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.

Reply
 
Thread Tools
Old 4th Mar 2019, 6:33 pm   #1
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,084
Default Hammond box mounting and RF tightness

I have picked up an old project again, the spectrum analyser, this week.

I have designed a 40dB post filter IF amp strip and built it manhattan style. This has been mounted in the lid of a Hammond box with the panel mount SMA for RF ports and FT cap for power sticking up from the top. The hammond box was picked so it was a fraction of the shortest wavelength long (it won't hit more than about 250MHz)

Now the question comes on how am I going to mount this in a chassis? I didn't think about this first typically and decided to wing it, perhaps stupidly ... I figure I can drill holes through the bottom of the "tub" part of the Hammond box and use M3 hardware to bolt it down to the chassis so:

bolt, washer, hammond box base, washer. At this point I'll have a Hammond box with a couple of bolts sticking out of the bottom. Then when it comes to set them in place I can unscrew the bolt, then gently drop it through the 1.6mm aluminium chassis and bolt underneath. I will end up with bolt, washer, hammond box base, washer, chassis sheet, washer, nut. This should give reasonable ground connection as well and allow me to open a module to adjust or fix something without getting a headache.

Can anyone think of any problems with this approach before I go and drill holes in my hammond box?
MrBungle is online now   Reply With Quote
Old 4th Mar 2019, 6:42 pm   #2
merlinmaxwell
Dekatron
 
merlinmaxwell's Avatar
 
Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 8,326
Default Re: hammond box mounting and RF tightness

IMHO that will be fine, a screw in each corner for tidiness and a wee bit more grounding perhaps.
__________________
Cats have staff, it's dogs that have owners.
merlinmaxwell is offline   Reply With Quote
Old 4th Mar 2019, 7:03 pm   #3
Scimitar
Hexode
 
Scimitar's Avatar
 
Join Date: Oct 2015
Location: Gloucestershire, UK.
Posts: 466
Default Re: hammond box mounting and RF tightness

Rivnuts in the bottom.
Scimitar is online now   Reply With Quote
Old 4th Mar 2019, 7:15 pm   #4
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,084
Default Re: hammond box mounting and RF tightness

Never knew those existed - thanks for the suggestion!
MrBungle is online now   Reply With Quote
Old 15th Mar 2019, 10:28 pm   #5
Philips210
Octode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 1,544
Default Re: Hammond box mounting and RF tightness

Hi.

The Rivnut is a good suggestion by Scimitar. In the past, I used something similar for fixing to aluminium chassis assemblies. I think they were known as Clinchnuts.

Regards,
Symon.
Philips210 is offline   Reply With Quote
Old 15th Mar 2019, 10:40 pm   #6
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,084
Default Re: Hammond box mounting and RF tightness

I found some of them on ebay in the end - they are very good!
MrBungle is online now   Reply With Quote
Old 15th Mar 2019, 11:27 pm   #7
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 7,113
Default Re: Hammond box mounting and RF tightness

There could be logic in mounting your Hammond box [assuming it provides all-round shielding] essentially 'free-floating' from the main chassis, using suitable standoffs and Nylon-66 nuts/bolts, then taking the RF/DC ins and outs to the rest of the circuit via coax and feedthroughs.

I did something similar in a piece of kit some time back, where the need was to isolate a lump of fast digital-circuitry [which lived in the shielded box] from the RF-chassis which had a Kilowatt or so of power flying around on transmit but also needed to hear 0.1Microvolt-or-better on receive.

"Floating" the digital stuff in its box was the only way I found to reliably stop it locking-up on transmit or injecting crud into the front-end on receive.
G6Tanuki is offline   Reply With Quote
Old 16th Mar 2019, 12:05 am   #8
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,084
Default Re: Hammond box mounting and RF tightness

Interesting. I am actually having some noise trouble with this. The power sensor is an AD8307 and I'm using a 12-bit MCP3208 ADC to pull the power reading off it. Spent two days trying to work out why I couldn't get a totally linear reading, playing with the ADC and the software and it turns out that the AD8307 is picking up the switching hash off my LED desk lamp! I didn't work that out until Sat when I got some time to work on it in daylight. I only tested the power sensor standalone in daylight too. Power sensor is now going in its own box!
MrBungle is online now   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 10:29 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.