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Old 10th November 2017, 03:05 PM   #111
Tubelab_com is online now Tubelab_com  United States
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Looking at slideshows of some of his Dayton presentations, he says beginning in 2003, the high performance receiver trend now is back to DOWN conversion in the 5-10 MHz
Whenever two or more engineers are working on a similar project, there will be strong differences of opinion on how things should be done, and if both players are competent designers, both may have valid, but different designs. Often both will meet the published design criteria, but each will have their own benefits and drawbacks. It is often the details that are NOT in the published specs or design criteria that will make or break the different designs in the real world.

Too often Motorola got products out into the real world to find that there were severe problems somewhere because of this. In my 41 year there were 3 major cluster f$^*s due to someone not paying attention to where the image frequency falls. As I alluded to earlier, my demonstration at an NFL game averted number 4 before it happened. It doesn't matter if you meet 80 db of image rejection if the radio has a plastic housing (UHF HT220) and there are powerful TV or cellular transmitters on the image frequency.

Try putting 20 or so good RF engineers in a room and asking them to design a cell phone. It takes months before the name calling and finger pointing stops. After being lead RF guy on several cell phone projects, I had come to the conclusion that either by boss was going to get a phone stuffed up his butt, or I was going to have a heart attack, either way I would be leaving the plant in a city vehicle (cop car or ambulance). I left the phone group before that phone ever shipped. The group imploded in a huge layoff and was eventually sold off a few years later.

There IS NO ultimate clear cut winner as to how to design anything, especially an RF product. There are design goals, and expected use cases, and of course cost, size and power requirements. Each designer must carefully balance all of these.

I brought up the upconversion idea for multi band hand held police radios and was immediately told how stupid I was......."That is stupid, it will never work." I explained the benefits, and the drawbacks, and explained that there were currently MILLIONS of such devices in use today. When it didn't go anywhere, I shut up. Life in the phone group taught me that corporate life expectancy works a lot like the TV reality game show "Survivor." You need to pull your own weight, don't excel at anything (you may be perceived as a threat) and NEVER do anything to threaten the alliance of power. There is one in every group, and it may not always be obvious.

My idea was perceived as a threat by those in control, and I was told later not to attempt to play in their sandbox, which is why I became a transmitter guy. That group was a disaster. The million seller with an upconversion receiver? They are called TV sets and cable boxes. Motorola was the industry leader in cable boxes before they sold that group too, and I had the schematics, and design documents for one of their high spec units. There are lots of reasons to do upconversion, but the big one is image rejection. With a 1.2 GHz first IF, the image is in the 1 - 2 GHZ region where mega strong signals are few. The drawback is that you need two synthesizers, but we needed them anyway.

.....I will be building one sooner or later.....using cable box saw filters from Mouser.
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Old 10th November 2017, 03:24 PM   #112
w5jag is offline w5jag  United States
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...... I look at the transmitter as the receiver running backwards, If you make your transmit signal at 455 KHz, or even 45 Mhz, then run the same converters in the other direction for TX .....
Here's what I'm thinking, if you guys can read my chicken scratch.

It may sound counter intuitive, but I think for my skill set, I'm better off keeping the common elements / switching to a minimum, and more or less (mostly more ) keeping the TX and RX strips, separate.

A big question mark I have, is that selectivity element at 45 MHz in the TX strip. Do I even need anything there? If I do, is a low pass filter OK? Or do I need to order another XTAL filter?

Some of this uncertainty relates to the repairability of that Dentron brick. If I can get it going, all my power gain can be after the last TX mixer. If I can't get it going, then I feel like I need to spread the TX gain over a few frequencies for stability purposes, hence do I need a low pass / band pass element at that 45 MHz TX IF?

If that makes any sense.

This is not a rush type decision, but I want to make allowance for this as I build out the RX. I need to get the RX going in at least some type of simple form, so I can run it in the car to proof it and see if I need noise blanking, etc., added in to it.

