Typical current draw on the uBITx

Greggory N5WLF  observes that he gets in the range of 1.4-1.8 amps current draw on transmit, SWR depending and asks if this correct.

Feedback from the group suggests that:

  • on receive current draw is around 0.16A for an unmodified uBITx; and
  • on transmit it runs around 1.4-1.8 amps depending on the SWR.  On high SWR the finals can draw up to 2.2A approximately.A 2A fuse on the TX line and 0.5A on the main board seems about right in order to protect your uBITx.

Reference

IRF510 bias current

Jerry KE7ER says:

“Farhan recommends 100ma for the push-pull IRF510’s on the uBitx. More is better, you get into a more linear region of the FET. But more means more power getting sucked from the battery if portable, that power gets dissipated as heat in the FET’s.  I’m going with 100ma.

“With a 500ma quiescent drain current when using a 24v supply, each FET is dissipating 24*0.5 = 12 Watts.   That’s a lot of heat. Back off to 100ma and it is only 24*0.1 = 2.4 Watts.   Which still seems plenty.

“You want to be very careful when adjusting IRF510 gate bias trim-pots, take it too far and the IRF510’s might be trying to dump 100 Watts or so.”

Note that a Mitsubishi D16HHF1 in push-pull requires a higher bias current setting (perhaps 250 mA or 300aA).

Update on Martin AE7EU Top Board

 
Pictures: Front panel:  Headphone, Microphone, Encoder (from uBitx kit), 4 pushbuttons, AF gain, uBitx standard display.
 
Rear Panel:  +8V input, +12V (or ‘PA’) input (switchable), RF output, Teensy micro USB (CAT), PTT, Key, DSP Audio (from Teensy3.2), Linear control.
Martin AE7EU provides a detailed update on getting his “top board” working:
1) Mechanical clearances are okay.  Front panel mic/headphones need to move up by about 0.15″ to be flush to the encoder/display level
2) .1″ headers are misaligned, just needs adjusting in the gerber files, shouldn’t be too bad.  Big ‘PITA’ will be wiring directly to the uBitx on the first run for power, and since I only care about single power supply, this mod will only be roughly tested.
3) Messed up on a few pin headers on the front panel; mostly in that the pins from the AF gain resistor interfere with the main PCB, requiring that they be sanded down.  A 0.062″ move is all that’s needed.
4) BoM was heavily not optimized.  Optimized out a bunch of components to make everything 50-ohm, 1k, 2.2k, 5k, 10k, and 100k resistors, 0.01uF caps (minus one required 1000pF cap), and removed a bunch of 0.01uF caps that can be replaced with capacitor arrays, but some testing with the new values will need to be done.  Board is populated with optimized values.
5) Footprint for HC595 is incorrect, but usable.  Too narrow footprint, component wider.  Failure due to rushing out the door with the design before checking the footprints on a printout (didn’t have the component in hand).
6) Display module is actually the limiting factor for overall height.  A smaller display module, and the whole thing could fit in 1.25 (right now, designed for 1.5″)
7) PA Gain cutout is slightly off; still useable with a phillips head screwdriver though.
8) Incorrectly specified Aluminum electrolytics; changing to TH in next design, all 10uF
9) Found the RTC battery was almost fully discharged… will have to check out current consumption when not plugged in, it’s probably trying to run the CPU full tilt.
10) Need to change $1.5 PV36W 20-turn pots to 3/4 turn TX33 pots ($.10 each or whatever)
11) Optimize mods comes next after powerup and verification.
12) Need to verify winding orientation of the SWR bridge
Reference

Relay K1 mod

Fred PE0FKO asks a question about relay K1 after looking at the very nice schematic of the uBITX.

“The K1 relay is used for the RX and TX power switching and also for connecting the antenna in RX to the LP filter.   On RX (and TX) the LP filter is also a connection to the TX power amp by C80, that will give a (very) small load on the antenna signal at RX and a mixer (Q90 diode BE) for strong received signals?  Could it be improved by switching pins 12 and 14 of K1 and connecting pin 16 of K1 to C80 (removing the connection to the Low Pass filter)?”

Jerry, KE7ER responded:

“It’s a good idea to make use of K1-16 to disconnect Q90 during receive.  This would also protect Q90 from local QRO transmissions into a local antenna,   The similar Q13 on the Bitx40v3 is often blown in such situations, even when the rig is powered down.”

Alf Baranda asks:

“Can it be the Mod that I have highlighted?”

Of course it is the same mod!   Alf goes on to  attach images with the signal paths in the RX and TX modes.

