RAN Technology

Hallicrafters AT-10 Antenna Tuner


Vintage Ham Radio 0 Comments 06/07/2021 

One even Dachis doesn't know about!

Posted By: Robert Nickels (ranickels)

 

A while back I acquired a six channel HF transceiver made by the Radio Industries division of Hallicrafters, probably in the 1960s, called an SBT-20.    It is capable of 20 watts SSB or 5 watts AM (or CW with an optional board) in the range of 2-12 MHz and thus was probably aimed at commercial and light-duty military applications.   The radio could by ordered with full 2-12 MHz range coverage, or where the six channels all had to be within one (or more) frequency ranges.   Because different tuned circuits had to be installed for each range, this allowed users to only pay for what they needed.

The unit I have was set up for only one frequency range, which I thought was a shame since I could use my frequency syntherzer modication to over 160, 75, 60, and 40 meters if the tuned circuits were adapted.   I've completed that for all but the PA, where a proper resonant tank circuit is needed for each band, and I'll post more information and photos of the SBT-20 when I've done so.

But in the meantime, a very rare accessory has come my way:  the companion AT-10 antenna coupler - courtesy of my friend Al Culbert KØAL.   He'd read my post looking for information on the SBT-20 and realized the coupler should be united with the radio.

My first thought was "But I'll probably never use it" - however after looking inside, I am so impressed I'll make a point out of using it!   What a nicely done (albeit overkilled?) job!    It is actually four tuners in one, each of which could be switched to match the transceiver to a long-wire or whip non-resonant antenna.   This was pretty common practice for marine HF radios as well, since only  a few preset coupler positions would suffice for the frequencies that would be used. 

As the interior photo shows, there are four large roller inductors (the 4th is hidden under the SWR pickup box on the right).   Since they were set-and-forget adjustments, instead of knobs the shafts have plastic screwdriver adjustements that can be locked in place.    The component are clearly capable of handling much more than 20 watts and the roller inductors are much classier than the typical marine coupler which uses airdux type coils with clips that must be manually positioned.    This is actuall four couplers in one box, where each acts basically as a loading coil for a short antenna.

The AT-10 is shown on a copy of a SBT-20 sales brochure (sorry for the low resolution) - but is not even mentioned in Chuck Dachis'  "Hallicrafters Bible" as an accessory, which is unusual indeed.

More surprising, the small diagram which is probably the only documentation on the planet - was found stuffed inside.   Older hams will recognize Trevose Electronics as a big ham dealer from years ago.

 

Click on the image title or on the image itself to open the full-sized image in a separate window.

Description Comment  
"Documentation"

    I'm always thinking about interesting combinations of equipment to try out on the air.   One day while rearranging the shack I was getting ready to connect my Globe Scout Deluxe back up with a Collins 51S-1 receiver when the LED (the energy-efficient version of the old light bulb) came on.When I first started playing with DVB-T dongles back in 2012 I wanted an upconverter so I ...  READ MORE
- Robert Nickels (ranickels),  05/29/2021 
  

6AG7-6LG Novice Transmitter

Classic circuit with some modern twists
Category: Vintage Ham Radio
 There's a good chance that more homebrew ham transmitters have been built using a 6L6 than any other tube, and when combined with the superior performance of the 6AG7 oscillator, it's a hard combination to beat (click here for an explanation of the 6AG7's benefits)I'll be adding more info about this project soon, but one of my goals was to reproduce what was a budget-friendly...  READ MORE
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- Robert Nickels (ranickels),  05/18/2021 
  

Hudson American Corporation

Manufacturer of marine radios in the 1940s
Category: Vintage Radio
 I enjoy playing with old marine radios that operated in the AM mode between 2-3 MHz.    This was the standard for "ship to shore" radio and telephone service from marine radio operators from after WWII until about 1970 when SSB was phased in and AM became obsolete.     Through this era a number of manufacturers were major players including RCA (Ra...  READ MORE
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    I've always thought that knurled aluminum knobs were a high-class option for radio gear, and while they are more durable than plastic they do accumulate tarnish, corrosion, and grunge from dirty fingers over the years and start to look poor.   Fortunately it is easy to restore them to a new attractive appearance using a bead blaster. Mine is a Harbor Freight floor-standing...  READ MORE
- Robert Nickels (ranickels),  04/29/2021 
  

Replacing C-frame fans

Boatanchor parts from the home improvement store
Category: Technical
 It's not often that you can buy a replacement part for a vintage transmitter or amplifier off the shelf at the home improvement store, but this is one example.   And since it's not a perfect drop-in replacement, here's now I adapted a new Broan-Nutone BP-27 bathroom-kitchen exhaust replacement fan to fit into a Johnson Desk Kilowatt.These small shaded-pole "C frame...  READ MORE
- Robert Nickels (ranickels),  04/23/2021 
  

My SWR Dilemma

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Category: Vintage Ham Radio
 When I got my Novice license in the fall of 1965, my dad had also decided that as long as he was taking me to the classes at Blue Valley Amateur Radio Club in Seward, Nebraska, he might as well try for his license too.    I was fortunate that not only were my parents supportive of my ham radio interest, but my dad could build anything.   So the first thing was a 40 f...  READ MORE
- Robert Nickels (ranickels),  04/13/2021 
  

The WRL Duo-Bander 84

An "only 50 cents per watt" transceiver
Category: Vintage Ham Radio
  Go Mobile!  That was an attractive marketing message to 1960s era hams who were enjoying the fun of operating SSB mobile, and WRL knew a low-cost rig that didn't have to be hauled back and forth to the car would be a winner.   Heathkit and Swan had already proven that with their single (mono) bander transceivers, but what if you're heading out in the middle of th...  READ MORE
- Robert Nickels (ranickels),  03/27/2021 
    After the conclusion of World War II, there were only about 300 radio amateurs in Japan.   In the  year 1952, the JARL reported that only 30 provisional licenses were granted.    Realizing the value of ham radio in developing a technological workforce, Japan introduced its entry level Class 4 licence in 1959 -  it would prove to be the world's most succ...  READ MORE
- Robert Nickels (ranickels),  03/24/2021 

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