03-03-2014, 03:03 PM
(This post was last modified: 03-03-2014, 03:05 PM by Ian - g4jqt.)
Thanks for the great feedback!
It just so happens that I'm looking to have some PCBs made for my MiniMod design. At the moment they are looking to cost about £6 each (2.5" x 2.5"), unless anyone knows of a cheaper supplier. (I've tried the toner-transfer method - unsuccessfully.)
Peter's design will probably have the advantage over mine of being able to give 100 percent modulation. My basic design will give about 80 percent, though in practice this is not really noticeable.
I've read an article in Feb 2014 Practical Wireless (p53) describing in detail the inductors I specified for use in the MiniMod and there's a point which needs highlighting.
The tapping in the tuned winding (L1) is 25 percent from the earthed end. Although I stated this in my BVWS article (and this is also shown in the circuit diagram) it may be worth repeating for anyone else wishing to build one.
I expect anyone who has already built one either measured the resistance to identify the correct end to earth, or referred to the Spectrum Communications information from the link in the article for pin identification.
I've also learnt recently that the BF256B has better defined characteristics than the 2N3819. I've not tried this substitute yet, but will probably be using it for any MiniMods I make from now on.
Providing a PCB layout has proved problematic. I use the free software ExpressPCB. I find it generally very good, but the catch is they really want you to email them your design for manufacture, and copying the 'track only' is not a feature in the software! It can be emailed to be read by anyone with ExpressPCB or printed out on paper.
Regards,
Ian
PS: I can provide pdf of my original article published by the BVWS in their Winter 2011 Bulletin and sheet with the PCB layout for a SAE.
It just so happens that I'm looking to have some PCBs made for my MiniMod design. At the moment they are looking to cost about £6 each (2.5" x 2.5"), unless anyone knows of a cheaper supplier. (I've tried the toner-transfer method - unsuccessfully.)
Peter's design will probably have the advantage over mine of being able to give 100 percent modulation. My basic design will give about 80 percent, though in practice this is not really noticeable.
I've read an article in Feb 2014 Practical Wireless (p53) describing in detail the inductors I specified for use in the MiniMod and there's a point which needs highlighting.
The tapping in the tuned winding (L1) is 25 percent from the earthed end. Although I stated this in my BVWS article (and this is also shown in the circuit diagram) it may be worth repeating for anyone else wishing to build one.
I expect anyone who has already built one either measured the resistance to identify the correct end to earth, or referred to the Spectrum Communications information from the link in the article for pin identification.
I've also learnt recently that the BF256B has better defined characteristics than the 2N3819. I've not tried this substitute yet, but will probably be using it for any MiniMods I make from now on.
Providing a PCB layout has proved problematic. I use the free software ExpressPCB. I find it generally very good, but the catch is they really want you to email them your design for manufacture, and copying the 'track only' is not a feature in the software! It can be emailed to be read by anyone with ExpressPCB or printed out on paper.
Regards,
Ian
PS: I can provide pdf of my original article published by the BVWS in their Winter 2011 Bulletin and sheet with the PCB layout for a SAE.