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Old 10th November 2017, 09:14 PM   #113
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hence do I need a low pass / band pass element at that 45 MHz TX IF?
You will need a bandpass element there, probably a crystal filter. Just as with the receiver there will be an image in the transmitter. Lets say you are running your LO at 44.545 MHz and mixing that with 455 KHz to make 45 MHz. The mixer will create the sum (45MHz) and difference (44.09 MHz) frequencies. Lets say that you mix the 45 MHz with a 59.1 MHz 2nd LO to make a 14.1 MHz 20 meter transmit signal. There will also be a 15.01 MHz (out of band) signal which will flow right through your transmitter and out the antenna, possibly torqueing off somebody, including the FCC. A filter is needed to kill the 44.09 MHz image from the mixer. Since the image is only 910 KHz away, a simple LC filter will not be sharp enough.

It is usually cheaper to switch the crystal filter and maybe the IF amp and mixer into the TX path and RX path. Cheaper yes, but more complicated, and maybe not worth the effort for a one off project.

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Some of this uncertainty relates to the repairability of that Dentron brick.
How much power are you looking for? If the Dentron was in the 100 watt class the common transistors used were MRF454's. Not sure how available they are any more, but sometimes CB (non)Linears are cheap at swap meets and hamfests. I used to grab them when they were $10 or less just to harvest the silicon and ferrites. I haven't looked for such items in years, so I don't know how available they are now.

I had some spare transistors for that HF brick that I made. I haven't got a clue where they are, or if I still have them, but the first place that I would look is very cold right now. Maybe tomorrow afternoon if it warms up.....it's 30 degrees F right now, and 18 is expected tonight.
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Old 10th November 2017, 10:10 PM   #114
benb is offline benb  United States
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[QUOTE=Tubelab_com;5239890]The "CA" parts did indeed originate at RCA. My first IC project used an RCA CA3020 1/2 watt "audio amp" IC in 1969 or 1970. Of course I played guitar through it, but it seems that at least one military contractor used it in a servo application. I guess it worked well there, because it went from RCA to Intersil to Harris to somewhere else, and it kept being upgraded along the way. National and others second sourced many of the military parts, and spares were needed for as long as someone was using the end product in the military.

I noticed Intersil has a very specific version of the 3046 transistor array that (veering back on topic of this thread) goes into the gigahertz, and costs $9 each at Digikey.
HFA3046BZ Intersil | Discrete Semiconductor Products | DigiKey
My problem(s) with it are I don't have enough RF knowledge to do anything near that frequency, and the chip is way too expensive for what I would want to use it for (synth audio and/or control voltage exponentiation).

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In a synth related note, a small company called OnChip has remanufactured the old Curtis Electromusic CEM3340 VCO chip, and are selling them for $15 each.....I got a few to play with. Now if they would only do the VCF chip......
Ahem ... looks like the competition is (pun intended for thermal stabilization) heating up in this area:
Application specific

There's someone (maybe more than one, there's enough activity that I'm losing track of who's reintroducing what) remaking one or more of the SSM chips as well.
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Old 10th November 2017, 10:24 PM   #115
wayne is offline wayne  United States
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No RF gear here?
I remember a Motorola pager that had a IF that was tunable. They did this to use the crystal for both the first and second LO. Saved some money I guess.
High side injection is a great idea makes tuning easier in some cases especially like a spectrum analyzer.
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Old 11th November 2017, 01:32 AM   #116
w5jag is offline w5jag  United States
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..... You will need a bandpass element there, probably a crystal filter.
Thank you, I need to get some parts, so I'll probably order another filter. Surplus Sales of Nebraska has some 4 pole 45 MHz filters for a price that is actually reasonable ( for them ), so I might get one of those for the RX, and use the 2 pole ECS for the TX.

The McCoy 30.1 MHZ / 10.35 MHz filter set that I have apparently came from some type of Collins set, and they have a Collins p/n on them, but that's where the trail goes cold. SSoN actually has NOS on them ( for an outrageous price ), but doesn't offer up any specs. Looking at the other McCoy filters they have, the in/out impedances are all over the place - sometimes not even the same at the input as the output.

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How much power are you looking for? If the Dentron was in the 100 watt class the common transistors used were MRF454's. Not sure how available they are any more, ....
I'm pretty flexible - 30 to 50 watts PEP out, would be fine, I think. Dentron claims 250 in / 130 watt out from the brick, but it's way undersized for that power level without forced air. They didn't even put vents in the cabinet. The schematic doesn't ID the power transistors. I'll try to scan and post the schematic next week when I'm back in town. I don't even recall it having any protection to keep the transistors from thermal runaway. It's hard to imagine Dentron using a quality part like an MRF454.

