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Author Topic: Requesting an SDR Recording of WWFD-AM Radio, Frederick MD  (Read 829 times)

Offline MrGuts10

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Hi everyone,

All-digital AM radio (NRSC MA3) is an accepted, but not widely used, standard. It could make the AM broadcast band better suited for music and performance, instead of just talk. The entire channel can either be devoted to near FM-quality audio, or can be divided into subchannels. All-digital AM also plays well with existing channel allocations, by staying confined to 10 kHz (corrected) spacing instead of bleeding over to adjacent channels as current IBOC HD is prone to do.

As far as I know, 820kHz WWFD-AM radio, based in Frederick MD, is the only fully digital AM broadcast radio station in the US. I for one would like to examine its packet structure and other aspects of digital broadcast signaling.

I am requesting that any SDR enthusiasts based around Mayland or Washington DC make I/Q recordings of WWFD and share them publicly so that the rest of us can study the format. Here is something to shoot for:

- I/Q samples MUST be recorded, not just Q-branch, so that symbol information is preserved
- on-air digital WWFD-AM MUST be recorded, not the repeater on WWFD-FM
- recording SHOULD cross the top of an hour (to include a time hack and station call)
- sample passband MUST be 10 kHz or wider, centered on 820 kHz
- sample rate MUST be greater than 2x the passband (faster than 20,000 samples per second)
- it is RECOMMENDED the sample passband be 22 kHz
- it is RECOMMENDED the sample rate be 45,000 samples/sec
- recording session SHOULD be about 300 seconds or longer
- share your recording publicly on GitHub or similar service
- notify this HFUnderground thread
- it is RECOMMENDED the recording be accompanied with a description of date, time of day, approx QTH, and equipment setup
- notify project https://github.com/theori-io/nrsc5 (for whom I do not speak)
- a 300 sec recording should come in under 100 MBytes, assuming 32 bits/sample and the recommended passband and sample rate

Recordings from various times, locations, signal conditions and equipment setup would be welcome. There is room for a lot of people to get involved here! I hope the all-digital AM format becomes more widely adopted in the US.

Please help make this request better with your suggestions.

Thank you!
« Last Edit: March 18, 2021, 1815 UTC by MrGuts10 »

Offline ~SIGINT~

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Re: Requesting an SDR Recording of WWFD-AM Radio, Frederick MD
« Reply #1 on: March 18, 2021, 2328 UTC »
May I suggest you try the DR SAINI MDUSAKIWI , NEAR COLUMBIA , MARYLAND WebSDR. I just tuned it in and it appears to receive the 820 kHz signal with no issues. There is an IQ option on the WebSDR you can select as well as a record option. The record option is not as obvious. It is the red circle next to the speaker icon.

As for the future of digital AM, my personal opinion, as well as shared by many others, is that it is a fruitless effort. As the younger generation is tethered to mobile devices, broadcasters need to come to terms with the reality that they have allowed the large telcos to sweep in and capture the market right out from underneath them. Those listeners are streaming content at bit rates far inferior to that of FM or AM quality --- and they do not seem to care. 16 ~ 32 kbit/s on ear buds seems good enough for them.

Aside from the electronic industry and the entire automotive industry most likely not having any appetite for change, I also do not see 100s of millions of listeners flocking to purchase new receivers.

I distinctly remember in the early to mid-1970 diligently tuning my Motorola tube receiver to WOWO radio, some 600 miles south of my location. The soul reason, they had programming I enjoyed listening to. Broadcasters will need to re-invent themselves and actually carry content that an audience wants to listen to in order to remain relevant. Sad to say so, and that is coming from myself with a 40 year history of broadcast and telcom engineering background.

Offline ChrisSmolinski

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Re: Requesting an SDR Recording of WWFD-AM Radio, Frederick MD
« Reply #2 on: March 19, 2021, 1104 UTC »
All-digital AM radio (NRSC MA3) is an accepted, but not widely used, standard. It could make the AM broadcast band better suited for music and performance, instead of just talk. The entire channel can either be devoted to near FM-quality audio, or can be divided into subchannels. All-digital AM also plays well with existing channel allocations, by staying confined to 10 kHz (corrected) spacing instead of bleeding over to adjacent channels as current IBOC HD is prone to do.

I have to respectively disagree with that. It wrecks the adjacent channels. Here is WWFD:



You can see the digital signal extends all the way to nearly 810 and 830 kHz.
Chris Smolinski
Westminster, MD
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Offline MrGuts10

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Re: Requesting an SDR Recording of WWFD-AM Radio, Frederick MD
« Reply #3 on: March 19, 2021, 1637 UTC »
Thanks to @Sigint for the Kiwi SDR link, it may indeed give me what I'm looking for! I'm now looking at WAV to raw IQ conversion.

Thanks to @ChrisSmolinski for your comment. Did you intend to have a waterfall or spectrum plot included in your note? Because if so, I did not see it. I have seen the spectrum display of WWFD-AM on a DC-based WebSDR, and it appeared to be nicely confined to it's channel.

Offline ChrisSmolinski

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Re: Requesting an SDR Recording of WWFD-AM Radio, Frederick MD
« Reply #4 on: March 19, 2021, 1838 UTC »
There's a waterfall plot in my post. WWFD's digital signal extends from 810-830 kHz, causing interference to both adjacent channels.  Here's another one, freshly taken:

« Last Edit: March 19, 2021, 1840 UTC by ChrisSmolinski »
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
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Offline redhat

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Re: Requesting an SDR Recording of WWFD-AM Radio, Frederick MD
« Reply #5 on: March 19, 2021, 1841 UTC »
An AM allocation includes 10 KHz of modulation each side of carrier.  Per the NRSC 5 description of mode MA3, there are two modes; standard mode which includes the primary and secondary digital sidebands (18.4KHz total), and a reduced digital mode which includes only the primary digital sidebands (9.81 KHz total).

This is outlined in NRSC 5 found here. https://www.nrscstandards.org/standards-and-guidelines/documents/standards/nrsc-5-d/reference-docs/1012s.pdf

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Offline ChrisSmolinski

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Re: Requesting an SDR Recording of WWFD-AM Radio, Frederick MD
« Reply #6 on: March 19, 2021, 1847 UTC »
One difference between analog and digital is that with an analog signal, there's typically very little spectral content above 5 kHz, resulting in minimal interference to adjacent channels. With this digital signal, the interference is much more substantial.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 400 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline JethTran

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Re: Requesting an SDR Recording of WWFD-AM Radio, Frederick MD
« Reply #7 on: June 15, 2021, 0738 UTC »
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