Digital MPX Forum

[sigmacom]

@camclone:
1) Not at the moment. Maybe later only for the controller firmware – not the DSP.
2) Hmmm… Why not? Temperature sensors already exist, I will make the software. The user will be able to enable or not this feature.
3) Unfortunately there is not enough space for a second fan at the back side of the chassis.
4) There is an add-on option for an Ethernet module to provide full control and readings via web interface.
5) Configuration data is stored in EEPROM – no need of battery. Battery uses only the real time clock module (add-on option too).

@Leif:
LOL man!!!

@yorkie98:
Well, I’m not proud of how this specific prototype looks (hand-made), but thank you for your compliments!
If you noticed, the rotary knob has been replaced with three ugly push-buttons – I have to restore that…
About the date of the next prototypes, I can have a prediction after this weekend (after the "big test").

Sorry guys for being persistent asking again and again this, but, what do you think about the "Audio adjustment" vs "Modulation adjustment" concept?

[Boki]

[quote author=”sigmacom”]Sorry guys for being persistent asking again and again this, but, what do you think about the "Audio adjustment" vs "Modulation adjustment" concept?[/quote]
hello Stelios,
I think all here is interest for Digital MPX input (coaxial/optical).
For inexperienced users your "modulation adjustment" is better. They don’t need special equipment to measure what actually comes from the antenna.

But my vote is "Audio Adjustment"

[camclone]

"Audio adjustment" vs "Modulation adjustment" concept?

…TO BE OR NOT TO BE 🙂

I think that you should think of ways to sell it to more target groups ( fm radio engineers )

If you chose only this " space technology "… 🙂 modulation adjustment many engineers who use cheap STL links and dont search ..wikipedia.. will have trouble until understand how it works.
i prefer modiuation adjustment anyway becuse it’s 100% proffesional and " new age " !!!!

You will be the first who will make such a " settings menu " which will help for making this DDS BOX work with 100% effficiency of audio quality.

just perfect! 🙂
keep up the good work and be focused on " ways for making this DDS BOX sell a lot and atract every level of radiostations "

wow!

[Leif]

[quote author=”sigmacom”]what do you think about the "Audio adjustment" vs "Modulation adjustment" concept?[/quote]

I’m not sure I understand the difference, since Audio directly controls Modulation on FM.

How about letting the user choose what dB input level will equal 75 kHz deviation, and leave it at that? 🙂

///Leif

[Anonymous]

Ok, im lost at this point! I get the idea of Digital MPX, but I don’t understand why this transmitter would give any advantage on the FM band. Im obviously missing something here 😀
Could one of you be so kind to enlighten me maybe?
Thanks

[sigmacom]

@Leif:
You are correct, there is no difference. It is the same thing, but in other words!

Many users do not feel safe about their actual deviation, until they measure it on air somehow.
This usually requires an instrument, or a good / reliable receiver with audio card & software.

In my approach, you simply define the amount of kHz deviation you want for a given audio level, and you are assured that this will be actually on air because it is software calculated in the DSP.

Damn! It’s still confuses people… 🙁

@dee:
What do you mean? There are many benefits to use DDS instead of PLL+VCO for FM.
For example, absolute linear modulation, less adjacent channel noise and better frequency accuracy.
Also, it is the only way to make FM from a digital signal (like AES/EBU) without D/A conversion.

[camclone]

Heyyyy………!!
for me , one of the most important things DDS exciters do GOOD and PLL exciters don’t do ..is LOW FREQUENCY effects on the fm frequency of the radio station.

For example with my RVR exciter which is old style PLL ( and without overshoots)i cannot play more than 58 KHz of FULL POWER modulation ( 6 , 7 , 8 and 9 dbr of sound energy ) becuse some recievers cannot stop on my fm frequency sometimes when breakaway makes 6 , 7 , 8 , 9dbr energy. ➡ ➡ ➡

with DDS exciters you can modulate 75 KHz or more and allllllllllllllllll recievers stop on your frequency in all kinds of bass frequencies !
that’s for me the most important who many many radio engineers will notice.

You can play with full sound energy and your station will not be bypassed by some radio recievers when you give more energy to your bass.

[Leif]

[quote author=”sigmacom”]Many users do not feel safe about their actual deviation, until they measure it on air somehow.[/quote]

Indeed. It would be really helpful if your transmitter had a display of the actual peak deviation in kHz.. As long as that meter is accurate (which it really should be in an all-digital transmitter), then you know where you are.

Best,
///Leif

[Anonymous]

Ok, I can see now how cool this actually is 😀
I was going to buy a new transmitter soon enough, now I think I may just wait and keep an eye on this instead!
Amazing indeed, Good Work!

[Leif]

Exactly…. DDS is the best FM we will ever get, and it also opens the door to single-frequency networks. The future of FM is looking pretty bright.

//Leif

[Dj Buik]

Well i’m following this thread from the beginning, but i’m lost here.

Can someone explain this whole thing in simple english please?

You’ve got here an ‘digital’ FM transmitter, but my good old (Sony) FM receiver is still analog…

What’s the advantage of this?

Thanks in advance for explaining.

[camclone]

well, …to be onest , the end user ( the listeners of a radiostation ) may not notice nothing more than a louder radiostation with more clear sound. nothing more ..spacy !

but , things are more complicated than just…loud and clear words..

for example if a radiostation has a DDS exciter and a bad STL and sound processor …then….the DDS exciter does nothing .
BUT , if you have a good " sound routing" ( sound source…a sound proccesor, a good STL and of course …linearity on your radiostation then….BoooooooooooOOooOOooom!!

[Leif]

[quote author=”Dj Buik”]Can someone explain this whole thing in simple english please?[/quote]

I’ll try. In a Direct Digital Synthesis (DDS) transmitter, all the work of generating the FM carrier (RF signal) happens in software, and is output through a D/A converter. Every step before is purely digital.

This means NO tilt issues, NO eq issues, NO signal loss, NO hum, NO overshoots (provided that the incoming digital MPX signal is overshoot free). It is the most accurate way to go from audio processor to broadcasting antenna, with literally no compromises.

Can a traditional exciter sound as good? Yes, absolutely, but it’s much harder to achieve. DDS makes it easy to have perfect sound and peak control.

For comparison, can a cassette tape sound as good a $20 CD-player? Yes, but you need a new metal tape, and you’ll need to spend several thousand on the tape deck, and make sure everything is setup correctly. Even then, it will only sound as good as the $20 CD-player for the first few plays — as the tape degrades, so will the audio.

Digital rocks.

///Leif

[yorkie98]

Hi Stelios, I like the idea of the modulation approach as opposed to the audio level approach but the thing I don’t quite get (and I guess many don’t quite understand either) is how the modulation level can be known without the digital input level being pre-determined also.
So wether we have a digital input of -12dBfs or -3dBfs the modultion would be correct at +/-75khz? My question would be how does the difference in the digital input levels get made up for within the exciter and set accurately to a level which is the known to produce the exact required deviation?
I hope this makes sense..??
Also, I assume that those opting to use the L/R inputs and the DSP stereo coder (or the analog MPX input) still have to use an old-fashioned audio gain approach? or is the difference taken care of in the same way as if using the digital MPX inputs?

I hope my questions are understandable..

Yorkie.

[Anonymous]

Is there any available STL that can support Digital MPX or is that in the pipeline too?
Just trying to figure out how I could keep my signal path completely digital in order to take advantage of all the benefits the DDS has to offer.

[Author]

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