If physical size is not a concern, cavity filters can be dynamic. They are
probably better tuned mechanically but you can use varactor diodes and
electrically tune them with a slight loss in performance. I did quarter wave
duplexors for 2 way radio that were dynamic. Had all the tuning screws coupled
with a mechanical set of metal belt and pulleys. Then a stepper motor for
tuning.
From: That One Guy via Af
Sent: Sunday, October 26, 2014 12:21 PM
To: af@afmug.com
Subject: Re: [AFMUG] questions about filters
to you design guys, the chucks in particular
theoretically, not a "it cant be done because it hasnt been done"
If you were tasked to design a component, strictly a proof of concept
component, size, power consumptive, relative cost aside.
The only requirement being dynamic adaptability to channel size. So If You are
using a 5 mhz channel, it filters to the 5mhz channel, 10 to ten, and its not
center channel dependent. 200mhz in its spread.
Not a single response of why it couldnt be done
It does not have to be mechanical
On Sun, Oct 26, 2014 at 12:36 PM, Bill Prince via Af <af@afmug.com> wrote:
Perhaps some innovation in improving efficiency? Maybe takes someone
thinking outside of the current box(es).
bpOn 10/26/2014 9:55 AM, Chuck McCown via Af wrote:
I was just going to mention that. Make a clean signal and you don’t have
to filter so much. Anyone remember what a Class A amplifier is? (45%
efficient at best) Cavity filters?
I would think that in this day and age, you ought to be able to go DSP
direct to antenna up to a 5 volt p-p signal. Or if you had to use a PA, inject
a pre-distortion component. The cable TV guys have been dealing with these
issues for decades.
And then there is the issue with physical size of filters. A nice filter,
with decent response and low insertion loss is large. SAW filters are about as
small as you can get but they are higher loss than, for example, a waveguide
filter however they are maybe 1% of the volume.
You want a small radio that consumes very little power, then ... it will be
more noisy than a large radio that consumes more power. That said, modern tech
is unbelievable in performance and it just keeps getting better. Perhaps Chuck
will get to come to AnimalFarm this year and show us something fun.
From: Chuck Macenski via Af
Sent: Sunday, October 26, 2014 10:24 AM
To: af@afmug.com
Subject: Re: [AFMUG] questions about filters
Hi again,
Another factor that causes expense is the linearity of the final stage
output amplifiers...these puppies are linear for most modern radios and more
linearity = more cost and higher power consumption. I will stop now...
Chuck
On Sun, Oct 26, 2014 at 10:47 AM, Chuck Macenski <ch...@macenski.com> wrote:
Hi,
There are many questions (explicit and implicit) in your question.
Focusing on the tx side only (since we are talking about band edge), the
filters you are talking about are electromechanical. Do a wikipedia search on
SAW filters and you will get a sense for what you are dealing with. There are
many other factors involved in meeting band edge requirements and other
filtering that is or can be performed, but, the expense is often in the
electromechanical components.
Chuck
On Sun, Oct 26, 2014 at 1:45 AM, That One Guy via Af <af@afmug.com> wrote:
with the changes in the 5ghz rules, it may force innovation in
filtering technology to bring cost down, assuming the innovators arent stuck in
a mindset of the only thing that would work is what there is.
How do filters works?
Are there electronically adjustable filters?
Where does the cost come from on filters? It is not new technology, so
recovery of R&D on a new tech has long since past, what is it that drives the
cost up? Is it primarily a matter of it being something needed, so its more
valuable, or is it something in the physical properties of the filters that
drives up the cost?
Can you filter electronically a transmitter using something along the
same lines of noise cancelling headphones
--
All parts should go together without forcing. You must remember that
the parts you are reassembling were disassembled by you. Therefore, if you
can't get them together again, there must be a reason. By all means, do not use
a hammer. -- IBM maintenance manual, 1925
--
All parts should go together without forcing. You must remember that the parts
you are reassembling were disassembled by you. Therefore, if you can't get them
together again, there must be a reason. By all means, do not use a hammer. --
IBM maintenance manual, 1925
