Punch cards

[Gene Heskett]

On Monday 07 April 2008, Da Rock wrote:
[...]
>Ok, if I may go OT a little- what's your opinion of digital? Is it hard
>to maintain, because its certainly appears worth it?

The problems will be different problems because the only place it is analog is 
actually on the air.  The transmitter linearity requirements will probably 
mean we run bigger stuff in relation to the actual power output just to have 
the headroom to maintain that linearity so its at least a correctable error.

OTOH, we can run with less ERP, by a factor of around 10 (so they are telling 
us anyway)  To compare, our current analog transmitter is making 26.7 kw at 
synch tip peak, which is derived from the average reading, often based on an 
actual heat measurement, and is multiplied by 1.68 when the transmitter is 
sitting in black without any setup and showing 16.xx kw on the power meters.  
That, multiplied by the gain of our antenna makes it equal to a 100 kw signal 
in terms of field strength.

Now, we have been told we will have the same coverage in digital, with only a 
10 kw *average* signal, one whose peaks are not over 6db above that 99.99% of 
the time.  That translates, using the same hardware and math, to an average 
power output from the transmitter itself, of 2.76 kw, or an absolute peak 
somewhere in the 12kw area.  I have 3 amplifiers on site now that can easily 
make that power level as one is rated at 35kw but may not have enough gain, 
and the other 2 are rated at 18kw and surely have sufficient gain when driven 
with the 200 watt average power starter transmitter we already have on the 
air on channel 6, but which will be retuned to channel 5 next February.

Our biggest problem ATM is that by staying in the low vhf band due to our 
proximity to the Green Bank Observatory, we are a very small minority of two, 
and we cannot find a vendor to construct the required channel 5 mask filter 
for us.  Inquiries are out to several makers of UHF sized such devices, so 
the math to calculate what it takes is at least moderately well known by now.

Heck, I'm not allergic to making it, my chopsaw cuts transmission line to 
whatever lengths I'd need quite handily, IF I can somehow become privy to the 
required math functions.  Right now, it seems to me that it is being treated 
as proprietary info by most.  We're obviously going to be held hostage unless 
we can get a waiver from the commission until such time as the conversion is 
largely done, and the coppersmiths suddenly find they have bodies standing 
around doing nothing.  That unforch, may put us in a bind till then.

More than you asked, and less, but its what I know ATM.  Stay tuned as they 
say.

>Also what is the difference in equipment for digital?

Whole new ballgame in the house.  A converter box will get a signal to your 
existing analog tv, with a good clean pix but no sharper that you are getting 
now.  New receivers will of course get you a pix as sharp as we are 
broadcasting, and some have chosen to effectively run more stations at the 
old sharpness because we can stuff 4 of those pictures into the same 
bandwidth.  But I think the public will smarten up, and demand the better 
picture once all the dust is beginning to settle.

The Nextel re-arrangement of our studio-transmitter linkage facilities in the 
7GHZ band will also effect this, and despite all the commissions grand plans, 
and the public pronouncements to us by Nextel, the reality is that they are 
dragging their feet, leaving quite deep trenches in the land from their heels 
because its turning into a project of about 10x the cost of their estimates.  
We can't get an answer from them either as to when it will be done in our 
market if ever, and its about a $100k question for us.  If we have to do it 
because of this conversion deadline, and then do it twice when the band 
re-assignment actually takes effect, Nextel is gonna need a whole army of 
lawyers I'd guess.

Sometimes I wonder why I didn't just learn to dig ditches or something, but it 
has been an interesting ride so far. :)

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Breadth-first search is the bulldozer of science.
		-- Randy Goebel