[BC] Re: Satellit maintenance - TDR

[Xmitters@aol.com]

In a message dated 2/1/2007 12:01:06 AM Central Standard Time, 
broadcast-request at radiolists.net writes:


> TDR for sat coax seems overkill. If in doubt, replace the RG-6 or 11.
> Probably costs much less than the TDR over the years. TDR is great for
> waveguide, heliax, hardline, etc. Especially direct bury lines.
> 
> Of course, never use a 'polarotor' for radio services. Not enough
> isolation from opposite polarity signal. 
> 
> Been installing TVRO this way since the early '80's.
> 
> 
> Phil Longenecker, DoE
> Milwaukee Radio Group
> 414.349.4130 
> 


Phil:


Right on the nose with regard to the TDR and cable replacement. perhaps most 
installaitons lend themselves to easily replacement of the cable from the 
dish. In my particular case, my installation is not that easy. 

At one site I have a significant run of buried cable from the dish to the 
building. At another site, the cable snakes around the building from the roof 
through various conduits and pull housings and such. That TDR would be 
indispensable for troubleshooting the underground stuff. The university grounds people 
get real hot under the collar when I dig a hole for nothing, when chasing a bad 
cable. I better have a damned good reson for digging and the TDR would give 
me that.

Regarding my other site, we have a cable splice "somewhere" in the building 
that we suspect as having problems (intermittent loss of signasl to In Touch 
demod ABR-202), but nobody remembers where it is. Now with a TDR, we could tell 
building engineering, for example, that we can see a splice 75 feet out from 
the demod room to the suspect splice. It would give building engineering a 
reasonable idea about where to statrt looking, as opposed to telling them that we 
have a splice "somewhere" between the demod room to the dish, which is about 
100 feet of cable. I think the advantages of having a TDR in these two examples 
is obviouse. 

I have not even touched on the advantage of having a TDR within arm's reach 
for testing FM transmission lines, and I have six installations to keep 
running, not counting STL and repeater receive feedlines. Fortunately, finding a 
rigger to go up the tower to place a terminator at the end of the cable is not a 
big challenge. However when the day comes when finding tower riggers for 
emergency work at a moment's notice becomes difficult, I will be posting a note here 
asking for a tower climbing siminar and where I can go to get fitted for a 
climbing belt :-D

I really hope that at my age, I don't have to resort to climbing towers :-D 
Doing my own dish maintenance and repair would however, be kind of fun! I have 
not done much of that over my 30 year career other than replacing an LNA/LNB 
or two and doing a crosspol optimization :-) I used a Tek 7L14 held in place 15 
foot off the ground with a block and tackle :-) Not my idea of fun. Remember 
those old, huge original NPR dishes made by andrew back in 1980? It was one of 
those monsters!

Jeff Glass, BSEE CSRE
Chief Engineer
WNIU WNIJ
Northern Illinois University