megalomania
June 19th, 2003, 11:13 PM
PYRO500
Moderator
Posts: 1465
From: somewhere in florida
Registered: SEP 2000
posted 06-08-2001 11:32 PM
--------------------------------------------------------------------------------
Recently I have been looking for a way to make the 800 MHz band get down converted to 400 MHz. I found a file on an rf converter but I am unsur if it would work beacuse it came from a PhReAkErS page (nothe the kewl capitilization) I want to know if anybody thinks this will work or if they have any experiences with downconversion for scanners.
SCANNER CONVERTERS FOR CELLULAR TELEPHONE
This article is presented for information only. The new Electronic Communications Privacy Act makes it illegal to monitor cellular telephone calls.
A UHF TV tuner can be used as a converter to listen to cellular telephone calls. Salvage a UHF tuner from and old TV set. Connect it to a power supply. Typical voltage requirements are 12 - 25 volts. If the set is still working, measure the voltage before removing the tuner. Connect the output cable from the tuner to the external antenna input of a scanner or tunable monitor. Tune the scanner or monitor to a frequency between 41 and 46 MHz which is the IF output of the tuner. If you are within a few miles of a base station, a pair of test leads clipped to the antenna terminals of the tuner will serve as an antenna. Turn off the squelch on the scanner or monitor and carefully tune through UHF channels 70 - 83.
It is easier to use a tunable monitor than a scanner for this application because the monitor allows you to compensate for drift in the tuner. Either will provide an adequate means of checking out the cellular activity in your area.
There are several crystal controlled converters available which will convert cellular frequencies to the UHF range of many scanners. There is a slight problem involved with these. The spacing between cellular frequencies is 30 KHz. Most scanners have a stepping interval of 12.5 Khz at UHF. This means that on most channels the frequency tuned to by the scanner will not be a perfect match. I have been assured by one of the converter manufacturers that this is not a serious problem. When using this type of converter, the scanner can be used in scan or search modes as usual.
I wanted to find out how much discrepancy exists between the output of the converters and the tuning intervals of most scanners. I took the specs of a typical converter and put my computer to work doing the calculations. What follows is the result of this examination. Listed are the cellular base frequencies followed by the frequencies after conversion followed by the closest tuning point of a scanner with a tuning interval of 12.5 KHz. Each of the base frequencies listed is paired with a mobile frequency located 45 MHz lower. The mobile frequencies are not listed.
All 666 base frequencies were checked. Only the first 33 of these are listed. The pattern repeats throughout the list.
CELLULAR FREQ. CONVERTER OUT CLOSEST SCANNER FREQ.
------------- ------------- --------------------
870.030 486.030 486.0250
870.060 486.060 486.0625
870.090 486.090 486.0875
870.120 486.120 486.1250
870.150 486.150 486.1500
870.180 486.180 486.1750
870.210 486.210 486.2125
870.240 486.240 486.2375
870.270 486.270 486.2750
870.300 486.300 486.3000
870.330 486.330 486.3250
870.360 486.360 486.3625
870.390 486.390 486.3875
870.420 486.420 486.4250
870.450 486.450 486.4500
870.480 486.480 486.4750
870.510 486.510 486.5125
870.540 486.540 486.5375
870.570 486.570 486.5750
870.600 486.600 486.6000
870.630 486.630 486.6250
870.660 486.660 486.6625
870.690 486.690 486.6875
870.720 486.720 486.7250
870.750 486.750 486.7500
870.780 486.780 486.7750
870.810 486.810 486.8125
870.840 486.840 486.8375
870.870 486.870 486.8750
870.900 486.900 486.9000
870.930 486.930 486.9250
870.960 486.960 486.9625
870.990 486.990 486.9875
c0deblue
Frequent Poster
Posts: 229
From:
Registered: JAN 2001
posted 06-09-2001 02:33 PM
--------------------------------------------------------------------------------
I don't see why the UHF tuner thing wouldn't work if used with a decent crystal converter. The step differences could present a problem though, in terms of distortion. Here's a way to get around that.
The frequency difference between the 30 KHz cellular spacing and the 12.5 KHz scanner interval forms a repeating 5-step pattern ranging from -5 KHz to +5 KHz. It's already necessary to switch either the converter or the UHF tuner back and forth 45 MHz between the base and mobile frequencies, and a similar switching technique could be used to adjust the converter frequency to compensate the step differences.
