Interesting things I learned about coax

  • Thread starter Thread starter TECHNOKID
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As the post was for my benefit let me explain what I was actually eluding to;

It would be a good idea if a reference to the preferred cable type (RG6) was included in the Installation Thread, I just looked over the 9200 Installation thread and it is not clear that cabling should be RG6 for everything from the LNBF's to the receivers, it tends to just say cable, not specifically RG6.

But I guess that if you prefer people to use the search feature, thats fine.
 
If the problem is ONLY with one receiver it most certainly NOT the input side of the SW44 that is the problem, otherwise all receivers would have the same problem.
 
Okay, it's happening on ALL my receivers -- when I change channels (not always, but at least half the time on any of the receivers) I lose the signal than if I wait long enough, the signal comes back after flipping through a bunch of transponders and then either finding the signal or telling me to push "up or down" in which case I usually have a signal, but not always. It has to be on the input side of the SW44 if it's affecting everything. I am getting pretty frustrated. I have checked the ends of the cables to ensure the connections are tight and all seems fine. I have even moved the power connection to ensure it's not that and no change. I think I will put back the SW21 and leave the SW44 alone. I will wait until I upgrade to HD and let Bell deal with it then.

Thanks again....Trish :)
 
Fixed. As suggested by someone in the SW44 discussion, I needed to run check switch on each receiver for it to "discover" the SW44. Once I did that, problem solved. Thanks!
 
Just for your clarification, an RF signal is voltage. The LNBF transmits the transponder signals (i don't remember which is odd or even) on 13V and 18V respectively. This voltage is AC (alternating current). RG59 will have problems with the 18V transponders because the resistance becomes to great after a certain distance and as such, people will commonly lose the 18V transponders. When using the SW44, DC voltage is transmitted from the power inserter to the switch. DC voltage encounters more resistance than AC and problems will arise again if RG59 cabling is being utilized. That is why AC voltage is used to transmit electrical energy to your house and not DC.
 
RG6 has less loss than RG59 per length, and is more suitable for satellite dish, but can be used for other things if you don't mind the thickness or price. The reason is that the LNBF output is a higher frequency than your typical signal from the RF modulator or even OTA antenna, and the higher frequency, the higher the loss a cable will make the signal. In other words, higher frequency requires better cables. But if the length is not very long, and if the satellite signal strength is quite strong, RG59 can be used as well.

The LNBF does not output the "13V / 18V". The receiver outputs a 12V or a 18V to the cable, and they are DC voltages. This power serves 2 purposes. One is to power any devices in the line, be they in line amp, switches, and LNBF. The second purpose is to tell the LNBF which antenna pattern it should be receiving in. 12V and 18V corresponding to either Right Hand Circular Polarization or Left Hand Circular Polarization. With 2 independent kind of polarization, a satellite can double its capacity without doubling the frequency bandwidth.

The transponder does not reside on the LNBF, it resides on the satellite in the sky.

Coaxial cables have a set limit on AC or DC voltage limit, but it is silly to say that it doesn't like voltage and will burn out without saying what the unit is. The DC present on the cable is merely 18V and can hardly burn anything unless there is a short.

One must be careful when using the terminology "RF" as some of you have said that "RG59 is only for RF only" and ironically it is not incorrect but I'm sure you meant that it was for TV out. RF stands for Radio Frequency and technically speaking the output from the LNBF is also RF. The difference is in the frequency. RF modulated output is usually set at TV channel 3 or 4, so it is in the lower VHF band and is considered fairly low in frequency. The LNBF outputs at aout 1.2GHz and is considered fairly high in frequency, but it is still RF. Basically a large part of the electromagnetic spectrum is considered RF.

An RF signal is not voltage, or should say it is not merely nor necessary voltage. Technically speaking, RF signal is an electromagnetic wave, and is considered in the form of a electromagnetic field. When the signal is received in a receiver, for example, then it is represented (or should say converted) to electrical signal of a certain pattern (same or representative), in AC voltage. One can argue that an RF signal is represented as an AC voltage in a receiver circuitry, but the signal itself is not voltage. It's like saying that your shadow on the ground is you, which is not true.

If certain receivers work better w/ an RG59, it is not because of them being older, or have better tolerances. It is possible that some receivers have a better receiver sensitivity and thus can pick up the signal better than others when the signal is weak. I have experienced that not all receivers have the same sensitivity (but do not judge it from the signal strength meter, which is artificial and relative).

It is only certain application that AC attenuates more than DC, and it is certainly not true in this and it should not be applied as in the electric power distribution. In this particular application, the more critical element is the AC part, which is the RF signal coming down from the LNBF to the receiver, and thus requires the better RG6 cable to carry. There is a certain loss of the DC power from the receiver to the LNBF etc, but it is usually ok, as there is a high tolerance on the devices using that, and is thus not considered critical. If it is so long that it becomes critical, then the RF signal coming down should be in even worse shape.