REFERENCE

 

Using a dynamic microphone

Dennis Yancey asked the group “Has anyone used a dynamic mic on the uBITx?”    Dave WI6R responded with a guide for modifying the uBITx to use a Dynamic Mic:

Referring to the uBITX Schematic.   The Gain of the Mic PreAmp is controlled by R63 in the Emitter of Q6 to C62/R64.  It basically decouples the audio bypass of R64 by C62 to limit gain for the high output Electret Mics.

Substituting a Dynamic Mic

Replacing R63 with a Zero Ohm resistor and putting a 10K potentiometer at the Mic input should allow a Dynamic Mic to work now with a Mic Gain Control.  Also, R60 that supplies Mic BIAS to the Electret-Condenser Mic needs to be removed.  If there is not enough gain after this mod, you might have to reduce the value of R64 to maybe 470 Ohms or so. 

If you cannot look at your transmitted signal on a scope at least listen to your audio on another receiver to verify you are not causing distortion.

More Gain for an Electret Mic
To simply get more gain with an Electret Mic you might try dropping another 47 Ohm resistor on top of the existing R63.  You can solder another chip resistor on top by soldering one end at a time.
[EDITOR:  you can also bridge the surface mount resistor with a standard through hole resistor.  Shorten the leads and bend over about 1/8″ or 3mm for soldering to the ends of the surface mount component]
Reference

IRF510 mod for mounting alternate FETs

Raj VU2ZAP made this 4 way female Dupont socket for mounting either the stock IRF510 or Mitsubishi parts such as the  RD16HHF1 or RD15HHF1 in the finals circuit of his BITx40.  You must first desolder and remove the stock IRF510.  An extra hole is drilled in the circuit board to the left of the three existing holes for the stock IRF510 . The new pin hole to the left of the regular 3 holes is wired to the gate pin of the IRF510.

By reversing the RD16HHF1 orientation, and inserting in the left-most 3 pins of the socket,  the device now substitutes for the IRF510.  But you can re-insert the IRF510 at any time by unplugging the MOSFET.

Raj’s parting comment is that “you will need to think of a heat sink plate that fits this way!”

Reference

A nice looking aluminium enclosure

 

And another aluminium case suggested by wishbone_aaa:

https://www.circuitspecialists.com/metal-instrument-enclosure-la-6.html 

Jim Sheldon, W0EB says:

“I’ve got one on backorder for my third uBITX. The uBITX should ship pretty soon, so I hope the case backorder doesn’t take too long.  I’ve used the smaller versions of this case on other projects and it’s really nice to work with, but the aluminum front and back panels are really soft aluminium. Be careful drilling holes and cutting out the LCD window.”

Reference

MAX9812 Mic Pre-Amp conclusions

David N8DAH has been testing the MAX9812L Mic Pre-amp module on his BITx40.  In theory this should improve the gain and signal quality.

David says “So far its working ok at best I sound a bit robotish.”

“I am TXing at around 20w with my amp. I took the audio out through a 10uf dc blocking cap to the bitx40 mic in.  I powered the board from a 9v just for testing.  R136 is about 1/4. If you use a pre-amp you should adjust this lower or you will cause one heck of a noise on tx.  I am not yelling or shouting to get audio out now but not sure I like the audio in any case.

This is without the pre-amp … with the audio files from Michigan to Milford PA websdr

This is with the pre-amp …

David has decided he “might just stick with the slight yell to get the audio out. I like the idea of not having to shout but do not like the audio from this version of preamp”.

Others may think differently.  Mike ZL1AXG thought his “more robot-like” voice was more intelligible because it was more “punchy”.

Jeff AD6RH says:

“I used another mic housing with a DPDT switch and wired it so voltage is supplied only when PTT is engaged. I am using a CR2032 3v button cell. It seems to work fine, but I have not compared the stock vs. preamp mic with anyone on the air yet. It definitely has more average power on the watt meter. I can hear some peaks come thru the speaker when transmitting. I may try installing a pot to dial back the gain.”

Reference

Nextion Display

Fred W4JLE writes that he has just discovered the NEXTION display and he has begun using it on his BitX.

He says “what makes it really neat is the software that can be downloaded from the manufacturer’s site. It takes all the pain out of graphics programming. I have replaced the UNO with an STM32 as in addition to the normal stuff I have added a GPS module.”

The display shows time/location/grid square data as well as using the 1PPS in the GPS module to do a continuous correction to the SI5351a oscillator. The higher resolution allows calculating the SWR etc. with much finer gradations.

Fred says he will be adding a filter board from a CODAN that will allow all band operation which he purchased for $12.00 on eBay.

Fred’s concluding comment is that it is “Amazing what is available to the homebrewer today!”.

We are eagerly awaiting a link to his sketch and to see photos of his uBITx!

Reference