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: [email protected] 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 <[email protected]> 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 <[email protected]> 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
