Yay!? This also means that we cant do away with the post mix amp altogether... Maybe. We need 80 db of usable, distortion free range for good measurements. Let's see how we will get there. With 14 dbm iip3 of the specan, this would mean, the most powerful signal you can feed into it is 14dbm - 80d /2 = 14 - 40 = -26 dbm. The noise floor will have to be -26 dbm -80db = - 106 dbm. At 20 Khz bandwidth and 20db noise figure, the projected noise floor will be -174 + 43 + 20 = -111 dbm. You should be there. The scan showa that, instead, your floor is -90dbm. You should shoot for that extra 10 db dynamic range. The mav11 could have given you that extra sensitivity without compromising on the iip3. Infinion has some mmics you could use. Alternatively, a discrete BFR106 feedback amplifier could do the trick (with 20mA collector current). It is my favourite transistor now. Allison pointed it out to me. The original software is very dated. A better written software or a nextion display will make it much more useful. - f .
On Wed 9 Jun, 2021, 3:49 AM David Cooper KV4FP, < coopers04@...> wrote: Farhan and Chris, With the GALI-6+ still in place (it's U2, after the first mixer), adding a 6 dB attenuator between the generator and Specan caused the distortion product to fall 17.9 dB.? But the tone level only dropped 0.8 dB.? I could see some harmonic distortion in the IF amplifier output with a scope, suggesting significant non-linearity in the signal chain. Then completely removed the U2 GALI-6+ (and re-calibrated the firmware power meter constants).? There was already a 6 dB pad after the first mixer, so took the LO module output from that pad.? Results are shown below and are much improved.? With the generator directly connected to the Specan, the IIP3 is now -20 + 68/2 = 14 dBm (I think?).? When a 6 dB attenuator is inserted at the Specan input, the measured tones fall 5 dB and the distortion products fall below the noise floor. This seems to vindicate the two-tone generator though don't have enough dynamic range for the 6 dB attenuator test.? This seems like usable performance, though I may search for a replacement for the MAV/GALI to improve the noise figure. Thank you for your help, -- David KV4FP 
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Re: Chinese Linear R.I.P.
I was WN6EPS. It was a nice call - dit di-dah-dah-dit di-di-dit!
The other day, I QSO'd a guy who was running a pair of Conar twins.
Sounded just like the old days...Bwee bw-bwee-bwee-bwee. Chirps & clicks. I enjoyed it.
Conar was the brand of a mail-order technician course. They ran ads in the electronics magazines showing a happy student surrounded by kit-built equipment. The school was called "NRI" ( National Radio Institute ).
- Jerry KF6VB
toggle quoted message
Show quoted text
On 2021-06-08 18:26, Gerald Sherman wrote: Birdies?? I've been a ham for over 50 years.? In one of my very early
days I worked a WN---- (don't recall the rest of the call). The signal
sounded like he couldn't find a key, so he was pulling the canary's
tail!!
Gerry
Sent by the Thunderbird
<SNIP>They better have some *good* gain-killer for higher frequencies,
or it'll tweet like a bird.<SNIP>
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Re: Chinese Linear R.I.P.
Birdies?? I've been a ham for over 50 years.? In one of my very early days I worked a WN---- (don't recall the rest of the call). The signal sounded like he couldn't find a key, so he was pulling the canary's tail!!
Gerry
Sent by the Thunderbird
<SNIP>They better have some *good* gain-killer for higher frequencies, or it'll tweet like a bird.<SNIP>
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Re: Chinese Linear R.I.P.
Hi John,
Well, it was coincidentally on 80M when it died. And that is surely the band on which the uBITX gives the most output. But if that's enough to fry the finals, the amp and the uBITX are just not well matched. I imagine one could design some sort of network that would gradually reduce the gain at low frequencies and up it at higher frequences AND
maintain good SWR looking at the uBITX, but that's surely beyond me.
I saw somewhere that these IRF5xx transistors are sensitive to excessive gate voltage, and the allowable voltage is quite low - on the order of 4 volts.
Hindsight being 2020, I probably *should* have checked S11/return loss on the LPF with the nanoVNA before powering it up. I *did* check the S21 logmag, and it looked good.