Even the tightest crystal oscillator can be capacitively tuned ("rubbered") a little to either side of its "natural" frequency, so it's a matter of using switching diodes to connect the necessary capacitance into the oscillator's resonant circuit at a rate synchronous with the scanning rate. If you have access to the scanner schematics, find a pulse or logic output that can be used to drive a 5-place counter or shift register, and use the outputs of that to forward bias each diode in turn, thereby connecting a miniature trimmer capacitor (4 required) into the appropriate place in the converter oscillator circuit. (Pay attention to phase and watch out for propagation delays when designing this.) Using a frequency counter, adjust each trimmer capacitor to give the desired frequency change.
This step compensator would provide a repeating pattern of converter-frequency adjustment as follows:
Step 1 = -5.0 KHz (capacitor in)
Step 2 = +2.5 Khz (capacitor in)
Step 3 = -2.5 KHz (capacitor in)
Step 4 = +5.0 KHz (capacitor in)
Step 5 = +0.0 KHz (no capacitor)
For example:
CellFreq * ConvFreq * ConvOut * ScanFreq
870.030 * -5.0 KHz * 486.0250 * 486.0250
870.060 * +2.5 KHz * 486.0625 * 486.0625
870.090 * -2.5 KHz * 486.0875 * 486.0875
870.120 * +5.0 KHz * 486.1250 * 486.1250
870.150 * +0.0 KHz * 486.1500 * 486.1500
(Repeats)
Depending on how the 45 MHz base/mobile frequency shift is to be accomplished (switching the UHF tuner to a second "preset" would be the most straightforward), either one or two such switched compensation circuits may be required.
[This message has been edited by c0deblue (edited June 09, 2001).]
PYRO500
Moderator
Posts: 1465
From: somewhere in florida
Registered: SEP 2000
posted 06-09-2001 04:28 PM
--------------------------------------------------------------------------------
my scanner pickes up 300-999 mhz fm only, but the cellular is blocked from 824-849, I can still pick up handsets but with no frequency counter that is pretty much impossible to try and track someone.
also my scanner can listen to two frequency's at once but 500-900 it can only work on one band. the 500-900 band was enabled by software on my computer loading onto my scanner/transcever it also picks up 10 weather channels, the aircraft band (only one in am)I can pick up 400-500 on one side and 435-454.99 on the other simultaniously playing. the frequency spacing is adjustible on the 400-999 band 10.0, 12.5, 20.0, 25.0, 30.0, and 50.0 so channel spacing wont be a problem.
I dont understand exactly what I am saposed to do with the uhf tuner from an old telivision, I hook it up to a voltage supply and it will convert 800 mhz to 400? where do I put the oscilator? I dont know much about rf circuts. BTW my scanner/ ham trancever is an IC-W32A
c0deblue
Frequent Poster
Posts: 229
From:
Registered: JAN 2001
posted 06-09-2001 05:35 PM
--------------------------------------------------------------------------------
My bad! The UHF tuner is used (alone) only if you want to convert down to 41-46 MHz (as clearly stated in the article) - with a proper crystal controlled converter the UHF tuner is unnecessary. I should probably learn to read better - or at least more carefully
With dual frequency monitoring in the 400-500 and 435-454.99 MHz bands, and with 30 KHz frequency spacing selected, it looks like all you'll need is a single cellular-range converter to feed the antenna input of your scanner. You should be all set without further ado.
Informative links:
http://pages.citenet.net/users/ctmx0718/Scanner/cell.html
http://www.hackerscatalog.com/model.htm
And here's one with everything needed (including a pcb layout) to roll your own!
http://www.ramseyelectronics.com/sitepages/pdf/hmanuals/scn-1-4a.pdf
Happy Scanning!
PYRO500
Moderator
Posts: 1465
From: somewhere in florida
Registered: SEP 2000
posted 06-09-2001 08:59 PM
--------------------------------------------------------------------------------
I tried to order from ramsey kits but since 1994 it has been illegal to make or manufacture devices that can easily convert cellular frequencyes to be in the clear.
the problem with the pdf is that the schematic on the othere side is missing and the pcb is two sided! they only show one! I read that ramsey electronics had been raided and concequently their scanner kits were taken.
the problem with image frequecncy listening is that post 1994 scanners have something like 39 dB image rejection traps in them. my scaner being an intermod magnet I dont think I'd want to remove that even if I could.
