11 battery cells is the maximum!!

John, PD7MAA reminded me of the fact that a healthy NiMH cell can charge up to 1.5V. With 12 cells in series, that makes 18 VDC which is beyond Yaesu’s tolerance specs: 13.8 +/- 15% would imply a maximum of of 15.87V. After one hour charging, the Voltage went up to 15.8 VDC so I’m on the edge already.

I’m going to remove one cell right now!

Homebrew FT-897D 13.2VDC @ 6000mA battery!

During my holidays, I always bring a “holiday radio”. On the camping sites we are used to stay, we always have 230 VAC @ 10A net power, so full 100W output. It is OK, but not very exiting to be honest, so… I’ve challenged myself to improve my CW skills and explore QRP’ing from /P locations during the holidays.

At first I wanted to buy a FT-817D radio, but as my FT-897D can hold batteries as well and power can be set as low as 5 Watts, I decided to first upgrade my FT-897D with one or two battery packs. The FNB-78 4.5 battery however sets you back $124 (around €100+) and bear in mind you probably want/need two and also need a specific (Yaesu) charger to go with it which probably sets you back another $100 or so.

Browsing the internet I say many people are making these batteries themselves so I decided to homebrew a battery myself as well. I started with ordering 24 NiMH “sub-C cells” (smaller dan normal C cells) with 6000 (!!) mA capacity that seemed exactly the right size. The 24 batteries were only $35. Maybe they’re rubbish, but for that amount you’re not taking a big risk I guess. Here are the batteries I ordered:

800_subc 6000 mA batterijenThe batteries arrived today (only 6 days from Hong Kong China to The Netherlands!!) but unfortunately the packing they were only packed in a bubble plastic envelope so 12 of the batteries were dented. I raised a case via eBay and mostly those Chinese sellers refund or replace the goods (if not: eBay’s buyer protection works pretty well). 12 of the batteries seemed fine so… let’s get started. I was thrilled to all 24 batteries will fit the FT-897D’s battery compartment so… two 14.4 VDC @ 6000 mA batteries for 35 bucks… Not bad at all!

After writing this article, I was made aware of the fact that a healthy MiMH cell can be charged up to 1.5V so my series of 12 FULLY CHARGED CELLS CAN POTENTIALLY PUT OUT 18VDC WHICH EXCEED’S YAESU’S OPERATING VOLTAGE TOLERANCE OF 13.8V + 15% = 15.87V!! After less than one hour of charging, the Voltage went up to 15.8 VDC which is on the edge of reason. Please be aware that I HAVE REMOVED ONE CELL FROM THE SERIES CELLS!! THE TOTAL NUMBER OF CELLS IS NOW 11. Max. Voltage would be (theoretically) 16.5VDC, “working Voltage” should be around 13.2 VDC.

800_20140326_152259I soldered a series of 6 batteries in series and soldered the two of these 6-battery-series in series as well (are you still with me?! HI).  !! I HAVE REMOVED ONE CELL SO NOW 6 + 5 = 11 IN SERIES !! Then I used a glue pistol to kinda glue them together and packed them in very thin PCB material that I got years ago at a ham fair. Wanted to use is as a point to point component board for guitar amplifiers, but the material was waaaay too thin. Always kept it because it seemed pretty sturdy, very well isolating and can be cut with normal scissors. In Holland we tend to say “wie wat bewaart, heeft what” and now, years later, it comes in very handy. So… glued the batteries and packed ‘m in the PCB board:


As you can see in the picture below, 24 of these batteries fit the FT-897D nicely:


Solderded the battery’s (+) to the LEFT pin of the A connector and (-) to right PIN of the A-connector, took out the batteries on the right side (just to show you what a nice fit they are), closed the FT-897D and fired it up…


Oh yeah! 14.6 VDC on the meter, excellent. I worked the local repeater from Utrecht with only 5W output, the Voltage dropped to 13.8 I think. I’m now listening to the radio for about 2 hours and Voltage is 12.8VDC on receive and 11.8VDC on transmit, still pretty good I guess. I’m now awaiting a 1A intelligent NiMH charger AND (!!) 10W solar panel (already got the charge controller) and then the real fun starts… QRP from my back yard in CW on a random length of wire tuned by a simple L/C tuner. What an adventure HI.

