UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Closed Thread
 
Thread Tools
Old 31st Oct 2018, 1:00 am   #81
FRANK.C
Heptode
 
FRANK.C's Avatar
 
Join Date: Feb 2006
Location: Roscommon, Ireland
Posts: 600
Default Re: Building the 'Minimod' AM modulator-questions!

Hi David and Terry
It is just any PCB manufacturer that I have used ask for the dimensions of the PCB before they quote a price. This is before the gerber files are uploaded. If I were ordering I would quote the 74.9 X 74.9 mm as I know of a case where the quoted dimensions were 0.5 mm larger that the board outline and the company refused to make the PCB as the quoted dimensions did not match the board outline. I think they were afraid that the files were inaccurate or the wrong ones.
I have used PCBway.com and ALLpcb.com I have no connection with them. Both give good service.

Frank
FRANK.C is offline  
Old 31st Oct 2018, 2:41 am   #82
Terry_VK5TM
Heptode
 
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 898
Default Re: Building the 'Minimod' AM modulator-questions!

Yes, some 'manufacturers' can be very picky.

In a lot of cases, I have found these ones to be aggregators, ie, they accumulate files from a number of people and send them off to be made elsewhere.

I've steered clear of AllPCB now, the last few quotes I have had from them have been up to 50% dearer then my regular place (that is all up price including freight).

PCBway at least does allow you to email them the gerbers to get a quote rather than use the online quote form.
__________________
Terry VK5TM
https://www.vk5tm.com/
Terry_VK5TM is online now  
Old 10th Nov 2018, 3:53 pm   #83
crackle
Dekatron
 
crackle's Avatar
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 3,052
Default Re: Building the 'Minimod' AM modulator-questions!

Quote:
Originally Posted by crackle View Post
I was wondering if someone could please explain more about changing the value of R2. Is this recommended change to reduce the extra output from Q1 or is it to help boost the level from Q1, I didn't quite understand it.
I was wondering if anyone could please make any comments to help me understand why this was changed to 2.2k.
I substituted a trimmer in place of R2 and found the best performance was when it was set to 5k.

I can also confirm that my issue with frequency drift (it was over 2kHz) was caused by the RF inductors supplied by Spectrum communications some time, they must have supplied me from a duff batch.
I have reverted back to using an inductor taken from an old transistor radio, (yellow colour ferrite, full width, not the tiny slug type.)
To assist in setting the frequency I have added a very tiny trimmer, probably less than 20pf. This gives a finer adjustment. With this combination the frequency drift, over a 2 hour period, is now less than 400 Hz either side of the set frequency.
Mike
__________________
BVWS Member
The KB Museum

My collection in the Radio Museum

Last edited by crackle; 10th Nov 2018 at 4:10 pm.
crackle is offline  
Old 10th Nov 2018, 5:13 pm   #84
Ian - G4JQT
Heptode
 
Ian - G4JQT's Avatar
 
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 910
Default Re: Building the 'Minimod' AM modulator-questions!

Mike, I must have missed your question the first time - sorry.

The 10k was chosen in the fist instance because that's what similar 2N3819 circuits with an NPN buffer used in various books. When I changed the FET to the BF256, I did just what you did, I put a pot there to see what happened. On the three I tried this on I found about 2.4k seemed optimum, but there really wasn't much difference.

Your 400Hz/2 hour frequency drift is probably as good as I've ever had. The only time you'll notice it is if you've chosen a channel with a strongish signal on it already, which you wouldn't chose to do anyway.

Veroboard shouldn't make much difference at these frequencies, but it's important to cut/separate any stray strips.

After I worked on yours and compared it to mine, the video I sent you didn't show any significant difference between the two in modulation quality when both were received on an Ekco A23 or a Sony ICF-SW7600.

Regards,

Ian
Ian - G4JQT is offline  
Old 10th Nov 2018, 5:26 pm   #85
crackle
Dekatron
 
crackle's Avatar
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 3,052
Default Re: Building the 'Minimod' AM modulator-questions!

Hi Ian
Thanks for your reply.

