[minima] Re: parts list & IF
- From: Joe Rocci <joe@xxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Sat, 06 Dec 2014 15:25:12 -0500
Ed
I'm also a big fan of GCB and have been since it's inception. Please keep me
informed of your progress.
Joe
W3JDR
Sent from my tablet
-------- Original message --------
From Ed LeBel <kd6kca@xxxxxxxxxxx>
Date: 12/06/2014 4:38 AM (GMT-05:00)
To minima@xxxxxxxxxxxxx
Subject [minima] Re: parts list & IF
Thanks for the input.
I have a lot of experience in digital and audio analog but RF is still a little
magic for me.
I'm writing my own firmware with Great Cow Basic.
I can use any 8 bit AVR or PIC that I want with that compiler.
In fact I blew up my last ATmega16A so I've got it ported to PIC16F887.
Only had to change like 3 lines of code.
I have tables that have license and sub band modes and I handle 60 meters as
channelized.
Same with 11 meters (just for monitoring).
No controls on the radio just a display, got 5 buttons on the mic I made.
This will be my first HF rig so I want the most with the least.
I try to read all the messages but it's a lot to keep up with.
If more Minima builders came to the Bay Area Radio Builders meetings we could
all benifit.
Thanks again
Ed KD6KCA
Date: Fri, 5 Dec 2014 23:33:35 -0500
From: ajp166@xxxxxxxxxxx
To: minima@xxxxxxxxxxxxx
Subject: [minima] Re: parts list & IF
On 12/05/2014 10:16 PM, Ed LeBel wrote:
I found what I think is the schematic for version 2.
It has a MOSFET for Q7 of the BFO but the version in the title box is version 1.
The date is 25/10/14.
Is this the latest version and where is a parts list for this version.
I have BS170 MOSFETs (n-channel enhancement) will it work in the BFO?
Looks like it's just for switching but MOSFETs have more inter element
capacitance than a BJT.
Just want to make sure.
I think a 2n7000 or 7002 is right for that, likely a bs170 should work its used
as a switch.
Also I see a few ideas to change the IF frequency.
But seems you always lose a band.
How figure? 32mhz would work. Anything in the 20 to 30mhz is out.
However 16mhz can be done as well as 12, 9, and 6.
What limits the IF frequency is nearness to a working ham band. At lower
frequencies the needed selectivity is easier to obtain. Commercial
radios simple use more filters with narrower bandwidths or one per
band for TX and wide band filter for RX.
This radio is however not a good idea for 60M so 5mhz is also possible
as an IF.
If the radio is kitted or produced signal purity has to be at least checked
to insure there are no out of band spurs when tuned for an in band signal
Things like IF leakage and Lo leakage are inconsistent with doing things
using best practices.
I'm building and testing the existing minima filter for the high segment
as thats the one that crosses 20mhz. I need to see if the notch is too wide.
If it is then there are other options.
Right now there seems to be a push for 1 filter and the problem with it is
a lot of unwanted signals will easily pass though it in both directions.
The commercial radios did this by upconverting to VHF forst IF then
down converting for selective stages. Even then with 45 to 78 mhz first IF
there are many filters before the first mixer. The amount of switching to
do bidirectional all through that and keep out spurs and noise gets
out of the scope of a simpler radio.
I think the V1 filter scheme is the path with may be the solution being
for 15M to go to filter 3 triple tuned band pass for 15M. Its not much
more effort and the micro can sort out when to switch.
One thought thats relevant to the V2 single filter design. Despite low
gain and strong mixer that design can suffer from a strong 40M op or
a 40/39M SWBC station creating a ton of IMD in the mixer when your
listening to 80M or even 20M. This is where simplicity ha a failing
as too wide is problematic for received signals not wanted or desired.
This is problemmaticn on antennas that work on harmonic frequencies
well (like and dipole on its third harmonic, multiband wires, and
multi-band beams)
Why not have 2 IFs for upper bands and lower bands.
Doesn't seem like it would be that hard to do.
2 crystal filters and 2 BFOs and maybe a mod to the band pass filters.
Its actually easy you don't need two IFs you need two crystal filters
and two or switchable BFOs.
I made modules for version 1 but I want to back up some and build the latest
version and I want all HF bands.
Also want to make modules that have room for improvements (like a 2 frequency
BFO).
Think about the 2 IF idea and let me know if it's a good idea.
See above.
The filtering scheme no matter what must do:
Never let any IF frequency out to the antenna.
Filter all harmonics transmitted.
Protect the receiver from one band to another.
Protect other users from spurs outside the ops selected band.
One possible is to build two radios. One optimized for 80 through 20 and
another for 20 through 10.
I've solved this once for myself but I used a 36mhz if and up converted to it.
I still needed a lot of filters to keep things I didn't want to hear out and
unwanted mixer products from escaping to the antenna. I was also only
interested in ham bands only.
Just tossing out ideas.
Allison/Kb1GMX
Ed KD6KCA
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