UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV 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 29th Oct 2018, 1:09 pm   #1
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
Default Homebrew RF power meter mark 2

This one is a prototype. I screwed the board up on this cycle (SMA footprint) but it works and is dirt cheap (under £10!). Decided to put together a proper RF power meter as most of the stuff from China is junk. That doesn't mean the parts are junk but the way they put them together is.

This is an evolution of the W7ZOI power meter here: https://www.vintage-radio.net/forum/...d.php?t=144088 ...

The original one suffered from a few problems. That was mainly due to the layout. Secondly it was poorly decoupled. Thirdly it was badly constructed. Fourthly, the output transform circuit actually pretty much made it useless. It was a hack job.

Now we have version 2...

Click image for larger version

Name:	7D9D3340-BF40-426E-A905-6D1044FE1EB7.jpg
Views:	292
Size:	92.4 KB
ID:	171755

Calibration is done as follows: Apply 0dBm. Record the voltage on the DMM here to get the 0dBm intercept. Stick a 20dB attenuator in line (or crank generator down by 20dBm) and record the difference in voltage. This gives you a y=mx+b transformation.

Click image for larger version

Name:	CBE3E83F-8CE7-48D6-AEFA-BD236D86FE96.jpg
Views:	187
Size:	88.6 KB
ID:	171756

Calibration is pretty much 100% linear and it has 60dB dynamic range which is good for most tasks with suitable attenuators and/or taps.

Click image for larger version

Name:	linearity-capture.png
Views:	117
Size:	25.3 KB
ID:	171758

Currently waiting for a suitable signal generator to appear so I can check it across a wider frequency range than my AWG kicks out. It's flat across 2-25MHz though.

The board is designed to fit inside a specific hammond enclosure with a pigtail on one end. Once I've fixed the boards and get hold of a signal generator, I may be offering this as a kit. Time will tell!

Edit: also to note, the output buffer and filter is designed to respond fast enough to allow a sweeping signal to be applied from the generator. This allows you to use this to do antenna (with return loss bridge) and filter sweeps with a sweeping generator and get a log-log output on a scope this turning it into a scalar network analyser too!

Last edited by MrBungle; 29th Oct 2018 at 1:25 pm.
MrBungle is offline  
Old 30th Oct 2018, 11:57 am   #2
vosperd
Hexode
 
vosperd's Avatar
 
Join Date: Oct 2007
Location: Bristol, UK.
Posts: 440
Default Re: Homebrew RF power meter mark 2

Hi, I built up one of these using strip board and through hole components. I can't say that I did any exhaustive tests or calibration but it seemed to give sensible readings with my FT817 on 80M.
if a kit ever becomes available I, for one, would be interested. Much tidier than strip board.
Don m5aky
vosperd is offline  
Old 30th Oct 2018, 7:59 pm   #3
Bazz4CQJ
Dekatron
 
Bazz4CQJ's Avatar
 
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,923
Default Re: Homebrew RF power meter mark 2

Mmm...maybe you could offer the board as an individual item?

B
__________________
Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.
Bazz4CQJ is offline  
Old 31st Oct 2018, 8:42 am   #4
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
Default Re: Homebrew RF power meter mark 2

That’s a possibility. They’re not exactly expensive to get done so I don’t mind ordering 100 or so (probably never get rid of that many!). Past the board and the AD8307 though, the entire parts inventory costs less than £1
MrBungle is offline  
Old 31st Oct 2018, 9:43 am   #5
ex seismic
Heptode
 
Join Date: Sep 2009
Location: Tonbridge, Kent, UK.
Posts: 685
Default Re: Homebrew RF power meter mark 2

I'd have a couple!

Gordon
ex seismic is online now  
Old 31st Oct 2018, 4:07 pm   #6
Bazz4CQJ
Dekatron
 
Bazz4CQJ's Avatar
 
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,923
Default Re: Homebrew RF power meter mark 2

Yes, the whole kit makes sense, as does taking two (my SMD skills may need the first just for practice ). Keep us posted.

B
__________________
Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.
Bazz4CQJ is offline  
Old 31st Oct 2018, 5:57 pm   #7
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
Default Re: Homebrew RF power meter mark 2

Will do. Waiting for another board run now after I screwed the last one up

If your SMD skills are a bit iffy, it's worth hitting a cheap £1 SMD practice kit for aliexpress/ebay/banggood. The one with the circle in the middle. Buy two as they don't always get the bits right. Just need some fine solder, flux pen, tweezers and some isopropyl alcohol and a paint brush to clean it with and done. Can also recommend a pint down the pub first to iron out any jiggly hands

Without alcohol I can solder an 0603. With alcohol, 0402

Edit: I'll post some applications in here as well.
MrBungle is offline  
Old 1st Nov 2018, 4:14 am   #8
Terry_VK5TM
Nonode
 
Terry_VK5TM's Avatar
 
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
Default Re: Homebrew RF power meter mark 2

I can't even see 0402, alcohol or not

A friend sent me a kit to repair one of my radio transceivers which I dare not open (the kit, not the radio).

I can see a pcb and what looks like specs of fly dirt inside (which I'm reliably told are actually the components).
__________________
Terry VK5TM
https://www.vk5tm.com/
Terry_VK5TM is offline  
Old 1st Nov 2018, 9:19 am   #9
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
Default Re: Homebrew RF power meter mark 2

I will say that I lose 50% of the parts when I do it. They just ping off the tweezers never to be seen again, followed by some swearing.

For my hand soldered designs I only go down to 0805.

With a bit of practice I don’t want to go back to through hole now. So much easier to rework SMD stuff.
MrBungle is offline  
Old 2nd Nov 2018, 10:24 am   #10
vosperd
Hexode
 
vosperd's Avatar
 
Join Date: Oct 2007
Location: Bristol, UK.
Posts: 440
Default Re: Homebrew RF power meter mark 2

With smd I find complete kits are better for me than bare pcbs.
Thr ICs are easy enough to source but the resistors and capacitors etc for a one off can be a problem. I find all you need is never available from a single source. They are cheap enough to buy in quantity but sometimes you can be paying a couple of pounds to buy 10 or 100 when you only need one or two of a praticular value.
I can manage the AD8307 pin spacing but I think the next size down the pin spacing is half that which is a problem.
Don m5aky
vosperd is offline  
Old 2nd Nov 2018, 11:23 am   #11
Terry_VK5TM
Nonode
 
Terry_VK5TM's Avatar
 
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
Default Re: Homebrew RF power meter mark 2

Quote:
Originally Posted by vosperd View Post
I can manage the AD8307 pin spacing but I think the next size down the pin spacing is half that which is a problem.
Don m5aky
As long as the pcb has a proper solder mask around the pads, it is not that hard - flood solder the pins and use flux and desolder wick to remove the excess.
__________________
Terry VK5TM
https://www.vk5tm.com/
Terry_VK5TM is offline  
Old 2nd Nov 2018, 1:25 pm   #12
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
Default Re: Homebrew RF power meter mark 2

Indeed. They're dead easy. I've done down to MSOP8 / 0603 now regularly. My eyesight isn't that great either. Years of avoiding it turned out to be a fuss over nothing.

In fact the best thing is that it's pretty easy to get the smaller parts off without trashing the board which is difficult on older PTH boards with some of the multi pin parts. I usually snipped off IC leads and then desoldered the pins individually to avoid this.

No need with these!

With respect to parts prices, I am using LCSC and they are incredibly cheap. I think I paid 10p for or so for 100 0805 1% resistors. Sometimes it's hard to get enough in the basket to get past the small order charge (which goes away at $10)
MrBungle is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 1:05 pm.


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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.