Mike
__________________
BVWS Member
The KB Museum

My collection in the Radio Museum
crackle is offline  
Old 12th Nov 2018, 9:37 pm   #86
JohnBG8JMB
Tetrode
 
Join Date: May 2006
Location: Poole, Dorset, UK.
Posts: 69
Default Re: Building the 'Minimod' AM modulator-questions!

HIGHER POWER

Can anyone advise of a higher power [sufficient to cover the house] version?

preferably no crystals/microprocessors/arduinos...

JohnB
JohnBG8JMB is offline  
Old 12th Nov 2018, 11:54 pm   #87
Ian - G4JQT
Heptode
 
Ian - G4JQT's Avatar
 
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 910
Default Re: Building the 'Minimod' AM modulator-questions!

I built one and had it published in the BVWS Bulletin Autumn 2000, but it uses a MW channel crystal with an output power that easily covers an average home and garden. It uses two BD131s and a BD132.

I've also designed one using a IRF510 as the output device which is series modulated with a TDA2003 audio amp and a small mains (mod) transformer, but that also uses a MW channel crystal. It covers the house and garden with just a telescopic whip.

But to be honest, these days with fewer stations on MW any old crystal can be used in the many gaps between stations. I think 1MHz crystals are quite cheap, but it's a nasty 1 kHz away from a channel!

I really wouldn't advise using a MiniMod type VFO without extensive buffering and screening for a more powerful circuit - more trouble than it's worth.

As long as you keep the antenna very short and signal strength down, a couple of hundred mW PA will have the required coverage just for your property. Remember that the antennas will have a very, very low efficiency so you're unlikely to attract attention.

Have a dig around the internet. There are a few designs that will do what you want, but are best not mentioned here...

Ian
Ian - G4JQT is offline  
Old 13th Nov 2018, 10:21 am   #88
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,685
Default Re: Building the 'Minimod' AM modulator-questions!

The 5-page article to which Ian (AKA 'Nick Sparks' whose cover is now blown!) refers, can be found here - pages 10 - 14:

https://www.bvws.org.uk/publications...letin_25_3.pdf

It radiates 500mW - 1 Watt depending on how it's set up, so we need to be mindful of the forum rule on discussing what are popularly called 'pantry transmitters', which states:

Quote:

F. Prohibited Discussions..

Small low powered transmitters with an output of less than 100mW e.i.r.p. for home use may be discussed in this forum.
The moderators will use their discretion as to what is acceptable.

Unquote.

Certainly an interesting design with a detailed description, including the setting up procedure, though given the time that's elapsed since it was published, sourcing some of the components might pose a challenge, albeit not insurmountable. Just a thought - given that the mini-mod is powered by a PP3 battery and is portable, which not just move it within range of whichever receiver on which it's wished to use to listen to its output - or even build more than one mini mod?
__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is offline  
Old 13th Nov 2018, 11:36 am   #89
terrykc
Heptode
 
terrykc's Avatar
 
Join Date: Nov 2010
Location: North Hykeham, Lincolnshire, UK.
Posts: 502
Default Re: Building the 'Minimod' AM modulator-questions!

Quote:
Originally Posted by JohnBG8JMB View Post
Can anyone advise of a higher power [sufficient to cover the house] version?
John, in Post #52, Mike (Crackle) claims to have covered the whole house simply by connecting his Minimod to the central heating pipes!

A lot simpler than what I was going to suggest - a wire running the length or width of the house, whichever is more convenient, at ground floor ceiling level (or floor level on the first floor).

It can be surprising how far a little power from a low power transmitter can go.

I built a one transistor VHF modulator in the 60s that covered our long workshop at the back of the building, where it was located but also gave excellent coverage of the shop downstairs at the front of the building.

The aerial? None! It relied entirely on radiation from the one coil and, unlike previous attempts, this one was so stable that it could just lie on the bench. It took a finger closer than half an inch from the coil to de-tune it!
__________________
Terry
When all else fails, read the instructions.
terrykc is offline  
Old 13th Nov 2018, 11:52 am   #90
ThePillenwerfer
Octode
 
ThePillenwerfer's Avatar
 
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 1,208
Default Re: Building the 'Minimod' AM modulator-questions!

