More IF Filters Than You Can Poke A Stick At

They say a picture is worth 1000 words, well here are 4 pictures so that has to worth a novel or 2. Anyway no opus this post, just the meat of it. I built 2 xtals filters, in each case i grabbed 8 random xtals out of the parts bins, no matching. The xtals are ebay specials 100 for $1 and are probably rubbish that did not meet specification and was taken out of the rubbish bins at the factory. So the highest quality man cannot buy in other words.

The difference between the 2 filters comes in the matching, filter one is matched with the traditional ferrite inductor, though i used binoculars as i prefer winding those for transformers over toriods and the 2nd filter was matched using low pass filters. The filter plots speak for themselves, the low pass filter matched has a better shape but -15db less attenuation in the stop band than the ferrite matched filter. And the losses were about the same -7db. -3db is 2200hz. So with some matching the crystals i should be able to improve the flatness in the passband and probably remove some losses.

But other than that, if you can live with -50db of opposite sideband suppression, the grabbing random xtals out of the box and matching with low pass filters might actually be a rather simple and crude way of IF filtering. For now, i think i will stick to winding the transformers, or buying 4:1 transformers off Mouser.

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SMD Is The New Black

I have a need, a need for speed. Well, not really, but I have a need for filter components that are small. I am building a hand held after all for 40 and 20m and you just cannot fit large toriods into a tiny box you can carry around very easy. Well, you might get them in there with some careful design, but the mechanical durability of thin wire being bounced about is going to be suspect at best.

And what if i want to sell 100 of these things? Who wants to sit there winding a bazillion toriods? Not me, that is for certain, i do not even want to wind 2 for a prototype. HEHE. Anyway, that got me to thinking, and my thinking i mean i really did not think a lot at all. I got on the confuser and did some jazz hands on my parts suppliers website and poked my peepers at what they stocked to see if there was an off the shelf solution to my problem.

So they have RF inductors, but the problem with these is the low Q. And we all know that Q stands for Quicksand and with a low Q your signal starts to sink into the mud and you might not hear the ducks anymore. Ok, so the question is HOW LOW CAN YOU GO. So i looked and I looked and in the end i found a 1.5uH inductor that had a Q of about 25. TWENTY FIVE you might rightfully exclaim and yes you would be right, that is a bloody low number. But such tiny inductors are always doing to have a low Q much like many hams have a low brow and low I and Q when they down convert their thoughts to base band.

So how bad is it. Well not as bad as you might think. -6db loss is -5.5db loss more than the same filter i built using hand wound T50-2 toriods, which on second thought is actually massively crappy. But hey, i still gotta stick this in a handheld box and have it mechanically secure. Thankfully there is a solution.

Back in the dark old days before time began, the Motorola company or was it Bell Labs, either way, it does not matter all that much as I am just spinning a tale here of those that do, or as I like to call them N Type and those that don’t, the P type and someone added in B J and T into this alphabet soup of inter-related terminology and created the PRE AMPLIFIER.

I need to have some gain in the system anyway so if i put some gain, i don’t know lets say somewhere between 6 and 10db before the filter, i can make up for those filter losses before we have even started. BUT WAIT you might ask, that is going to cost more, and yes sirreee Bob you would be right. But i can take those 2 SMD Trimmers out as they are not going to be needed and replace them with 2 1 cent caps and that just saved me $1 on my BOM cost.

WOO HOO i can do radio design me.

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Nothing New Under The Sun

In response to my state of the hobby address here: https://robs-blog.net/2019/10/18/we-promote-the-things-we-value-most/ I had someone send me this. Not sure how readable this will be for most people, but its from 1938 in a magazine called T&R Bulletin, which later became the RSGB magazine. It would seem that even way back when in the dark ages, there were those who were becoming disillusioned with the hobby due to the attitudes of predominantly the old guard.

There is no fool like an old fool, and there is nothing so pathetic on the air as a veteran amateur, who presumably is old enough to know better, making a complete idiot of himself. 

It would seem that even back in the old days, black box operators and shit dribblers on 40m were becoming the norm and it was the newbies for the better part that were setting the example. Not a lot different today is there. Fcalls get all the abuse, but its their betters who are setting the shit example.

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We Promote The Things We Value Most

Let me preface this post by saying that for sometime I have been rather disillusioned with amateur radio as a hobby. The reasons are varied but can all be distilled down to a couple of core issues and the main one is that what attracted me to the hobby, namely home brew and electronics, which at one point was the core point of doing ham radio, is now, rather non existent.

