Re: Anyone ever use one of these to build a Raduino clone?
Yes.? I did that with a nano and 2lin display to modify and test code without messing
with the uBitx until I was happy.? It was an easy wireup and while its not as pretty/compact
it works just fine.
Allison
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Meanwhile, over on the Zed, KE0EYJ asks, "I was wondering if there is any kind of 5w HF radio (BITX?), combined with a Rasberry Pi (or something similar) running Fldigi (or similar) as one unit, that fits in the hand, yet can transmit digital modes (not like DMR -- I want intercontinental chat)? My idea is... what if we had an inexpensive HF-based radio for text communication using Domino EX or Thor -- which automatically transmitted/received on a few set frequencies, or a swath within the digital band, so that all users of that handheld radio model could easily connect?"
It seems that someone is probably working on integrating a Pi running digital with the ?B, as a standalone without a PC?
Thanks!
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It is just a dipole with 300ohm line. Also use a CHA 250 b.?
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Re: uBitx V4 linearity mod in final audio amplifier
#ubitx
Once I looked I noted that.? The DC quiescent point for the amp is not guaranteed due to HFE
of the transistors.? All of the traditional designs use the output (junction of the emitter resistors)
as the feedback and bias reference point for the amplifier.? Failure to do that can end up with
the devices at the output? close to the ground or power rails that you get asymmetric clipping.?
The LU1 design posted by Rahul offers better control of the DC operating point and very low distortion.
Also with feedback the crossover distortion issue is less likely.? However the one I use when not using?
LM386 is the circuit on page 1.12 figure 1.17 in EMRFD. The EMRFD design has a number of features
that make it desirable, actively set bias and feedback being significant. It always works when I build it
and? its clean sounding.??
However what is so bad about the LM386???
Allison
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Re: Nextion Displays >> warning
NOTE: I purposely ordered the 3.5 inch display.
Tom
AB7WT
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Re: Nextion Displays >> warning
I ordered a 3.5 inch enhanced display from what I think is the vendor ITEAD.? I used guidance from the ubitx.net reference.? Any confirmation on this model being correct or incorrect would be much appreciated.
Thanks!
Tom
AB7WT
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Re: Transmit indicator light.
Circuit diagram to enable this idea?..
On Sat, Apr 21, 2018, 3:51 AM Don, ND6T via Groups.Io <nd6t_6= [email protected]> wrote: In my opinion, the very best LED transmit indicator was the one that Derry Spittle (VE7QK [SK]) used in his Epiphyte QRP SSB series. That was just a 470 ohm quarter watt resistor through a small toroid and attached to a panel-mounted LED at each leg. The lead to the antenna passed through next to that resistor. That was it! When RF went to the antenna, it lit. You could easily tell if you were speaking loudly enough into the microphone, etc. Fast response, little panel space, and EASY. 73, Don
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Damage to uBITX from nearby QRO transmitter (no power out on TX) ?
#ubitx
Has anyone reported damage to their uBITX (little or no power out on TX) caused by previously keying a QRO rig nearby ??
This was a common problem with the BITX40 as high voltages present on the antenna input during RX,
caused by transmitting with a QRO rig close by, was frying Q13.
The?solution was to put a pair of parallel 1N4148 diodes to ground (each with opposite orientation) at relay K1 PIN12.
This is well documented in message # 25062.?
Looking at the corresponding part of the uBITX (v3) schematic it looks virtually identical to the BITX40 except the transistor in question is labelled Q90.
It seems that there is the potential for the same issue as with the BITX40 to occur (unless I am missing something).?
The solution appears to be the same, a pair of parallel diodes (opposite orientation) from relay K1 PIN 12 to ground.?
Cheers
Michael VE3WMB?
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Re: BITX QSO Afternoon/Evening, Sunday, June 17, 3PM & 7PM Local Time, 7277 kHz in North America, 7177 kHz elsewhere.
Skip, Sorry, I had been in the basement most of the evening. Didn't want wifey to feel neglected, happy wife-happy life! So I headed upstairs after the qso. The band was crazy last night. tim ab0wr On Sun, 17 Jun 2018 19:09:47 -0700 "Skip Davis via Groups.Io" <skipnc9o@...> wrote: I just heard AB0WR on trying to work a W9 call. I tried giving you a
cal. But you cleared out, you were strong here in western NC.
