Lash up Direct Conversion Receiver

[pwdrive]

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.

No objections from me ( and no doubt not from anyone else) The one Al (Skywave) did is spot on with his correction . I did not include the component values in my inital description as the thing was a lash up (ugly style, cave man style or whatever) The actual values are what you would typically expect to find in the valve stages employed but as a clue the total HT current consumption is well under 50 ma, if it goes over that then something is doing overtime. I have to say though that it is not a finalised design so I don't want it all over the web as the be all end all receiver designed by me if you see what I mean, when I do the final acceptable project then we can tell the world. So yes do use your new circuit software and post it up if you can.

Lawrence.

[Mark R]

Lawrence in view of your last comment do you want this thread moving to the members section?
I can create a sub forum in the service data section, for say........ongoing secret projects.
This part of the forum is viewable by all.

cheers Mark

[Skywave]

Hi Lawrence,

The original circuit; my sketched drawing, based on your text. Why the 100 pF cap. at the grid of the R.F. amp.? It isn't needed: there's no AGC voltage to keep away from the input L/C; no -ve bias rail fed to the grid: bias is set at the cathode.

Al.

[Shaman]

Hi Lawrence, if i remember, without going through all my old Practical Wireless. F.G. Rayer was a d/conv receiver man, goodness i have made up some of his desighns in the past.....Alan.

[pwdrive]

Hi Mark no, no worries leave it where it is if that's ok.

Hi Al, no need of it whatsoever it just happened that there was a 100pf hanging of the valve socket along with other bits of existing components on the scrap chassis I knocked it all up with. Initially I made use of it in an attempt to have a double tuned (ganged) grid circuit for the RF amp but I decided to use one of the coils as the detector grid tuning instead, what a lash up....

Lawrence.

[Mark R]

Lawrence I shall put it back when my cock up is sorted out

[Skywave]

Lawrence: it's not a 'lash-up': it's called an 'R & D project, initial stage of', least that what I have always found design engineers term such 'configurations'.

Incidentally - and again referring to the Mk. 1 design - did you find it necessary to introduce any screening between the grid and anode ccts. of the R.F. amp.? I ask that since there are tuned L/C ccts. in both: feedback, instability, etc.

Al.

[pwdrive]

Hi Lawrence, if i remember, without going through all my old Practical Wireless. F.G. Rayer was a d/conv receiver man, goodness i have made up some of his desighns in the past.....Alan.

Yes I believe he was, here is a link to a DC receiver overview by Pat Hawker.

http://www.epanorama.net/sff/Radio/Commu...rt%201.pdf

Lawrence.

[pwdrive]

Lawrence: it's not a 'lash-up': it's called an 'R & D project, initial stage of', least that what I have always found design engineers term such 'configurations'.

Al.

Ok then it's a lash up of an R&D project...Seriously I always do a basic of a design to see if it vaguely works before spending any money on any posh bits in the final design and build. While I'm on the subject Al am I correct in thinking you have a Racal? if so whats the crack on that harmonic generator they use with a 1 mhz xtal in the 1st mixer, I was reading up about freqency doublers/multipliers etc and the concensus seems to be yes thats fine up to around the 5th harmonic of a fundamental osc but over that the output from a Nth harmonic tuned tank circuit falls off rapidly, any ideas ?

Lawrence..

[ed731pdh]

Heath Robinson would have been proud. I'll hold on the SD until all has been finalised.