If the amp does give a lot of spurious, most of THAT energy is surely reflected back by the LPF...
- Jerry KF6VB
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Re: RF power transistor all gone
BLF861 16
BLV861, 20 available
BLF278 6 available?
SRF3943 6 available
SRF426 (Mrf426)? 4 available
MRF150 gone
MRF314 4 available
MRF148 gone
MRF450 2 available
SD1480 gone
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Re: Chinese Linear R.I.P.
On Tue, Jun 8, 2021 at 06:52 PM, jerry@... wrote:
Hi Doug - no offense intended. QRP is fun. That's what ham radio is for - for me, anyway. Fun. But it's no fun when people don't hear you. And at my QTH, with my antenna, people mostly just don't hear me with 2 watts.
All very fair points.? I clearly misinterpreted an intention that wasn't there.
Doug, that's just unkind.?
You're right, it was.? I latched on to one word and ran with it.? As long as you're having fun with your radio the rest is noise. ? --
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Re: Chinese Linear R.I.P.
On 2021-06-08 14:11, jerry@... wrote: All, Nope, it was the linear. Almost a dead short across the supply
pins. It sucked all 35A out of the Astron power supply and wanted
more. I'm guessing that one of the final transistors let out the
magic smoke.
*** Unsoldered the final transistors - one of them tests as a MOSFET, the other one as a 1.8 ohm resistor. I'm guessing the latter is the bad one :). There is another Chinese amp that uses a real RF transistor. HOWEVER - this RF transistor is made for 850MHz up. They better have some *good* gain-killer for higher frequencies, or it'll tweet like a bird. Maybe I should just start from scratch, find a proper device and design ( or find a design ) around it? The MRF101AN looks good. It's an LDMOS device, designed for HF... - Jerry KF6VB
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Re: Chinese Linear R.I.P.
Jerry,
Did you measure the input impedance to the changed low pass filter before you applied power through it? It might not present an impedance that makes the transistors happy. Also, given the vastly different output power on the different bands, are you sure you did not drive the FETs to hard on the band it died?
John
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Re: Chinese Linear R.I.P.
Hi Doug - no offense intended. QRP is fun. That's what ham radio is for - for me, anyway. Fun. But it's no fun when people don't hear you. And at my QTH, with my antenna, people mostly just don't hear me with 2 watts. Also, I'm a ragchewer, not a QSO collector. 599-599-tnx QSO 73, not for me. And the instant somebody exits a QSO because they couldn't hear me, my hand goes for the power button. However, if you don't
like your QRP gear you could probably sell it and added to the money a
100w amp would cost buy a decent used 100w rig. Doug, that's just unkind. Shame on you. Actually, I have a perfectly functional TS-590S on my desk, and an Alpha 78. And an IC706MKII in the closet. And a 30L-1 in the shed. And a bank balance that would let me drop $12K on an ultimate whiz-bang ham station without even sneezing. But what would be the fun in that? - Jerry KF6VB --
www.bitxmap.com [1]
Links:
------
[1]
[2] /g/BITX20/message/89040
[3] /mt/83406567/243852
[4] /g/BITX20/post
[5] /g/BITX20/editsub/243852
[6] /g/BITX20/leave/10189903/243852/952924773/xyzzy
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Re: Chinese Linear R.I.P.
Discussion of amplifiers of modest size (50-100w) is pretty common across several large QRP mail reflectors I subscribe to, it came across here as little more than a playful jab.
As I recall, Ashar specifically designed the uBitx to allow the finals to operate off a higher voltage to increase RF output (25W+?). Ken, N2VIP
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Show quoted text
On Jun 8, 2021, at 19:25, Doug W <dougwilner@...> wrote:
?On Tue, Jun 8, 2021 at 04:11 PM, jerry@... wrote:
to boost a QRP rig into usefulness
I am assuming your intention was not to insult the 7,101 other members of this list that find QRP very useful.? However, if you don't like your QRP gear you could probably sell it and added to the money a 100w amp would cost buy a decent used 100w rig. ? --
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Re: Chinese Linear R.I.P.
