Pages: [1]   Go Down

Author Topic: qrp 40 Meter SSB transceiver $45 on Amateur Radio Roundtable  (Read 5037 times)

W5KUB

  • Member
  • Posts: 318

This week on Amateur Radio Roundtable, Rich Moseson W2VU, editor of CQ Magazine, will be with us talking about next months edition. Katie Allen, WY7YL will be back with us and showing us the new tower they recently constructed. Tom W5KUB will talk about and demo the new BITX40 40 Meter SSB transceiver for $45.00  See the first contact made on it.  It was with ZS6CCY in South Africa, not bad for a qrp radio and dipole antenna.  Tune in at W5KUB.COM at 8 PM central time Tuesday nights to watch. Phone lines and chat room will be open to viewers for questions and comments. This show is also simulcast on famous international shortwave radio station WBCQ on 9330 KHz each night.  (0200 UTC Wed)
Logged

W6EM

  • Member
  • Posts: 1944
RE: qrp 40 Meter SSB transceiver $45 on Amateur Radio Roundtable
« Reply #1 on: November 29, 2016, 05:27:22 PM »

This week on Amateur Radio Roundtable, Rich Moseson W2VU, editor of CQ Magazine, will be with us talking about next months edition. Katie Allen, WY7YL will be back with us and showing us the new tower they recently constructed. Tom W5KUB will talk about and demo the new BITX40 40 Meter SSB transceiver for $45.00  See the first contact made on it.  It was with ZS6CCY in South Africa, not bad for a qrp radio and dipole antenna.  Tune in at W5KUB.COM at 8 PM central time Tuesday nights to watch. Phone lines and chat room will be open to viewers for questions and comments. This show is also simulcast on famous international shortwave radio station WBCQ on 9330 KHz each night.  (0200 UTC Wed)
Here's the link to the BITX40 website.  http://www.hfsigs.com  I ordered one last week.  Unbelievable deal.
Logged

W3TTT

  • Posts: 324
    • HomeURL
RE: qrp 40 Meter SSB transceiver $45 on Amateur Radio Roundtable
« Reply #2 on: November 30, 2016, 11:43:01 AM »

 :D

I just bought, received, and completed in a commercial enclosure, a BITX 40.  I think it is a nice radio, especially for the price. 

Just a couple of things:
Frequency drift in the first half hour. 
Loud snap in the headphones when I key the transmitter.

Many people have installed a outboard VFO to solve the first issue.

I don't have a solution to the second issue yet.  Just turn down the volume before keying up.   ???

73, Joe W3TTT
Logged

AC6AN

  • Member
  • Posts: 46
RE: qrp 40 Meter SSB transceiver $45 on Amateur Radio Roundtable
« Reply #3 on: November 30, 2016, 02:21:49 PM »

Try a quick experiment to isolate the thump: temporarily remove C122, it's the 1uF cap from the mic amp Q12.
If the thump is gone then the issue is most likely the abrupt switching of the DC voltage on that cap.
The simple bidirectional design does not have a mute circuit before the audio preamp. It may be required.
Logged

KB1GMX

  • Member
  • Posts: 2252
RE: qrp 40 Meter SSB transceiver $45 on Amateur Radio Roundtable
« Reply #4 on: December 03, 2016, 11:46:43 AM »

This is the BITX, and long running and well known minimal art transceiver originally done for 20M.
For minimal art radio this is a great design.   One heck of a bargain for what you get too.

This issue "pop on RX" is old and well known and seen on may other as well is a result of the effort
to keep it simple.  The basic cause is your switching the audio amp and the preamp off on TX and
on for RX and the amplifier needs a bit of time to "settle" due to the various caps that discharge
during TX.

I'd note the KNQ7A also has the same problem for mostly the same reason.

The easiest fix is back to back diode at the output to limit the amplitude of the pop.  Downside is
distortion at high volume and its not 100% effective.  Makes it tolerable.

Another is adding a resistor (try 10K) from point M1 to ground.  That keep the voltage across
C115 stable.  Same for the junction of C107 and C116.  It may help.

In mine (older 20M version) I used the switched voltages  and kept the RX audio amps live
but muted using TX+ to turn on a 2n7000 across the volume control and RX+ delayed using
RC (10k and .1uf) to the gate of a 2n7000  in series with the headphone output.  Didn't get
rid of it 100% in that instead of a really loud pop it was more like a mild low frequency thump.
I stopped playing at that point as it was adequate but playing with it and the various caps
could produce a better result.

Anyone solving it completely without adding a ton of parts should publish it.  Also note that
playing in that area can degrade TX audio as well, use care and test.


Allison

Logged
Pages: [1]   Go Up