layla Post subject: passive RF attenuator Posted: Thu Aug 10, 2006
7:29 pm Captain Joined: Thu Aug 10, 2006 7:09 pm Posts:
7 I want to design a 50 ohm variable attenuator (0 -100 db) that
attenuates a 315 MHz signal, i know the design would be either R-R or
R-C attenuator but i cant seem to find proper pdfs or websites to start
learning how to design, can anyone help me? Top IR
Post subject: Posted: Fri Aug 11, 2006 4:30 am Site Admin
Joined: Mon Jun 27, 2005 2:02 pm Posts: 373 Location:
Germany Hello Most probably the attenuator you will use will
be a pure resistive one. In this case there is no meaning to the frequency
raneg you will use (Up to a frequency in which the resistors have parasitics).
You need to consider few things beforhand: 1. What is the
maximal power that this attenuator has to handle? 2. How will you
change the attenuation value (Mechanicaly or electrically controlled?)
These things will effect your design... You can find calculators
to calculate the resistors values: https://home.sandiego.edu/~ekim/e194rfs0
... atten.html If you need more information, please let me know.
_________________ Best regards, - IR Top
nubbage Post subject: Passive RF AttenuatorPosted: Fri Aug
11, 2006 5:01 am General Joined: Fri Feb 17, 2006
12:07 pm Posts: 218 Location: London UK Hi Layla The values
you will need to choose from the ref IR mentions, are 1dB, 2dB, 4dB
and 5dB With combinations of those values switched in or out of circuit,
you go from 0dB thru 10dB Then you need to cascade 10 of these
modules. Use PIN switches or at 315MHz toggle switches with very
short connections to switch the values in and out. Top
layla Post subject: passive RF attenuatorPosted: Fri Aug
11, 2006 5:01 am Captain Joined: Thu Aug 10, 2006 7:09
pm Posts: 7 Hello Thanks a lot for your reply, power considerations
will not be a critical issue since I think I will be dealing with low
power values in general. what will be the difference in design if
I wanted the design to be mechanically controlled or electrically controlled?
However, I'll think I'll go with mechanical switches, does that mean
I have to calculate the values of resistors for each attenuation value
then put these resistors in a cascaded manner where I change the input
output ports? Just an additional thought, is there any tips
or advices for how to be a good Rf enginner and where to start reading
or how? Top layla Post subject: Re: Passive RF
AttenuatorPosted: Fri Aug 11, 2006 5:13 am Captain Joined:
Thu Aug 10, 2006 7:09 pm Posts: 7 nubbage wrote: Hi Layla
The values you will need to choose from the ref IR mentions, are 1dB,
2dB, 4dB and 5dB With combinations of those values switched in or
out of circuit, you go from 0dB thru 10dB Then you need to cascade
10 of these modules. Use PIN switches or at 315MHz toggle switches
with very short connections to switch the values in and out.
Thanks for the reply, but can u give me a rough diagram of the connections
coz i have a vague idea of how the connections will be to get the range
from 0-100 dB. Sorry for the trouble Top nubbage
Post subject: passive RF attenuatorPosted: Fri Aug 11, 2006 8:01
am General Joined: Fri Feb 17, 2006 12:07 pm Posts:
218 Location: London UK Hi Layla Diagrams are a sore point
on this site. Unkonwn Ed??? I will be able to consult
my circuits library this weekend, and get back to you next Monday, if
by then we have a diagram facility. What is the possibility UE?
IMHO diagrams are kind of essential to circuit explanations.
Top IR Post subject: Posted: Fri Aug 11, 2006 9:06 am
Site Admin Joined: Mon Jun 27, 2005 2:02 pm Posts:
373 Location: Germany Hello, As nubbage suggested you
will have to build a group consisted of 1dB-5dB attentuators which are
cascaded. Then in each group for example you will have to match
the respective attenuators to the value of attenuation. For example:
9dB=4dB+5dB 8dB=3dB+5dB That means you will have
to connect the discrete attenuators separately. And on top of that to
connect 9 groups of 10dB attenuators (tens of dB). _________________
Best regards, - IR Top fred47 Post subject:
Variable AttenuatorPosted: Tue Aug 15, 2006 11:42 am General
Joined: Wed Feb 22, 2006 3:51 pm Posts: 104 Hi!
A few points: 1. At 315 MHz, the switches are almost guaranteed
to be a problem - ordinary off-the-shelf miniature toggle switches might
be good enough, but the only way to find out would be construction and
test. 2. Small TO-5 can relays (like those made by Teledyne)
can have good RF characteristics up to at least 500 MHz, but are a bit
pricey. 3. 50-Ohm microstrip on an appropriate PCB would be a
good idea. 4. Use surface mount resistors on a PCB if you want
good accuracy at VHF - the leads for ordinary resistors can form unwanted
inductors. 5. I'd like to emphasize the wisdom in some of the
previous replies: it's much easier to get 10 dB of attenuation accurately
at VHF than 20, 40, or 80 dB. The advice from IR and nubbage this way
(use 9 or 10 10-dB variable stages) is top-quality. Ignore it only if
you don't need precision. 6. I presume that you're looking for
something that can be produced in some quantities, so that the attenuators
made by Agilent (at the high end) and MiniCircuits Labs (at the low
end) etc. are too costly. If that assumption is wrong, and you're doing
a one-off project, unless you're going for the experience and knowledge
gained in construction, you'd do better buying rather than building.
Good Luck! Fred
Posted 11/12/2012
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