In a previous post I wrote about using the UT-100C DVB-T modulator on linux and I promised to follow up how to use the modulator with live video sources. In this post I am going to describe how to setup the modulator on a Raspiberry Pi equipped with a RaspiCam camera module, effectively turning the Pi into a live HDTV transmitter.
I have now waited more than two weeks for the 2SC1969 that I have ordered from El Supply. Since the Easter holidays are coming closer and closer and I want to have the K1 with me, I looked for another source. I found Brinck Elektronik who has a shop in Copenhagen city. I was lucky enough to get the last piece they had on stock. They can still order it for me later but it will cost twice as much.
Yesterday I have done the transmitter signal tracing using my Velleman PCS500 pc-based oscilloscope. Here are the results:
PRE (0.04-0.09) 0.025 V
ATTN (0.02-0.05) 0.047 V
OSC (0.01-0.04) 0.019 V
MIX (0.1-0.2) 0.042 V
BUF (1.5-2.0) 1.74 V
TR1 (0.5-1.0) 0.66 V
BPF (0.5-1.0) 0.78 V
TR2 (0.5-1.0) 0.72 V
TR3 (<0.01) 1.5 mV
DRV (0.9-1.6) 3.7 V
PA (10-15) 0 V
ANT (10-12) 0 V
RFD (1.7-2.0) 0 VDC
That was enough to convince me that it the the PA stage that is doing something wrong. I took the chance and cut Q7 out and it was indeed dead. I couldn’t measure any BE/BC resistance in any direction and the hfe was 0, too.
First I wanted to order replacements from Elecraft but the postage and Danish VAT would have made it 4 times as much as the price of the transistors. Instead I ordered two of them from the Danish El Supply together with some 1.5 and 2.0 amp fuses 😉
Unfortunately, El Supply did not have them on stock so I will have to wait about two weeks. Well, I can concentrate on other projects in the meantime.
I have done the TX voltage checks without the filter and noise blanker boards mounted. Everything was fine just like when I finished the assembly. So no help there.
I finished the KNB1 noise blanker today and installed it in the K1. When finished, I connected the K1 to my ATX-1080 set to the 40 meter band. I put the OHR WM-2 wattmeter and the T1 antenna tuner in between the K1 and the antenna. First I tried to put the T1 into bypass mode, but I wasn’t quite sure whether the yellow LED meant bypass on or tuner on… Later I found out that green led means tuner on, yellow led means bypass on.
I was just about to panic when I first set the K1 into TUNE mode. I have hooked up the K1 to my variable power supply, set the current limiter to 1 amps (as instructed by the manual), turned the K1 on and set it into TUNE mode. The only thing that happened was that the K1 turned off and the current limitin led on my power supply was lighting up, meaning that the K1 wanted more current then it was given.
I have finished mounting all the transmitter parts on the RF board yesterday. The only part missing are the two transformers, T3 and T4.