receiver vs. demodulator

[misterpaul]

Hello,
I'm a little confused so I was wondering if someone could shed some light as to what are the differences between a demodulator and a receiver. Looking at the specs of a demodulator vs. a receiver I cannot see any differences, both seem to have inputs/ ouputs, be able to process the streams and so on and so forth.

Thanks

 

[Mr Tony]

a receiver picks up the various channels and outputs it on channel 3, 4 or a/v outputs.
The demodulator takes a source and puts in on a specific channel (ie: 6,7,12)

demodulators are used mainly for cable/satellite headends

 

[misterpaul]

Thank you for your quick reply.

So if I were not to care about outputting it to my tv, but rather watching everything on my monitor I could just go with a demodulator with ASI out and this would allow me to record / watch the stream on my monitor?

Thanks

 

[Stefan]

If your talking about commercial demodulators, they generally only have some kind of digital transport stream output and don't have any kind of video output that you would be able to feed to a monitor. Some of them have ASI or LVDS ( sometimes also referred to as SPI). In that case youd need either a video decoder with the ASI or LVDS input or youd need an adapter that takes this type signal and feeds it into a PC. When your getting to this level your not talking cheap anymore. ASI PCI cards cost around $1k and video decoders that take asi or LVDS input usually cost about the same or even more. Rod Hewitt does sell a cheap usb LVDS adapter that works with Tsreader for $399. If you have commercial equipment with LVDS ouptut or can get a cheap asi to LVDS converter it's a real bargain at that price.

Anyway, if your looking at demodulators on ebay, or anywhere else for that matter, be careful. You need to make sure you find out from the seller exactly what features, like what kind of inputs and outputs, the specific unit he or she is selling has. For satellite reception you'd want to make sure the one you got had L-band input. Some of them have other types of input. Also you want to know exactly what kind of output you need for your equipment and what kind of output the demodulator has. Some of them were used for Ip type data services and had odd type outputs like HSSI. In some cases those can be modified to get LVDS but that requires some electronics skill. One more thing is that on some units the ability to receive certain types of signals (like 8psk or 16Qam) was optional and some units may or may not have those options enabled. In the case of some demodulators the original purchaser had to purchase a code number that had to enter into the demodulator that would unlock such features. That's the case with the Comtech boxes. Anyway make sure you research as much as possible before spending a lot of money. Do a internet search for the specific model number of the unit your thinking of purchasing and download as many manuals and/or datasheets on it as you can find.

 

[misterpaul]

Hi Stefan,
thanks for your reply.

I'll give you the scenario I'm looking at:

I found a Comtech demodulator with ASI output. If I were to get a PCI ASI card I will be able to feed the signal to TSReader via the ASI card and wouldn't need any other decoders/ processors or am I completely off here?

I may have been a little unclear in my previous post about what I'm trying to achieve - I'm not trying to feed the signal directly to my monitor but rather record it/ stream it through TSReader.

Thank you

 

[Stefan]

Yes, that'll work fine. Just make sure your ASI card is supported by Tsreader and it either comes with drivers or you can get the drivers for it. In this case your PC and VLC or whatever software video player you use becomes the decoder.

 

[misterpaul]

Excellent,
got my tax return the other day so I need to spend it on something

So like iceberg was saying you only need an IRD if you want to be able to watch the pic on your tv, whereas a demodulator can be combined with an ASI card and it will work fine via TSReader.

Thanks again for the info Stefan (iceberg as well), very helpful,
Paul

 

[Tron]

As Stefan mentioned, the expense here is in the ASI-PCI card. Here is one of the more popular manufacturers of such cards: DekTec - Home

 

[Anole]

huh?

Other than bagging rights for having commercial equipment, I fail to see the attraction over a PCI DVB card.
And for a whole lot less money.
A computer would be involved either way.
And it's doubtful either could do blind scanning (better off with a stand alone FTA receiver for that).

