[time-nuts] Why a 10MHz sinewave output?
lists at rtty.us
Tue Feb 7 22:19:03 UTC 2012
As long as you are running a sine wave, and you don't change cables, you can
run just about anything. The phase errors / reflections will work themselves
50 ohm plastic dielectric cable turns out to be the best for power handling
at reasonable loss. 75 ohm cable turns out to be the best for loss per mile.
Telcom and TV people went with 75 ohms. People who ran transmitters went
with 50 ohms. If you change the dielectric, you can get "best" cases at
somewhat different impedances.
50 ohm cable works best / easiest with 50 ohm connectors. Mixing 75 ohm
connectors and 50 ohm connectors is not a good idea. The inner conductors on
the connector are often different diameters and you tend to break one side
or the other.
Given the cost of (cheap) RG-58 or RG-59, I don't see a big advantage to
switching impedance to save money at 10 MHz. Down there the skin depth is
what will impact your shield the most. The fancy extra aluminum foil layers
don't have much thickness. Of course if you go to hard line then it's a
whole different story...
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Chris Albertson
Sent: Tuesday, February 07, 2012 3:19 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Why a 10MHz sinewave output?
Related question: Assuming I'm using 10MHz sine wave. What's the
best physical cable to use? Is there any good reason to use 50 ohm
cable? What about 75 ohm? I looked at a schematic of my counter
and it looks like the 10MHz signal hits some high impedance chip
inside. RG6 seems like the way to go. It's double shieled and
lots of cable TV parts could be used.
On Tue, Feb 7, 2012 at 11:12 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
> lists at rtty.us said:
>> Thank goodness for that inertia. I can still cable up a 100Kcps sine wave
>> standard to run stuff from "long ago". When I run into a box that uses a
>> signal for a clock reference - not so easy in the basement.
> How much gear is there that uses T1 for a clock input?
> Is there any interest in a board/chip/whatever that converts 10 MHz to T1?
> clean design using a decimal DDS should fit into a small FPGA, maybe a
> These are my opinions, not necessarily my employer's. I hate spam.
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