RF Parts has matched pairs of MRF454 for about $100, and lesser wattage ones for, well, less, but not necessarily in matched pairs. Depending on the ferrites and other transistors in it, it might be better to go with 50 Mhz parts if I repair it. I'll just have to open it up and see where I'm at.

Don't go out in the cold just yet - I still have some zero cost options. In the vast trove of unbuilt kits, I have one of Virgil, K5OOR, HF Packer amps, HF Projects for Radio Amateurs the early one that uses MOSFET's ( IFR510?) that is good for 50 watts that I could build out. And that Yaesu FL-110 that sat in the same place on my bench for years - I've verified it works. And it seems like somewhere I have a board for a 10 or 15 watt amp using MRF475's, and I have found a couple of pairs of MRF475's in stock, and a suitable heat sink.

With the tunable LO now in hand, I'm looking forward to being able to make real hardware mistakes as opposed to merely drawings on paper mistakes, I just hope they're not real expensive, or embarrassingly stupid ......

I've also got to build out that stereo FM receiver that I slapped the tuner together for, so several things going on at once. I'm still weighing a big stick, dual push pull SSE boards, or an SPP, maybe hot rodded, maybe flea power, for the outputs ....

Win W5JAG

Last edited by w5jag; 11th November 2017 at 01:44 AM.
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Old 11th November 2017, 02:28 AM   #117
Tubelab_com is online now Tubelab_com  United States
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I just hope they're not real expensive, or embarrassingly stupid ......
The only stupid mistake would be calling CQ for hours only to find that you have been talking to your neighbors TV set.

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Don't go out in the cold just yet
I need to go looking for some tubes...after it gets a bit warmer. I have a bunch of stuff stored in a derelict mobile home next door. Somewhere in that trailer is a box full of our RF breadboard experiments that might have found their way around the scrap bin when I left Mot.

We had our own PCB fab in house for everything including multi layer HDI. I asked if they could make me a board with 2 layers of Rogers Duroid stacked on 2 layers of FR4 with an aluminum heat spreader in the middle....."yeah, we will try it, but it might take a day or two." They built it, it worked. It was for a 20 watt LTE transmitter on 2.5 GHz. Simple 2 layer boards were made in 6 hours. Sadly it, along with the machine shop and the engineering stock room all were shut down and all the people laid off at the same time I left.

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dual push pull SSE boards, or an SPP, maybe hot rodded,
Yeah, I've got a pair of mystery OPT's that I need to hook up. I need to try one of those in a little guitar amp that I made that currently uses a line matching transformer for an OPT.
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Old 14th November 2017, 07:28 PM   #118
w5jag is offline w5jag  United States
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make real hardware mistakes as opposed to merely drawings on paper mistakes, I just hope they're not real expensive, or embarrassingly stupid .
Well, nearly both. I got back in town late Sunday night, so began trying to figure out the DDS. I got the assembled version, but had some glitches with it. I had it clipped up in a fur ball of jumpers, and once in a while, the display would just unexpectedly blank, which I blew off, thinking it was just the clip leads. Last night, I hard wired it up, and saw the same problem, and a bit worse. The blanking is solved, I think, by reflowing the solder joints on the display.

The bit worse, is, a bit worse - it has a provision to read a dc voltage applied to pin 1 of the microprocessor, ( 0 to + 3.3 ) and output that to a bar graph on the display, and it began doing exactly that, except there was supposed to be no dc voltage at that point. Looking at it on the scope, there was in fact an unwanted 3.3 volts at pin 1 of the microprocessor, and no apparent way to get there, except internal to the microprocessor. Somehow I corrupted the firmware, or the processor.

This was a real problem, as that pin 1 has to be driven high to program the DDS. I made a workaround by jumpering across the meter input to pull pin 1 low, and fashioning a kludge to drive pin 1 back high for programming. The kludge was cutting a pin off an old TTL IC, soldering a thin wire to it (not as easy as it sounds), and pushing this into the pin 1 socket so it is in contact with the real pin 1, and can be driven high to set the prograaming. ( Again, not as easy as it sounds ).

Oleg is sending me a new microprocessor.

In the meantime .....

Quote:
If these are anything like the Chinese class D audio boards they may be anywhere from somewhat useful to junk.
Well, I donít know. I havenít really played with one, so donít know what to expect.

