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Lex PH2LB <lex@...> added folder /Brooks FDU-7 - logic counting device

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The following files have been uploaded to the Files area of the [email protected] group.

• /Brooks FDU-7 - logic counting device/Brooks FDU-7 - logic counting device for FRG-7.pdf

By: Lex PH2LB <lex@...>

Description:
Scan of the Brooks FDU-7 logic counting device for FRG-7 installation document.

Hi Lex,
Thanks for uploading the Brooks FDU-7 display install instructions. Looking at the instructions I see that it uses two coaxes to count the MHz frequency and the VFO frequency for a 5 or 6 digit readout (EG : 10.000 or 10.0000?).? I have never heard of the Brooks unit and there is nothing on Google. Were they sold in Europe? If you happen to have one in your FRG-7 I would appreciate a picture.

73
Roger VE7LB

Hello Roger,

I used to have one in a FRG-7 which I got from a OM (the FRG-7 belonged to his father (SK OM Joop PA0JPC) and was in a bad shape). The counter worked, but I didn't like the look of it (and the jumping last digit made me nervous HI). So when I got my hands on a donor FRG-7 (which was in even worse shape), I removed the counter and restored the original drum.?

Last week the OM wrote to me that he was sorting through his fathers stuff and found all the original documentations including the (unused) warranty card and bill dated 19 may 1978, and he send it to me for my collection.?
Yesterday I received it and finally got installation documentation (Unfortunately no schematic) from the 3 digit the counter (it only slows the 0-999 KHz).?

Now having the name I googled around and found a ad in a magazine ( ) 1978. Indicating it's from B.Brookes Electronics from Norwich UK.
?

Scrolling through the video's on my mobile phone and I found 2 video's I made when I started the restoration of this FRG-7. So I uploaded them to YouTube the public can see them.

?&??

When I removed the Brooks FDU7 counter I documented how it was installed in the FRG-7. When you look a the photo's you can clearly see that it's digital technology from the 70's (reminding me of the components my father used for his electronics experiments in the 70's).?

I believe the aluminum case isn't original (it looks hand made).

For those who are interested, I don't use it and have it on sale on my website :??(?price is negotiable HI )

73 and stay safe

Lex PH2LB?

Hi Lex,

Thanks for adding to the information about the FRU-7 display. I have previously contacted you off list about buying the unit.

I gave to much credit to the 70's technology in my first post. The MHz digits could be derived by subtracting 3 from the H.GEN MHz signal.

Looking at the Block Diagram on page 8 of the FRG-7 manual. The FRU-7 must be counting the 3 - 32 MHz output of the H.GEN and subtracting the VFO frequency. Then the counter circuit must have a preset of .455 MHz that adds to the sum above. For example when tuned to 10 MHz:

H.GEN output is 13 MHz and the VFO is 3.455 MHz (13 - 3.455 = 9.545). Then add the IF frequency of .455 MHz to the above and you have 10 MHz. The FRU-7 doesn't display the MHz digits and shows .000 on the LED's.

It should be a more accurate display, on the upper bands, because the 1 MHz crystal doesn't have a calibration trimmer and any inaccuracy will show up as you increase the receive frequency. For example if the 1 MHz is off by 100 Hz the H.GEN output would be off by 300 Hz on the lowest band and 3,200 Hz on the highest band. Because the FRU-7 counts the H.GEN and VFO frequencies and the VFO can correct for the H.GEN offset the FRU-7 should show .000 when tuned to WWV.

73
Roger VE7LB

Hi Roger, Lex,

I think the operation is much simpler. The pick-off point in the H.GEN will have a comb of frequencies and the FRU-7 has no way of determining which one is selected in the receiver; that depends on the setting of the MHz dial (55.5-84.5 MHz 1st oscillator). Also, from the photos the display electronics looks like some pretty simple CMOS - probably presettable counters plus decode and display chips. There doesn't appear to be a crystal on the display board either. What this points to is using the H.GEN as the timebase for the FRU-7, with probably a simple LPF to suppress everything above 1 MHz.

The only way to determine what the MHz reading should be is to measure the 1st oscillator and calculate as follows; MHz(set)? = [freq (1st osc) - 55.5] MHz. Round to nearest MHz as the Wadley loop takes care of any fractional MHz ( over +/- 100 KHz say).

I have been thinking of a "full" digital display for the FRG-7 for a while. So far? I have a 'Blue Pill' board (STM32F103C8 micro) driving a 6-digit led board (TM1637- based) working. Total cost is under AUS $10. A bit of programming and a few transistors should take care of the KHz part of the display (the micro has some neat counters but the insane complexity of configuring them has me on a steep learning curve). Then a few more transistors and a HCMOS decade counter (to divide the 1st oscillator down to something the micro can handle) should take care of the MHz side of things. Will report back when I have the whole working.