Search found 142 matches

by COMMENG
Wed Feb 12, 2020 8:32 pm
Forum: Ask the Engineers
Topic: Belar FMS-2 Docs Needed
Replies: 4
Views: 261

Re: Belar FMS-2 Docs Needed

...So, I am now looking for a matched pair of AA119 diodes.... or trying to figure out how to do my own matching. ... Any suggestions welcome. Thanks, Might I suggest theses suppliers and order say 10 of them and check them on your DMM for the best 2 matches. https://www.rf-microwave.com/en/telefun...
by COMMENG
Tue Jan 14, 2020 2:50 pm
Forum: AM Radio
Topic: Gates 5--no audio
Replies: 28
Views: 1238

Re: Gates 5--no audio

Nothing like that, although there is audio on the carrier now. I see a narrow spike, and a sine wave (at very low level) with something riding on it. Changed jumpers on the PDM amp cards to get audio. Best guess is the round IC's U12/U15 are bad, which are going to be next to impossible to replace....
by COMMENG
Tue Jan 14, 2020 12:30 am
Forum: AM Radio
Topic: Gates 5--no audio
Replies: 28
Views: 1238

Re: Gates 5--no audio

ncradioeng wrote:
Mon Jan 13, 2020 10:56 am
According to the manual, you should have 13-14 Vp-p square waves coming out of the PDM generator.
Here is what ncradioeng is explaining in terms of how the PDM output should appear on your scope:


Commeng
by COMMENG
Thu Jan 09, 2020 11:20 am
Forum: FM Radio
Topic: How to feed mono only audio into base band input on tx?
Replies: 14
Views: 414

Re: How to feed mono only audio into base band input on tx?

...I'd be interested to find out how the new car radios have the same range with mono or stereo. I've always thought the S/N ratio was better with mono. Mono does offer less noise since you eliminate the Double sideband suppressed-carrier AM modulation of the stereophonic subcarrier at 38kHz and th...
by COMMENG
Thu Jan 09, 2020 11:03 am
Forum: AM Radio
Topic: Gates 5--no audio
Replies: 28
Views: 1238

Re: Gates 5--no audio

"They operate very well until a lightning strike hits the tower." I think that applies to just about every transmitter. One MW-1/1A in my area does seem to be quite susceptible to any nearby lightning strike, not just on the tower, and it will blow out diodes in the SWR/feedback circuit even when o...
by COMMENG
Sun Jan 05, 2020 5:16 pm
Forum: AM Radio
Topic: Gates 5--no audio
Replies: 28
Views: 1238

Re: POLYPHASE PDM

I would like to enter a comment regarding the invention date of the Harris Polyphase PDM modulation technique. While the patent documents date it at 1984, the actual invention and implementation preceded that date by quite a bit. The Harris SX series was introduced like in 1980-ish... Fossil Polyph...
by COMMENG
Fri Jan 03, 2020 5:46 pm
Forum: FM Radio
Topic: How to feed mono only audio into base band input on tx?
Replies: 14
Views: 414

Re: How to feed mono only audio into base band input on tx?

We are going to be testing an FM transmitter for use as a translator. As I understand it the unit expects an MPX baseband audio signal at the input.... which as I understand it is... 0 to 15khz = mono audio meaning the left channel sum'd with the right channel... aka L+R 19khz pilot signal 23 to 38...
by COMMENG
Fri Jan 03, 2020 5:07 pm
Forum: AM Radio
Topic: Gates 5--no audio
Replies: 28
Views: 1238

Re: Gates 5--no audio

The four PDM outputs from the generator board should be square waves that change width with audio and power level adjustment. The outputs are displaced by 90 degrees from each other - hence the term "polyphase". As general info, Polyphase PDM was invented by Hilmer Swanson at Harris in 1984. https:...
by COMMENG
Sat Dec 28, 2019 8:14 pm
Forum: AM Radio
Topic: AM Digital NPRM
Replies: 54
Views: 2375

Re: AM Digital NPRM

What happened to the AM Stereo preference for the expanded band as stated in Note 5?

§ 73.30 Petition for authorization of an
allotment in the 1605–1705 kHz
band.


...NOTE 5: The preference for AM stereo in
the expanded band will be administered as
follows:.....


COMMENG
by COMMENG
Tue Dec 24, 2019 6:10 pm
Forum: AM Radio
Topic: AM Digital NPRM
Replies: 54
Views: 2375

Re: AM Digital NPRM

Even still, the Commission saw fit to squeeze-in too many allocations all around the country, causing over-congestion to the band. Listeners under 30 had already abandoned AM as a place to go for music, so the aging-out of the AM audience was well underway. A good example was the whole AM stereo de...
by COMMENG
Tue Dec 24, 2019 5:50 pm
Forum: AM Radio
Topic: AM Digital NPRM
Replies: 54
Views: 2375

Re: AM Digital NPRM

Dupe
by COMMENG
Mon Dec 23, 2019 7:53 pm
Forum: AM Radio
Topic: AM Digital NPRM
Replies: 54
Views: 2375

Re: AM Digital NPRM

I suspect that most self-described "Old Farts" won't bother trying to receive an MA3 AM station. Anymore, AM has their chosen forms of programming anyway; usually right wing talk, news, or some other form of spoken word programming. If you'd prefer the AM band die with you, then I guess it's okay t...
by COMMENG
Fri Dec 20, 2019 10:45 am
Forum: AM Radio
Topic: AM Digital NPRM
Replies: 54
Views: 2375

Re: AM Digital NPRM

Does all-digital do stereo? Yes it will. When the receiver first locks-on audio may be mono for a few seconds until enough bits are captured. It can do stereo depending on the CODEC used. But here is that catch. Since there is a maximum bitrate for a specified RF bandwidth (maximum bitrate is defin...
by COMMENG
Wed Dec 18, 2019 1:21 pm
Forum: AM Radio
Topic: AM Digital NPRM
Replies: 54
Views: 2375

Re: AM Digital NPRM

They can do it because the audio is digitized and processed (i.e. compressed) down to a bit rate that fits in the 10 kHz wide slot. Just like OTA HDTV and mp3's. I am surprised the Xperi and Nautel people haven't come on here to explain or to at least answer technical questions. According to an acq...
by COMMENG
Fri Dec 13, 2019 1:28 pm
Forum: AM Radio
Topic: AM Digital NPRM
Replies: 54
Views: 2375

Re: AM Digital NPRM

They can do it because the audio is digitized and processed (i.e. compressed) down to a bit rate that fits in the 10 kHz wide slot. Just like OTA HDTV and mp3's. I may have missed it, but I haven't seen anywhere in the NRSC or IBOC documents that any audio compression is being done. Now in footnote...