Below are some pics. I have made up a test jig for it so I could go to work on the actual radio - each output goes to a pot for attenuation ( this looks to be a bad idea, and will be modified ), and a small 12 volt supply for powering test boards.

It is anything but clean. The 999 KHz shot is the fixed oscillator. The 1.2 MHz shot is the variable oscillator. Not the time base difference between the two - I believe my cheap scope was having difficulty with the harmonics, but the frequency counter display is correct. The 3.610 MHz capture clearly shows the second and third harmonics. The only good news here is my 1 MHz scope clearly responds out past 10 MHz. I verified the harmonic content with a general coverage receiver. The third is as strong as the fundamental, maybe stronger. The second is weak and raspy. Both DDS outputs exhibit the same behavior.

It may be better at the VHF frequencies I need for a tunable LO and conversion oscillator. It for sure needs to be filtered and conditioned to use as a low HF oscillator.

So, still at square one, maybe backwards one or two ....
Attached Images
File Type: jpg Fixed Lo at 1 MHz.jpg (277.5 KB, 105 views)
File Type: jpg Tunable LO at 1.2 MHz.jpg (278.7 KB, 104 views)
File Type: jpg 3.61 MHz and harmonics.jpg (297.2 KB, 103 views)
File Type: jpg kludge test jig - working.jpg (415.2 KB, 54 views)
File Type: jpg partial test jig - fried.jpg (808.0 KB, 22 views)
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Old 16th November 2017, 03:52 PM   #119
w5jag is offline w5jag  United States
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... It may be better at the VHF frequencies I need for a tunable LO and conversion oscillator. ....
After playing with this a bit more, and doing some belated cursory research on this DDS chip, all this looks to be completely normal behavior. As best I can tell, the kit performs just as described. Properly used, it will be satisfactory for a single band transceiver, which is how it is described.

The data sheet says square wave output, but some of the pics I've now seen just barely approximate a square wave. The waveform ^^ above actually looks pretty good.

The data sheet says nothing about harmonic generation. The third harmonic is just horrendous. I can tune it through the 48 MHz region and stop the scan, and fully quiet my homebrew two meter receiver. The antenna is at least sixty feet away on the roof.

It may or may not be exactly on frequency. I think it's a little off. The firmware allows for exact calibration of the oscillator crystal. I haven't done this, yet, as I expect the crystal to age a bit.

This place: QRP Labs Kits has a bunch of DDS kits based around this chip and for support of this chip, as well as a fair amount of information about it, Arduino code and shield boards to support the chip, BAND PASS filters, etc., .

One of their kits has outputs to switch low pass filters - useful for transmitters, but it's not hard to infer that the same function could be used to switch in band pass filters to kill the harmonics and condition the waveform output to make it suitable for actual use.

Their kits can accept a GPS clock signal and use this as the reference - this resolves the frequency calibration issue.

So, anyway, with suitable filters on each of the outputs to clean things up, this will be a satisfactory LO, but it's not as plug and play as I naively expected. I think the same can be said of anything using this chip.

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Old 16th November 2017, 09:03 PM   #120
Tubelab_com is online now Tubelab_com  United States
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The data sheet says square wave output.......The data sheet says nothing about harmonic generation. The third harmonic is just horrendous.
The Silicon Labs chips use divider technology to make the output frequency, and therefore make square waves of varying duty cycles.

A square wave by definition contains ALL of the odd order harmonics. The distribution of these is defined by the duty cycle. A 50 50 duty cycle affords the highest 3rd harmonic content.

Many of the typical diode or fet ring mixers actually work better when the LO port is driven by a square wave. The reason has to do with minimizing the time where the diodes or fets are operating in their transition (quasi linear) region. Ideally you want one pair of diodes fully conducting while the other pair is off. The transition where the conducting and off pairs are swapped needs to be minimized, because that is when higher order mixing products are generated, and conversion loss increases.

If your synthesizer can operate at twice the needed LO frequency, the usual trick is to run its output through a divide by two flip flop like a 74HC74 to create a pair of complementary square waves with a 50 - 50 duty cycle.


The typical DDS type synthesizer outputs something more like a sine wave, since they have a sine wave look up table in ROM, and just play it through a DAC.
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