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Old 15th July 2018, 06:19 PM   #301
anatech is offline anatech  Canada
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Hi w5jag,
Sounds like you're winning with that project. This should spur you on to complete it.

Just went to a Hamfest yesterday in Milton, Ontario. Smaller turnout of dealers and guys who sell from their trunks, but lot's of good stuff that spans the categories from junk, old computers and bits, test gear (some relics) and even some HAM related stuff. I scored a book on antennas, a Heathkit IT-18 transistor checker in pristine condition
and also an M-Audio Pre-USB mic preamp. Lots of things I would love to buy, but the cash just wasn't there. There's always next year!

-Chris
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Old 15th July 2018, 07:22 PM   #302
gpauk is offline gpauk  Scotland
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Your project is in the finest tradition of amateur radio - you've experimented a lot, and learned a lot! And, I've lurked but not commented before, but I think many of us are enjoying the process! Keep up the enthusiasm and good work! Definitely the Right Stuff!
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Old 17th July 2018, 04:18 PM   #303
w5jag is offline w5jag  United States
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Thanks for the words of encouragement - I thought this project would be drama free, especially considering that I have a pre built 9 MHz back end.

It's my own fault for digging my heels in with that seriously flawed VFO. I must have unknowingly damaged the firmware implementing the fixed LO output. Since I cannot rule out that I am the one that botched the thing, I have not shared my observations with the designer / vendor.

With my "antenna" connected, the background noise increase at 14 MHz is slight, so I added an MMIC between the crude front end filter and the input to the mixer. This definitely increased the gain - it's hard to say for sure that it increased the sensitivity. This NEC upc1651 is not a low noise device to start with, and it's not implemented correctly. It's unmatched at the output ( I was hoping that would lower the gain ), and I haven't got the voltage right. The data sheet says best NF is between 5.5 volts and 6 volts ( max for the device ). I can't get it dialed in with the SMD 1206 zeners I have - a 5.6 volt device is giving me about 5.1 at the chip, and a 6.X device put me at 6.6 - over the max spec. It makes a difference - according to the sheet, NF goes up 2.5 dB between 5.5 and 5.1 volts ...... I find rework to be really difficult on this type of board with my present tools. You really need to get it right the first time.

This is not the front end filter that will actually be used, so fooling with it is a dead end. The MMIC's are interesting though - it looks to be next to impossible to make one oscillate, even when badly implemented.

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Old 18th July 2018, 03:41 AM   #304
w5jag is offline w5jag  United States
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As part of the SMD thing, I've had these HP IAM 81008 chips laying around, so I tore down the 2N3823 mixer, and substituted one of these in it's place.

Not much to it - 50 ohm in and out, so I just hooked one end to the input filter, and the other end to the FT-817. A couple of bypass caps, blocking caps, the usual decoupling from the supply line, that's pretty much it.

Seems to work okay; the battery was low on the FT-817 so I didn't get much time to play with it, but it heard the local 25 watt LF NDB, and 50 watt BCB station in the next town over, quite well. CW on 40 meters was good, also.

These chips are cheap on eBay, and apparently genuine. Datasheet attached. There is an old patent for it, #5379497, but my copy is too big to upload

Win W5JAG
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Old 19th July 2018, 02:14 PM   #305
w5jag is offline w5jag  United States
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The IAM 81008 looks like it could have some potential.

It is a doubly balanced mixer, so here are some FFT captures of the port to port isolation. I am taking the IF at 45 MHz, and was listening to CW on 20, so the VFO is running about 59 MHz.

I am running the VFO flat out, so this could be right at, or slightly over, the spec for LO input. The chip is at 8 volts, again the maximum recommended operating spec for this device. Max, period, is 10 VDC.

Capture 1 is the VFO amplitude at the LO port of the mixer. I put the pip at the horizontal mark to make it easy.

Capture 2 is at the IF port - the LO is suppressed about 25 dB.

Capture 3 is at the RF port - LO suppression here is only about 17 dB, and some spurious response is showing up.

I haven't looked at the rules since last summer, but I doubt that this meets the rule for spurious emissions, so something more is needed here. I do recall that the rule was that spur readings have to be taken at the antenna port - any suppression from a narrow bandwidth antenna can't be counted in meeting the rules.

The low pass filter at the antenna input should take care of this, so I took a look at it, and determined it's not working properly - at the antenna terminal, I am only seeing an additional 3 dB attenuation of the LO at 59 MHz. So, if I go with a wideband front end, that will have to be sorted out. The MW high pass filter looks to be working as intended.

I will probably follow up with a double conversion down to 9 Mhz to see if these chips have any merit, or not.

Win W5JAG
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File Type: jpg pic_59_1.jpg (48.7 KB, 113 views)
File Type: jpg pic_59_2.jpg (47.4 KB, 114 views)
File Type: jpg pic_59_3.jpg (48.1 KB, 113 views)

Last edited by w5jag; 19th July 2018 at 02:39 PM. Reason: sp
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Old 30th July 2018, 02:51 PM   #306
w5jag is offline w5jag  United States
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So, maybe someone more experienced at reading data sheets can look at this Toko sheet, which appears to be the only slug tuned SMD coil in the Mouser catalog.