Perhaps someone can enlighten me?

 

[ftarock]

For the hobby, Dektec is overkill, the cheapest way is to get Rod board LVDS-USB.
Try to get a LVDS <--->ASI unit, they listed on ebay once in a while for really cheap. EVS is the brand, got one for $30.
Rod's lvds-usb board is $400 as I remember, plus a EVS box, it's cheaper than any other Transport stream - USB units on the market.
FTARock

As Stefan mentioned, the expense here is in the ASI-PCI card. Here is one of the more popular manufacturers of such cards: DekTec - Home

 

[ftarock]

Most people go for commercial units because they are the only that support the modulation they want (8psk Trellis, DC2 Combo...)
Therefore, having ASI or SPI out for transport stream is important if one plans to record the program.
FTARock

Other than bagging rights for having commercial equipment, I fail to see the attraction over a PCI DVB card.
And for a whole lot less money.
A computer would be involved either way.
And it's doubtful either could do blind scanning (better off with a stand alone FTA receiver for that).

Perhaps someone can enlighten me?

 

[misterpaul]

Hi ftarock and thank you for your input.

I've been looking for one of those asi to lvds converters for a few months and have not been able to find one. I'll keep a search open on ebay and hopefully one will pop up soon.

Rod's dvb-spi is down to $299 now, so it would be an awesome deal but I still need to find the converter first.

As you're saying the dektec / dveo asi cards are extremely expensive - around a grand when new, but I'm also looking on ebay for used ones.

It is an expensive hobby sometimes, but a lot of fun and it always makes you wanting more and more

Paul

 

[ftarock]

Before you spend your $, make sure you know what you gonna get with the EF Data Comtech:
1. Modulator and Demodulator are totally different. What you need is a Demodulator with ASI or LVDS out. Further explain for the Modulator, that's the unit takes the transport stream in either via ASI, LVDS, M2P...modulate in in qpsk, 8psk...or other modulation scheme, outputing the mux via 70 or 140Mhz. Other words, Modulator is what the uplinker use to uplink the video/audio/data to the satellite.
2. Email the seller asking what modulation option that Comtech has. Do not assume any thing, EF DATA does have 8psk TRellis as option but the Standard firmware is qpsk.
3. Email the seller asking for the output, ASI or LVDS is what you want. Some come with HSSI that you must modify it to make it work with Rod's board.
FTARock

Hi ftarock and thank you for your input.

I've been looking for one of those asi to lvds converters for a few months and have not been able to find one. I'll keep a search open on ebay and hopefully one will pop up soon.

Rod's dvb-spi is down to $299 now, so it would be an awesome deal but I still need to find the converter first.

As you're saying the dektec / dveo asi cards are extremely expensive - around a grand when new, but I'm also looking on ebay for used ones.

It is an expensive hobby sometimes, but a lot of fun and it always makes you wanting more and more

Paul

 

[Stefan]

Try to get a LVDS <--->ASI unit, they listed on ebay once in a while for really cheap. EVS is the brand, got one for $30.

There used to be one particular seller, who seemed to have a lot of these units and use to sell them regularly for that price. I think his ebay handle was "natbray". Anyway, when you bought one of his units they came in what appeared to be the original box. So, if your really interested you might could try contacting him and see if he might either have some more or know where to locate one.

Also the way to properly use them for this purpose is not immediately obvious. For example if you want to convert from ASI to LVDS, you use one of the ASI inputs but instead of connecting to the LVDS output as you might expect to do, you connect to the LVDS input which is on the same input channel and directly above the ASI input port your using. This seems odd but works because were not using the box as it was originally intend. It was originally intended to be a part of a more complex system and has "data" ports on the opposite side that look like 68 pin SCSI connectors and probably were connected to another box or a PC.

