emergency STL

It's just radio with pictures! :)
Post Reply
grich
Posts: 434
Joined: Fri Sep 02, 2011 11:19 am
Location: MP89.5, Mason City Subdivision

emergency STL

Post by grich » Fri Apr 19, 2019 3:44 pm

I've been staring at the MRC QM2 mod and demod that was used with the old Twinstream system, and wondering if they could somehow be used to push a SMPTE310 signal through a 2GHz ENG radio as an emergency STL?

I just started playing with this on the bench using a spare MRC Strata TX transmitter and MRX4000 receiver. My reading of the documentation is the QM2 output is 70MHz IF modulated at 16QAM, so I've programmed the radios accordingly. So far, no go. Anyone else ever thought of trying this?

User avatar
NECRAT
Site Admin
Posts: 3100
Joined: Sat Nov 17, 2007 9:13 pm
Location: Taunton, MA
Contact:

Re: emergency STL

Post by NECRAT » Sat Apr 20, 2019 1:03 pm

We did something very similar to this in Providence, and it can be done. But the trick is with the IF level. It tends to come out very hot, and needs to be badly padded down. I think I had something on order of a 30db pad on the IF input of the Twinstream. The details of it are hazy to me, as it was over 10 years ago now, but I remember that.
http://www.necrat.us

"Arguing with an engineer is like mud wrestling with a pig. After a couple of hours, you realize the pig likes it"

User avatar
RCATTU55C
Posts: 11
Joined: Thu Oct 06, 2016 7:56 am

Re: emergency STL

Post by RCATTU55C » Thu Apr 25, 2019 9:58 am

Hello,

If I am following you correctly, you want to send DATA over an existing analog video link. There is a way to do this by defeating the audio sub carriers and using the baseband. I purchased a cost effective pair of boxes that allow ASI to be transported over a traditional analog modulated link. This also eliminates the need to do anything with FCC license because, as far as anyone is concerned it looks likes white noise being transmitted. I used this method to get ASI from a MRX4000 Plus at my main transmitter back to the studios so my live trucks could run HD.

Depending on the SNR, you can squeeze about 21mb/s out of the bandwidth if your lucky.

https://www.microwavevideosystems.com/p ... 0Demod.pdf

Sorry if this is not what you are looking for.

Steve

grich
Posts: 434
Joined: Fri Sep 02, 2011 11:19 am
Location: MP89.5, Mason City Subdivision

Re: emergency STL

Post by grich » Thu Apr 25, 2019 12:40 pm

I've seen the brochure on the MVS stuff before. If I can't get the QM2's to work, that should work, but I have a $0 budget amount for this project. :wink:

Our Stratas (portables) and MTX5000's (in the trucks) have digital modulators but the station didn't buy the HD-SDI option. We use Sony camera-back encoders (mounted in-truck)to get HD-SDI to a 15MB ASI stream, and stuff it into the radios that way using 16QAM modulation. I have one radio preset for HD via the ASI input, and a SD-SDI QPSK preset for the tough shots. Sencore decoders take the ASI from the MRX4000's and convert to SDI.

As to the QM2's, all of the pads are at the transmitter site, and I have to baby-sit a tower crew tonight, so I'll snag the bag o'pads and try padding down the IF input of the Strata and/or the MRX4000 and see if I can get it to work on the bench.

Thanks for the suggestions...hopefully have an update in a few days.

grich
Posts: 434
Joined: Fri Sep 02, 2011 11:19 am
Location: MP89.5, Mason City Subdivision

Re: emergency STL

Post by grich » Sun Apr 28, 2019 8:20 pm

NECRAT wrote:
Sat Apr 20, 2019 1:03 pm
We did something very similar to this in Providence, and it can be done. But the trick is with the IF level. It tends to come out very hot, and needs to be badly padded down. I think I had something on order of a 30db pad on the IF input of the Twinstream. The details of it are hazy to me, as it was over 10 years ago now, but I remember that.
30dB pad on the Strata IF input was just the ticket...the demod acquired lock and the TS analyzer was very happy with the stream output. Next step is to move the demod to the receiver rack at the tower and try this from a distance. Thanks for the help!

Post Reply