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Author Topic: POCSAG Pager Encoder and Transmitter  (Read 21084 times)
KE5YUU
Member

Posts: 12




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« on: July 11, 2013, 01:28:54 PM »

Hello,
I am trying to build a pager encoder to send messages to a pager when I am at home. I live on a farm and we do not have cellphone service here.

I found a very interesting project at http://www.winpe.com/gascop/ that has software and hardware plans for performing this task. I think this would be the perfect solution for me. When I am out of the house, my wife could just send me an email, and it would get sent to my pager.

I have the Raspberry PI and the software is installed. I am confused by the circuit he is building though.

I am currently trying to order the parts he used, but cant find the PHT6N03LT. Does anyone know if there is a compatible replacement for this part?

Also, looking at his images, I see two blue devices on the circuit board. I am assuming they are some type of pot?

My ultimate goal would be to take this design, put it into eagle format and get my first professional circuit board printed. I could really use any advice I can get.

Thanks for your time
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KE5YUU
Member

Posts: 12




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« Reply #1 on: July 11, 2013, 03:44:40 PM »

If someone is able to help me with designing this circuit in Eagle format, I would be more than happy to have multiple boards printed and mail you one for no cost as a re-payment for your help.
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KA4POL
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Posts: 1978




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« Reply #2 on: July 11, 2013, 09:47:39 PM »

It is obviously a very simple circuit. The blue parts are the 100k pot, seems to be the 25 turn type which is better for good adjustment. Unfortunately the 2N7000 is very low current in comparison to the PHT6N03LT. However, it may not be required to have a high current FET.
As you are asking for help with EAGLE design, is that due to lack of experience? I would be willing to support you here. I do a lot of those PCBs myself. As I am not interested in the circuit I wold not need a PCB sent to me.
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KE5YUU
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Posts: 12




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« Reply #3 on: July 11, 2013, 10:04:00 PM »

Thank you very much for the reply!  I thought the blue devices were some type of pot, and I appreciate your conformation.  I can go ahead and order a few 2N7000 as the replacement part and give it a shot if you think I have a chance... 

In short, yes I am looking for help getting this circuit into Eagle format to get it professionally printed.  I have watched a few tutorial videos, but am struggling getting started.  I found a website called www.circuits.io and started laying it out there.  I'm confused on the part next to the 100k pot that says "To Tx Mod". 

I have never done anything in Eagle before, and given the simplicity of the circuit, I would assume this should be an easy task.  Do you have any recommendations for me?  Should I just attempt to get this circuit in to Eagle or would you recommend I take a different approach (such as www.circuits.io)?

73's
Tommy
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KA4POL
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Posts: 1978




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« Reply #4 on: July 11, 2013, 10:25:10 PM »

I think keying does not require more than the 200mA which the 2N7000 can produce. It is widely used.
The 'To TX Mod' means connect to your transmitter's modulation input. You need to be sure that there is no problem with DC. Probably a capacitor could be added for decoupling. I'd say about .1 µF.
I'll sit down later to make up the circuit as a sample. But I also encourage you to give it a try yourself as it is so easy to do.
If you send me your mail address via the message function in eham I'll send you the circuit files as I design it.
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KE5YUU
Member

Posts: 12




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« Reply #5 on: July 11, 2013, 10:44:42 PM »

Thank you for the fast reply.  I really do appreciate your help.  I plan to continue learning the Eagle system, but this is the first time I have done anything like this.  It really helps to have someone to guide me and point me in the right direction. 
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G3RZP
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Posts: 4567




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« Reply #6 on: July 12, 2013, 03:19:31 AM »

What frequency are you figuring on using?

Original POCSAG wide area paging was on about 150MHz and used 512 b/sec with +/-4.5kHz FSK. How things have changed.......Incidentally, POCSAG was the acronym for Post Office Code Standardisation Advisory Group, because the work on it started when radio regulation in the UK was done by the Post Office. Later, it became the ITU standard paging system.
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KE5YUU
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Posts: 12




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« Reply #7 on: July 12, 2013, 08:56:53 AM »

Interesting information!  I have not picked a frequency, but based on what I have read, I plan on using VHF and including my call sign before each transmission.  I have not seen anything that would suggest this to be outside of the rules and regulations.  I am going to try and get away with 1 watt and see if that will get me good enough coverage, if not, I can email some of the local Ham groups (90miles away) and see if they recommend a frequency. 

73's
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AA4PB
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Posts: 12836




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« Reply #8 on: July 12, 2013, 09:44:04 AM »

Actually, if you wife does not have a ham license then it would not be legal for her to operate the transmitter to send you a message unless you were physically present at the transmitter location to act as the control operator (in which case she wouldn't need to send you the message in the first place).
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KE5YUU
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Posts: 12




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« Reply #9 on: July 12, 2013, 01:09:59 PM »

Very good point!  Thankfully she does have a general license.  Normally thats how we communicate via Simplex.  Sometimes I leave the radio in the truck because Im working.  I think it would just be easier to clip on a pager, that would be with me the entire time.

73's
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K5LXP
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Posts: 4482


WWW

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« Reply #10 on: July 12, 2013, 01:37:23 PM »


Why is it you'd want to lay out a board for such a simple circuit?  Just build it on a proto board/deadbug and be done with it.  You could do that way faster and easier in my opinion.  I've been using Eagle for about 15 years and make my own double sided boards at home, and I wouldn't bother laying something like this out unless I intended to build quantities.


Mark K5LXP
Albuquerque, NM
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KE5YUU
Member

Posts: 12




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« Reply #11 on: July 12, 2013, 03:01:25 PM »

Good question.  I have been wanting to learn Eagle and the procedure to get a board professionally printed, and thought this would be a perfect starter.  There is no plan to distribute the boards, I just thought it would be good for me to learn. 

73's
Tommy
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KE5YUU
Member

Posts: 12




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« Reply #12 on: July 12, 2013, 05:07:44 PM »

I have a Kenwood V71A that I was hoping to use with this setup.  Do you think this radio would be compatible with this circuit?  I can't seem to find any info saying I can do FSK with this transceiver.

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AA4PB
Member

Posts: 12836




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« Reply #13 on: July 12, 2013, 05:28:04 PM »

I think you are planning to do AFSK rather than FSK. If you will be feeding audio tones into the microphone input that is AFSK and your FM transceiver will work fine. Be sure to keep the modulation level down so that you don't drive the limiter in the transmitter into clipping. Take a look at some of the packet radio adjustments on the Internet to get an idea how to adjust the level.

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WD4HXG
Member

Posts: 182




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« Reply #14 on: July 13, 2013, 12:13:45 AM »

Will your pager be able to acknowledge receipt of the
message? If not you may want to check this link.

http://wireless.fcc.gov/services/index.htm?job=about_1&id=amateur#One-Way%20Transmissions

Chuck WD4HXG
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