Don Kupferschmidt wrote: > Nate, > > I'm wondering if you can point me to a link that would further explain lo / > hi injection. Hate to admit, but I'm not all that familiar about the > subject, especially in repeater operation. > > TIA, > > Don, KD9PT
Hi Don, Shorty did a nice summary of the low-side/high-side thing -- if you're looking for more information on the design aspects of the receiver itself, probably the best source for that, that includes some background information of how to design a receiver, is the ARRL Handbook. (There's many pages on receiver design, and that section may be a bit dated and seem to apply mostly to HF, but the math and design information still applies to VHF, UHF, etc. It's great "background" information. I also dug up a couple of links that mention the low-high stuff for you below, but they're not really what I think you might be asking for. It seems your real question might really be, "How does a receiver work by using a fixed IF frequency and mixers to detect a signal..." Maybe I'm misreading your question and all you needed was the "recipe" -- Shorty did a very nice job giving you that. If you're looking deeper into the "how does that thing work?"... that's a bit more in-depth. That question definitely gets further back into receiver design RF engineering "basics". And trust me, I'm not an RF engineer, so I won't be embarrassing myself attempting to write that particular article! (GRIN) Being Amateurs, we're all coming from different places in this "stuff", and there's folks here on the list who design things like this for a living. Me, I'm a data jockey by day, and RF nerd by night... Trust me, coming from a hobbyist background in this stuff, trudging through an LBI and a schematic can feel like -- even on a relatively old design like the MASTR II -- can feel quite like quick dip in the "advanced topics" hot-tub! It's all about where you are on the learning curve. http://www.repeater-builder.com/ge/mastrIIsplitconv.html http://www.hallelectronics.com/getech/m2icoms.htm http://www.icmfg.com/generalelectric.html The LBI for the oscillator/multipier board in the receiver also talks about it what's actually going on in the receiver... kinda. You have to apply a bit of knowledge about the design of the receiver itself, which really isn't in the document -- but the document's description is great if you understand how a fairly typical RF receiver works. http://www.repeater-builder.com/ge/lbi-library/lbi-30029j.pdf And of course, the LBI is the critical piece to understanding any GE radio -- it's the document a "real" engineer wrote for the service techs (and hobbiests!) of the world. And one thing you'll find in an LBI you hardly find anywhere else... an honest to goodness schematic! Find that for an iPod, I dare ya! (GRIN) You can spend hours looking over the circuit at a test point or a specific note from the side-bar figuring out... "They say if I put this jumper here, it will do X. Now why is that?!" I find it fun -- wish I had more time to do it. Nate WY0X
