Pititico ultra simple transceiver

As far as I can tell this ultra-simple transceiver has a passive receiver. It was designed initially by PY2OHH and this version appeared in this Canadian club magazine. Others have made versions for other bands. 

Clearly with such an insensitive receiver, it is better to call others calling CQ as you may not hear others on the frequency. The RX sensitivity will depend how good the headphones are.

See https://www.calameo.com/read/0076654746ade7e23a716 .

See also https://hackaday.com/2024/07/12/tiny-transceiver-gets-it-done-with-one-transistor/ .

PY2OHH pages

One of the best web resources is on the pages of PY2OHH.  Many pages are now in English and the site is filled with good ideas for simple circuits. If you are a home brewer then please do check this out. You will not be disappointed.

See http://py2ohh.w2c.com.br/ and look for the English translations.

Simple audio filter designs

The PY2OHH pages contain a useful link to a TI paper on active filters. In my experience, virtually any audio or RF transistor (e.g. 2N3904 NPN) can replace the op-amps with little effect. Some prefer "perfect" op-amps whereas I find transistors easier to work with and place. The performance difference is very very small.

2N3906 is a ubiquitous PNP equivalent.  The 2N3904 and 2N3906 devices are available from a range of suppliers for just a few pence each only. A few 2N3904s in parallel with small emitter resistors make a good HF/LF QRP PA replacement for a 2N3866 too. My recommendation is buy 100 of each (2N3904 and 2N3906) and stock your junk-box. Less than £10 and it will be a long time before you run short! Think of all those projects.
 
See http://py2ohh.w2c.com.br/trx/filtroativo/filter%20design%20in%20thirty%20seconds.pdf for the active AF filter paper.

PY2OHH's Pititico 10 parts transceiver for 40m

Andy Cutland has sent me this link. It is from, Miguel,  PY2OHH's excellent site which is full of ideas for QRP and QRPp enthusiasts. I can thoroughly recommend it for ideas.  I would expect this RX to hear signals, but be quite deaf as there is no audio gain apart from that in Q1.

Apparently the headphones were around 500 ohms impedance. I guess a crystal earpiece might work as audio is derived across R2. Maybe then C5 could be deleted?

Q1 must act as a (crystal controlled) regenerative detector on RX with the level of oscillation set by R2. Not sure of RX-TX shift as this will depend on RX and TX current. There is no low pass filter either, as shown. This means harmonics will also be detected and emitted. Still, this is meant to be VERY simple. I must try it.

http://4.bp.blogspot.com/-TlNqb0N-7V0/U0SFVljBTjI/AAAAAAAAUkY/xbyhirCu7AU/s1600/pititico.gif

Colpitts VFO parts value calculator

PY2OHH is a very creative ham with an excellent website full of good circuit ideas. I noticed a neat Colpitts VFO calculator there today. You put in the frequency range needed and the variable capacitor range available and out pop all the capacitor values in the tank circuit.

Since including this link the original site has removed the schematic.