Skip NC9O
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Re: uBitx V4 linearity mod in final audio amplifier
#ubitx
Here is a nice similar design by LU1AGP for discreet AF amp. I also remember assembling few designs from Elektor as a kid in particular there was a very nice low noise one in a ZN414 based MW Rx.
73
Rahul VU3WJM
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It is a V3 ubitx board. I'm using CEC firmware. I get about 10w on 20m and 5w on 10m.?
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Re: Help with AGC kit wiring
What John and Bill said.
Joel
N6ALT
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Re: Transmit indicator light.
Another LED approach that works well is what's used in OZQRP's MDT DSB tx.?
As the uBitx is higher power it may be possible to use a smaller coupling capacitor (try 5-10pF instead of 22pF - not tried by me yet)
Circuit on p15 of the manual.?
73, Peter VK3YE
?
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Re: BITX QSO Afternoon/Evening, Sunday, June 17, 3PM & 7PM Local Time, 7277 kHz in North America, 7177 kHz elsewhere.
I heard a heterodyne on .277 around 8:30PM local....that was it ...did hear one station on CW calling CQ lower in the band but couldn't make out the call.
Conditions are terrible.?
don
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Re: Help with AGC kit wiring
What John said, a photo or two of the of the three pin mod would be great.
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Well there actually is some feedback, it is in the form of those emitter resistors in the final audio amplifier. R75 R77
The crossover distortion may be that in order to properly bias those transistors ¡°on¡±, just a bit of emitter current has to flow, creating a voltage drop across those two emitter ?resistors (e.g. choose 10mA * 4.4 ohms=44mV), which is not accounted for
by the Voltage drops across the?diode¡¯s on their base side.
Current through R75 should be about 0.6 mA.
Suggests added series R = 44mV/0.6mA= 75 ohms
Gordon (back of the envelope calculation¡¯s)
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Hi all.
I¡¯m about to buy another ubitx, but I¡¯m a little concerned about one or 2 of the posts concerning the audio of this latest board.
Has anyone with the V4 experienced any distorted audio or any other related issues? I¡¯m hoping this was an isolated case and not an issue with the audio circuit on these new boards....?
Regards
Carl M0CLS
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Re: Homebrew from scratch
#ubitx
Hi Richie, tnx for the pics re your ubitx modular approach . This is? homebrewing in the true sense.
Tnx for sharing .
73? Frank??? EI / GM0CSZ??? and KN6WH
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Re: uBitx V4 linearity mod in final audio amplifier
#ubitx
Mike and all UBITX enthusiasts,
when In looked on the schematic of the new audio amp my first thougt was: why is there no feedback from the output to the input?
Please have a look on the very old schenatics of "old" and discrete audio amps and even tube amps!!!
In all circuitries a feedback is installed to cancel the nonlinearities of the active elements.
Henning Weddig
DK5LV
Am 17.06.2018 um 23:23 schrieb Mike:
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Show quoted text
I believe there is an nonlinearity problem on some of the newer V4 uBitx radios (the one with transistors in the final audio amp). Two of my radios had this problem.
The problem is that the two diodes in the final amp doesn't make a voltage drop that is larger than the drop over the BJT B-C junction drops, so there will be a crossover distortion problem.
I did a mod: cut the trace between the diodes. Soldere in a 500 ohm pot paralelled with the a 125 ohm resistor. I adjusted the pot from a low value and increased the resistance until the nonlinearity disappeared by listening to a moderately strong cw signal. I checked the lower transistor so it didnt become too warn from the quiescent current.
73s
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Hi all.
I¡¯m about to buy another ubitx, but I¡¯m a little concerned about one or 2 of the posts concerning the audio of this latest board.
Has anyone with the V4 experienced any distorted audio or any other related issues? I¡¯m hoping this was an isolated case and not an issue with the audio circuit on these new boards....?
Regards
Carl M0CLS
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Arvo W0VRA
Raj vu2zap
Joel Caulkins/N6ALT
Peter Parker