tomf@bechtel.colorado.edu (Thomas Fredericks) (12/18/90)
Has anyone out there built the Signal Descrambler from May of 1990's Radio Electronics? If so how well did it work? This may have been discussed before, so don't flame me send me a summary if you have it. -- ================================================================================ tomf@boulder.colorado.edu "Illusion is stronger than reality..." ================================================================================
harrist@jacobs.CS.ORST.EDU (Tim Harris) (12/19/90)
In article <1990Dec17.184710.28481@csn.org> tomf@boulder.Colorado.EDU writes: > >Has anyone out there built the Signal Descrambler from May of 1990's >Radio Electronics? If so how well did it work? This may have been Funny you should ask. I just got mine put together last night and am having a few minor problems. At first it didn't work at all. the signal was jumping around all over the place because it wasn't phaze locking(this is what my brother said anyway, he's the one who really knows what he's doing). My brother poked around the board with his finger and BAM, it locked up and was working pretty good but unfortunately when you unplug it you have to poke at it again to jump start it. At that point we took it off the vidio scope and took it home and hooked it up to a tv set. Since it works on baseband video we hooked it to the back of the vcr and then into the video port of the tv. It worked pretty good on the unscrambled stations but the vcr's rf modulator seemed to have problems with signals that were already missing a sync pulse so the picture was completely missing the color and rolled horizontally a bit. I'll probaly tinker with it a little more tonight. Has anyone else had similar problems or just have any suggestions? Tim H.
quodling@bunyip.enet.dec.com (12/20/90)
In article <1990Dec18.224950.7142@usenet@scion.CS.ORST.EDU>, harrist@jacobs.CS.ORST.EDU (Tim Harris) writes: > In article <1990Dec17.184710.28481@csn.org> tomf@boulder.Colorado.EDU writes: >> >>Has anyone out there built the Signal Descrambler from May of 1990's >>Radio Electronics? If so how well did it work? This may have been > . > the one who really knows what he's doing). My brother poked > around the board with his finger and BAM, it locked up and was > working pretty good but unfortunately when you unplug it you have > to poke at it again to jump start it. At that point we took it I would say that either you have a bad solder joint and his poking nudged it enough to come good, or There is a poor ground somewhere, and his finger provided a better one... -- Peter Quodling Internet: quodling@blumon.enet.dec.com Digital Equipment Corporation UUCP: ...!decwrl!blumon.enet!quodling Nashua, NH. I disclaim everything!!!
parnass@cbnewse.att.com (Bob Parnass, AJ9S) (12/20/90)
In article <1990Dec18.224950.7142@usenet@scion.CS.ORST.EDU>, harrist@jacobs.CS.ORST.EDU (Tim Harris) writes about debugging a home built analog circuit: > the one who really knows what he's doing). My brother poked > around the board with his finger and BAM, it locked up and was > working pretty good but unfortunately when you unplug it you have > to poke at it again to jump start it. At that point we took it I don't know if your project employs an oscillator with a tuned circuit on the oscillator output. If it does, the tuned circuit should usually be aligned off to the side of the slope, NOT peaked for maximum signal from the oscillator. I've found that adjusting such tuned circuits for maximum signal tranfer often loads down the oscillator so it won't start oscillating reliably when power is applied. My first experience with this was on a tube-type 2 meter ham transceiver (Knight Kit TR-108) back in 1960s. I finished building and aligning it. When I turned it off then on, the thing wouldn't work and I'd have to realign the darn thing again to get it to work. The problem was that I was tuning for maximum local oscillator output. -- ============================================================================ Bob Parnass, AJ9S - AT&T Bell Laboratories - att!ihlpy!parnass (708)979-5414
bruggink@vms.macc.wisc.edu (12/21/90)
I finished building this in the past couple of days.
On unscrambled channels: it's easy to get
a vertical lock, but i have problems getting the horizontal. I also
can't seem to get consistently good color (stable and saturated);
increasing the dc level improves the color immensely, but then
tearing begins and renders the picture useless.
On the scrambled channels the same applies, but when I get both a
vertical and horizontal lock, the picture is fine except there are
4 alternating vertical regions on-screen where the picture is too light
and too dark, i.e.:
-------------------
| | | | |
| | | | |
| | | | |
| | | | |
-------------------
^ ^ ^ ^
light dark light dark
The image is there, and is watchable, but these bands are also prominant.
I don't have a scope, but the VOM values matched what was in the article
and the subsequent corrections (I ordered the parts from the source; they
sent addenda/corrections). 2 of the voltage regulators get so hot
a touch would burn you (the negative and one of the positive supplies);
I run a cable signal into a vcr, line level to descrambler, line level to
TV.
-dbgeorgep@vice.ICO.TEK.COM (George Pell) (12/21/90)
+In article <1990Dec18.224950.7142@usenet@scion.CS.ORST.EDU>, +harrist@jacobs.CS.ORST.EDU (Tim Harris) writes about debugging +a home built analog circuit: + + > the one who really knows what he's doing). My brother poked + > around the board with his finger and BAM, it locked up and was + > working pretty good but unfortunately when you unplug it you have + > to poke at it again to jump start it. At that point we took it + And many others reply...... Actually what is happening is that the capture range of your PLL is smaller than the lock range. The cap that sets the free running frequency for your PLL is just a bit too small. Put a 10 pf in parallel and it will lock every time.
