It's really not that hard but I can see how someone can feel intimidated if they have never worked with BCD before. Binary Coded Decimal. Each of our base-10 digits 0 through 9 is encoded as its 4-bit binary equivalent. That is the reason the switches are treated in groups of 4. The weighting (value) of the switches is 8, 4, 2, 1 reading from left to right. Obviously zero would be 0000 (all switches off). One would be 0001, switch one is on. Simple enough. But what is two? If you said switch 2 on you would be correct, 0010. Since the most convenient way to get to three would be to add 2 + 1 that would be switches one and two on, 0011. Four is just switch 4 on, 0100. And so on up through nine, which is 8 + 1 or 1001. Alert readers may note that if we used three bits instead of four we would have to stop at 7 (111) which would not work very well for us.
Once you have the magic number figured out by doing the math for the actual RF frequency you just set the switches accordingly - paying close attention to the switch layout diagram because things look backwards. You might need to twiddle the least significant switch group number a little to compensate for oscillator error in the rig but the formula should get you pretty darn close. Note that there an 800 Hz offset for CW mode, and the TR5 formulas are a little different so don't use those. :)
While you are bending your mind around binary stuff, think about this: What can we two with two bits? That gives is four numbers, 0 1 2, and 3. The filter switches on the TR7 are a two bit switch, giving us a choice of three optional filters. Where else do we see a two bit switch? The A and B buttons on the RV75! Without changing much at all Drake could have given us a third Fixed switch bank by using the case of both buttons pushed in just like the filter switches! And yes, I have thought about doing just that...
How about computer frequency control? I remember hearing of someone doing just that in the pre-CAT days. A relatively simple hardware interface connected in place of one of the switch banks and some custom software would make for a basic CAT interface. But that's a project for someone else.
73
-Jim
NU0C
On Sat, 3 Feb 2024 15:29:58 -0800
"VE7PS" <ve7ps@...> wrote:
Bob:
You are correct....the manual is a nightmare, especially for those of us
not familiar with programming BCD switches. I also believe there is an
error in the manual in one of the mathematical calculations they show.
You have two programmed frequencies available, A and B. A is the right
half of the entire BCD switch row on the back and consists of two 8 switch
groups and one of four. I found it faster and easier to just alter the
switches, starting with the most significant group of four (the 100's) on
the extreme right (as you look at the rear) and get it set right.....for
40m SSB you may want 200 khz. Continue working to the left with each 4
switch group (treat the 8 switch groups as two 4's) until you get down to
the HZ group. Repeat for Switch B on the left, again starting with the 4
switch group just left of the centre of that entire switch row, and working
to the left.
This is harder to explain than it actually is!
Once you get the hang of what the switches do to the numbers, it gets
easier fast.
Good luck!
73
Peter
VE7PS
On Sat, Feb 3, 2024 at 3:08?PM K6OXN Bob <bobk6oxn@...> wrote:
How do I set the Fixed A or B on the back of the RV-75. I am looking at 40
meter SSB frequencies. The manual is not very clear.
Help
73 Bob
--
73
-Jim
NU0C
Jim Shorney