Category: Helpful hints

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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
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Arduino Nano Lights

John Backo answers the question:  “What are those lights on the nano anyway? And do I need them?”

There are usually 4 LEDs on the nano. They are usually in a row and labeled “RX TX PWR L”.

The RX and TX lights are connected to the lines that connect both the USB interface and the ATMega628P. They connect to TX0 and RX0. They are very useful as their flashing shows that communication is taking place during an upload. Likewise, if RX flashes once and then not again during an upload, there is a communications problem. Usually they are red and green; some may be orange. Messing with them will probably mess up RX0 and TX0. It is best to leave them alone. They are always out (low) with no serial communication to the chip. If they stay on, something is wrong…

PWR refers to a direct connection to the voltage regulated 5v line. It is NOT connected to the input voltage, whatever that may be. It is an indication that the board has power either from Vin or USB. That is all it does. It is usually red though I have seen many orange lights. It is useful, but it could be eliminated, I guess.

L is connected to D13. It is a good light and should not be disconnected. If the ATMega has a bootloader (which it should in a nano) this will flash three times when the reset button is pushed and released. That is not guaranteed because earlier versions of the bootloader did not show themselves through D13. And if the ubiquitous Blink program is loaded, it will falsh D13. That alone makes it a good light to retain. It is your “diagnostic visual indicator”.

Reference
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Warning: Some uBitx kits shipping with incorrect female connectors

KF2510 headers in uBITx

There are two 8 pin wiring male headers in the kit – one on the main uBITx board and the other on the Raduino.  Today, Arvo KD9HLC started assembling the wiring on his kit.  He found that the female plugs didn’t match the headers on the board.  After a bit of head scratching and further investigation he found that the female header plugs with flying leads only had 7 pins!

It is likely that other kit purchasers may have the same issue.

These headers are of KF2510 type, widely used in China and are very affordable.  Sets of 50 male/female pairs of 2, 3, 4 and 5 pins are available for about US$3 ex China if you can wait.  And 8 pin females can be found on the various Chinese merchant sites as well.   However, these headers are a bit harder to source in the US.   In NZ and Australia they can be sourced from Jaycar.

THe uBITx kits come with  2 x 8 pin, 1 x 3 pin, 1 x 2 pin wiring harnesses with KF2510 female plugs.   The Raduino unit connects to the main board with a 16 point pre-soldered header.

HINT:   You can substitute ordinary Dupont header strips or single female pins.  They won’t be polarised, so you will need to be careful making connections.

Reference
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Speaker Grill templates

Peter Cousins G4NJJ suggests that to get a tidy speaker grill on your EF01 or other enclosure you should have a rummage in the kitchen utensil drawer.

You may find the perfect template.  Peter used a plastic sifter lid as the holes were the size he wanted.

He drew a center line where he wanted it positioned, lined up the template, drilled one hole on the outer circle and inserted a nut and bolt, drilled a hole at the opposite end of the template, inserted a nut and bolt, and then drilled out the rest of holes in perfect place.  Hot glue allowed the speaker to be placed on the underside of the lid of the enclosure.  Done!

Oh and in case you wanted another idea for the template …  And just make sure the XYL is not aware of your minor “alterations” to essential kitchen equipment!

And if you want a variant on this theme of making a speaker grill look real classy, check out Glenn VK3YY’s website for  a ham shack alternative that won’t get you in so much trouble with the XYL:   https://vk3yy.wordpress.com/2017/01/22/bitx40-v3-and-raduino/

 

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Tuning up

End whistling into your mic with this suggestion from David GW4AKZ:

When using an antenna tuner on SSB, we could easily add a tone generator and switch to do that.

I have fitted a switchable -6db pad between the output of the pcb and the antenna socket. With the circuit switched in the worst case SWR is about 1.65 to 1 with an open or short circuit.  This prevents the finals from ever seeing a poor SWR.

Tune is easily achived with the key down and reduced radiated power when tuning up.

I use 2 watt carbon resistors 33 ohms in a t attenuator circuit. 2 in parallel to give 16.5 ohms which is close enough to the calculated value.  A relay is s used to switch this attenuator in and out.

Chris suggests replacing the 51 ohm resistors with 2x 100 ohm 3watt resistors.
REFERENCE
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IRF510 failure avoidance

Arv K7HKL notes that the problem with IRF510 RF amplifiers failing seems to be a recurring one for those who are not quite careful with antenna matching, bias level, and drive level.

As a way to start looking into this situation Arv performed some on-line searches to see how others were working around this problem.

There are a number of potentially useful ideas contained in those articles and discussions, but nothing that obviously applies directly to the problem of blowing IRF510 devices at only a few watts of power if the antenna is mis-matched.

Reference

 

Marco – KG5PRT notes from one of the stories reviewed …

… In the middle of the page:
“I destroyed many IRF510 FETs during testing. In fact I blew a small hole in one and another into several pieces. It was quite a shock when the first one was destroyed because it made a loud noise like a rifle being fired.

Once I got tired of replacing the FETs, I built a current sense circuit, which shuts off the bias once the amplifier draws more than about 3 amps from the PSU. I think this circuit is essential. You can build it into the Power Supply or into the Amplifier. I built it into the Amplifier because the power supply, which is also homemade, does not limit until 7 amps. With the current limit circuit the amplifier now survives transmitting into any SWR from an open circuit to a short.”

He notes that the  current limiting circuit has only 7 parts.

Reference

 

And  Arv K7HKL suggests implementing this bias control circuit used by AC2CZ in his 50 watt IRF510 linear.  He suggests you could probably do this using 2N3906 transistors.  Arv likes the fact that it includes a warning
light/LED.

Inline image 1
from: http://www.g0kla.com/scpa/SimpleCheapPA.php

Or this one:

Conclusions about protecting the IRF510 devices

Arv’s conclusions to date are:

  • Power supply current limiting (2.5 to 3A) seems to work.
  • Bias voltage shutdown on high current (3A) seems to work.
  • Driver impedance to IRF510 gate should be quite “stiff”.  Use a 50 ohm pad.
  • Use a low resistance (4.7 ohms) in series with each IRF510 gate lead.
  • Keep IRF510 leads short.
  • Impedance presented to the IRF510 drain should be 12.5 ohms.
  • RF output transformer should be 1:2 windings for 1:4 impedance transition. A Binocular core may work better…?
  • Avoid the problem by using some other MOSFET.
  • Use plastic fuses at 3A for self-healing action.
  • Fuse rig power at 2 to 3A to avoid IRF510 failures.
REFERENCE