QRP T-tuner for $16 / €12 ?!?!

As I’m planning some short holiday /P sessions, I’ve ordered 24x 6000 mA (yeah right!) NiMH batteries, a 10W solar panel and an MPPT solar charge controller for my FT-897D on eBay (from China). This evening I was browsing eBay for a second hand QRP tuner and to my great surprised, I saw an auction for a QRP T-circuit tuner kit from Hong Kong China for only $16 with free shipping worldwide option. Incredible! I just couldn’t resist, this is the one I got: www.ebay.com/itm/271357343348.

It’s a typical T-circuit tuner with a 12 position inductor to ground and input / output capacitors. Bonus is a nice SWR dipper tuning aid circuit that helps you tune (LED lights up when SWR is high and dims when SWR is low). I think the circuit is very similar to a product that sells on eBay (also from Hong Kong) for $79.50!! >> www.ebay.com/itm/221204948808

The kit I bought uses a coil wound on a T106-2 toroid, good for around 17.5 uH. The “expensive” ready-made version’s circuit is indicating the bigger T130-2 toroid that has (?!) a lower Al value so only has 14.5 uH with 36 turns. Also, the SWR dipper circuit is slightly different. The transformer for this circuit is wound on a FT37-43 toroid, but my kit has a 2:5 (1:2.5) turn ratio whilst the “commercial” version has 5:20 (1:4). Will try the kit’s circuit, if it doesn’t work, I will experiment with the “commercial” version’s circuit.

I will keep you posted on the kit building progress and the results! Here are some pictures of the kit:

The PCB with “SWR dipper circuit”:qrp tuner kit 05

All the parts:qrp tuner kit 04

The built product:qrp tuner kit 03

The circuit:qrp tuner kit 02

Here are some pictures of the $79.50 “commercial version” of a similar tuner:

qrp tuner kit 07

qrp tuner kit 06

20m end-fed works OK but…

I hooked up 10m of speaker wire to the auto transformer pictured below and hard wired a length of RG58 to the transformer as well. After cutting to correct length, I got a nice 1:1.2 SWR dip around 14.050 MHz and tested it out. It seems to work great and can handle the 400W PEP that I used. I worked some Canadian stations in what I believe was the ARRL contest; VY2TT, VE9HF and VO1SA. Distance is around 6000 km pretty good but…

I noticed the signals on the 80/40 end fed, that hasn’t even good a decent SWR on 20m, were 1 S-point better with less noise. I can tune the 80/40 end-fed to 20m and it seemed to work pretty well in the PACC contest. Question is how it compares to this new 20m end-fed. If performance is comparabe, (again reception was around 6 dB better so maybe it’s even better than the 20m end-fed), it’s no use using a dedicated end-fed for 20m. Have to sleep on that HI.

20m / 15m dual band QRO end-fed

While I only got space for a relative small “rotable” antenna it will always be a compromise on 20m and even on 15m. While my 80/40 QRO half wave end-fed seems to be working perfectly, I decided to make another QRO end-fed for 20m and 15m and will have a dedicated rotable antenna for 10m (maybe combined with 6m). I started off making a 2:16 (1:8) auto transformer on two stacked Fair-Rite FT240-43 toroids:



I used 1.8mm wire for the primary turns and 1.2mm wire for the secondary turns. The first two turns are bifilar turns with primary and secundary wires twisted together. Then the secundary wires makes another 6 turns on the same side. Then the wire crosses the core to the other side and there’s another 7-8 turns so there’s a 2:16, or actually a 1:8 turn ratio which will result in a 1:64 impedance transformation nicely matching the typical 3k3 – 3k5 impedance of the end of the half wave to 50 Ohms. A “Voltage fed” antenna requires very little counterpoise. On my 80/40 QRO end-fed I have no counterpoise, the coax is sufficient and just before it enters my shack I have an RF choke to avoid RFI which seems to be working fine, even with QRO power. It seems that a length of about 5% of the wave length is sufficient so I will connect 1m of wire to ground and use an RF choke (2 FT240-52 cores with 11 turns of RG58) right after the auto transformer.

For now, I will hook up 10.2 meters of wire to test on 20m. When the transformer is OK, I will be adding a trap for 15m: a 3 uH air core inductor combined with a 20 pF high Voltage ceramic door knob capacitor. I will keep you informed!