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Old 1st Jan 2021, 9:59 pm   #41
baza100
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Default Re: First project (mini mod)

Hello again, Totally scrapped the minimod I made first. Tried again and halfway through I realised | had started back to front. This is the third time and I think it is looking good. Should be able to try it in the next couple of days. Found it very therapeutic and interesting going over my mistakes and rectifying them. Will let you know if it works. Thanks
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Old 1st Jan 2021, 10:21 pm   #42
Ian - G4JQT
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Default Re: First project (mini mod)

Quote:
Originally Posted by baza100 View Post
Hello again, Totally scrapped the minimod I made first. Tried again and halfway through I realised | had started back to front. This is the third time and I think it is looking good. Should be able to try it in the next couple of days. Found it very therapeutic and interesting going over my mistakes and rectifying them. Will let you know if it works. Thanks
Those mica capacitors look quite expensive, but ideal. Make sure that whatever FET you've used the GSD are in the right place as there are different configurations. S/D often don't matter, but the gate is not the centre lead in the later recommended FET. Your gate is the centre lead in your Veroboard diagram. This applies to the 2N3819, but I later changed that to a BF256 as they have more predictable characteristics but the gate of that FET is not in the centre. (This is all discussed in the long MiniMod thread elsewhere on the forum.)

Good luck with the smoke test!

Ian

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Old 1st Jan 2021, 11:27 pm   #43
baza100
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Default Re: First project (mini mod)

Thanks for the quick reply. I have fitted the BF256 Hopefully I have fitted it right Are the legs in the right holes? Thanks
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Old 2nd Jan 2021, 10:24 am   #44
Ian - G4JQT
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Default Re: First project (mini mod)

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Originally Posted by baza100 View Post
Thanks for the quick reply. I have fitted the BF256 Hopefully I have fitted it right Are the legs in the right holes? Thanks
It's hard to see clearly, but the gate needs to go to R1 and D1. Looks like you might have the drain going to R1 and D1.

Also make sure that with Verobard all the required cuts are completely cut, and also that no fine slithers of cut track touch adjacent tracks.

I find Veroboard layouts are much harder than "Manhattan" board construction, "ugly" construction or even single sided board and underneath wires following what would be the track - which is my favoured technique!


Good luck.
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Old 2nd Jan 2021, 9:41 pm   #45
Stuart R
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Default Re: First project (mini mod)

Hello Barry,

Don't give up!

When working with Veroboard, I've sometimes tried to take a 'brass rubbing' of the track side of the Veroboard. Then try sizing-up the components on that and working out where to put the track breaks and linking wires, comparing at all times to the circuit diagram. It is all to easy to get things up-side down or back-to-front. You're not the first!

My first introduction to Veroboard was after reading a 'Fun with Electronics' Children's book by Usborne. The illustrations in that book were quite deceptive - the first example, shows a 7x11 hole board being as large as a child's hand! I was surprised it all looked so much smaller when I finally bought my first small sheet. It was very easy to create accidental solder bridges between tracks or not clear one of the copper strips entirely.

I've got a Mini-Mod that I am yet to finish-off, so here are a couple of readings that might be useful for comparison. Mine isn't on Veroboard, it's on a ready made PCB which made life very easy. I don't think the PCB is available any more.

My inductors, L1 and L2 are marked with stickers saying 90µOL, so it sounds like you have the same ones.

With a fresh PP3 battery, I've got 10.48V across the battery terminals when the Mini-Mod is connected.

I have heard my Mini-Mod running; things may still need some adjustment as it sounds a little distorted, but that's probably the audio level coming out too high from the back of my Stereo.

I have it tuned to 1287kHz, but for the purposes of these measurements I removed the audio input and had no antenna wire on the Mini-Mod's RF output.

When running in this state, the DC current measurement (my multimeter on mA range and in series between battery + terminal and Mini-Mod's + power input terminal) is 12.6mA. My Mini-Mod also has a 'Power On' LED, so that will account for a a bit more current, your reading may be a little bit lower.

Some DC measurements from my Mini-Mod. The negative lead of my multimeter was left connected to the negative terminal of the battery and I probed around the component pins with the positive lead. Take care not to accidentally short-circuit your meter probe across the legs of adjacent components or the case of the BC109 transistor.

IC1 - With the notch uppermost.
Pin 1 1.47V (To the left of the Notch, then count down to pin 4)
Pin 2 0.01V
Pin 3 0.01V
Pin 4 0.01V
Pin 5 5.27V (This is opposite pin 4, then start counting up to pin 8)
Pin 6 10.45V
Pin 7 5.27V
Pin 8 1.47V (To the right of the notch)

Q1 BF256B
G -3.34V
S 0.01V
D 8.75V

Q2 BC109

E 0.01V
B -0.35V
C 3.81V

L1 where it joins with C1 and C2 0.01V
L1 where it joins with C3 and Q1 S 0.01V

L2 Primary where it joins with R8 4.05V

I am no expert. Maybe these numbers will help you or Ian who is doing a great job via 'remote control'.

