Proper Blind Scan Technique?

[yuzhanin]

What is the best technique for blind scanning? In my receiver, I have an option to set blind scan stepping from 5 MHz to 16MHz. I usually scan in 16MHz-steps first and then rescan in 5MHz steps. Is there a better way of doing it?

[yuzhanin]

I am figuring, many of those MHz steppings are somewhat useless. If I understand the process correctly, I see this:

5 MHz - OK, slow but the most thorough stepping.
6 MHz - OK, will hit unique frequencies not covered by 5 MHz with minimal overlap
7 MHz - OK, will hit unique frequencies not covered by 5 MHz with minimal overlap
8 MHz - OK, will hit unique frequencies not covered by 6 MHz with minimal overlap
9 MHz - OK, will hit some unique and some of the same frequencies as 6 MHz, 50% overlap with 6 MHz
10 MHz - Useless, will hit no unique frequencies but half as many as 5 MHz (although twice as fast)
11 MHz - OK, will hit unique frequencies not covered by 5 MHz with minimal overlap
12 MHz - Useless, will hit no unique frequencies but half as many as 6 MHz (although twice as fast)
13 MHz - OK, will hit unique frequencies not covered by 5 MHz with minimal overlap
14 MHz - Useless, will hit no unique frequencies but half as many as 7 MHz (although twice as fast)
15 MHz - Useless, will hit no unique frequencies but a third as many as 5 MHz (although in a third of time)
16 MHz - Semi-Useful. The fastest way to blindscan, BUT will hit no unique frequencies but half as many as 8 MHz (although twice as fast). The fastest way to blindscan

So, if you wanted to be as thorough as possible (at the expense of time), you can do scans in 5MHz, 6MHZ, 7MHz, 8MHz, 9MHz, 11MHz and 13MHz. The other steppings will hit no unique frequencies.

[rainman]

with my Mercury I usally set it at 4 Mhz detailed scan and it don't miss to much. I guest all receivers are a little different and you will have to find what method works best for you.

[wejones]

Depends on the receiver. In the Mercury, it does seem best to scan with the 4 MHz, but with the Lifetime Ultra, if you scan with the narrow step (low SR) option, you miss high SR transponders, and if you scan with wide (high SR) setting, you miss low SR transponders, and if you scan in the all mode, then you miss some of both. I think you should experiment to see what you find in each mode.

[yuzhanin]

Originally Posted by wejones

Depends on the receiver. In the Mercury, it does seem best to scan with the 4 MHz, but with the Lifetime Ultra, if you scan with the narrow step (low SR) option, you miss high SR transponders, and if you scan with wide (high SR) setting, you miss low SR transponders, and if you scan in the all mode, then you miss some of both. I think you should experiment to see what you find in each mode.

So, it does look like multiple scans with different steppings are a good approach. I usually do a 16 MHz scan to get a quick idea of what's available and then a 5 MHz scan to see if I missed anything.

Here is a related question. Let's say I use 5MHz stepping. The scan will start at 11700 MHz, then "land" at 11705, 11710, 11715 etc. What happens if there is a transponder at, say, 11712? Will it be found? From what I have seen, the answer is yes. But would a scan that actually "lands" at 11712 be more accurate?

[rainman]

not really what i have seen most TP freq can be off by plus or minus 5 megahz and still will scan in.

[wejones]

Originally Posted by yuzhanin

So, it does look like multiple scans with different steppings are a good approach. I usually do a 16 MHz scan to get a quick idea of what's available and then a 5 MHz scan to see if I missed anything.

Here is a related question. Let's say I use 5MHz stepping. The scan will start at 11700 MHz, then "land" at 11705, 11710, 11715 etc. What happens if there is a transponder at, say, 11712? Will it be found? From what I have seen, the answer is yes. But would a scan that actually "lands" at 11712 be more accurate?