On 2021-06-08 16:22, Terry VK5TM wrote: On Wed, Jun 9, 2021 at 06:41 AM, jerry@... wrote:.....I see the
same Chinese vendors have kits that use an actual RF FET - instead
of a switching FET. I wouldn't bet on that, a large percentage of 'RF Transistors/FETs'
out of China are faked.
*** Doubt it. That package is used only for dual RF devices. But the device could be used/surplus, or failed-QC. And the amp I'm looking at uses a device that's characterized at 850MHz. The fact is, one proper HF LDMOS device costs more than an entire Chinese kit. - Jerry --
Links:
------
[1] /g/BITX20/message/89039
[2] /mt/83406567/243852
[3] /g/BITX20/post
[4] /g/BITX20/editsub/243852
[5] /g/BITX20/leave/10189903/243852/952924773/xyzzy
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Re: Chinese Linear R.I.P.
On Tue, Jun 8, 2021 at 04:11 PM, jerry@... wrote:
to boost a QRP rig into usefulness
I am assuming your intention was not to insult the 7,101 other members of this list that find QRP very useful.? However, if you don't like your QRP gear you could probably sell it and added to the money a 100w amp would cost buy a decent used 100w rig. ? --
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Re: Chinese Linear R.I.P.
On Wed, Jun 9, 2021 at 06:41 AM, jerry@... wrote:.....I see the same Chinese vendors have kits that use an actual RF FET - instead of a switching FET.
I wouldn't bet on that, a large percentage of 'RF Transistors/FETs' out of China are faked. ? --
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Re: Chinese Linear R.I.P.
Jerry
I used to recommend that you set the bias pots for minimum current and then slowly increase one pot to increase the idling current by
100 ma, then increase bias on the other MOSFET until it increases by
another 100 ma.? Now I am not so sure.?
The device datasheet is probably your friend.? Calculate the load-line and find a current that is within dissipation limits and in a linear part
of the load-line.?
Gate capacitance (Ciss) should be the lowest capacitance device,
usually IRF510, not IRF520 or IRF530.
Arv _._
All,
? ?So I set up a test station in the garage, and was trying out the
Chinese linear again.? The uBITX was feeding the linear in CW mode, and
I was giving it toots with the mike switch.? The linear was plugged into
the LPF, and the LPF into a 30dB 20W Narda attenuator.? The Narda was
plugged into a cheap step attenuator, and the step attenuator into a
tinySA.
? ? Yup, the 3rd harmonic still really high.? Let's try another band...
All of a sudden, the power supply started buzzing louder, and the uBITX
screen went blank.? Oh, no did I burn out the uBITX?
? ?Nope, it was the linear.? Almost a dead short across the supply pins.?
It sucked all 35A out of the Astron power supply and wanted more.? I'm
guessing that one of the final transistors let out the magic smoke.
? ?So people - what's the class act in 100W ( or so ) final amps to boost
a QRP rig into usefulness?? I see the same Chinese vendors have kits
that use an actual RF FET - instead of a switching FET.
? ? ? ? ? ? ? ? ? ? ? ? ?- Jerry KF6VB
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Re: RF power transistor all gone
To make it easier,?
BLF861 20available.
BLV861, 20 available
BLF278 12 available
SRF3943 6 available
SRF426 (Mrf426)? 4 available
MRF150 4 available.
MRF314 4 available
MRF148 2 available
MRF450 2 available
SD1480 3 available.