 

[ftarock]

Yes, I got mine from that seller. I have not seen that seller listed these EVS boxes anymore.
I agree, the way of connection to make this box work is odd, but it does work for for TS format conversion.
Some have report that there is bitrate limit for the lvds of this unit, up to 75Mpbs or close to it. I have not verified this, highest datarate of sat mux I get is 55Mpbs...75Mpbs is more than what we need for satellite, but for those playing with mulitplexor, the limit of lvds might be a problem, just want to point it out.
FTARock

There used to be one particular seller, who seemed to have a lot of these units and use to sell them regularly for that price. I think his ebay handle was "natbray". Anyway, when you bought one of his units they came in what appeared to be the original box. So, if your really interested you might could try contacting him and see if he might either have some more or know where to locate one.

Also the way to properly use them for this purpose is not immediately obvious. For example if you want to convert from ASI to LVDS, you use one of the ASI inputs but instead of connecting to the LVDS output as you might expect to do, you connect to the LVDS input which is on the same input channel and directly above the ASI input port your using. This seems odd but works because were not using the box as it was originally intend. It was originally intended to be a part of a more complex system and has "data" ports on the opposite side that look like 68 pin SCSI connectors and probably were connected to another box or a PC.

 

[Stefan]

Yeah, I've heard of the bit rate limitation as well, but I only use mine with a Digitrans DTE-7100 and since it only does DCII and Qpsk DVB, the limitation isn't an issue. I think it would only be an issue with 8psk as that's likely the only way you'll see bit rates that high. Anyway, my 8psk boxes have LVDS out. So, I don't need the convert to use those.

 

[misterpaul]

Yup, I've made sure to get a very detailed description of the receiver since as you pointed out it'd be a waste of money to realize after the purchase that it won't demodulate the signal I bought it for in the first place (8psk in this case). The seller is looking for a board that has both LVDS and ASI, so I should be able to choose whether I want to go the ASI or SPI router.

Reading the specs of the unit that Rod offers as well as other DVB-SPI cards I take it that they support up to 108 mbps, so I assume they wouldn't choke at signals lower than 80-90 mbps, would they?

Thanks

 

[ftarock]

If specs of Rod's board indicates up to 108mbps, it won't be any problem. We were talking about the bitrate limitation of the EVS LVDS-ASI converter.
If the EF Comtech has SPI out, that's perfect for Rod's board.
FTARock

Yup, I've made sure to get a very detailed description of the receiver since as you pointed out it'd be a waste of money to realize after the purchase that it won't demodulate the signal I bought it for in the first place (8psk in this case). The seller is looking for a board that has both LVDS and ASI, so I should be able to choose whether I want to go the ASI or SPI router.

Reading the specs of the unit that Rod offers as well as other DVB-SPI cards I take it that they support up to 108 mbps, so I assume they wouldn't choke at signals lower than 80-90 mbps, would they?

Thanks

 

[misterpaul]

Awesome,
thanks a lot guys.

I've wanted something like this for some time and now I finally have all the necessary info (and funds) to purchase it.

Thank you,
Paul

 

[Tron]

Guys, I hate to dig up an older thread, but I was hoping either FTARock or Stefan might know more about this product, and if it does basically the same thing as the DekTec solution:

IMEDIA S25-7000142 INPUT DVB-ASI PCI CARD - eBay (item 250096334848 end time May-12-08 14:18:58 PDT)

Can't find much about it, might be discontinued or the company might be out of business? That would spell trouble for finding drivers. I notice the seller is overseas, but has a decent feedback rating. I was wondering if the card is trash or if it might be a decent solution for PCI ASI (I just picked up another Digitrans, the 7100). This one has ASI out

EDIT: To partially answer my own question, further research seems to indicate that IMedia was bought out by Terayon, and they in turn have been bought out (by Motorola?)... Anyway, looks like the card in question goes into a Cherry Picker, which as far as I can tell, is a dedicated PC for stream manipulation. I guess the question now is can these cards be used in an ordinary PC with 3rd party software to record the ASI stream?