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Proud Mary

Sat May 20 2017, 11:48PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Sulaiman, the BAT15s came super quick in the post today, and they are even smaller than in my nightmares!

My first step has been to send off for a better magnifying glass!

Sulaiman

Sun May 21 2017, 08:51AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

O O
\_/

can't say I didn't warn you

At work, stupid-small smd components have come to be known as 'fleas'
I could not understand why for months, I thought it was because of the size only,
until I found how easy it is for them to leap over a foot through the air when handled by tweezers,
they usually land in a pile of something then hide

I remember my first job in the early '70's when an older colleague was complaining to me about
having had to move from 0.15" veroboard to the stupidly small pitch of 0.1" due to dil ICs
... now I'm the grumpy old guy !

I think that miniaturisation is just a sneaky way of removing older, higher-earning, poorer-sighted employees
to make way for younger, cheaper, more energetic youth.
It's a conspiracy !

Proud Mary

Mon May 22 2017, 06:30PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Here is the circuit diagram of my first UHF/SHF project.

The author, Mr Paul Wade, N1BWT, relates that he took the circuit of an existing VHF VSWR meter which was good up to 450MHz, and effectively translated it into the UHF/SHV domain by specifying all components as chips.

N1BWT comments: "Now that we've gone to the effort of using chip components and making the VSWR bridge as small as possible, how much have we gained? With good 50Î© SMA terminations at J2 and J3, return loss was greater than 30 dB (VSWR > 1.2) from 10 MHz through 2304 MHz, while at 3456 MHz, the return loss was 22 dB (VSWR = 1.9), so performance is degraded but still usable. However, at 5760 MHz it was worthless. So we have increased the upper frequency limit to at least five times as high as the original version. It is possible that this style of VSWR bridge could be pushed even higher in frequency by making it even smaller, using tiny (and more expensive) microwave chip capacitors and resistors."

Exciting stuff, but it means I've got to learn what for me is a new technology.

Sulaiman

Mon May 22 2017, 07:50PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

I think that you may be employing the wrong topology,
google stripline swr e.g.

Proud Mary

Mon May 22 2017, 09:41PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Thank you for that reference, which I shall read with interest.

My plan for now is just to follow the circuit and copy the PCB diagram as best as I can from Paul Wade's 1995 article A UHF+ VSWR Bridge here:

The article seems well thought through, and modest in its claims, but would I notice even the most terrible of errors? I'm not so sure!

As for getting things wrong. I don't know very much about this subject, and am sure I have gotten a lot of things wrong - but don't yet know what they are. If the day arrives when I get more right than I get wrong, I shall count myself a fortunate person! :)

Hazmatt_(The Underdog)

Tue May 23 2017, 02:11AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

from 1GHz and up you want to use back to back directional couplers and detector diodes, or a pre-fabricated detector, and a circuit to compare forward to reflected to give you VSWR.

Couplers are very wideband if constructed well, and are accurate.

Proud Mary

Tue May 23 2017, 06:06PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Thanks for that, HazMatt.

I don't as yet know very much about it - but better late than never - so I am going to continue with the UHF+ VSWR project as I've ordered the parts - some have arrived already from China - and the author seems a very knowledgeable fellow who gives enough info about the circuit, including the all-important board layout, for me to proceed quite quickly once I've put in some flying time soldering/desoldering junk chips to/from scraps of board.

From what I've seen of hobbyist SDR so far, most - but by no means all - hobbyists are dependent on kit designed and constructed by other people, with the result that there are plenty of part-assembled kits and modules for listening in to air band, satellite weather, listening in to the cops, and so on, and not very much about, for example, radio astronomy.

Anyway, I'll keep everyone posted on my first UHF/SHF project, and maybe get some good advice if things do not always go as hoped! :)

Sulaiman

Sun Jun 04 2017, 07:15PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

Radio astronomy is a non-starter for most of us due to antenna size and antenna positioning requirements and background noise.

The only achievable stuff is solar and Jovian observation, e.g.

Proud Mary

Sun Jun 04 2017, 10:22PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

May 29, 2017
Detecting Pulsars with a Circularly Polarized Yagi and an RTL-SDR

I don't have anywhere to put up even a modest antenna like this one, so your point is well made, Sulaimann, but is is nonetheless remarkable that radio astronomy that could only be undertaken by major institutions is now within the grasp of committed individuals.

My dismay at finding I could do nothing at all with the jumping flea SMD chips has been reversed by a compromise that took me ages to fall upon due to my unfamiliarity with the technology. I can nothing with 100 pF 50V chip capacitors, but found that 100 pF 1000V was just about big enough for me to use my standard soldering skills. The same with chip resistors: I can work with the 2W ones just fine! This still means that I shall not be able to reach the higher microwave frequencies, but is still a big advance over my previous thru-hole axials in the direction of miniaturisation.

Dr. Slack

Mon Jun 05 2017, 06:10AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Proud Mary wrote ...

My dismay at finding I could do nothing at all with the jumping flea SMD chips has been reversed by a compromise that took me ages to fall upon due to my unfamiliarity with the technology. I can nothing with 100 pF 50V chip capacitors, but found that 100 pF 1000V was just about big enough for me to use my standard soldering skills. The same with chip resistors: I can work with the 2W ones just fine! This still means that I shall not be able to reach the higher microwave frequencies, but is still a big advance over my previous thru-hole axials in the direction of miniaturisation.

Are you sure that the limitation is that you can *do* nothing? I used to think I didn't have the control skills to solder small stuff until I used a decent microscope. Then I realised it was simply because I could *see* nothing. Once I had sufficient gain in my optical feedback path, I found I could achieve good connections with 0402 parts routinely, and 0201 with a bit of care. Even stacking an extra pair of +4 reading glasses over your standard ones can bring about huge improvements.

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