And now what masquerades as a technical hobby is nothing more than Adult CB for those who passed a test one time that made them instant experts of everything or Amateur politics for small men with no life who want power, IE WIA and RASA. How many of these people do you ever hear doing radio? Other than Chapman and Smith, who i think are both shit stains on the hobby, I have never heard any of the others on air ever. So essentially you have people who for the most part do not partake in the hobby, deciding what should be done for those that do.

Take the LCD update as a classic example of how short sighted this hobby is. The WIA consulted with clubs on what to do with Fcall privileges. Have you looked around clubs? They are mostly old, grey and bald and male who has been an amateur for 30+ years with an advanced call. People who for the most part have no clue about the newbie experience in practical terms of what it is like to be a newbie, now, today. In other words, the opposite of who could give some insight into what its like to be an fcall or to be thinking about being an fcall.

If you want to know what the fcall gets right and what could be done better, why not ask some bloody fcalls or people who have been fcalls in the last 5 years? Of course we don’t ask fcalls because in reality, they do not matter, what matters are the opinions of advanced calls. Remember the title of this thread, we talk to those we value most and fcalls do not matter to the WIA because they make up such a small part of the membership as to be irrelevant. So what remains is Advanced call confirmation bias.

Oh sure, I can see some now who are reading this going, well that is not me. I do stuff and am part of a silent majority . And yeah you might do stuff, but is your voice one that is ever heard? A none heard voice is irrelevant. Take a tune though 40 and 20 meters any day of the week and have an actual listen to what transpires. I am running a transceiver i bought into an amplifier i bought, with a signal running through a feedline i bought into an antenna i bought, which is mounted on a tower i bought, so I am the king of ham radio.

You know this SKILL bullshit that people always go on about, my skill as a DX’r means I work more DX. Well, the actual skill is not in electronics or radio for that matter, its in comparative shopping methods and who has a bigger wallet, bigger yard and ultimately bigger amp, because the main skill in VK is who can run the most power without getting caught by an ACMA that is not looking.

One you get passed the dick waving about whose IcYaWood is bigger than someone elses, you get all the other stupidities. Sexism, racism, homophobia, misogyny, fcall bashing and other assorted hate passing as rag chewing. Yeah this is the pinnacle of amateur radio, there are less hateful people on the Brisbane UHF CB repeater and it takes a lot of class to out class the classy characters making animal noises on there.

So ultimately for me, I look at the dominant voices in this hobby and think to myself, I do not identify with these people, i do not relate to these people, I do not like these people and I certainly do not respect these people, so why the hell would i want to associate with these people. And as for people like myself who are trying to self educate in electronics and construction, who are trying to build a station from scratch that is worth using and is not just a novelty, well, they just don’t seem to exist or have been marginalised to the point where they just do not bother operating anymore.

You see, we promote the things we most value, and it would seem that the things we value the most are talkie talkes, wackers, contestors and those who want to be amateur politicians. The real ham radio, the stuff from the pre 1970’s where the first part of building a station was to own a soldering iron and know how to not make cooked chicken smells, well that no longer exists. It has been replaced with the Baofeng.

As for me, well I still have some goals left to achieve amateur radio. Yeah goals. A foreign concept to the talkie talkie crowd. But once they are achieved, I certainly do not see any compelling reason to remain in the hobby. I can easily switch to other forms of electronics where I can continue to learn and to grow. I have come a long way in 5 years, from not knowing what a resistor does, to now being able to design and build a transceiver that has practical use, covering everything from schematic capture and pcb layout to mechanical design.

But when i look at the hobby and those who are partaking in it, i don’t see myself represented anywhere. I see a lot of back in my day, old, white, bald, grey and male, i see a lot of conservative politics, anti science and fake news. But i don’t see a lot of ideals, morals and ethics worth emulating. And without people to look up to, people who are prominent and stand for something more than self interest and self indulgence, then there seems little reason to keep bothering.  The very thought of turning a radio on, including the one i have just finished building, and making a qso or 2, just seems cringe worthy to me.

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Shielded Filter Boards

I have been working on a few different things of late. One of the major ones has been to design some plugin filter boards that I can add shielding cans to. There are 2 different xtal filter IF boards, one using binocular inductors for impedance matching and the other using LC low pass filter matching. The latter is more an experiment to see if it is feasible to get a good passband ripple and impedance match using off the shelf SMD inductors and caps. Its easier to solder in 4 parts than wind inductors.

The other filter is a bandpass filter for a receiver. Again using SMD components rather than winding toriods. In simulation using a Q of 60 for the inductors the losses were acceptable. How they will go in practice is another thing. Worst case scenario is i add a MMIC amp onto the board and add some gain before the filter losses to make up the difference. My hand wound filters of the same topology had 1db loss in them. 2 or 3db loss using off the shelf components would be probably quite acceptable.

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