Listening to ISEE3

1.0 Background

A few days ago I made a parent-y type tweet, which was more a badly hidden humblebrag over my kid saying "dish" before "mama." *shrug*



That tweet led to at least three more technically aimed questions over how it was we were planning on listening to ISEE-3. So this post is an attempt to answer those, and cement my own thoughts. It's not a new method - see Section 2.3.2 of this post for links to other people doing exactly this. See Section 2.3.1 if you're going "WTF is ISEE-3?"

Major Disclaimer

I am not the mad engineer behind all of this, I am the cheerleader (and now PR person). The things reported in this post come from the brain of the eminently brilliant [redacted due to request for mild anonymity], who has been kind enough to let me share his life with him. Errors in this post are entirely my own.

The enthusiasm for the ISEE-3 mission is also my own.

2.0 The Device

2.1 General Layout

2.2 Equipment

2.2.1 The Dish

Not as cool as The Dish.

• 90cm offset fed "Sat TV" dish. 
• Mounted on our Skywatcher EQ-6 equatorial mount that we temporarily borrowed from the optical telescope. 
• Mount is driven on both R.A. and declination axes, but this is not strictly necessary. The dish has an approximately 2.5° beamwidth, which should allow for several hours of "tracking" with a stationary mount. 

2.2.2 The Feed - LHCP Helical Antenna

• Homebrewed 5-turn helix feed, centre frequency 2271 MHz. Wound in a left-hand circular polarisation (LHCP), which is converted to RHCP once reflected in the dish. Deodorant can wrapped in a toilet roll tube comes out pretty close to the right diameter for winding copper wire.
• See the links in 2.3.2 or google "S-band helix feed" or particularly "AO-40 feed" for lots of designs that will work. Helicals are very broadband and forgiving in construction tolerances. 

2.2.3 Low Noise Amplifier (LNA)

• LNA4ALL, 25 Euros with shipping. 
• Approximately 11 dB gain at 2.3 GHz. Noise figure ≤ 1 dB. 
• Mounted directly after feed. 
• Powered by 2x 9V PP3 batteries in parallel for approx. 1200 mAh. Just for simplicity and noise considerations. 

2.2.4 Downconverter

• Modified MMDS downconverter for 2.2 - 2.4 GHz, 25 USD with shipping. 
• Modified to be directly supplied with 12V (12V, 7Ah lead-acid battery), to avoid use of the bias tee (2.2.4a). 
• Approx. 40 dB gain. Noise figure 1.4 dB. 
• Local oscillator at 1998 MHz, 200 - 400 MHz after downconversion. 

2.2.5 Software Defined Radio (SDR)

• Cheapy (10 USD) R820T RTL-SDR dongle. 

2.2.6 Laptop (Laptop)

• Windows 7 running SDRsharp (SDR#), with plugin for auto-doppler correction, or HDSDR. 
• No need for FFT integration expected over next 2 - 3 weeks of reception [August 9]. 

2.2.7 Others

[Not shown in block diagram but might be inserted, as and when, depending on what happens when we plug everything together.]

• Attenuator between downconverter and R820T dongle, in case 40 dB gain + 11 dB from LNA might swamp the tuner (although doubtful). 
• FM-trap (i.e. broadcast band notch filter/band-stop or VHF notch filter if there are strong TV stations present). 
• 1/4 wavelength impedance matcher between LNA and downconverter to match 50Ω to 75Ω. Will use a 1/4λ 62Ω microstrip line, etched on PCB material. Possibly not necessary if LMR-195 length is kept very short. Probably. 

