AH6RP amateur radio blog

A different way of making variable inductors

2005-11-08T12:26:00.000-10:00

From a note by Ed Tanton, N4XY, to QRP-L 08 Apr 2003:

"OK... I took one of these [surplus SMT] inductors and measured it at 525nH (0.5mH) [...] and brought the inductor near the 'face' of the 1.5' x 3.5' x 5/16' (3.5cm x 8.9cm x 0.8cm) magnet. Interesting: the inductance changed to ~ 200nH (0.2uH). Then, I moved the tweezers/inductor to the end of the magnet. Wow. The inductance went from its usual 525nH to 43nH (0.043uH)!!!"

Merton Nellis, W0UFO, commented:

Yes, inductors with magnetic material as cores change inductance from a maximum with no biasing magnetic field to a lower value as a bias field is applied. [...] The bias field can be applied to a core with a separate winding carrying d.c. rather than with a permanent magnet. This principle is used to make saturable reactor controls and magnetic amplifiers.

Mounting a magnet near a toroid with a screw for adjustment would let you build variable inductors without having to locate a slug-tuned coil form. Also, it could be used to build an SMT variable inductor with an adjustment big enough to be useful. Attaching a man-sized knob directly to a eensy SMT inductor is begging for the leads to be torn off the board.

ATS-3 sold out

2005-09-26T21:04:00.000-10:00

Re: [QRP-L] CW QRP Kits? (ATS-3 not sold out): "Yes, the ATS-3 IS sold out. Just changed the web page yesterday. Time to get busy on the next version..."

Oops. Looks like I waited too long for the ATS-3, due to work and such. I hope Steve can get the ATS-4 ready soon. Time to go and look at the Small Wonder SW+ series again. They are single band, no DDS, but a third the cost of the ATS-3.

Energizer 9v lithium

2005-09-17T22:50:00.000-10:00

In this note on the Energizer L522 9v lithium battery, Everready claims "the L522 at 1200 mAh has twice the capacity of alkaline batteries."

Ultralife Batteries - U9VL

2005-08-07T11:29:00.000-10:00

This is Ultralife's specs for the battery that Thomas sells:Ultralife Batteries - U9VL. Note that the maximum pulse discharge is rated at 400 ma... that is just adequate for the ATS-3, which draws about 420 ma at 7.8v (see AE5X's statistics for a 9v alkaline transistor radio battery).

Weight is good at 33.8 grams. Also note the discharge/capacity curve for 60 ohms (125 ma) shows a decline to 7.0 volts at 80% capacity (960 mah apparently.) Short circuit current is initally 3 amps, but falls to about 1.3 amps and then levels off until minute 3, where the current falls again, presumably when the current limiter kicks in (and that's not reversable.)

Current draw from the ATS3 would be about 110 ma in a QSO. The battery will probably last a bit over 5 hours to 7.0 volts. [How did I get that? Assume 44% key down while transmitting... that's exact for "PARIS", 50 elements, 22 with key down... and say 50% transmit time in a QSO, that's 22% transmitting and 78% receiving time. At 7.5 volts, the ATS3 has an output of 2.05w, drawing 404 ma transmitting and 27 ma receiving.]

On continuous recieve, the battery would last around 42-45 hours.

9 Volt Ultralife Lithium Battery

2005-08-07T10:34:00.000-10:00

Thomas Distributing carries the 9 Volt Ultralife Lithium Battery, with a 1200 ma nominal capacity... at 10 ma drain, to 5.4 volts. At 27 ohms, it briefly supplies about 10 volts, drops quickly to about 8.3, and remains above 7.2 for 39 hours (see curve at Thomas site, note 27 ma into 300 ohms is 8.1 volts.)
That's about 1,050 mah.

Kester on Sn/Bi 42/58

2005-07-24T13:32:00.000-10:00

Kester - Alloys: "SnBi58 Alloy

* Low melt point lead-free alternative potentially suitable for some consumer electronics. Low melt point precludes its use for applications where operating temperature is close to 138C.
* Large Bi proportion greatly reduces melting point of the solder, but alloy is more brittle. Bi improves wettability, but is somewhat offset by higher oxidation rate. In the presence of lead from HASL boards or components Bi can greatly reduce thermal cycle fatigue resistance due to the formation of Sn16Pb32Bi52 (MP=95C) which can diffuse along the grain boundaries."

C&L Finescale

2005-07-23T22:27:00.000-10:00

C&L Finescale in England offers "145 deg C Tin/Lead/Cadmium in the form of a 1.2 mm wire," product code C2002, 0.5 kg for 25 pounds. They also have eutectic tin/bismuth as a no-clean paste, but a 35 gram syringe is 27 pounds.

Sources for low melting point solder

2005-07-23T21:47:00.000-10:00

Here's a small quantity of Sn/Bi wire solder: Tools (at alltronics.com): "Melcor Low Temp Bismuth Tin Wire Solder... Melcor part number 16-65-019-01... includes 2 feet of 138 deg C solder (Indalloy # 281) and the instruction sheets, spec sheet and warning sheet (don't eat it). Alltronics part number 04Z054... Unit Price : $2.95". They don't mention the diameter, but from the illustration I would guesstimate 1/30" very roughly.

Melcor themselves sell 16-65-019-01 online for $1.35, 25/$32.50, apparently without the literature that Alltronics includes.

More on low melting point solder

2005-07-23T21:33:00.000-10:00

According to the table at Indium Corporation of America » Wire Products the only indium-free wire solder that is normally available with a lower melting point than the eutectic Sn/Pb/Ag alloy is Indalloy 281, 58/42 Bi/Sn, melting at 138 C / 281 F. The shear strength is poor, 500 psi, compared to 6200 for 63/37 Sn/Pb, and the conductivity about half.