Kind Regards,

Stuart.
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Old 8th Jan 2021, 11:04 pm   #46
baza100
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Default Re: First project (mini mod)

It is only me again. minimod not working only get a very small signal when I put it on top of the radio.Took the BF256 out and just want to confirm is this the right pin read out so I can solder it in right? Thanks Barry
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Old 9th Jan 2021, 1:39 am   #47
ThePillenwerfer
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Default Re: First project (mini mod)

The Gate is right but the Drain and Source are reversed, ie the Source is in the middle.
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Old 9th Jan 2021, 11:09 am   #48
Ian - G4JQT
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Default Re: First project (mini mod)

Quote:
Originally Posted by baza100 View Post
It is only me again. minimod not working only get a very small signal when I put it on top of the radio.Took the BF256 out and just want to confirm is this the right pin read out so I can solder it in right? Thanks Barry
With the MiniMod within a yard of the radio with about a yard of antenna wire connected:
  • Using L1 can you tune the signal to the middle of MW? If so it suggest L1 and Q1 are working. (Please only use a plastic or wooden tool.)
  • Using L2 can you peak the signal so that any noise is lost under the MiniMod carrier?
  • When feeding the audio input from the headphone socket of your audio player is there any modulation?
The voltages given by Stuart R seem about right from a 10V supply. They'll be a little lower if you are using a 9V battery. (The negative voltages are probably caused by a bit of RF getting into his meter.)

Double check that the component values you have are correct. The markings on some capacitors in particular can be confusing. Also ensure that the correct windings of L1 and L2 are used.

Let us know how you get on.

Ian
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Old 9th Jan 2021, 4:02 pm   #49
baza100
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Default Re: First project (mini mod)

Tuned the radio into radio Sheffield. The strongest signal I can get. Put the minimod on top of the radio, it works fine. Move it a couple of inches away and it stops working. Have I got the minimod tuned to the same wave as radio Sheffield? Is this swamping the signal from the minimod? If so do I have to tune L1 to fine a clear part of medium wave? Thanks again Barry
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Old 9th Jan 2021, 4:45 pm   #50
Ian - G4JQT
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Default Re: First project (mini mod)

Are you trying to tune the MiniMod to the same frequency as R Sheffield? No.

Tune your radio somewhere in the middle of the medium wave band where there are no stations. This is easier during the day as European stations fade in during the evening and night. You want the MiniMod to operate on a clear frequency not on top of or adjacent to another station.

Put the MiniMod and its one yard-ish wire antenna close to the radio and gently turn L1 until you can hear the carrier and modulation on the radio - it might be quite weak. Then gently turn L2 until it peaks the MiniMod signal. (L1 and L2 must be tuned to the same frequency.) There cores should be at about the same depth - probably just below the top of the metal can. If you cannot peak L2 or you cannot find the signal when adjusting L1 check both C1 and C13 are the same value - 270pF, although 250pF to 300pF should still tune on MW.

I've posted below the instructions I include when I make them and send them out. (I have none at the moment and doubt I'll be making any more.)

Ian
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Old 11th Jan 2021, 9:54 pm   #51
baza100
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Default Re: First project (mini mod)

Hello It is me again. Okay getting somewhere. I can get a perfectly clear signal that swamps the station and is absolutely brilliant. It only works if i put the Ariel lead to L2 pin 4 or pin 6. Cannot get anything out of the earth side pin 3 or C13. Maybe this is because i couldn't tune L2 in. Tried wooden cocktail stick, piece of wood filed down to the right size, it would not budge. Finally tried screw driver, it just broke it but still would not turn. Got spare one just about to solder it in, it turns freely. If I tune L2 in I should be able to get something out of the earth side of C13. Thanks sorry for the long saga Barry
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Old 11th Jan 2021, 10:25 pm   #52
Ian - G4JQT
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Default Re: First project (mini mod)

Why are you still tying to "swamp" stations? You shouldn't need to swamp any stations if you tune L1 to a gap between stations as I described.

The circuit diagram shows the antenna connected to the 'hot' side of C13 not the earth. I don't know why you're trying to connect the antenna there. Don't connect the antenna to the earthed side becasue it won't radiate. You may connect an earth connection or a counterpoise to the earth (-ve) of the minimod which may extend range. But remember to retune L2 slightly if you do that.

If this is your first project, it is quite an ambitious one - especially using Veroboard rather than the much easier "ugly construction" or "Manhattan construction" or other simple techniques. You've done well to get it working in this case.

(You can unscrew the cores and turn them round if you break the slots. They have slots at both ends.)
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Old 11th Jan 2021, 10:51 pm   #53
baza100
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Default Re: First project (mini mod)

Thank you all for your advice. I am sorry for being a novice and a pain. Admin can close thread now. Thank you again Barry
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