There are quality differences among RG6 brands and models and so do RG59 ones. Poor quality cables will have higher loss among other problems, regardless of the type. If the cable is worn or has crack or fold, then the performance will suffer as well (signal loss or interference etc).

I hope this clears up some of the incorrect or confusing descriptions in this thread.
 
Bandwith and voltage drops aside, only one point was not yet mentioned in the discussion. The input connectors of the equipment are either met to receive RG59 or RG6; we have to realise that the inside connection is leaf spring type action therefore, in most cases inserting RG6 into a connector which normally would be met for RG59 would work without any problems however, the opposite (RG59 into a connector met for RG6) could well be a problem since the RG59 copper core is smaller therefore the core and the leaf connection doesn't mate properly thus creating poor connection (intermittent and/or permanent). This can also happen with an input connector wich would normally be used with RG59 but at some point was used with RG6 cable, the input connector spring action would then be somewhat modified and if you try to use RG59 cable again would not work properly anymore.

As far as I am concerned, all newer equipment are met to be used with RG6 cabling and even if using older gear which could use RG59 cabling, I would tend to match all the cabling with RG6 thus avoiding any potential poor contact of any inner connectors with RG core. I've experienced that at one time after fixing an older CRT set, it was passing all in shop tests but kept on coming back to the shop. I proved the TV set working fine by testing in front of the customer. I started asking the client what they were using for in-home connection and found out that cheap coax was used and that the problem was actually the center core making poor contact with the inner input connector of the tuner. Unless you are stuck with a near full roll of RG59, I would use RG6 for ALL crucial video connections and simply recycle the RG59 left over to make your own coax RCA type cables or straight video cables (component etc...).

Right after writing the above;

Just read your good post fortissimo and I feel a little more clarification is required when it comes to coax (or any other communication cables) and Radio Frequencies.

The impedance of a cable will affect greatly the bandwith that a specific cable will be able to process. IE: RG58 (50 ohms) was used greatly for straight video (secure video cameras, internal monitors and even still processing IR signals). The older analogue TV signal (RG59) and many other communication signals use carriers (many people seem to confuse with AC power) over DC power to send their TV bandwith. As we know, RG6 can process larger frequencies which RG59 will not accomodate with as much accuracy.

Now, cable impedance properties is a mixture of LCR (inductance, resistance and capacitance). In this case, the cable resitance will affect power lost in cable lenght. As we all know, the gage of a cable is the main factor to consider. Therefore, RG59 has greater power drops than RG6 when using longer lenghts of cable therefore, depending on the importance of the voltage drop it may affect or not the equipment.

The other very important difference between RG59 and RG6 is shielding as the shielding is the capability of the cable of isolating it self from emanations coming from other cables and even from air borne signals (cable acting as an antenna). It also isolate its own signal to feed through other cables as the shield acts as and antenna returning any emanations through the return path. As we know, RG59 uses only one shielded strand while RG6 can include 2 or more therefore providing a much more effective isolation of its signal from and to others.

In conclusion, one or a combination of the above mentioned can create problems which in the case of digital signals is simply works or doesn't compared to analogue which could go from perfect to degraded or total failure of the signal.
 
I'd like to add my 2cents..

I just got back from my parents for the holidays. They got a new 46" Toshiba HDTV and also called Bell to have them come and install 82, new reciver, etc... They did it early in December to avoid the rush.

They had been complaining after that they couldn't really see a difference, and the 4100 in the office also only got a few channels.

I take a look - Bell tech guy really mucked it up. Left all defaults on the reciever - so it was in 480.. after a quick change everything was in HD.

The relocated 4100 reciever in the office - tech guy didn't do a check switch - so it only knew about 82. Very unprofessional.

However, during Christmas the HD reciever started to fail randomlly - loss of signal, searching for signal, etc. Checkswitch would only work after a few tries. The 4100 in the office had no problem at all. Bell guy had left the RG56 connection to the HD reciever and installed a new RG6 connection to the office. The RG56 connection simply seemed to give up passing the signal after a few weeks on the old cable.

Dad went up to the roof on Boxing Day and swapped them (easier than doing it in the house) and everything is flawless. The 4100 seems to handle the dollar store coax a lot lot lot better.

Wish you posted this on Christmas Eve when the problems developed :)

Happy New year,
Craig
 
It just goes to show that not all installers are created equal. I hope you called and complained.
 
Just a little response to the fine post by TECHNOKID.

