Sunday, February 21, 2016

New recorder for SDRsharp breaks 2GiB limit

In my post ATSC now possible on magnetic drives I said that SDRsharp was the perfect solution for TV recording but lamented its 2 GiB limitation.

In my opinion, HDSDR and SDRsharp are the two best SDR applications. HDSDR has minuscule computing requirements (low CPU usage) and more reliable recording while SDRsharp draws a slightly better waterfall and (at least for older versions) is more fun to use overall.

I especially like that HDSDR is written (AFAIK) in rock-solid, no-frills Win32 C++ instead of SDRsharp which was done in C# .NET. Pure C++ produces smaller and lighter programs that don't crash or bog down the CPU quite as easily.

Since the recording function is so reliable and well-written in HDSDR, not to mention the support it has for files of unlimited size, I have written 2 emails to the author of HDSDR asking him to add 8-bit recording. However, he has not gotten back to me. On the HDSDR website it says the latest version is from 2013, implying that he has halted development. That fine by me, though. Apart from the lack of 8-bit recording, HDSDR is perfect and I hate when software developers mess with perfection.

Last week I emailed Youssef Touil, the author of SDRsharp, requesting that he update SDRsharp to support larger files. After I explained that it wasn't specifically for the SDRplay he kindly sent me links to plugins that will unlock >2GiB recording. Here they are:

Baseband Recorder (
WavPlayer (

Today I had a chance to test the Baseband Recorder. To use it yourself, open the zip file after downloading and go into the basebandrecorder folder:
I only needed the Baseband Recorder because my goal is to convert the files in Audacity, not play them back. Just select the 4 files you see and do Ctrl+C. Then go into your SDRsharp folder and paste.

Then you will need to open MagicLine.txt and do Ctrl+A and Ctrl+C. Close MagicLine.txt and open Plugins.xml in your SDRsharp folder. Paste the line in where indicated:
You may have more or fewer plugins than I do, but you get the general idea. Also, as you can see, it needn't be tabbed over.

Save Plugins.xml and open SDRsharp. You should see the new recorder at the bottom of the sidebar.
Click the arrow to expand it.
And there you have it: a flexible new recorder that even supports choosing an output directory. To show just how flexible it is, here is the Configure dialog:

What... did that just say WAV RF64?!? Yes it did!

With this plugin we are very close to being able to do some awesome stuff with ATSC decoding. Now the last step is to figure out how to capture the necessary 7 MHz bandwidth as opposed to SDRsharp's baseband which is limited to 250 KHz. I was really hoping I could capture the whole bandwidth with this plugin.

(Update 03/01/2016)

I made a mistake above. I had confused Baseband with passband. Baseband in SDR# is the same as RF in HDSDR, which means that this plugin will record your full RF bandwidth. I had my SDRplay set to about 200 kHz during the first test, and so the WAV file's properties said 200 kHz sampling, reinforcing my false assumption that this plugin only records passband.

I am very pleased to see that progress bar underneath "Dropped buffers: 0". In case you didn't know, the progress bar represents the recording buffer. In a previous post I suggested that a buffer be used to smooth out the latency inherent in magnetic hard drives. It seems that the author of this plugin has taken that into account. I don't think the buffer is very big, but it's certainly better than nothing (ever notice how the native SDR# recorder seems so prone to dropping samples? I suspect the native recorder has no buffer.)

Today I made some TV recordings on 8-bit with this plugin, converting them to 16 bits in Audacity and decoding them. Sure enough, the plugin works as I had hoped. I was able to take recordings of unlimited length and I chose to stop them at 8 GB because I didn't want Audacity to take too long to convert them. Both final decodes were rife with errors, although WACH had some perfect spots. I only used the two blowtorches in my area, WJBF and WACH. These two have always been the most reliable, so it is obviously something wrong with the new method. I think it has something to do with 8-bit and the reduced dynamic range because no buffers were dropped.

In conclusion, if you can get around the reliability problem then it is now possible to take TV recordings of virtually unlimited length using magnetic hard drives.

Special thanks to Youssef Touil for showing me the final piece of the puzzle that made this possible.

No comments:

Post a Comment