John
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Re: RF power transistor all gone
On Tue, Jun 8, 2021 at 02:30 PM, Jamie Anderson wrote:
2SC3102
Sorry, that is a 12V part, the transistors I have are mostly commercial use with 28/32V or 48/50V
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Farhan and Chris, With the GALI-6+ still in place (it's U2, after the first mixer), adding a 6 dB attenuator between the generator and Specan caused the distortion product to fall 17.9 dB.? But the tone level only dropped 0.8 dB.? I could see some harmonic distortion in the IF amplifier output with a scope, suggesting significant non-linearity in the signal chain. Then completely removed the U2 GALI-6+ (and re-calibrated the firmware power meter constants).? There was already a 6 dB pad after the first mixer, so took the LO module output from that pad.? Results are shown below and are much improved.? With the generator directly connected to the Specan, the IIP3 is now -20 + 68/2 = 14 dBm (I think?).? When a 6 dB attenuator is inserted at the Specan input, the measured tones fall 5 dB and the distortion products fall below the noise floor. This seems to vindicate the two-tone generator though don't have enough dynamic range for the 6 dB attenuator test.? This seems like usable performance, though I may search for a replacement for the MAV/GALI to improve the noise figure. Thank you for your help, -- David KV4FP 
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All,
So I set up a test station in the garage, and was trying out the Chinese linear again. The uBITX was feeding the linear in CW mode, and I was giving it toots with the mike switch. The linear was plugged into the LPF, and the LPF into a 30dB 20W Narda attenuator. The Narda was plugged into a cheap step attenuator, and the step attenuator into a tinySA.
Yup, the 3rd harmonic still really high. Let's try another band... All of a sudden, the power supply started buzzing louder, and the uBITX screen went blank. Oh, no did I burn out the uBITX?
Nope, it was the linear. Almost a dead short across the supply pins. It sucked all 35A out of the Astron power supply and wanted more. I'm guessing that one of the final transistors let out the magic smoke.
So people - what's the class act in 100W ( or so ) final amps to boost a QRP rig into usefulness? I see the same Chinese vendors have kits that use an actual RF FET - instead of a switching FET.
- Jerry KF6VB
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Re: RF power transistor all gone
I¡¯m sure you don¡¯t have a surplus?board with a 2SC3102 Mitsubishi transistor on it, do you? ?I want to get my Yaesu 857 running on VHF and UHF again and need to roll up my sleeves and get some parts and start soldering.
On Tuesday, June 8, 2021, 12:47 PM, John Cunliffe W7ZQ <n2nep@...> wrote: Wow I probably could have a hundred of those and still would not be able to satisfy the need.
They are all spoken for.
That said though, I have plenty of other devices, mostly 50V or some 28V devices. They are used though and some are on circuit boards you can remove using a hot air gun.
If anyone is looking to build their own amps let me know I might be able to help with a device or two.
I had a couple of people asking me where the devices are from and how come I give them away.
The new devices like those 30 are left overs found somewhere in a corner of analog transmitter buildings that are being torn down. I rescue those and any power amplifiers, test equipment, cables or other items that might be usable to hams? before they are thrown into the trash or going to be recycled / destroyed. I give all test equipment (power meters, scopes,analyzers) away to the local Ham radio or hacker community. I give away VHF and UHF final amplifiers to the local community or take them apart for parts if they are not usable like water cooled units.The "used" transistors come from that environment I test those before giving them away.
Lastly, I give the items away because by corporate rules I can't make any profit of them.
All those who have send me requests, I will put them into the mail probably by this weekend and I will include instructions on how to pay for shipping. Please do not pay more than the actual postage on the package.
John
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Re: RF power transistor all gone
Wow I probably could have a hundred of those and still would not be able to satisfy the need.
They are all spoken for.
That said though, I have plenty of other devices, mostly 50V or some 28V devices. They are used though and some are on circuit boards you can remove using a hot air gun.
If anyone is looking to build their own amps let me know I might be able to help with a device or two.
I had a couple of people asking me where the devices are from and how come I give them away.
The new devices like those 30 are left overs found somewhere in a corner of analog transmitter buildings that are being torn down. I rescue those and any power amplifiers, test equipment, cables or other items that might be usable to hams? before they are thrown into the trash or going to be recycled / destroyed. I give all test equipment (power meters, scopes,analyzers) away to the local Ham radio or hacker community. I give away VHF and UHF final amplifiers to the local community or take them apart for parts if they are not usable like water cooled units.The "used" transistors come from that environment I test those before giving them away.
Lastly, I give the items away because by corporate rules I can't make any profit of them.
All those who have send me requests, I will put them into the mail probably by this weekend and I will include instructions on how to pay for shipping. Please do not pay more than the actual postage on the package.
John
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