Moderator
Posts: 1465
From: somewhere in florida
Registered: SEP 2000
posted 06-08-2001 11:32 PM
--------------------------------------------------------------------------------
Recently I have been looking for a way to make the 800 MHz band get down converted to 400 MHz. I found a file on an rf converter but I am unsur if it would work beacuse it came from a PhReAkErS page (nothe the kewl capitilization) I want to know if anybody thinks this will work or if they have any experiences with downconversion for scanners.
SCANNER CONVERTERS FOR CELLULAR TELEPHONE
This article is presented for information only. The new Electronic Communications Privacy Act makes it illegal to monitor cellular telephone calls.
A UHF TV tuner can be used as a converter to listen to cellular telephone calls. Salvage a UHF tuner from and old TV set. Connect it to a power supply. Typical voltage requirements are 12 - 25 volts. If the set is still working, measure the voltage before removing the tuner. Connect the output cable from the tuner to the external antenna input of a scanner or tunable monitor. Tune the scanner or monitor to a frequency between 41 and 46 MHz which is the IF output of the tuner. If you are within a few miles of a base station, a pair of test leads clipped to the antenna terminals of the tuner will serve as an antenna. Turn off the squelch on the scanner or monitor and carefully tune through UHF channels 70 - 83.
It is easier to use a tunable monitor than a scanner for this application because the monitor allows you to compensate for drift in the tuner. Either will provide an adequate means of checking out the cellular activity in your area.
There are several crystal controlled converters available which will convert cellular frequencies to the UHF range of many scanners. There is a slight problem involved with these. The spacing between cellular frequencies is 30 KHz. Most scanners have a stepping interval of 12.5 Khz at UHF. This means that on most channels the frequency tuned to by the scanner will not be a perfect match. I have been assured by one of the converter manufacturers that this is not a serious problem. When using this type of converter, the scanner can be used in scan or search modes as usual.
I wanted to find out how much discrepancy exists between the output of the converters and the tuning intervals of most scanners. I took the specs of a typical converter and put my computer to work doing the calculations. What follows is the result of this examination. Listed are the cellular base frequencies followed by the frequencies after conversion followed by the closest tuning point of a scanner with a tuning interval of 12.5 KHz. Each of the base frequencies listed is paired with a mobile frequency located 45 MHz lower. The mobile frequencies are not listed.
All 666 base frequencies were checked. Only the first 33 of these are listed. The pattern repeats throughout the list.
CELLULAR FREQ. CONVERTER OUT CLOSEST SCANNER FREQ.
------------- ------------- --------------------
870.030 486.030 486.0250
870.060 486.060 486.0625
870.090 486.090 486.0875
870.120 486.120 486.1250
870.150 486.150 486.1500
870.180 486.180 486.1750
870.210 486.210 486.2125
870.240 486.240 486.2375
870.270 486.270 486.2750
870.300 486.300 486.3000
870.330 486.330 486.3250
870.360 486.360 486.3625
870.390 486.390 486.3875
870.420 486.420 486.4250
870.450 486.450 486.4500
870.480 486.480 486.4750
870.510 486.510 486.5125
870.540 486.540 486.5375
870.570 486.570 486.5750
870.600 486.600 486.6000
870.630 486.630 486.6250
870.660 486.660 486.6625
870.690 486.690 486.6875
870.720 486.720 486.7250
870.750 486.750 486.7500
870.780 486.780 486.7750
870.810 486.810 486.8125
870.840 486.840 486.8375
870.870 486.870 486.8750
870.900 486.900 486.9000
870.930 486.930 486.9250
870.960 486.960 486.9625
870.990 486.990 486.9875
c0deblue
Frequent Poster
Posts: 229
From:
Registered: JAN 2001
posted 06-09-2001 02:33 PM
--------------------------------------------------------------------------------
I don't see why the UHF tuner thing wouldn't work if used with a decent crystal converter. The step differences could present a problem though, in terms of distortion. Here's a way to get around that.
The frequency difference between the 30 KHz cellular spacing and the 12.5 KHz scanner interval forms a repeating 5-step pattern ranging from -5 KHz to +5 KHz. It's already necessary to switch either the converter or the UHF tuner back and forth 45 MHz between the base and mobile frequencies, and a similar switching technique could be used to adjust the converter frequency to compensate the step differences.
