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[quote author=”Diekgait”]Stelios, are you going to implement GPS for cariersync and maybe digitall mpx delay?
Dennis[/quote]
Hi Dennis,
Not for these 5 prototypes, but yes, there is plan for SFN support.
There will be a separate box (SFN Adapter) at each DDS exciter, plus one SFN Controller at the studio.
The concept is based on DVB-T standards and it is viable only with digital audio or D-MPX.@djscooby:
If you have analog MPX signal from your radio link receiver, you can send it to Port C of the Exciter, and enable the External BB mode.
This exciter is capable to accept any source (see here), but of course you will have lower audio quality comparing to a digital source.
To have perfect results, you need to send digital audio (or D-MPX) signal. You can find some cheap solutions for this, like Barix with a 5.8GHz WiFi link (like Ubiquiti Bullet5).
In the future there will be a digital radio STL (ricardogerassi I didn’t forgot you). Also, I think Leif has plans for an IP STL.@yorkie98:
Xonar D2/PM will be tested for optical D-MPX, I will have one soon.
Later I will edit this post to upload some pics of coaxial D-MPX test.
Until then guys, I can offer you the following video by George:Hi yorkie98,
Unfortunately that day we had only Juli@ available. It was feeding the exciter with optical L/R and the internal stereo encoder was used.
Currently I’m working on those you asked here in the forum. If you have any requests for the last upcoming "mountain-test", please let me know.PS: George, we’re still waiting for videos and more photos…
The deviation limiter of course will be user selectable and "off" by default, don’t worry guys!
I have already done some research about SFN and I have selected the DVB-T principle.
Of course there is need for SFN adaptors with GPS reference at each TX site, plus a MIB inserter at the studio.
All these are achievable only with digital audio source (AES/EBU L/R, or D-MPX, or IP).A few minutes ago, we (John, George & me) returned from the TX mountain "Hortiatis" where we tested the DDS exciter with a 20kW amplifier.
George took videos and photos, I hope he will find some time to prepare and upload them here soon. 😉[quote author=”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?[/quote]Hi yorkie98,
There isn’t any special technology here! It’s just a different approach to make the deviation adjustment easier and safer.
Tell to the DDS the audio level you send (this idea was suggested by JesseG, thank you!). Then tell to the DDS how many kHz deviation you want for this amount of audio, and it will accurately do that.With BBP for example, when you set "-12dBFS" output, you are sure you will get -12dBFS, correct?
– With an analog exciter, you have to adjust the "audio input level" knob, relying on the exciter’s deviation meter (if any), or using a modulation measurement equipment, true?
– With this exciter, simply set "Input level = -12dBFS" and "Deviation = 75 kHz" and you are done. No measurements, not anything else. Leave it and go!In case you increase to -3dBFS without changing the "Input level = -12dBFS" at the exciter, you will overmodulate. If you think it’s necessary, I can easily add a deviation limiter – to be completely protected.
[quote author=”yorkie98″]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?[/quote]The same way as described above. Doesn’t matter what the input source is (L/R analog or digital, MPX analog or digital, internal stereo or mono).
Did I understood your question correctly? 🙂
@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:
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?
[quote author=”JesseG”]It should be made to be able to adjust what the nominal level is too, if that is possible. -3dBFS is way more than enough for Breakaway, and will improve where the 16bit noise floor is a tad.[/quote]
OK, I will add this!Hello everyone, and I apologize for my long absence… 😳
Some very good things happened for me in my day-job, and had to put aside everything else.
Now I am gradually returning to my regular activities! 😉"Yeah, yeah… What about the DDS exciter?"
The prototype is assembled and tested already by some people. Well, I wish they could write here their impression!
Any suggestions and problems have been addressed. Now remains a final test in a very harshed environment, and then can go to camclone.
If you people need any special tests to make before it leaves from my hands, please tell me soon!Some (poor quality) pictures of the hand-made prototype:
"Audio adjustment" vs "Modulation adjustment"
All radio stations today have an audio processor – like BBP. Also, all stations concern about their deviation (+/-75kHz).
Would you like an exciter with "audio level" adjustment, or an exciter where you can dictate it’s deviation with precision?
In this exciter, I don’t provide an "audio level" adjustment, but a "modulation adjustment" instead.This maybe confuses you, but it is very simple. There is no clipper, just a different approach:
The user feeds the exciter with a nominal audio level -12dBFS, and then defines from the menu how many kHz deviation he wants.
In other words: give -12dBFS from BBP and set "75kHz" from the DDS menu. Now you can be sure that the exciter deviates +/-75kHz.
The "75kHz" is an example, you can set it from 20 to 150 kHz which results in +/-20 up to +/-150 kHz deviation.Everyone who saw it got confused, but were amazed when I explained it.
Would you guys like to share your opinion about this concept?Prototypes are almost finished, production & price after compliance tests.
Estimated release to ETSI market: 1Q 2010, FCC market: 2Q 2010.[quote author=”yorkie98″]Wow, thats very impressive, this is going to be a formidable piece of kit.
If it’s cost effective to make one main board for all needs, this has to better for consumers than having different variants right?[/quote]
Yes, we’re talking about +10…15% manufacturing cost, that results in flexibility and added value.
I believe it doesn’t worth to split into variants – except for marketing reasons.@Sparky:
Thank you Sparky, I really appreciate that! 🙂
On the original exciter (modular version), I remember around -130dBc/Hz at 1KHz.
Unfortunately, I don’t have now a signal source analyzer to tell you exactly.
I promise to upload some screenshoots of the compliance tests.@yorkie98:
Yes, it has built-in stereo encoder! 🙂
Yes, [ST] is for stereo, [MO] for mono, [EX] for external baseband (A-MPX or D-MPX).
viewtopic.php?p=5560#p5560
Yes, it can recognize AES3 or S/P-DIF!@rocco123456
D-MPX via Toshlink (Port B) yes, only if your sound card support optical output @192kHz.
Otherwise, you have to use AES/EBU electrical interface (Port A) @192kHz.Unfortunately I will make only 5 prototypes, and already arranged to give them around.
It is not wise to make more prototypes before passing the certification tests.
Please be a little patient! 🙂Happy new year to everyone!
Just an update:
There was a little issue with PCBs, but hopefully will have them in the next 5-7 w/days.
Being impatient, I printed myself one unit of the new mainboard, to see actual component layout.
I thought to share with you how it looks:
From top-left:
Port A (XLR), Port B (Toslink), RS-232, Port C (XLR x 2).This mainboard produces 50mW and drives the RF filter / amplifier section.
There is also a control panel (LCD display and rotary switch), for UI.Will keep you informed…
