# BPSK output abnormal **URL:** \ **Category:** GNU Radio\ **Created:** [May 24, 2015, 10:55am UTC](https://www.ruby-forum.com/t/bpsk-output-abnormal/242064 "2015-05-24T10:55:13Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [May 24, 2015, 10:55am UTC](https://www.ruby-forum.com/t/bpsk-output-abnormal/242064/1 "2015-05-24T10:55:13Z")
Hi everyone, I try to simulate file transfer using BPSK with block diagram File Source --\> PSK Mod --\> PSK Demod --\> File Sink The block setting is File Source : -file type = .jpg (282,8 kB (282.765 bytes)) -repeat = no -vec length = 1 PSK Mod : -num of constellation = 2 -gray code = yes -diff. encoding = yes -sample/symbol = 2 -excess BW = 0.35 -verbose = off =log = off PSK Demod : -num of constellation = 2 -diff. encoding = yes -sample/symbol = 2 -excess BW = 0.35 -frequency BW = 6.28/100.0 -timing BW = 6.28/100.0 -phase BW = 6.28/100.0 -gray code = yes -verbose = off -log = off File Sink -vec length = 1 -unbuffered = on -append file = overwrite The size of input file = 282,8 kB (282.765 bytes) but the size of output file = 2,3 MB (2.262.066 bytes) What’s wrong with my fg? Thank you, Surya A. ---
**Author:** ![Surya\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e7dd6/32.png) [@Surya\_A](https://www.ruby-forum.com/u/Surya_A)\ **Post date:** [May 24, 2015, 7:35pm UTC](https://www.ruby-forum.com/t/bpsk-output-abnormal/242064/2 "2015-05-24T19:35:44Z")
On Sun, May 24, 2015 at 4:54 AM, Surya A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > -vec length = 1 > PSK Demod : > > Thank you, > Surya A. The output is unpacked. So each sample only represents a single bit. You have to repack them into 8 bits per byte, but you’ll also need to know where to start through some kind of frame synchronization. 282765\*8 = 2262120 The rest of the difference is due to delays in the filters. You can zero-pad the input to “push” the samples through. Tom ---
**Author:** ![Surya\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e7dd6/32.png) [@Surya\_A](https://www.ruby-forum.com/u/Surya_A)\ **Post date:** [May 26, 2015, 10:13am UTC](https://www.ruby-forum.com/t/bpsk-output-abnormal/242064/3 "2015-05-26T10:13:52Z")
On Sun, May 24, 2015 at 4:25 PM, Surya A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Oh thank you Tom, I can recover the file size. About frame synchronization, > am I need Polyphase Clock Sync Block? And also I have no idea about “You > can zero-pad the input to “push” the samples through.”? (please keep emails on the mailing list) The PFB clock sync handles symbol synchronization – it finds where the bits are. You’ll need another level of synchronization to find the start of the frame, usually by looking for a known start pattern, preamble, etc. And there are many ways to accomplish the zero-padding. I’ll leave that up to you to figure out 🙂 Tom ---
**Author:** ![Surya\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/8e7dd6/32.png) [@Surya\_A](https://www.ruby-forum.com/u/Surya_A)\ **Post date:** [May 26, 2015, 11:29am UTC](https://www.ruby-forum.com/t/bpsk-output-abnormal/242064/4 "2015-05-26T11:29:16Z")
Oh sorry I forgot to reply to all. Now there’s a new problem. I use Packet Encoder to add preamble, the setting is: Encoder - sps = 2 - bps = 1 (bpsk) - preamble = 1010010011110010 - access code = 1010110011011101101001001110001011110010100011000010000011111100 - pad for USRP = no - payload strength = 16 Decoder - access code = 1010110011011101101001001110001011110010100011000010000011111100 - threshold = -1 both access code and preamble are from [http://gnuradio.org/doc/sphinx-3.7.2/digital/pkt\_utils.html](http://gnuradio.org/doc/sphinx-3.7.2/digital/pkt_utils.html) The output now become 0kB