Posts

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New uBITx: This is what you should not do!

Berenstain Bear tells the new uBITx owner:

  • Check and recheck every connection.   Wrong connections can result in major damage to your uBITx.
  • Check that you have your power supply wired around the right way.  There is little protection for reverse voltage mistakes on the uBITx withouth modification.
  • Check that you have not inserted the digital connector in the audio connector (or vice-versa).  This WILL damage your uBITx!   Mark these connectors now.
  • Do not power up without a 4.7K pull up resistor to 5v on the CW key pin.  Without this pull up resistor, the uBITx will arbitrarily go into TX.
  • Connect a 50 ohm dummy load, or a well matched antenna to the uBITx before attempting to transmit.  Failure to do will result in finals (IRF510s) that will blow up.
  • Do not touch any settings on the board. Boards are adjusted at the factory for correct operation. Do not adjust driver or bias pots, without having carefully read the instructions.  Over-driving the finals or setting abnormal bias levels can be catastrophic to your IRF510s.  Generally speaking, these controls should not be adjusted and do not require adjustment, even if you have read comments to the contrary on the email list.
  • Ask for help on the IO groups BITX20 list.  Fellow amateur operators are only too happy to provide assistance.
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How to even out uBITx power out

Bill Schmidt K9HZ has come up with a way of evening out the power output from the uBITx.

He says, “I had a couple of hours of spare time today so I started off my measuring the gain of the pre-drivers in the uBITx.. and sure enough, there is a lot of variation from 1.8-54 MHz (where I want mine to work).  Substituting the RD15HVF1 (my choice of RF PA) into the circuit with no other changes gives results similar to what John saw.. but it is because of the pre-driver stages.  I contemplated ways of compensating the drive with frequency but there isn’t a really good solution using reactive components because it causes some other non-desirable behavior (like a peak in drive at 21 MHz that is too high for the PA).

“I did land on a rather bruit force method that does work well… I removed RV1 (drive control) from the circuit board and replaced it with a tiny board with three small relays and four 100 ohm 10 turn pots.  The relays are controlled by the KT1, KT1, and KT3 drivers…  The short story is that now I have gain that is adjustable for essentially each of the bands (at least sets of bands that follow the LP filters).  I’ve adjusted the drive so that the PA puts out the same power (+/- about 2 watts) across the entire frequency spectrum.  I suppose this should have been an obvious answer, but I’m not fond of using relays for stuff like this even if they only draw milliwatts…”

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Wind 32AWG onto small toroids

 

Eric KE6US uses big blunt upholstery needles to wind toroids.  Just twist one end of the wire on. Thread it through the toroid, then just let it drop from gravity. It’ll weight the end down while you sort out kinks, etc., then pick up the end and drop it though again. Sometimes I’ll stand while I’m working if the wire is long. It goes very fast once you get a rhythm going.

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Power Amp fix

Erhart DF3FY, as well as providing a fix for the audio pop problem, has upgraded his PA output stage with RD16HHF1s.  Erhart suggests  the IRF 510s are not ideal for portable field operation.  The small output transformer represents a mismatch for power outputs greater than 5 W so he has incorporated a new output transformer.  He is now achieving 18w output on 20m and 12w on 10m, with an average of 15w output on all bands.

For details see his PDF file: fixes PA.

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Extron case

There has been a bit of discussion on the list about Extron cases.  These are aluminium cases that can be found with a search on eBay that come with other componentry that may be useful for a uBITx builder.

Vince Vielhaber KA8CSH found one that was big enough for a Bitx and would be a good fit. The BITx40 fits quite comfortably in it (after moving the power supply), but the only way the uBITx will fit is if the raduino is detached.  As you can see in the attached pics, it has plenty of BNCs for other projects and a power supply. Being 12v and 5v, the 7805 on the raduino could potentially be eliminated (provided, of course, the supply puts out over 1 amp).

Reference
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W0EB/W2CTX Firmware release v2.01R


Jim Sheldon W0EB has announced a further release of Firmware (v2.01R) of the W0EB/W2CTX firmware intended for I2C driven displays (including the newly announced “RadI2Cino” card which is an (almost) drop-in replacement for the Raduino.

This release effectively covers all the enhancements for the non-I2C Raduino released earlier (v 2.00R)

The following changes have been incorporated in the firmware:

“The CW Keyer module has been completely re-written in this version. The keyer is now totally interrupt driven which helps make the transition to CW transmit much faster and it doesn’t tend to clip the first dot as it did occasionally in past versions. This version also moved the DASH paddle input from the analog A7 input. It now shares the analog A3 input with the PTT line as normally PTT isn’t used in CW mode and the Hand Key isn’t used in CW Paddle mode or the Paddles aren’t used in CW Hand Key mode so all three can share the same input easily. This gives A7 back to those wishing to use it for metering applications. Complete, illustrated documentation on everything in this release is contained in the zip file as a PDF. Menu operation has been slightly improved from V2.00R as well. We hope you enjoy using this version. Jim – W0EB and Ron – W2CTX”

You can access the release details file as follows:
https://groups.io/g/BITX20/files/ubitx_V2_01R.zip

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Top Band (160m) external LPF

Bill NG1P provides a bit more detail on his Top Band (160m) mod success.

“I’m having a blast on 160m I did add larger heat sinks and a pair of small fans that I can turn on and off as needed to keep the finals cool if I’m long winded or using digital modes.

“Qrp labs makes a great low pass filter kit:
Read previous news iteM
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RX-TX Audio Pop Fix

Erhard Haertel DF3FY comments, “There are a lot of proposals for addressing the RX-TX audio pop with the uBITX, but none of them really works”.

Erhard has come up with his own pop-fix that involves muting the TDA amplifier during TX, turning the IC on with the 12V RX line (to prevent SSB noise in headphones during transmit) and additional decoupling for the 12V line.

Erhard says, “This fix cures all the issues”.  Write and tell us if you have tried this fix.

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Anderson Powerpole chassis mounts

Dave WI6R showed off his aluminium chassis to the list, but this resulted in questions about how he mounted his Anderson 12v powerpole connectors.

The answer is that you can use either of these mounting systems (the second was used in Dave’s case):

#1 https://powerwerx.com/powerpole-connector-chassis-mount-4

Note, that the mouting clamps do not have to be mounted on the exterior of an enclosure.  They can just as easily be mounted on the inside, making the who affair look more presentable.
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