Lash up Direct Conversion Receiver

[pwdrive]

Pouring with rain today so stayed in and lashed up direct conversion receiver, pulling in amatures on 40 meters quite well on a short piece of wire, 3 valves and a sig. gen. for the direct injection.

Lawrence.

[Shaman]

Hi, come on Lawrence, more details please....Alan.

[Mark R]

Indeed!

cheers Mark

[pwdrive]

Hi, come on Lawrence, more details please....Alan.

I was afraid someone might say that, definately no pics!
Made this afternoon with junk/spare bits...6AC7 rf amp, 6AC7 det, 6F6 audio o/p.
A/E inductively coupled to tuned secondary which connects via 100pf to G1 of RF amp, anode of RF inductively coupled to tuned sec. which feeds G1 of the detector, the sig. gen. (VFO) is also fed to the same G1 via 4.7pf.
Anode of the Det. has audio choke as the load, capacitor couples from signal end of said choke to G1 of the single ended sound output via vol. control, usual grid,cathode,screen resistors used and caps for decoupling/coupling etc, currently running on 175v HT. Seperate tuning capacitors for the two tuned circuits as the coils are from old scrap sets and have different inductance values....

Lawrence.

[Skywave]

Hi, come on Lawrence, more details please....Alan.

I was afraid someone might say that, definitely no pics!
Lawrence.

I just love a challenge.   From your descriptive text, I'll hazard a guess that it looks something like this . . .
it's only a rough sketch . . . .

[attachment=4777]

Whoops! The cathode of the mixer should be shown connected direct to gnd. / 0v.

Al.

[Shaman]

Well Lawrence this could be a homebrew special, there is nothing wrong with it, its nice now again to go back to basics, eg remember the HAC kits, see link below. One valver,s worth a bomb now on the Ebay site, why i wonder. When things like this can be made, well done....Alan.

http://vintageradio.me.uk/kits/hac_dx.htm

[pwdrive]

Hi Al....Good man, your spot on.

Hi Alan, yes I'm just going back to my youth with all this messing about, it's fun though.

Lawrence.

[pwdrive]

Hello again Al, at some point I would like to use an EB91 or similar as a balanced detector instead of the pentode, D/Conv. receivers work very well for what they are, as you no doubt know the ssb audio quality is crystal clear in D/Conv. receivers but as to be expected they need plenty of AF gain so it will be a triode pentode job for the AF if I build a proper one to make up any losses in an AF low pass filter or CW filter which I will probably incorporate. A stable VFO is mandatory.

Lawrence.

[ed731pdh]

Any complaints if I have a go at drawing this up proper? Have just upgraded my PCB software and lots more features to play with.

[pwdrive]

Ok, confession time, before I replied today on forum members comments about the D/Conv. lash up receiver I decided this morning to change it's nature, I have altered it to test the regenerodyne circuit in a very basic form, those in the know will have heard of the regenerodyne those that havn't it's basically a front end converter followed by a tunable regen detector it therefore has an IF but no IF amp, the center frequency of the tunable regen corresponds to the difference between the center of the frequency band required and a local osc frequency. The local osc frequency is usually fixed by a xtal so is very stable but in this lash up (just to prove it works) the local osc. is my signal gen.
Used the same three valves again, the RF amp is now a mixer (the converter) tuned grid from A/E as before but osc. frequency is injected at the cathode of this valve, the AE/RF tuning coil is the same as before it tunes approx 4 to 11 mhz so it is still covering the 7 mhz amature band as well as Shannon volmet and Shanwick down on the 5.5 mhz band.
I found another old SW coil with an anode primary and tuned secondary, this tunes from approx 2 to 5 mhz, I have chosen the center freqency of 3 mhz for the regen detector to kick off with so this coil was ideal, primary connected as anode load of the mixer, secondary to G1 (via 100 pf) of the regen detector, this coil needed a feedback coil winding on it for regen, I used 4 turns of insulated single strand, this coil was connected from the anode of the detector to the bottom end of the AF choke previously employed (with RF decoupling) for simplicity regen is obtained by sliding the coil up to the main winding 'till the magical point is reached (it's actually quite smooth..no ear screeching) I have "bandspreaded" the regen detector tuning capacitor with a series pf, it gives a tuning range of around 800 khz I have no drive reduction but it is still poss. to tune ok.
It works quite well, I first set the sig. gen. to 10 mhz to cover the 7 mhz amature band, and the RF tuning to 7 mhz, tuning the regen detector pulled in some transmissions ok, I then set the sig. gen to 4 mhz just to double check, it pulled in the same transmissions. Retuned the RF to 5.5 mhz and set the sig. gen. to 8.5 mhz, pulled in Shanwick, Shannon Volmet and RAF Volmet.
All in all everything ok and will be the basis for a proper regenerodyne come winter time, probably a cascode RF, seperate mixer and osc. low mu regen det., triode pentode AF. I will build and refine the regen detector first and optimise it for smoothest regen over as wide a frequency spread as poss without readjusting this will then serve as the basis for the rest of the receiver. I have not decided fully on the tuning range of the regen det. but probably 500 khz or 1 mhz...ish.

Ok Al, I need a revised circuit now......?

Lawrence