How about https://www.vintage-radio.net/forum/...d.php?t=141464

The circuitry seems very similar to the commercial Spitfire so should be good.
__________________
"Experts are only good at one thing: explaining why something will not work!"
ThePillenwerfer is online now  
Old 13th Nov 2018, 12:10 pm   #91
Ian - G4JQT
Heptode
 
Ian - G4JQT's Avatar
 
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 910
Default Re: Building the 'Minimod' AM modulator-questions!

Quote:
Originally Posted by terrykc View Post
A lot simpler than what I was going to suggest - a wire running the length or width of the house, whichever is more convenient...
Careful when significantly extending the MiniMod antenna. A point will be reached where the antenna tuned circuit won't peak unless you reduce the value of L2 and/or C13.

I have not tried the following, and this is only an idea:

The current through L2 is limited by R8 390R to stops it saturating on modulation peaks. If L2 (~90uH) is rewound on a ferrite ring or small rod with a few coupling turns and C13 made variable, it may be possible to get a bit more power out. But it won't be much more; the LM386 is probably already near its maximum output.

Ian
Ian - G4JQT is offline  
Old 13th Nov 2018, 6:03 pm   #92
Ian - G4JQT
Heptode
 
Ian - G4JQT's Avatar
 
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 910
Default Re: Building the 'Minimod' AM modulator-questions!

Forgot to add too late too edit my post:

The point of rewinding L2 as a physically larger inductor is so that R8 can be removed. The larger inductor is very unlikely to saturate. Not sure how the LM386 will react though!
Ian - G4JQT is offline  
Old 14th Nov 2018, 9:37 am   #93
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,685
Default Re: Building the 'Minimod' AM modulator-questions!

Quote:
Originally Posted by ThePillenwerfer View Post
How about https://www.vintage-radio.net/forum/...d.php?t=141464

The circuitry seems very similar to the commercial Spitfire so should be good.
It looks a great design, not that I can claim to understand it!

If anyone fancies having a go at making the PCB, the artwork for the mask, correctly sized, is attached.

I make the number of 0.8mm holes that need to be drilled as being 225.

Having drilled more than 1,400 holes on sixteen Mini-Mod PCBs in recent weeks, I'll sit this one out!
Attached Thumbnails
Click image for larger version

Name:	PCB Mask for low power synthesised MW TX_edited-1.jpg
Views:	65
Size:	97.8 KB
ID:	172786  
__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is offline  
Old 28th Dec 2018, 12:36 pm   #94
Ian - G4JQT
Heptode
 
Ian - G4JQT's Avatar
 
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 910
Default Re: Building the 'Minimod' AM modulator-questions!

Quote:
Originally Posted by David G4EBT View Post

Having drilled more than 1,400 holes on sixteen Mini-Mod PCBs in recent weeks [...]
Just curious David, but how many boards have you made all together? I must have built and dispatched about 30 MiniMods in total over the past few years. There must be getting on for a dozen built by forum members, so wonder how many there are out there, and how often do they really get used I wonder?

Ian
Ian - G4JQT is offline  
Old 28th Dec 2018, 2:26 pm   #95
FRANK.C
Heptode
 
FRANK.C's Avatar
 
Join Date: Feb 2006
Location: Roscommon, Ireland
Posts: 600
Default Re: Building the 'Minimod' AM modulator-questions!

Hi Ian
Just so you an add them to your total I have built 3 minimod's 2 for myself and 1 for a friend. They work extremely well and are in occasional use.

Frank
FRANK.C is offline  
Old 28th Dec 2018, 8:10 pm   #96
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,685
Default Re: Building the 'Minimod' AM modulator-questions!

Quote:
Originally Posted by Ian - G4JQT View Post
Quote:
Originally Posted by David G4EBT View Post

Having drilled more than 1,400 holes on sixteen Mini-Mod PCBs in recent weeks [...]
Just curious David, but how many boards have you made all together? I must have built and dispatched about 30 MiniMods in total over the past few years. There must be getting on for a dozen built by forum members, so wonder how many there are out there, and how often do they really get used I wonder?

Ian
"How many have been built and are used" is a good question, the answer to which is anyone's guess!

Back in 2015, I made 3 mini mods - one for myself, one for my son and one for a friend.