Again, this probably depends on the specific receiver, but I know that my ULTRA can be off by HUGE amounts in both Freq and SR value and still lock, however the problem is that if there are two channels close together, then it's possible that you might find one and not the other. I don't think that there would be any problem finding that channel at 11712 if there wasn't another channel nearby, but if there were three channels, like one at 11710, one at 11712, and one at 11714, then it might find the 11710 and 11714 but not the 11712. In fact I've seen situations where close together channels had been found and saved as channels, and when I went to play them, sometimes my Ultra would only find one channel when going there from above but not from below, or visa/versa. So there are some weird problems you sometimes run into. Re being more accurate. Again depends on receiver. When my Ultra finds a transponder, it usually finds the exact freq, no matter how the scan is done, however my Mercury often finds the transponder at the wrong frequency, so I'm thinking that it might be like you say, ie if the Mercury searches at 11710, it might find the 11712 transponder, and save it as being at 11710, while my Ultra will save it as being at 11712.

[yuzhanin]

Originally Posted by wejones

Again, this probably depends on the specific receiver, but I know that my ULTRA can be off by HUGE amounts in both Freq and SR value and still lock, however the problem is that if there are two channels close together, then it's possible that you might find one and not the other. I don't think that there would be any problem finding that channel at 11712 if there wasn't another channel nearby, but if there were three channels, like one at 11710, one at 11712, and one at 11714, then it might find the 11710 and 11714 but not the 11712. In fact I've seen situations where close together channels had been found and saved as channels, and when I went to play them, sometimes my Ultra would only find one channel when going there from above but not from below, or visa/versa. So there are some weird problems you sometimes run into. Re being more accurate. Again depends on receiver. When my Ultra finds a transponder, it usually finds the exact freq, no matter how the scan is done, however my Mercury often finds the transponder at the wrong frequency, so I'm thinking that it might be like you say, ie if the Mercury searches at 11710, it might find the 11712 transponder, and save it as being at 11710, while my Ultra will save it as being at 11712.

Very interesting.

I guess I now have a related question. Don't most satellites usually have wider spacing between transponders? So, MOST of the time, you will not have a 11710 transponder AND a 11712 transponder AND/OR 11714 TP, right? I think pretty much the only time you have a very narrow spacing is on satellites with lots of occasional feeds.

[wejones]

Originally Posted by yuzhanin

Very interesting.

I guess I now have a related question. Don't most satellites usually have wider spacing between transponders? So, MOST of the time, you will not have a 11710 transponder AND a 11712 transponder AND/OR 11714 TP, right? I think pretty much the only time you have a very narrow spacing is on satellites with lots of occasional feeds.

Basically, they try to use every bit of bandwidth that is available, by squeezing signals as close together as possible. What this ends up meaning in terms of how far apart the transponders are (actually the word transponder isn't really correct here, but that's the common terminology) is completely determined by how wide the signals are. For example, look at one of the spectrum scans I posted some time in the past:




Looking at this scan, you see that there are signals that are very wide, and signals that are quite narrow. THe width of the signal is pretty much determined by the SR value. In the above scan, the wide signals at the right have SR values of 30000, while the narrower signals to the left of them are in the range of 4000 to 6000. If you have a bunch of narrow signals, you can squeeze them in close together. Generally you can get reasonable good video with an SR of around 4000, although some 24/7 channels only use SRs around 2000- 3000, although the quality suffers. Those wide channels can either be carrying one or two HD channels that require a high bitrate, or they can be carrying a MUX containing multiple SD channels.
THe place where you see multiple narrow channels close together are usually the sats like G26, that have a bunch of news feeds. If you look at a scan of G26, you'd see places where there are a dozen transponders side by side, separated by about 4-5 MHz, each with an SR of 3978. Ie the 3978 SR pretty much equates to a width of around 4 MHz.
Now, on a satellite like one of the NIMIQ or ECHO DBS sats, basically all the transponders have 20000 SR values, so it is just a lineup of broad signals, all separated by roughly 20 MHz, but this is because all the channels are coming from the same uplink site. With Newsfeeds, which are coming from all over the country, they need to put one channel on each signal, since you can't have someone from the west coast uplinking into the same MUX as someone on the east coast.
Anyway, I've used 10 times as much bandwidth as I should have to answer the question, so I must have a high SR value.