Even the tightest crystal oscillator can be capacitively tuned ("rubbered") a little to either side of its "natural" frequency, so it's a matter of using switching diodes to connect the necessary capacitance into the oscillator's resonant circuit at a rate synchronous with the scanning rate. If you have access to the scanner schematics, find a pulse or logic output that can be used to drive a 5-place counter or shift register, and use the outputs of that to forward bias each diode in turn, thereby connecting a miniature trimmer capacitor (4 required) into the appropriate place in the converter oscillator circuit. (Pay attention to phase and watch out for propagation delays when designing this.) Using a frequency counter, adjust each trimmer capacitor to give the desired frequency change.
This step compensator would provide a repeating pattern of converter-frequency adjustment as follows:
Step 1 = -5.0 KHz (capacitor in)
Step 2 = +2.5 Khz (capacitor in)
Step 3 = -2.5 KHz (capacitor in)
Step 4 = +5.0 KHz (capacitor in)
Step 5 = +0.0 KHz (no capacitor)
For example:
CellFreq * ConvFreq * ConvOut * ScanFreq
870.030 * -5.0 KHz * 486.0250 * 486.0250
870.060 * +2.5 KHz * 486.0625 * 486.0625
870.090 * -2.5 KHz * 486.0875 * 486.0875
870.120 * +5.0 KHz * 486.1250 * 486.1250
870.150 * +0.0 KHz * 486.1500 * 486.1500
(Repeats)
Depending on how the 45 MHz base/mobile frequency shift is to be accomplished (switching the UHF tuner to a second "preset" would be the most straightforward), either one or two such switched compensation circuits may be required.
[This message has been edited by c0deblue (edited June 09, 2001).]
PYRO500
Moderator
Posts: 1465
From: somewhere in florida
Registered: SEP 2000
posted 06-09-2001 04:28 PM
--------------------------------------------------------------------------------
my scanner pickes up 300-999 mhz fm only, but the cellular is blocked from 824-849, I can still pick up handsets but with no frequency counter that is pretty much impossible to try and track someone.
also my scanner can listen to two frequency's at once but 500-900 it can only work on one band. the 500-900 band was enabled by software on my computer loading onto my scanner/transcever it also picks up 10 weather channels, the aircraft band (only one in am)I can pick up 400-500 on one side and 435-454.99 on the other simultaniously playing. the frequency spacing is adjustible on the 400-999 band 10.0, 12.5, 20.0, 25.0, 30.0, and 50.0 so channel spacing wont be a problem.
I dont understand exactly what I am saposed to do with the uhf tuner from an old telivision, I hook it up to a voltage supply and it will convert 800 mhz to 400? where do I put the oscilator? I dont know much about rf circuts. BTW my scanner/ ham trancever is an IC-W32A
c0deblue
Frequent Poster
Posts: 229
From:
Registered: JAN 2001
posted 06-09-2001 05:35 PM
--------------------------------------------------------------------------------
My bad! The UHF tuner is used (alone) only if you want to convert down to 41-46 MHz (as clearly stated in the article) - with a proper crystal controlled converter the UHF tuner is unnecessary. I should probably learn to read better - or at least more carefully
With dual frequency monitoring in the 400-500 and 435-454.99 MHz bands, and with 30 KHz frequency spacing selected, it looks like all you'll need is a single cellular-range converter to feed the antenna input of your scanner. You should be all set without further ado.
Informative links:
http://pages.citenet.net/users/ctmx0718/Scanner/cell.html
http://www.hackerscatalog.com/model.htm
And here's one with everything needed (including a pcb layout) to roll your own!
http://www.ramseyelectronics.com/sitepages/pdf/hmanuals/scn-1-4a.pdf
Happy Scanning!
PYRO500
Moderator
Posts: 1465
From: somewhere in florida
Registered: SEP 2000
posted 06-09-2001 08:59 PM
--------------------------------------------------------------------------------
I tried to order from ramsey kits but since 1994 it has been illegal to make or manufacture devices that can easily convert cellular frequencyes to be in the clear.
the problem with the pdf is that the schematic on the othere side is missing and the pcb is two sided! they only show one! I read that ramsey electronics had been raided and concequently their scanner kits were taken.
the problem with image frequecncy listening is that post 1994 scanners have something like 39 dB image rejection traps in them. my scaner being an intermod magnet I dont think I'd want to remove that even if I could.