I made a narrowband front end with the slug set to midpoint, and an appropriate resonating cap, only to find it was impervious to 14 MHz signals, and no amount of diddling would change that. I swept it with the Feel Tech function generator while looking at the FFT on the Hantek, and resonance was well into the low VHF range. I pulled the coil, measured it as best I could, and found it was nominally about 0.23 uH, and can be varied from about 0.2 to 0.3 uH. Thinking I had damaged it, I checked another and got the same result. Maybe not coincidentally, 11 pf and 0.23 uH is resonant at the 100 MHz test frequency specified.

Looking at the sheet, I thought I was getting a slug that would go from 0.05 to 2.7 uH.

So, I backed up and made a single tuned circuit with a toroid and a link, that worked OK, but looked too fragile for the rough roads around here.

I switched to a fixed inductor, and instead of a link, rigged up a series capacitive divider to get a Lo-Z point for a 50 ohm antenna, as well as a Hi-Z point for the random wire I am testing with. This looks like it might work, and the trimmer can be substituted with a tuning diode that can be tuned remotely if I stay with just one pole, or multiple poles can be stagger tuned to make a fixed front end.

I probably need to diddle with the capacitor values in the divider some, this is just for a test of concept.

I was listening last night with this set up hooked to the FT-817 as a 9 Mhz IF, RF amp off, and 20 dB attenuator turned on to make the FT-817 as deaf as possible, and heard a local guy about two towns north working phone on 20. From about 11:00 PM local to midnight, he worked Nebraska, Michigan, Indiana, Minnesota, and Wisconsin, and, with the random wire, this set up could Q5 copy every station he worked.

I ordered some more of those HP mixer chips, but haven't had a chance to do anything more with the ones I have.

The board looks just flat out awful at this point. It is not apparent from the picture, but I am starting to mix in some 0805 with the 1206. I have 0603 also, but haven't tried any 0603 yet.

Win W5JAG
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File Type: jpg IMG_20180730_084307.jpg (465.2 KB, 13 views)
File Type: jpg tuned circuit.jpg (278.8 KB, 15 views)
Attached Files
File Type: pdf toko smd coil.pdf (247.3 KB, 6 views)
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Old 31st July 2018, 06:48 PM   #307
w5jag is offline w5jag  United States
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I played with this circuit for an hour or so last night.

I set up the FY6060 as a signal source at 14 MHz, injected into the "Lo-Z" series point, hooked the scope up to the gate, and peaked the trimmer cap for maximum response.

I then swept it with the FFT, and found it was actually resonant at about 12.5 MHz, the trimmer was just going to minimum capacitance. I changed the lower cap to 130 pf in parallel with the trimmer, and this brought it to resonance in the twenty meter band.

It doesn't behave like other single tuned circuits I've played with / used. Instead of a sharp response on the resonant frequency with a steep slope, if the Hantek FFT is to be believed, and I am testing this correctly, it has a very flat response across the resonant frequency, with very shallow skirts. Shallow enough that I only saw 6 dB difference between the original resonant point and the bottom of the twenty meter band. Once modified, I didn't have any trouble finding a point where it was ruler flat across the twenty meter band, together with a good 75 Khz either side of it.

I"m aware of Q, but won't pretend that I understand it. I came across some slug tuned coils in my junkbox that would work here, and eliminate the need for the trimmer cap, and that might have a sharper response than this molded inductor, but I'm not sure the broad bandwidth is a bad feature. A few poles of this would sharpen the filter, and it should not need to be peaked from the front panel. I just want to keep what I don't need out of the weak mixer.

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Old 31st July 2018, 07:19 PM   #308
benb is offline benb  United States
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Quote:
Originally Posted by w5jag View Post
Looking at the sheet, I thought I was getting a slug that would go from 0.05 to 2.7 uH.
That seems like a really wide range (50 to 1) for a slug-tuned variable inductor. I wonder if it's a misprint. Do other models from that manufacturer have (or claim to have) similar ranges?

There's something called a variometer (google it and see how it works) that can go over a wide range of inductance (two coils, one on an axis, they could add or cancel depending on the angle of one in relation to the other), but it seems doubtful that a slug-tuned coil could do that.
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Old 31st July 2018, 07:46 PM   #309
jackinnj is offline jackinnj  United States
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Quote:
Originally Posted by benb View Post
There's something called a variometer (google it and see how it works) that can go over a wide range of inductance (two coils, one on an axis, they could add or cancel depending on the angle of one in relation to the other), but it seems doubtful that a slug-tuned coil could do that.
Also -- Collins R-390 used a "Permeability Tuned Oscillator" which was quite linear.
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Old 31st July 2018, 08:35 PM   #310
w5jag is offline w5jag  United States
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They are indeed. Everyone should own an R-390, R-390A at least once, if your back is in good shape. Sadly, I am old enough to remember when you could get those Collins PTO's from mil rigs as cheap surplus.

I think these Toko SMD coils are the only shielded SMD part in production. Relevant to this trainwreck, these coils are not totally useless - they might make an okay 45 MHz IF transformer. Would take a lot of C, but it would probably be okay for amateur grade stuff. A lot easier than winding a toroid.

There is probably surplus stuff on eBay that would be better for HF.

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