Posts

24GHz LNA design

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So, here are my thoughts on an LNA design for 24 GHz, inpired by Ron Schiltmans DU3T design, I thought I would try something similar. The basic concept is a waveguide input, 2 stage desgin for 24GHz,  with a CE3520K3 FET on the input, and a MMIC amplifier as the second stage.  For the second stage I plan to use an HMC341 I will include my calculations and assumptions for the design, if you can spot an error in my thoughts, I would be of course, delighted to hear from you! The circuitry on the left is a simple 3.3V regulator, feeding a ICL7660 negative voltage generator. The 3.3V is used to feed power to the MMIC amplifier and the input FET.  A simple P type FET prevents power being supplied to the front end FET before the negative voltage is present.   The  CE3520K3 was selected as it is pretty much the only real option easily obtainable from Mouser. I'd like to give you a better answer based on cost and performance, selection of matching parameters etc, but basically, it comes dow

Dish update ... pretty much there.

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 Finally completed the 3 little stainless steel "pucks" that form the locking arrangement for securing the dish "L Bracket" to the pan and tilt head's quick release mechanism.  Those innocuous little lumps of stainless where a pain to machine and adjust, Not something I would want to do again, although I suspect I will have to as I have 2 of these pan and tilt units!  I'll probably add some sort of trianglular brace, just to take some strain off the bolts, but, its pretty rigid as it stands. The basic sequence is tripos erected, L bracket clipped on to the pan and tilt unit. Dish hooks on to the front with the 4 prongs. Feed is inserted through the hole, big brass nut tightened up, job done.  

Mounting plug and securing nut for the feed.

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 Mounting plug for feedhorn. The idea is to have multiple of these, so the dish can be used with different feeds for the different bands.  The thread was a joy to cut ... 60mm by 2.5mm pitch.   A lump of 80mm dia brass bar was bought and a nut made on the lathe, nicely knurled and finally given a bit more "finger grip" in the mill. It's all coming together now.

Clip-on dish mount

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 Here you go, a bit more progress.  I added some stainless bosses to engage with the keyhole slots I had cut in the mounting plate.  Need to trim off the excess material and work on the locking plates to engage with the quick release mechanism on the pan/tilt unit. If I was to do this again, I would do it differently, probably just two studs and a support pad ... and I'd make the keyholes smaller with an obround machined into the front face to help guide the pins and make the head of the pin smaller, so the whole pin can't push through.  This will do for now though  Onward buttercup!    

A bit of metalwork for the 3cm dish ...

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I've been trying to get a good, portable 3cm system set up for some time.  Some time last year I obtained an absolutely lovely pair of pan-and-tilt heads designed for miltary use with very long focal length spotting scopes. Mounted on a surveying tripod, these will be ideal for microwave dishes for portable use.   I also picked up a very nice 600mm dish, brand new and in 3mm aluminium, this is a precision spun communications dish; from a now defunct company in Leominster. I also had a very nice "shepherds crook" feed that had originally come with another dish many years ago. A bit of measurement suggested the focal length would be spot on.  A bit of work on the lathe would be needed to produce a suitable mounting boss for the feed, so a lump of aluminium was purchased and I set to. I think it came out OK; turning the curve into the mating surface was the hard part. 6 holes were drilled and countersunk and the feed now fits very nicely in the dish centre. Lathe work Comple

Feeders for my surface mount machine

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 I have a pick and place machine for placing SMD parts, at some point last year I ordered the parts for a new project and it used quite a lot of "oddball" components.  I didn't really notice how many until the reels turned up. Unfortunately, it was more reels than I had reel holders (feeders) ...    I had a few more in a box somewhere, but those were mostly my rejects so I managed to order a few from the USA at a good price.  Unfortunately what turned up from the USA was mostly marked "faulty" or "occasionally jams", "misses steps" and other encouraging words. I was at best dubious about getting them going and the few I tested did indeed appear to be faulty. These things are notoriously tricky, they use compressed air and a small cylinder to actuate levers and ratchets and if any part doesn't perform perfectly, it will not correctly advance the components. Gloom set in.  Christmas came and went and amongst the festivities I found a chap i

A bit of Maths

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Having another go at calculating the optimum output match for a generic LNA I had a play in MatLab, but being less than familiar with MatLab I wanted to double check my results. Perl is an easy to use programming language, and has an extenion for complex numbers, which makes things easy.  Supplying the input gamma, along with the S-parameters for the optimum input match for minimum noise from the datasheet, this attempts to calculate the optimum output match from the formula:  It is reasonably simple to use Perl to calculate this once the Math::Complex library is loaded, complex numbers can be manipulated with the same ease as real numbers, thanks to the wonders of operator overloading. To check the program, the values from the  paper which included a worked example. However when I ran the calculation, I did not get the published results ...infact, it was not even close ... and after two days of head scratching and questioning whether I could even do basic maths, I posted the question