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GTBecker
Joined: 18 Jan 2006
Posts: 457
Location: Cape Coral
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Posted: 01 August 2010, 23:15 PM Post subject: 150-175MHz programmable receiver |
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I have been asked to consider an unusual application, a programmable audio receiver that can select any 5kHz-deviation NFM channel between 150MHz and 175MHz from Comcast cable. It must be inexpensive.
A remote-controlled scanner seems like a reasonable start, but would be far more than this project needs and much too expensive for a system in volume.
Can anyone suggest an alternative method?
Tom
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twesthoff
Joined: 17 Mar 2006
Posts: 191
Location: Fredericksburg, VA
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Posted: 02 August 2010, 2:39 AM Post subject: Re: 150-175MHz programmable receiver |
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What price range do you have in mind? (What is inexpensive?)
Does it need to be as sensitive as a commercial receiver?
Tom W.
| GTBecker wrote: | I have been asked to consider an unusual application, a programmable audio receiver that can select any 5kHz-deviation NFM channel between 150MHz and 175MHz from Comcast cable. It must be inexpensive.
A remote-controlled scanner seems like a reasonable start, but would be far more than this project needs and much too expensive for a system in volume.
Can anyone suggest an alternative method?
Tom |
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GTBecker
Joined: 18 Jan 2006
Posts: 457
Location: Cape Coral
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Posted: 02 August 2010, 16:14 PM Post subject: |
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Inexpensive is inexact, but less than $50 for the receiver would be reasonable, I think. It will be receiving translated off-air signals, so it should be typical of communication receivers that exhibit ~1uV or better sensitivity.
The more I think about it the more I think a programmable scanner is probably the simplest initial solution - but those I've identified are not cheap.
Any scanner aficionados out there who might know what the least expensive remotely-controlled (RS232, USB) scanner might be?
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twesthoff
Joined: 17 Mar 2006
Posts: 191
Location: Fredericksburg, VA
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Posted: 02 August 2010, 17:04 PM Post subject: 150-175MHz programmable receiver |
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On 8/2/2010 12:14 PM, General wrote: | Quote: | Inexpensive is inexact, but less than $50 for the receiver would be reasonable, I think. It will be receiving translated off-air signals, so it should be typical of communication receivers that exhibit ~1uV or better sensitivity.
The more I think about it the more I think a programmable scanner is probably the simplest initial solution - but those I've identified are not cheap.
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About the best price I have seen is about $70 for a scanner that does not have a computer interface. It may be possible to figure out how to control it. I did it to two different models many years ago, bu have not tried on any of the newer models... It may be hard to find something at $50 price point.
Tom W
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Any scanner aficionados out there who might know what the least expensive remotely-controlled (RS232, USB) scanner might be?
Tom
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GTBecker
Joined: 18 Jan 2006
Posts: 457
Location: Cape Coral
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Posted: 06 August 2010, 15:39 PM Post subject: |
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I've located a pile of refurbed Uniden BC72XLT handheld scanners for ~$50 and got one to play with. It nicely disassembles and the keyboard scan lines are easily tapped.
I'm thinking of bridging each 4x4 keypad switch with a 4066 switch. The obvious solution would use 16 switches but, to simulate a single-button key press, I think I can do it with eight. Any reason why this would not work?
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twesthoff
Joined: 17 Mar 2006
Posts: 191
Location: Fredericksburg, VA
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Posted: 06 August 2010, 18:29 PM Post subject: 150-175MHz programmable receiver |
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I have done that before and it does work. You could do it with onlyt 4 switches if you monitor the the other 4 scan lines. I did it with transistors (2N3904) years ago open collector on the lines with the pull-up resistors. I waited for the proper scan line to go low, then turned on the appropriate transistor to press the switch.
There is more than one way to scan a keyboard, but the one I was working on had pullup resistors on the Columns, and then they brought each row line low and read the column inputs.
On 8/6/2010 11:39 AM, General wrote: | Quote: | I've located a pile of refurbed Uniden BC72XLT handheld scanners for ~$50 and got one to play with. It nicely disassembles and the keyboard scan lines are easily tapped.
To simulate single-button key presses, I'm thinking of bridging the keypad with a 4066 switch. The obvious solution would use 16 switches, but I think I can do it with eight. Any reason why this would not work?
Tom
http://www.ustream.tv/channel/bowcam
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stevech
Joined: 23 Feb 2006
Posts: 657
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Posted: 07 August 2010, 4:33 AM Post subject: Re: 150-175MHz programmable receiver |
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| GTBecker wrote: | | ... audio receiver that can select any 5kHz-deviation NFM channel between 150MHz and 175MHz from Comcast cable. |
Curious about NFM and Comcast Cable in the same sentence. Does Comcast put narrowband public safety or marine analog FM signals on their cable?
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GTBecker
Joined: 18 Jan 2006
Posts: 457
Location: Cape Coral
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Posted: 08 August 2010, 16:11 PM Post subject: |
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| Um, I can't answer that. You might put a scanner on your cable and take a look, though.
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stevech
Joined: 23 Feb 2006
Posts: 657
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Posted: 09 August 2010, 5:24 AM Post subject: |
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OK. I jumped to the wrong conclusion that this is what would be in that frequency range. Wrong-0.
I note that DOCSIS cable modems' upstream is in the 30MHz area on the cable.
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