# HRPT receiver

**URL:** <https://www.ruby-forum.com/t/hrpt-receiver/242536>\
**Category:** GNU Radio\
**Created:** [June 30, 2015, 10:49pm UTC](https://www.ruby-forum.com/t/hrpt-receiver/242536 "2015-06-30T22:49:55Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\
**Post date:** [June 30, 2015, 10:49pm UTC](https://www.ruby-forum.com/t/hrpt-receiver/242536/1 "2015-06-30T22:49:55Z")

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Hello,

In the gnuradio/gr-noaa/README file under usrp\_rx\_hrpt.py, there is a  
comment that  
reads as follows:

“The present HRPT demodulator is only tested at decimation 16. The  
only other  
valid decimation rates are 24 and 32, which may work, but with more bit  
errors. No  
other decimation rates will work.”

```
My (perhaps naive) question is whether the important parameter is 

```

the decimation  
rate, or the sampling rate. For example, with 64 MHz USRP, a  
decimation of 16 would  
give 4 MHz sampling, whereas with a higher rate USRP, the same  
decimation would  
yield a higher sampling rate.

```
I would appreciate it if someone could clarify this point for me.

```

Sincerely,  
Dan Marlow

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**Author:** ![danmcb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/13edae/32.png) [@danmcb](https://www.ruby-forum.com/u/danmcb)\
**Post date:** [June 30, 2015, 10:58pm UTC](https://www.ruby-forum.com/t/hrpt-receiver/242536/2 "2015-06-30T22:58:06Z")

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Hi Daniel,  
that README refers to things of the past (when you specified a  
decimation rather than the sampling rate you want), and “USRP” refered  
to what we nowadays call the USRP1.

In the version of the usrp\_rx\_hrpt.grc, from which the .py gets  
generated, the USRP source is just configured to 4MS/s.

The question is whether 4MS/s is really the optimum rate; I haven’t  
studied the HRPT signal enough to answer this. In principle, for the  
100MHz devices (N210/N200), 4MS/s is a suboptimal rate, since the  
decimation (25) is odd, and I’d try with something less strange, like  
5MS/s.

Best regards,  
Marcus

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**Author:** ![danmcb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/13edae/32.png) [@danmcb](https://www.ruby-forum.com/u/danmcb)\
**Post date:** [June 30, 2015, 11:03pm UTC](https://www.ruby-forum.com/t/hrpt-receiver/242536/3 "2015-06-30T23:03:21Z")

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Hi Marcus,

Thanks. That explains it. Will try 5 MHz with our N200.

Cheers,  
Dan