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Author Topic: Your opinions on best transmitted bandwidth  (Read 2926 times)

Offline Antennae

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Your opinions on best transmitted bandwidth
« on: May 23, 2015, 1956 UTC »
I think this info would be useful to operators. 

With my SDR I can demodulate 24kHz maximum.  But I don't use it because usually the pirate stations I receive are weak and a wider filter helps to a point but after that more noise will enter and render it noisy. 

Listening to an SDR recording of KCPR, a pirate on the same side of the Mississippi as me, I was able to tell that I could hear more of the music at 24kHz wide.  The conditions were noisy and at 24kHz the noise was annoying.  So I settled on 16kHz for the best reception quality.

Most SW broadcast stations use 10kHz wide. But a SW Chinese broadcaster has a wider signal that really lets in more sound if I widen my filter to take advantage of it.   

I recently learned that a transmitter's power gets used up on whatever music its transmitting. So if you only give it 10kHz, it will focus its power and strengthen that range of bandwidth. And hopefully be more legible for the listeners  ::)

-For the pirate listening mavens, is there a sweet spot that transmitters could shoot for? 
-Do you agree it depends on the background noise conditions at the time of broadcast?

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Offline ChrisSmolinski

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Re: Your opinions on best transmitted bandwidth
« Reply #1 on: May 23, 2015, 2011 UTC »
I typically use 3 kHz bandwidth when listening. Sometimes, if the signal is very good, I will open it up to 4 kHz, 5 at the absolute most. With poor conditions, I may go down to 2 kHz, although anything less and usually becomes more difficult to decipher the audio.
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Offline refmo

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Re: Your opinions on best transmitted bandwidth
« Reply #2 on: May 23, 2015, 2038 UTC »
Same as Chris here, usually between 2.5 and 3 khz. Up to 4 or 5 khz for very strong stations such as Wolverine, XFM, and some TCS relays.
Most of the transmitter power will get used by the bass frequencies - spectral power will generally decrease by around half (3db) per each octave, so raising the lowest bass frequency you transmit will allow more average power in the mid-range where most of the intelligibility for making out ID's resides.
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Offline atrainradio

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Re: Your opinions on best transmitted bandwidth
« Reply #3 on: May 24, 2015, 1518 UTC »
I typically stay at 4kHz as well. But with my sears/roebuck 1971 8 track and MW/FM radio, I am not sure what the exact filtering is, but it sounds like 7-9 kHz wide. It sounds beautiful and is definitely the best sounding radio I own.
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Offline jFarley

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Re: Your opinions on best transmitted bandwidth
« Reply #4 on: May 24, 2015, 1523 UTC »
I agree with Chris and refmo's comments, and the BW is opened as QRM/signal strength allows.

For overnight recording, which tends be be an audio recording on a single frequency, I have gotten the best longterm results using a BW of approximately 2.4 kHz.
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Offline Pigmeat

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Re: Your opinions on best transmitted bandwidth
« Reply #5 on: May 24, 2015, 2250 UTC »
I'll give you an operators point of view on audio.

It all depends on how wide of an audio bandwidth your transmitter/receiver can handle. Most pirates use old or off the shelf ham equipment. You can widen the bandwidth to a point, but they were designed to pass about 300 hz. to 3 khz. For ragchewing that's fine, for high-fidelity music, it blows.

I found what Refmo said to be true. I knew my transmitter had a steep dropoff below 80hz. As I've got a deep voice, I would cut the low bass below 100 hz. and give it a bump at 125 hz., then do a slow rise above 500 hz. to 3 khz. cutting gradually above that to about 6khz. Above that, I rolled it down to nada, as most receivers bandwidths cut off about 8khz., tops. (SDR's are an exception.)

Most of the guys in Europe I've talked to cut the top end at 4.5 khz. As they like that "thump" they kick up the bass above 20-40 hz.

You want your transmitter to deliver the most power to where it can be heard. Conversely, you want the filters on your receiver set to best receive the limited bandwidths most pirate transmitters are stuck with.

Noise is something you have to live with as an operator. You look for the sweet spot when noise is low, propagation is solid, and in a time period with the most listeners. Low atmospheric noise is why SW/MW pirates love the winter.

Good luck.

Offline redhat

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Re: Your opinions on best transmitted bandwidth
« Reply #6 on: May 25, 2015, 1355 UTC »
I leave the audio processor set at 10 KHz audio bandwidth, as anything less makes the air monitor sound too midrange heavy and gets really fatiguing after several hours with the cans on.

I have noticed that most of the off-air recordings I receive run around 3-4 KHz audio bandwidth.  I'm not sure if this has to do with listener preference or equipment limitations, but that's what I've observed.  When the signal is strong, the wide audio really shines, but it takes a lot of power to make it that far, probably more than most pirates have access to.  I do like hearing the wider recordings, and several recent samples from Kilokat7 and Dimbulb sounded quite nice.

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