May 31, 2019 at 5:11 pm #41769
In a DOH moment, I forgot the other, and so very obvious spectral difference between ATSC1 and ATSC3 transmissions.
Like ATSC1, ATSC3 is sent in “frames” or groups of data. In ATSC1, the frame length is a fixed 24.3 mS and you have to be decoding the signal to observe it. In ATSC3 the length of the frame is variable and is always preceded by a discovery or Bootstrap transmission that narrows the transmission bandwidth to 4.5 MHz for 500 uS (centered in the channel). At the station’s discretion, the length of the ATSC3 frame can be as short as 50 mS or as long as 5 Seconds with the typical said to be 250 mS.
The photos so kindly moved to this site by Andy Brown show a typical off air spectrum of the two signals (ATSC3 is the lower photo). I can’t identify a dip in the spectrum at 250 kHz from the lower channel edge mentioned by Jr Tech so I can’t comment. The photos were taken after a bunch of antenna rotation to make the signals flat as possible but some residual bumps remain. Ideally both signals would be flat across the middle of the channel.
If one is using a manually tuned receiver to measure the signals, I would expect an ATSC1 signal to have a CW signal at 309.44 above the channel edge that will make a nice coherent tone when the BFO is turned on. Everywhere else will be loud white noise.
The ATSC3 signal, on the other hand will have a distinct buzzing sound when you are tuned within half a MHz or so of the upper or lower channel edges due to the signal suddenly narrowing to a 4.5 Mhz transmission bandwidth during the Bootstrap cycle leaving dead air where there was a data signal a moment before.
I haven’t tried this, but the ATSC3 signal is also likely to have a number of semi-coherent “tweets” as you tune across it with a communications receiver in say a ~2.5 kHz bandwidth with the BFO on. The ATSC3 signal has a fairly large number of pilot signals that are, in theory, scrambled in phase. However, their sequence of phase shifts is slow enough that they stand out as being, larger than the adjacent data carriers and thus are “not noise like” on a spectrum analyzer. I was able to identity the transmission mode of the WatchTV ATSC3 transmitter when it was on by noting the number and frequency of the pilots.
In addition, there are always pilots at the extreme upper and lower edges of the ATSC3 channel. ATSC3’s documentation indicates their phase is scrambled but those of WatchTV transmitter were CW. We will learn more when ATSC3 arrives in Portland.June 1, 2019 at 11:17 am #41775
“ We will learn more when ATSC3 arrives in Portland.”
And hopefully, the more distant stations such as Seattle, Eugene will be detectable here, but perhaps as easily as the distant ATSC1 stations.June 2, 2019 at 11:18 am #41781
KKEI-CD RF36 Vir38 has returned to high power operation again yesterday. The other WatchTV stations on RF15, RF16 and RF35 in the Portland market remain silent.
WatchTV’s applications for K28FP-D, Astoria; K14SC-D, Ashland; K25GA-D Redmond/Prineville; and K28GG-D, Medford to convert to ATSC3 were granted on Friday May 31.June 10, 2019 at 9:52 pm #41833
Except for putting it on the record I would omit mentioning that after two days at full power KKEI again was back to low power when I checked on the evening of June 4. It has remained at low power the six days since then. It was my intent to reduce the number of postings by noting it had be low but had returned to full power when it came back. Good idea but a total of seven down days (so far) makes one wonder when it will return.June 22, 2019 at 11:10 am #41892
Today, June 22, is the day all phase 3 repack DTV stations are to be on their new frequencies. This morning KNMT Vir.24 has moved from RF45 to RF32 as expected. A rescan will be necessary if you are a KNMT fan.
KATU Vir.2, RF43 was also expected to move from RF43 to RF24 today, but is still on RF43 this morning. KATU received a hurry-up STA yesterday to delay its move until phase 6. While phase 6’s completion date is October 18th KATU has been told to shut down its transmissions on RF43 by August 2nd.
The station pleaded that while it had all the material on hand to install its new antenna, there were delays in obtaining the necessary permits to do the tower work. The STA documentation says that antenna work is scheduled to start on July 8th and is thought to require 60 days for completion. That doesn’t seem to jibe with the FCC’s orders to vacate RF43 so that is something to watch for.
Sinclair Broadcasting filed for and got that STA in a day or two; Liberal amounts of “grease” must have been applied to get it that fast. Amazing.
KKEI-CD remains at very, very low power.
June 22, 2019 at 7:27 pm #41894
- This reply was modified 4 days, 10 hours ago by LinleyG. Reason: Corrected KATU's virtual channel to vir.2
“We are tentatively aiming for a September 6th transition date.”
In Milwaukie, I can get 2 on the living room TV with a Terk amplified antenna but not in my bedroom with plain rabbit ears.June 26, 2019 at 9:40 pm #41917
This is the third night that KKEI (Vir38, RF36) has been back to full power again. It appears that it may stay awhile to it’s worth mentioning.
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