Incidentally, the name in the table for the eutectic Sn/Pb/Ag alloy is Indalloy 62/36/2...! That probably negates part of my previous post; I would imagine this implies that the Radio Shack solder is most probably 1.4% Ag and not 2.0% Ag.

Low melting point solder

2005-07-23T10:52:00.000-10:00

Common eutectic solder, 63/37 Sn/Pb, melts at 183 C, 361 F.

Indium Corporation has a spreadsheet of solder compositions here in HTML or here in an Excel spreadsheet . It lists 62.5/36.1/1.4 Sn/Pb/Ag as melting eutectically at 179 C, 354 F. It doesn't list exactly 62/36/2 Sn/Pb/Ag (e.g., Radio Shack 64-013 0.022" wire solder, 1.5 oz for about $4) but the alloy selection section of this guide from Indium mentions that it has a melting range of 179 - 188 C, or 354 - 370 F.

That's only a 4 C or 7 F difference in favor of 62.5/36.1/1.4, and 62/36/2 is actually WORSE, since it is still slushy up to 5 C / 9 F hotter than the melting point of 63/37.

52/30/18 Bi/Pb/Sn melts at just 96 C, 205 F. That's a 87 C, 156 F difference from 63/37. That seems interesting, although the only reference to it in electronics that I have found was in an explanation of why Bi/Sn/Cu lead-free solders are on hold for the next decade or so: if there were any lead at all on the board it would dissolve into the solder to form this very 52/30/18 Bi/Pb/Sn alloy, and melting at 96 C is seen as a problem.

(There are much much lower melting points available in indium-based solders, but they form brittle alloys with copper, making them useless for electronics; see the substrate metallization section in this guide from Indium.)

I haven't been able to find much about solder availability in small quantities of anything more exotic than 62/36/2, though. Bummers.

Carpets and SMD

2005-07-23T10:42:00.000-10:00

Several cautionary tales of SMD at home are in the SMK-1 trials and tribulations thread in QRP-L. (The SMK-1 was a much smaller QRP transceiver, now out of production.) The oddest piece of advice was to stretch a nylon stocking over the nozzle of a vacuum cleaner so you could find lost SMD components by vacuuming them up. Oh. On second thought, make that ONE SMD component; if you vacuum up two different unmarked components you would have to measure the eensie things before you could solder them in.

Soldering jig for SMD

2005-07-23T10:12:00.000-10:00

KD7S has plans for an SMD hold-down that probably contains the absolute minimum number of parts - just two. One is a bent piece of coathanger wire and the other is a wooden slat with a groove in the bottom.

Bamboo skewer and paste flux

2005-07-22T21:25:00.000-10:00

A slightly bigger version of the toolpick-and-beeswax method of handling SMD's: from the Elecraft reflector.

SMT soldering

2005-07-21T07:47:00.000-10:00

Luke Enriquez, VK3EM, has published a 101 level discussion of soldering SMT projects in A Guide to prototyping with surface mount technology (SMT) - HTML Version. (Also available as a PDF file.)

Highlights:

invest in a really good pair of tweezers. However, other people, including (I think) KD1JV, have suggested using a toothpick dipped in beeswax as the easiest way of handling SMT components. In particular, an accident with tweezers will send the components flying off into never-never land. Hmm: would soldering flux be a good replacement for beeswax? By the way, having tweezers on hand is essential anyway, in case you have to desolder a component.
Luke recommends LMP - low melting point - solder to avoid frying components. He goes on to define LMP solder as the 2% silver variety. That doesn't sound quite right. Although I've seen a lot of people recommend silver-bearing solder recently, the solder makers do NOT show it melting at lower temperatures. More on this later, in a post about Indium Corporation.
cream solder is not as good as wire solder for hand soldering with an iron; the shelf life is short, and it is easy to boil the water in the cream and splatter tiny solder balls which can cause shorts.

VHF: EARC net at 7:30 pm nightly

2005-07-17T12:37:00.000-10:00

If you are on Oahu or Molokai, please join us on 146.88- at 7:30 pm HST for the EARC nightly net. No PL tone is needed. On Saturday, I am the NCS. 72/73...

ATS-3/ATS-4 ... it was actually 7/05

2005-07-16T21:34:00.000-10:00

Actually Steve Weber KD1JV had announced the ATS-3 was back in stock on 7/05/05 in a QRP-L posting ([QRP-L] Time to order an ATS-3!) I think he didn't update it on his homepage for at least a few days afterwards.

In the posting, he also mentioned there will be a slightly larger ATS-4 with LED display. He thinks it may be ready in a few months. It will have latching relays to change bands instead of the tiny band modules of the ATS-3. It looks to me like it probably be quite a lot more than $160, though.

WH7N

2005-07-16T11:28:00.000-10:00

My VHF Elmer's blog: wh7n.net.

ATS-3 back in stock about 7/13/05

2005-07-16T10:48:00.000-10:00

The ATS-3 (also referred to as the ATS III or KD1JV Appalachian Trail Sprint-III) went out of stock about the beginning of March. KD1JV went off on a two month hike...! He put the ATS-3 back in stock about 7/13/05.

Reviews are on the eHam site. Also see AE5X's review, builder's tips, and battery life measurements and the online copy of the AT Sprint III Assembly Manual.

Welcome

2005-07-16T10:17:00.000-10:00

Welcome to AH6RP's blog!