What is the purpose of a DC injector?
 

Good day!

In some of the articles that I'm reading, I keep seeing references to
a DC injector use in RF ports. I really don't know what this means and
what the DC injectors are used for. The only think that I can think of
is for some DC voltage control for a voltage controlled oscillator
(VCO).

Thank you!

What is the purpose of a DC injector?
 

"MRW" wrote in message
oups.com...
Good day!

In some of the articles that I'm reading, I keep seeing references to
a DC injector use in RF ports. I really don't know what this means and
what the DC injectors are used for. The only think that I can think of
is for some DC voltage control for a voltage controlled oscillator
(VCO).

Thank you!

Supplying DC power for a preamplifier or transverter trough the antenna
cable for instance.

What is the purpose of a DC injector?
 

On Apr 2, 8:09 am, "MRW" wrote:
Good day!

In some of the articles that I'm reading, I keep seeing references to
a DC injector use in RF ports. I really don't know what this means and
what the DC injectors are used for. The only think that I can think of
is for some DC voltage control for a voltage controlled oscillator
(VCO).

Thank you!

Besides the use Philo mentioned, such beasts are also used with
network analyzers to inject a DC voltage (or current) to bias a device
that's being tested. For example, if you want to use a network
analyzer to look at the impedance of a varicap diode, or just to
characterize the capacitance versus reverse voltage of an ordinary
diode, you need a way to put a controlled DC bias on the diode. They
typically consist of an RF choke to feed the DC onto the output
connector, and a blocking capacitor to keep the RF input from shorting
out the DC.

Cheers,
Tom

What is the purpose of a DC injector?
 

"MRW" wrote in message
oups.com...
Good day!

In some of the articles that I'm reading, I keep seeing references to
a DC injector use in RF ports

They are often referred to as Bias Tee's and are usually found under that
name in manufacturers catalogs.

What is the purpose of a DC injector?
 

On Apr 2, 11:23 am, "Philo" wrote:
Supplying DC power for a preamplifier or transverter trough the antenna
cable for instance.

I see. Does this mean that the AC signal going thru the antenna cable
is biased with a DC source?

Thanks!

What is the purpose of a DC injector?
 

MRW wrote:
On Apr 2, 11:23 am, "Philo" wrote:
Supplying DC power for a preamplifier or transverter trough the antenna
cable for instance.

I see. Does this mean that the AC signal going thru the antenna cable
is biased with a DC source?

Thanks!


No. It is just two power sources using the same conductor. That is why
there are capacitors at each end of the conductor. They permit the rf/ac
signal to pass but block the dc from passing. The satellite tv systems
use this to tune the block down converters out at the dish antenna.

Dave WD9BDZ

What is the purpose of a DC injector?
 

In article ,
"David G. Nagel" wrote:

The satellite tv systems
use this to tune the block down converters out at the dish antenna.

Well not quite, Block DownConverters are not "Tuned". They take a
Fixed Bandwidth from the Input Frequency, and DownConvert it to
an equal Fixed Bandwidth at a lower IF Frequency. Back in the LONG
Past era, there were First Generation SAT Receivers that did have
the Frequency Selecting Mixer out at the dish, and used an IF of 70Mhz
to bring a Single Channel of Wideband FM Tv to the DeModulator in
the SetTop Box. This system was universally designed out of the
Consumer SAT systems due to Temperature Insability and other problems.
The system used today, which is basically Standardized now, have a Low
Noise Preamp, feeding a Block Downconverter, (LNB) and feed the total
Fixed Bandwidth of the SAT Segment, (500 Mhz) to the SetTop Box at a
lower IF Frequency. (900 Mhz - 1400 Mhz approx) They still use DC Bias
on Coax Feeds to the LNB's, and these both power the LNB's, and also
select the Polarization of the FeedHorn.

Bruce in alaska
--
add a 2 before @

What is the purpose of a DC injector?
 

"Bruce in Alaska" wrote in message
...
In article ,
"David G. Nagel" wrote:

The satellite tv systems
use this to tune the block down converters out at the dish antenna.

Well not quite, Block DownConverters are not "Tuned". They take a
Fixed Bandwidth from the Input Frequency, and DownConvert it to
an equal Fixed Bandwidth at a lower IF Frequency. Back in the LONG
Past era, there were First Generation SAT Receivers that did have
the Frequency Selecting Mixer out at the dish, and used an IF of 70Mhz
to bring a Single Channel of Wideband FM Tv to the DeModulator in
the SetTop Box. This system was universally designed out of the
Consumer SAT systems due to Temperature Insability and other problems.
The system used today, which is basically Standardized now, have a Low
Noise Preamp, feeding a Block Downconverter, (LNB) and feed the total
Fixed Bandwidth of the SAT Segment, (500 Mhz) to the SetTop Box at a
lower IF Frequency. (900 Mhz - 1400 Mhz approx) They still use DC Bias
on Coax Feeds to the LNB's, and these both power the LNB's, and also
select the Polarization of the FeedHorn.

Bruce in alaska
--
add a 2 before @


Some satellite dish sets also use a 22 kHz signal to switch between 2 local
oscillators in a "dual band" LNB.

What is the purpose of a DC injector?
 

"Philo" wrote in message
...



Some satellite dish sets also use a 22 kHz signal to switch between 2
local
oscillators in a "dual band" LNB.



... and some of them vary the DC voltage between two low voltages (like
14V and 18V) to switch between polarizations. The electronic package uses
12V and regulates it down from whatever it gets; the variable voltage is
strictly a control signal.

There's a lot of clever stuff running up that coax even if the
programming coming back down is sometimes gawd-awful.

What is the purpose of a DC injector?
 

Also, at VHF, these may be used to feed power to
Low Noise Preamps, for overcomming feedline loss.
And used with sequencers, to switch the preamp in
and out. Jim NN7K

Sal M. Onella wrote:
"Philo" wrote in message
...