First Name Bob
  QTH Freeport, IL
  Prior Call(s) ⇰ KE∅T
  Other interests ⇰  Recumbent Biking, Paddling, Camping, Homebrewing, Radios old and new from tubes to SDRs
  Email W9RAN
   My External Web Site  vintage gear


   The Spilsbury and Tindall PRT-20

    You may have heard me check into the MCRN with this one watt rig. It is a Spilsbury and Tindall PRT-20. They were used as
    "bush radios" in Canada where Spilsbury is located (Vancouver area) and for logging, oil exploration, forest-fire fighting, etc
    in the late 50s-early 60s until SSB versions replaced them. Click here for more info and better pictures. Bob  (page opens in new browser window)

   The Amalgamated Wireless Ltd. (AustralAsia) Model FP-1 "FORESTPHONE"  
    Throughout most of the 20th century AWA was Australia's leading electronics company, providing a wide range of radio, television, and audio equipment as well as broadcasting services. Over that time period the company partnered with other companies including RCA, Thorn, Rediffusion, and others to broaden it's product offerings. But as an Australian company, the Forestphone FP-1 no doubt was it's own creation, a small, easy-to-use, portable transceiver designed for use by forestry crews and similar commercial endeavors back when HF radio was the primary means of communication beyond line-of-sight. According to the seller, the FP-1 I recently acquired was "Originally built for the Forestry Commission in the state of Victoria, the last user of this rig was a gliding club, before gliders and balloonists were compelled to move to the VHF air band in the 1980s. They were also used by mobile bee-keepers, inland waterways craft such as houseboats and dredgers, and local government operators in the inland."

    The FP-1 is all solid-state, a big plus for battery operation in the field, and being a mid-1960s design uses germanium transistors, including a pair of 2N301As as the modulator, a transisitor I remember scavenging from hybrid car radios as a young ham! The PA uses two 2N3879 transistors in a push-pull neutralized output stage which uses a toroidal inductor having 11 taps and a second inductor for antenna tuning/matching. Two output connectors are provided with a switch to select between taps that have been set for mobile (presumably close to a 50 ohm load) and as a loading coil for a portable whip. Unlike some similar sets, the FP-1 uses an external battery, which I see as a plus given how often battery leakage causes damage to portable radios. As the pics show, the interior of the FP-1 is very clean and quite interesting to look at, since many of the locally-sourced components look a bit different from the ones we're more accustomed to seeing. The frequency range is 2-5 Mhz.

    Picture from hfradio.com.au FP-1 Radio Only Internal View (Top) Internal View (Bottom)

    The receiver is a single-conversion superhet that requires a crystal 455Khz above the desired operating frequency and is very sensitive (Under 2µV). Fortunately for me, the radio came equipped with transmit and receive crystals for 3888 Khz, which the seller said was outside the AM allocation in Oz and thus he never was able to use the radio on the air. It took only a slight tweaking of the IF cans to peak it up 3Khz away, on 3885. For transmit, I merely substituted one of the inexpensive HC-49/U crystals from N4ESS, which did not oscillate to begin with. Fortunately again, the radio came with a complete technical manual where I saw that a 33pF cap had been placed in series with the crystal in the Colpitts oscillator, and which was reducing the feedback too much. Bypassing this cap brought the oscillator to life with full output of 12-15 watts with 13.8V supply, or a solid 10 watts from a 12 volt battery. Transmit current drain is as high as 3.8A but the receiver draws only 20ma in standby yet produces lots of audio. For this reason we plan to have the Forestphone "guarding 3885" during next year's Hamvention at Xenia, OH so calls on 3885 AM might just be heard!

    I found little information about the FP-1 online but the pic shows one with the cover and canvas carry bag which I do not have, obtained from hfradio.com.au  (page opens in new browser window)

    Small AM (and later SSB) field radios like the Forestphone were the mainstay of the Forests Commission in Australia until the mid-70 when VHF took over. But HF still plays a role in remote regions of the world, and when used with a decent antenna, radios like this are still capable of communication over several hundred miles.

   Virtual Radar from a Digital TV Dongle

    An article published in QST (January 2014). It appears on page 38 and is titled Virtual RADAR from a Digital TV Dongle. You can click here to go directly to an online version of the article.  (page opens in new browser window)
   The All American 75


    The October 2013 issue of Electric Radio Magazine includes my article showing how to convert a basic "All American 5" broadcast radio into a simple 2-watt 75 meter AM transceiver, named "All American 75." MCRN members as far as 300 miles away have heard its Heising-modulated QRP signal.

    The AA75 conversion consists of adding an external power supply to eliminate the hot chassis shock hazard and building a simple crystal controlled transmitter using a 35L6 that replaces the original rectifier tube in the series filament string. Re-tuning the receiver from the BC band to 75 meters provides about the same performance as an S-38 type receiver which is good enough to hear any station that can receive the AA75s QRP signal.

    I was motivated to try the AA75 conversion after finding an AA5 radio with a hopelessly broken plastic cabinet in an antique shop for $5. As a result, this rig is housed in a homebrew cabinet made of scrap wood and plastic (note how the dial has been carefully calibrated for AM operation!) I hope others will be motivated to try similar conversions and with their own innovations. Since the basic AA5 circuit was used by hundreds of manufacturers, the AA5 was possibly the original Open Source Design!

    Unfortunately, a couple of errors crept into the 35L6 transmitter schematic that appears on page 19 of the article, and I urge anyone wishing to give this idea a try to use the following corrected version of 10/13 instead of the one published in ER.

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  Last update December 14, 2017