I'd used your original PCB layout as a guide to design my own PCB and posted that on the forum at post #85 in this (now closed) thread:

https://www.vintage-radio.net/forum/...t=98221&page=5

I posted the layout for anyone to use if they wished, not intending to make boards for other forum members due to time constraints. I'd suggested that anyone wishing to make a PCB who didn't have UV facilities might wish to try the 'toner transfer' method, which only calls for a normal laser printer. Having transferred the toner to the PCB laminate, the board can be etched and drilled.

I did however end up making ten boards for forum members back in 2015 in addition to the three Mini-Mods I'd made myself.

That thread went to sleep in August 2015, then on 8 Sept 2018, this thread brought the Mini-Mod back into the limelight. I updated the earlier PCB design, still using your original component placement Ian, but leaving more copper on the board to reduce etching time, and to give the best chance for anyone who doesn't have a decent mini-drill and stand, to allow a bit of leeway for misaligned holes.

I built another Mini-Mod using that updated PCB layout to make sure it worked and was stable, which proved successful. Since 2015, the UV ‘dry film’ technique has come to prominence which requires negative artwork. For anyone who still uses positive resist boards or wanted to try the toner transfer method, I posted the positive mask as well as the negative one, in post #65 in this thread.

Relatively few people had contributed to this thread at the time, and I was asked if I'd consider making a few PCBs. I said I could cope with half a dozen, which would have more than covered the interest shown in forum posts in this thread, so I made six and said that would be it. However, as with any thread, there is an unknown number of 'lurkers' who read threads but don't post. I don't use the term 'lurker' disrespectfully - that's the way it is with any forum. As a result, I received many requests by PM and just had to draw the line.

All told, with those I made back in 2015, I've made four Mini Mods and 33 PCBs.

This makes no sense for me as DIY PCB production is labour intensive, can't possibly be put on as commercial footing, and that's not what I'm about - I'm a hobbyist, pure and simple, enjoying my 25th year of retirement in my twin hobbies of vintage radio and woodturning/woodworking. I like to gain inspiration ideas and advice from others, and to share my own ideas for others to maybe replicate or improve upon.

Ordinarily, I have little 'hobby time' but at end of May I had a knee replacement operation, so I was 'grounded' for several weeks. As I'm a fidget, to keep me occupied, I etched a quantity of PCBs for the FM/AM converter and built and tested some boxed-up converters as well as Mini-Mod PCBs. I'd like to think that the PCBs have all been built and put into use rather than requested and put in a drawer to be built sometime/never. I know that some have been successfully built as I've had follow-up responses.

I believe that there are firms who will produce PCBs at very low cost to a very high standard, but to do so, they require ‘Gerber Files’ which are a complete mystery to me and will remain so. At post #74 in this thread, Terry, VK5TM very kindly converted my PCB layout to a Gerber File and attached a jpeg of the component layout. Anyone wishing to get a PCB (or a batch of PCBs) made professionally to that design is welcome to do so. As far as I’m concerned, it’s in the public domain. Ian conceived and designed the Mini-Mod and the original PCB layout – I just copied his component layout down to the last hole, and re-jigged the artwork for my own needs.

The Mini-Mod is certainly a great little performer and an enjoyable project to build and use.

I’d like to reiterate that while I've been very pleased to have helped several forum members with PCBs, I can’t cope with making any more for this or any other project due to time constraints.
I'm almost fully recovered from my knee replacement op, so I'm up and about, gadding about all over the place - Liverpool, London, Essex, Nottingham, York, fully engaged in family life as a husband, father and grandfather, and that's as it should be!

Waffled David, duty windbag.
__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is offline  
Old 28th Dec 2018, 9:01 pm   #97
Bryan M
Pentode
 
Bryan M's Avatar
 
Join Date: Jul 2009
Location: Brightlingsea, nr. Colchester, Essex, UK.
Posts: 137
Default Re: Building the 'Minimod' AM modulator-questions!

My Minimod (using your board, David) was to have been a Christmas project but my other life got in the way. A couple of weeks should see me clear of such distractions.
Happy new year, all.
Bryan
Bryan M is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 1:40 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.