2.3 Notes

Image credit 

2.3.1 ISEE-3

ISEE-3 stands for International Sun/Earth Explorer 3, which nods to the spacecraft's function when it wasn't named ICE (International Cometary Explorer). In a nutshell it is a spacecraft which was abandoned by NASA, which has been subsequently hijacked by crowdfunded private citizens operating out of an old McDonalds. I don't think it gets cooler than that. You should look through all these fabulous linkages:

• The official page for mission news and updates: http://spacecollege.org/isee3/
• The ISEE-3 team twitter profile: https://twitter.com/ISEE3Reboot
• And oh lordy you should really play around this page. For the rest of the day: http://spacecraftforall.com/ 

At the time of writing, ISEE-3 was on track to flyby the moon later on August 10th. Its signal should remain fairly strong for home-brewers for the next month or so.

2.3.2 The work of others

• (Mis)appropriating standard TV dishes for use in antenna setups is not new. Howard Long has a very decent write-up on the exact shennanigans described in this post here. 
• UHF-SATCOM gives options for suitable LNAs, as well as some more detail on the helical antenna design, for the lower S-band frequencies. Also look at that site's image gallery and scroll down to "S-Band receiver systems." 
• Twitter user @PA4DAN has gone and done all this himself already - so go look at his photos for a non-Visio version. 

If I've missed something that really should be in this list, lemme know in the comments.

Building a house

Ah look, a use for a blog.

So, I’d like to build a house.

A little house.

Like the sort that might fit on to the area of a decent-sized car bonnet.

And be made of plywood.

My intention is for it to be a space to try out smart ideas for smart homes, and green ideas

for green homes, on a tiny little scale (well, depending on the car bonnet). So I’m looking for

ideas; they can be outrageous or tempered, whatever. What do you think would be a cool

system to have in a smart home, or green home? (I know those two don’t necessarily go

together.) I’d like to have a good few ideas before I start chopping up plywood, as some of

them are likely to affect the layout.

I’ll look at the ideas and give their implementation my best shot in due course. This is also

a sort of test to see whether I have any design or creative (or fabrication, or electrical, or

programming) skills at all, and if I don’t, to get some. For green ideas I’d like to do tests of

the efficiency of the systems as well, once they’re in place.

I’ve already decided that I want it voiced by Paul Bettany, which is going to be a sound-

bite hauling labour of tedious love. Or, you know, if anyone knows Paul personally and he’s

willing to do an Ironman-sized project for free…

Types of systems that I need to give some thought to:

• Lighting
• Air-flow
• Water circulation
• Water heating
• Centralised door/window/ventilation/lighting control
• Paul Bettany sweet-nothing whispering system
• What else?

So when you wake at 3 in the morning with a random idea which sounds a bit mad (or not)

but might be kinda cool -- @kathrynrosie

Kathryn

Tinkies (with a side serving of Bar One)

I'm aware that there are many things going on around me that require more comment than this, but I have chosen to honour the Tinkie with my inaugural post.

Or rather, how absolutely crud Tinkies have become since their glory days in during my youth.

Tinkies (or Twinkies, I believe, to the more Westerly-located) are rectangular-prismatic sponge cakes infused with cream. Or they were... now they're sea-sponge textured cakes shot up with a miniscule amount of cream which results in a millimetre thick layer of cream occupying about 50 - 60% of the length of the bar.

The Tinkie brand, I swear, is surviving on the misplaced memories of my generation. Tinkies were creamy goodness in a box. Nowadays they're a disappointing reminder of what life was like before cost-cutting measures and the customer-is-an-idiot-they'll-never-notice mentality. I mean, look at the cream part in the Tinkie image above... it's fake! They can't even make a perfect Tinkie for the box! If the cream in the image is a full moon, the actual cream present in todays Tinkie is a God's-thumbnail sliver of lunule on the first day of the moon month.

Which reminds me of a Bar One rant I once had, in which I suggested that the next time Nestle are about to embark on cost-cutting measures they consider reducing the amount of wrapper in order to more conform with the volume of chocolate inside the wrapper. That way they can save on wrapper costs as they have already saved on chocolate. 14cm of (volumetrically correct) wrapper for a 10cm chocolate bar! Are you kidding me?! Asses.

Maske out.