Mobile shack

Happened to be in W4 (Florida) this winter so I took my FT817 with me. Thanks to reciprocity between Canada and the US, I can operate using my Canadian callsign while in the US.

Being in a car country, it looked sensible to me to set up a mobile shack. My VE3 elmer has had a great success with MFJ miniature hamsticks mounted on the trunk of his car so I started looking in that direction too.

After quick research on what’s available at HRO online, I ordered two versions of MFJ hamsticks: miniature 3′ and longer 7′ hamsticks for the most popular bands. For the base, I ordered a mighty MFJ-336T mag mount with 3/8″ mount.

The first one to arrive and to install was MFJ-1620 – 7 feet tall antenna for 20m. The fiberglass base is about 4 feet long and is hollow inside. A stainless steel whip that screws on top is adjustable.

MFJ-1620

When fully extended, it resonated nicely on 13.540 MHz (perfect 1:1 match!) which was way too low… After shortening the whip by about 4″ the center of resonance shifted towards 14.060 QRP CW frequency (with the lowest SWR about 1:1.2). Could not get it match 1:1 anymore.

The whip is very hard to cut. After some trial and errors, the best tool happened to be a triangular file. Cut through the steel half-way then snapped it easily.

While busy with all this hard work, I did not notice it got really dark outside and the 20m band faded away. After scanning back and forth, a weak but workable signal of ZL3GA emerged and my tiny 5W signal just barely made it across the Pacific (7,220 nautical miles!) . Not bad for QRP with a mobile whip!

The 40m was alive and kicking so the next one to install is a 7 MHz hamstick.

The length of the whip makes driving a bit difficult – have to watch out for clearance, low hanging tree branches, etc. Also, at speeds of more than 45 mph, the whip starts buzzing in the wind.

Photo of my new mobile shack:

Mobile QRP

Hope to see you on the air!

73s,
Paul

Chinese QRP VHF-FM radio restoration – continued

The replacement transistors BG1, BG2 (3AA9, 3AA7) are obsolete and next to impossible to find as it’s been 40 years since the radio was built. However, given the known voltage/power/frequency parameters and a friendly help from experienced radio-engineer ham, a reasonable replacement was identified: 2SA1930 from digikey.

Later, I found more data online at http://www.114ic.com/

Model: 3AA7 Model: 3AA9
Manufacturer: China semiconductor companies
Production of materials: Ge-PNP
Nature: RF / high-frequency amplifier (HF), power amplifier (L)
Package: in-line package
Limiting Voltage: 35V
Maximum current allowed values​​: 0.5A
Maximum operating frequency:> 120MHZ
Pins: 2
Beta: 30
Maximum power dissipation: 5W
Possible substitution: B772
Manufacturer: China semiconductor companies
Production of materials: Ge-PNP
Nature: RF / high-frequency amplifier (HF), power amplifier (L)
Package: in-line package
Limiting Voltage: 25V
Maximum current allowed values​​: 0.5A
Maximum operating frequency:> 120MHZ
Pins: 2
Beta: 30
Maximum power dissipation: 5W
Possible substitution: B772

The parameters were exactly as predicted. After installing new transistors, the radio came back to life. However, predictable the output power is too low – less than 100mW.

The bias/feedback seems to be wrong as the bias voltage is different for silicon (0.6V to 0.7V for silicon vs 0.2V to 0.3V for germanium). Also, the operating frequency (50MHz) is too close to the 200MHz limit which also limits the gain.

It may require readjusting the circuit / voltage dividers to ensure proper bias and gain.

While googling the radio, I also found some decent translation of the operating manual: 884_manual_translation

As the radio works on 45-50.1 MHz, it only slightly touches the lowest CW portion of the amateur 6m band. Re-tuning it to 50-55 MHz may not really worth the effort so I may put it on eBay. Would be nice to fix the finals though first.

The full schematics are here:

884_p1

884_p2

 

 

New Year resolutions / to do list for 2013

Merry Xmas and Happy New Year everyone. On this post I’ll try to summarize the goals for 2013:

  1. Build permanent shack, install antenna distribution box, new grounding system, antenna feed lines, dedicated PC for digital modes / DSP / CW / logging,
  2. Install antenna distribution box outside, improve lightning protection, grounding system at the entrance

Antenna projects:

  1. Build 10m halo antenna for digital modes, portable use
  2. Build 20m magnetic loop antenna for digital modes
  3. Install new grounding and radials to the main vertical antenna, weatherproof distribution box, retune antenna, calculate diagrams (EZNEC), bury new feed line in a rodent-proof conduit
  4. Locate and identify source of S7 QRN on 40m
  5. Build new HF / VHF antenna
  6. Build and install discone antenna on attic with remote RTL-SDR / Raspberry Pi receiver
  1. Finish SoftRock RXTX kit
  2. Convert Softrock 20m lite for WSPR / PSK usage
  3. Build WSPR beacon
  4. Build APRS gateway using Raspberry Pi
  5. Finalize MCU homebrew paddles CW-keyer (add enclosure, paddles)

Shack updates

The shack updates:

1. I am considering ordering Ameco K-4 Brass Key AM-K4 – it’s $24.95 at http://www.mtechnologies.com/ameco/keys.htm

It has some good reviews (4.8/5.0 score) at http://www.eham.net/reviews/detail/3383
I will most likely add a solid heavy thin base to it or simply attach it permanently to the desk.

2. For my Softrock, I am going to build a simple magnetic loop. This place happens to have inexpensive variable air capacitors ($10-20) that I am going to try for this: http://midnightscience.com/catalog5.html#part3

3. My new LDG S9v31 vertical is behaving strangely. The SWR which was close to 1:1 on most of the bands now is 1:1.5 or 1:2 at best. I guess the change of weather changed the electrical qualities of the soil so I may need to try elevated radials. I think I also need to borrow an antenna analyzer to check the actual impedance and resonant frequency before and after the 4:1 unun. Update: it’s back to normal now.

I came across some interesting links related to ham radio:

Changes in the shack

Finally installed a new vertical antenna – LDG s9v31.
http://www.eham.net/reviews/detail/8067

The antenna seems to be performing quite well on receiving. The SWR on 40m and 80m is close to 1:1 (with tuner of course), and is close to 1:2 on higher bands. Not so good on transmit, probably, because I only have two radials for now which is definitely not enough.

The old mic which came with the rig was in need of replacement so I ordered a replacement MFJ mic for $25. Shipping was $20 on top and took 2 months to deliver… Once it finally arrived, the wiring was loose and not secured to the connector so it shorted right out of the box… ah well… Took a soldering iron and rewired it. Seems to be working okay now.

Other updates – got my first QSL card from my first DX Italian contact. That was a very nice surprise for the New Year.

Kenwood TS-520 classic rig

Went to a ham radio garage sale in Newmarket and now I am a happy owner (the third owner) of a wonderful Kenwood TS-520 hybrid rig (SN#250226) – thanks to VE3NX (was the second owner).

The rig is very clean and seems to be in great shape!

Also, thanks to VE3IZZ, who practically donated to me an MFJ-941E tuner and a 20m dipole along with coax cables. Thus, by 7pm I was dipping plates and CQ DX!

One problem though – the tuner has no internal dummy load. That I discovered a little late.. after tuning the rig a couple of times… but seems like luckily did no damage to the finals.

So I ordered 20 x 1000 Ohm 2W carbon resistors on eBay to build a dummy-load myself.

K4EAA has provided great building instructions on his wonderful website dedicated to Kenwood hybrids: http://k4eaa.com/dummy.html

Kenwood TS-520 Manual