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 Post subject: Re: AM Stereo (C-QUAM)
PostPosted: Tue Jun 23, 2015 10:46 pm 

Joined: Sat Jul 05, 2014 4:12 am
Posts: 62
My transmitter is a BW 1A with a C-Quam card in it already setup for stereo. I just need to know how to feed it.


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 Post subject: Re: AM Stereo (C-QUAM)
PostPosted: Thu Jun 25, 2015 12:12 am 
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Joined: Mon Mar 17, 2008 1:40 am
Posts: 9500
Some transmitters accept left/right input, I've heard that some also require L+R and L-R as input and I haven't built that in yet (it's very simple to do though, so if you need it just shout and it will be in the next build).


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 Post subject: Re: AM Stereo (C-QUAM)
PostPosted: Sun Sep 23, 2018 6:32 pm 

Joined: Sun Sep 23, 2018 6:03 pm
Posts: 3
Hi! I happen to use stereo tool with my DRMAX instead of ASMAX for AM stereo transmission. I tweaked for a while and now the it sounds good basically. I think there will be better setups till I discover in the future.
Now, for current setup, some advice I would like to suggest.
First, if you like hot sound, turn off AGC. Vice versa, use AGC. Using AGC, you can turn on Matrix function and adjust the stereo in accordance to Stereo Boost. To a proper level, you'll have a very wide sound without excessive phase "tilt". By the way, some AM stereo receivers are quite sensitive to 25Hz pilot tone. Too hot sound will make them drop stereo out.
Second, some parameter to share for you. As to Band mix in Multiband 2 tab, 130Hz=+4.40, 330Hz=+6.02, 860Hz=+4.40, 2240Hz=+2.48Hz. Such setting sounds warm and full of fidelity.
Third, cutoff 60Hz below in case of stereo dropping out.
Last, a rule of thumb: the final output level (if you can measure that) should at most -6 dbFS. Of course if you tx mono sound, the threshold can be up to -3 dbFS.
The loudness can beat up all local mono stations. Thinking of it an AM stereo station, the result is so cool. Only 30mw power, the signal can travel 300 meters.

I don't have any meter to measure the asymmetric modulation. The problem for me is that I cannot sense the difference between 100% modulation and 200% modulation. Maybe there is still more to go deeply.


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 Post subject: Re: AM Stereo (C-QUAM)
PostPosted: Sat Oct 20, 2018 6:15 pm 

Joined: Sun Aug 23, 2015 3:50 pm
Posts: 20
Quote:

First, if you like hot sound, turn off AGC. Vice versa, use AGC. Using AGC, you can turn on Matrix function and adjust the stereo in accordance to Stereo Boost. To a proper level, you'll have a very wide sound without excessive phase "tilt". By the way, some AM stereo receivers are quite sensitive to 25Hz pilot tone. Too hot sound will make them drop stereo out.
Second, some parameter to share for you. As to Band mix in Multiband 2 tab, 130Hz=+4.40, 330Hz=+6.02, 860Hz=+4.40, 2240Hz=+2.48Hz. Such setting sounds warm and full of fidelity.
In the US, you can use a full 10KHz bandwidth according to the NRSC standards. Most radios manufactured in the last 10 years have a 3KHz bandwidth for noise rejection. Some newer radios (and almost all C-QUAM radios) have a much better frequency response - and some Nissan radios are reported to have adaptive bandwidth capabilities. This is where you have to work on trade-offs for how much extra preemphasis vs. a screechy sound on radios that have frequency performance above 3 KHz.

I've played with a +5 dB boost on the low band and a +9 dB boost at 5Khz with some success.

The Optimod AM processors (going back to the 1970's) have a 5 KHz boost to counter frequency roll-off and give crispness to voice programming.

Here is an article about AM frequency response filters and phase issues in analog processors. Stereotool's filters are much more advanced and seem to get around these issues (outside of frequency response issues in directional arrays).
https://www.radioworld.com/news-and-bus ... ing-good39

Page 11 of this study shows typical frequency responses for radios in the market:
https://www.nrscstandards.org/standards ... g100-a.pdf

To deal with the 25 Hz pilot tone, we've used a 35Hz high pass filter with a very sharp roll off.

Here are two of my presets - one for music and one for talk programming. They both sounded great on a BE 2.5 KW transmitter into a 4 tower array. The receiver was a Carver TX-11a.
viewtopic.php?f=10&t=23966


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