In my experience, most video signal (base band stuff) traditionally travels on 75 Ohm cable, like RG59, RG6 etc, rather than 50 Ohm cable like RG58, as in your post. I know it will work in 50 Ohm cable, with a little mis-match in impedence but with a little higher loss. I even have a friend who used RG58 for his satellite LNBF feed and it worked for him but I'll never recommend it!

Video signal or RF signal, as long as these are small signal source, it works better on 75 Ohm cables. 50Ohm cables are designed for 2-way radios, as the impedence is chosen as a special compromise between the optimal impedence for transmission line for transmitter (RF) and small signal (receiver). (Technically it is calculated as 52 Ohm).

I didn't think of the spring action inside the connector, and thanks for mentioning that, and indeed it could be a problem. I'm actually dismay at the industry choosing F connector for such a high frequency (LNBF output at 1.2GHz), but I know they choose it for convenience and cost. But now we have this "convenience" and many people are re-using old cable TV feed and not so great. I'd think a proper 75 Ohm BNC connector would be much much better, although increasing the cost. BNC has been very commonly used in the industry, especially in the commercial and professional video industry (the 75 Ohm type).

The double shielding is also very important, of course.
 
RG58 was at one point widely used with commercial product using straight analogue video such as CCTVRG58 was also used for ethernet connections: http://www.tech-faq.com/rg-58.shtml

You are right, video signal on carrier(s) (RF) are much more efficiently transmitted on 75 ohmns coax versus the 50 ohmns which was causing some issues. However, BNC connection(s) should have been favored to the cheap and inefficient "F" connector. As you point out, BNC is widely used in the industry and proffessional sectors. As far as I am concerced, neither RCA or the "F" connector come close to the BNC connection. The only reason for a bad BNC connection is poor termination NOT actual poor contact between the male female connectors. As you state,BNC connections are available in the 75 ohmns and for the keeners that wants proffessional install, they can consider doing their install using them versus the crappy "F" connector.

Interesting reads:
http://www.pacificcabling.com/Coaxial%20Cable/Coaxial_Handbook.htm#History
http://inventors.about.com/library/inventors/blcabletelevision.htm
The below one is very interesting reasonning behind the ohmnique value of the cable:
http://lists.contesting.com/_towertalk/1999-06/msg00184.html
Chapter 7 (.1 and .2) are very interesting:
http://books.google.ca/books?id=MCj9jxSVQKIC&pg=PT133&lpg=PT133&dq=history%2Bcoaxial%2Bcable&source=web&ots=A6DqL456Yn&sig=9_D0lmw6U3-SLWJ2PpL3aQqK4N4&hl=en&sa=X&oi=book_result&resnum=9&ct=result#PPT134,M1
The History of... Cable:
http://www.fcc.gov/cgb/kidszone/history_cable.html
 
Getting out of topic, but would like to comment on a few things. I know you didn't write the context inside the quotes, but I guess either it is missing something or is quoted out of their original context.

RG-58 and BNC would not be the cause or culprit for any ground loop issue as anything improperly grounded would have a ground loop issue and it is not unique to RG-58 or BNC. The quoted context might give someone an impression of such, even though it didn't say such explicitly and thus I feel I should clarify the part.

Interconnection between a BNC and RG-58 could be well made or poorly made, and it might produce all kinds of problems, but again it is not the nature of the types of components or compatibility of such things (unless one uses a connector not designed for the cable etc).

10Base2, not always use RG-58, but does use 50 Ohm coaxial cable, and RG-58 is one of the many types that is used. This style (but not necessary the same model) is called ThinNet Ethernet. (Another much bigger coaxial cable used in ethernet will be called ThickNet).

You mentioned ARCnet but the paragraph did not mention the impedance that this one uses. ARCnet uses 93 Ohm impedance and not 50 or 75 Ohm, so that article can be read incorrectly if someone doesn't know.

The first paragraph also mentioned using RG-58 and BNC for commercial video signal cable. I found that statement is somewhat misleading as if that it is common practice. As I said earlier, RG-58 is 50 Ohm and thus is not the standard that video signal should travel in, but rather in 75 Ohm cable, and thus RG-59 should be used instead.

I am a little surprised that you didn't notice these though.
 
I stand corrected as I should have totally avoided talking about RG58 as you are totally right could be misleading, confusing and leads the thread totally out of its context. The military is a world of its own and the applications made there should possibly be kept out of this thread in order to avoid confusions. However, it gave us the opportunity of sharing about the better connectivity of the BNC connector ;) This something we do both agree on and it is nice to share this with other DHCers doing their own install that they have a better alternative than the crappy "F" connector. Matter of fact, my main video test bed was equipped with ALL BNC connections making the tests that much more reliable!

Cheers!
Ren
 
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