cook@stout.atd.ucar.edu (Forrest Cook) (12/21/90)
In article <1990Dec19.112229.1@bunyip.enet.dec.com> quodling@bunyip.enet.dec.com writes: >In article <1990Dec18.224950.7142@usenet@scion.CS.ORST.EDU>, harrist@jacobs.CS.ORST.EDU (Tim Harris) writes: >> In article <1990Dec17.184710.28481@csn.org> tomf@boulder.Colorado.EDU writes: ... >> the one who really knows what he's doing). My brother poked >> around the board with his finger and BAM, it locked up and was >I would say that either you have a bad solder joint and his poking nudged it This sounds to me like the PLL is free running above or below it's maximum capture frequency. Try tweaking the frequency determining components of the PLL VCO circuit for starters. Compare the VCO frequency in the unlocked and locked states to determine which way to go. This requires a scope or counter of course. If you don't have such tools, you can always try guessing :-) -- ^ ^ Forrest Cook - <<< Weirdness is Relative! >>> /|\ /|\ cook@stout.atd.ucar.edu WB0RIO (This posting is my OPINION) /|\ /|\ {husc6|rutgers|ames|gatech}!ncar!stout!cook
wood@drift.dec.com (John F. Wood) (12/21/90)
While poking around on the Radio Electronics BBS the other day, I found the
attached list of FAQs about the universal descrambler. I hope they help.
And I hope they don't mind that I posted it...
File name: descramb.txt
The following are the most frequently asked questions about the universal
descrambler/synch regenerator. A 20 Mhz scope and frequency counter are a
must for trouble shooting.
1. R7 There has been some confusion as to the correct connections around
R7 and the polarity switch S3. If one closely examines the PC board, R7 can
either return to +5V or to ground. R-E Fig3 and Fig4 (P40,41) seem in
conflict. If R7 is returned to ground then +5V is supplied through S3. If R7
is returned to +5V, then ground should be supplied through S3. Actually R7
was intended to either return to ground or +5V to allow various interfacing
methods for experiments in automatic polarity switching.
2. Pin 9 IC5 This pin will normally read +0.2 to +0.3 volts; not -0.2
volts as in R-E P43 Column 1. Q2 produces a narrow(2msec) positive going
pulse during burst intervals to IC5 pin 9 and therefore a VOM or DVM will read
only a very small positive voltage.
3. Pins 5 & 10 IC1 are -5V and +5V respectively.
4. The correct frequency signal at pin 23 IC9 is 503.496 khz (503.5 khz
nominal) not 1.08 Mhz as shown in R-E. The output from IC6 (divided by 455)
should be 7867.13 hz. If this is not the case, check D1-D6.
5. One must have a 4V to 5V P-P square wave at P23 (503.5 khz) before the
decoder will operate.
6. IC9 The voltage at pins 13, 11, and 5 may vary considerably or even
read zero, depending on the meter used to measure them. Verify 503 khz clock
is present on Pin 23 IC9.
7. IC8 divides by 64, not 128. Pin 12 shown is actually pin 2.
8. IC10 may run somewhat hot. Do not apply more than 15 vac to J3
without providing a heatsink on IC10. This heatsink is not provided with the
kit.
9. Ringing on picture - Check IC1 and verify that C2, C3, C4, and C5 are
in the circuit and OK. Try a .01 bypass between IC1 pin 14 and ground
(connect across R4)
10. -0.45 volts is supplied to IC3 Pin 2, not IC2 Pin 2 as in Column 1
page 43.
11. Locking of picture in some cases can be improved by changing R20 and
R21 (1K each) to 470 ohm. However, before doing this check C17, L1, Q1, R22,
R23, and C18.
12. Incorrect hue can be shifted to improve color by adding capacitance
(try 33 pf) across C32. If this makes things worse, then try changing C30
from 56 pf to 33 pf without the 33 pf across C32.
13. Color stability is a function of accurate lockup. The burst key pulse
(IC9 Pin 11) is somewhat narrow. Try resetting lock with S1. If no help,
make sure that the video signal is clean. Some experimenters have reported
that IC6 can produce "glitches" or momentary intermittent miscounting. A
change of value of R36 (try 1K ohm) and also of C36 (try values from 820 pf to
.0015 uf) has helped in these cases.
14. Smear may be caused by incorrect frequency response somewhere in the
video system. This is generally an interface problem. Try the following:
A Remove IC2 and IC3.
B Jumper IC2 pin 2 to pin 15 and IC3 pin 3 to pin 15.
C Now using a good off the air NTSC signal (not scrambled),
connect video into J1 and examine video out of J2. If OK, the problem is not
in the descrambler video circuit.
D restore normal connections and check IC2 and IC3. If OK, the
problem is in the video source. A typical case with a non-scrambled signal,
the picture is OK, but with a scrambled signal, there is smear, blotchy color,
shadowing,or poor contrast.
Remember that your VCR, TV tuner or video source may not operate properly with
a scrambled video signal. The horizontal and/or vertical pulse are missing or
distorted. Your equipment may contain circuitry that depends on these pulses
for some phase of operation (AGC, DC restoration, etc.) and therefore may
further distort a scrambled signal. The reconstituted signal may therefore
show these distortions. Therein were no such problems in the prototype
circuits, so there shouldn't be any problems inherent in the descrambler. The
following points should be considered:
A The video source should ideally be right off the video
detector of the TV tuner or receiver with no extra amplifiers or other
circuitry. Sag, excess tilt, or other waveform distortions can occur due to
low frequency response or phase shift in the coupling capacitors.
B The fact that "every else works OK without the descrambler in
the system" is meaningless due to the aforementioned considerations.
----------------------------------------------------------------------
John F. Wood | EIS Engineering
Digital Equipment Corporation | ARPAnet: wood@acesmk.enet.dec.com
Continental Blvd. | EASYnet: ACESMK::WOOD
MKO2-1/J12 | Usenet : ...!decwrl!acesmk!wood
Merrimack, NH 03054 | AT&T : (603) 884-4686
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Disclaimer: Views expressed herein are my own and do not necessarily
reflect those of my employer.
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