is layout has to be good or they will oscillate.
Allison
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Are the amplifiers used in the uBITX actually bidirectional? They just look like two independent amplifiers pointed in opposite directions and independently switched on so they don't create a big feedback loop.
Tom, wb6b
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Warren and Allison ?and others, excellent work! ? This is great teamwork! ??
Gordon
On Sep 15, 2018, at 16:56, ajparent1/KB1GMX < kb1gmx@...> wrote:
toggle quoted message
Show quoted text
On Sat, Sep 15, 2018 at 10:34 AM, Warren Allgyer wrote:
I don't have a lot of experience in this but my gut tells me pushing interstage gains to the 1 dB compression point is too much. When I did that with the MMIC boards the IMD jumped dramatically at even 0.5 dB compression and was borderline unacceptable at 1.0
dB. 1 dB compression, in my experience, generally makes my goal of -30 dBc third/fifth order IMD unattainable. I would not plan for any measurable compression for interstage blocks..... but that is me.
Absolutely correct.? Once you hit gain compression even a little you going to get undesired products as your in nonlinear land.
That is true for any amplifying device.
The mar8 at 30db is a possible in the q90 slot.? It hits the -1db gain at 12dbm so it has more than enough dynamic range for q90
or as 45mhz IF.? ? Watch their noise figures some are very unspectacular.
The ROT I use is 3db (power) headroom minimum.? Most MIMICs 10dbm out is about it unless you want to pay! Many barely do that.?
For example the ERA5 (at 75ma per) is -1db compression by 18dbm so back off 3db you seeing maybe 15dBm or about 31mW,
not enough for the predriver slot.
Where do I get that 3db... two equal tones (power).? More is better, that is the minimum.
A 2n2222A biased at 20ma or better a 2n3866 biased for 40ma and 11db of gain will hit about 22-23dbm (over 150mW!)
without stress and do 3-30MHz.? That would drive a heavier stage easily.? IF that one also did 10db you are in the 1W
region comfortably.? We do not need four transistors to do that as one 5109 or maybe even 2n3866 can do that.
For efficiency two devices at 10-12ma idle current push pull will easily hit the 2W mark (plenty of headroom).
Allison
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Re: My list of Firmware, Executables and Nextion Screens for the ubitx
Dr. Lees 3.5 is actually a 2.8 compiled for 3.5 ie it will only fill up 3/4's of the screen in the upper left corner. The only 3.5 screen that is a true 3.5 that I know of is Rich Neese's.??
If there is another out there i'm not aware of it.
Marty
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N5KBP
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ITs a mix of bitx and the plessy BIDI from EMRFD.
I've used the plessy Bidi and its two transistors and works well at 9-17db (depends on how you
bypass the emitters) included is a picture of page 6.61 of EMRFD.
I built a 6M compact radio using that. With the devices selected it works to about 30mhz at 17db
and at 14db good to 50.? The voltage applied must not exceed 6-8V.
Its upside is good gain easily laid out, reproducable, and compact.? Downside not easily understood
unless standing on ones head for the other direction.? The TR lines must switch to voltages with no
drop.
Allison
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Re: 2N2222A vs 2N3904 sourcing
Hi Allison,
I believe I've followed most of that thread. Assuming the BITX40 would also have issues at 10M, if it was driving another PA, in this case the uBITX Push-Pull PA, there may still be enough power from the "BITX40 PA" (uBITX pre-driver) to drive the uBITX PA at a decent power level.?
I'll go back and see what I may have missed in that thread.
Tom, wb6b
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Re: 2N2222A vs 2N3904 sourcing
On Sat, Sep 15, 2018 at 02:07 PM, ajparent1/KB1GMX wrote:
A BS170 or 2n7000 (pair) will do a watt push pull, and that is what we need.??
Hi Allison, Good information on the IRF510 still needing high?quiescent current even if it is run at substantially lower power levels. But I do see the transistors you list above are mosfets rather than bipolar replacements in the pre-driver. Do they provide greater gain in the pre driver? Although with the new added 45Mhz filter, maybe that is still not enough extra gain, assuming they provide more then the 2n2222s. Tom, wb6b
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Re: 2N2222A vs 2N3904 sourcing
I'd also point out that the ubitx as is can easily do 7W on 40M I've seen more.
That not the problem its what would the power chain for bitx40 do at 20M or 10M?
Based on prior work, badly.? IT was designed for 40M.
The problem your trying to fix is at 80m 12-15W is easy at 10M 2W is doing good.
and its gain distribution and device choices that are not up to it.? And its before
the IRF510.
See the tread stating at #49729 back in May.? It is very repetitious topic with everyone
not looking at what has been done by several people.?
Allison
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Allard PE1NWL
MadRadioModder
