{"id":65188,"date":"2026-01-18T08:16:37","date_gmt":"2026-01-18T12:16:37","guid":{"rendered":"https:\/\/swling.com\/blog\/?p=65188"},"modified":"2026-01-18T08:16:37","modified_gmt":"2026-01-18T12:16:37","slug":"bobs-radio-corner-what-is-it-about-radio-dials","status":"publish","type":"post","link":"https:\/\/swling.com\/blog\/2026\/01\/bobs-radio-corner-what-is-it-about-radio-dials\/","title":{"rendered":"Bob’s Radio Corner: What Is It About Radio Dials?"},"content":{"rendered":"

\"\"<\/a>– Recollections of Bob Colegrove<\/strong><\/p>\n

In the late \u201860s, I worked as a mechanical assembler at Communications, Electronics Inc. (CEI) in Rockville, Maryland (acquired by Watkins-Johnson Company).\u00a0 We produced military-grade receivers, mainly for the military (whom else?).\u00a0 These covered the spectrum from VLF through microwave.\u00a0 It was the early days of electronic digital readouts.\u00a0 There were no LEDs or LCDs.\u00a0 Instead, some of our models featured the Numeric Indicator eXperimental, or \u201cnixie\u201d tubes.\u00a0 These were glass tubes filled with low-pressure neon\/argon gas, featuring stacked wire cathodes shaped like numerals (0-9) and a mesh anode.\u00a0 An analog-to-digital circuit encoded the frequency to illuminate the correct digits.<\/p>\n

Below is shown a DRO-50 Digital Readout from the 1968 CEI catalog.\u00a0 It contained 6 nixie tubes for the frequency display, and the unit had an accuracy of \u00b1100 Hz.\u00a0 Interestingly, this frequency display was designed specifically for the Hammarlund SP-600 Receivers (R-274A\/FRR (Army), R-274B\/FRR (Navy)).\u00a0 I never saw a DRO-50 come across our line and suspect it may not have gone beyond the prototype.\u00a0 About that time, the SP-600s were ending their military service, so there wasn\u2019t much of a market for upgrades.\u00a0 It would still be a few years before I owned an SP-600 of my own, but how would I love to have one fitted with a DRO-50.<\/p>\n

\"\"<\/a><\/p>\n

What I had instead of nixie tubes were variable capacitors or inductors, which changed the tuned frequency through a kluge of pulleys and strings, all these hidden behind a Raymond-Loewy-designed bezel and operated by the tuning knob.<\/p>\n

What was visible on the front of the radio was an irregular representation of frequencies covering the tuning range of the radio, in other words, the dial<\/i>.\u00a0 As you rotated the tuning knob, you set the whole tuning mechanism in motion.\u00a0 Signals were progressively tuned, processed, and reported through the speaker or headset as you advanced higher or lower.<\/p>\n

Somehow the frequencies never quite agreed with the numbers or divisions on the dial.\u00a0 It could be that the circuits inside the radio were out of alignment.\u00a0 Just as likely, the design of the dial was determined using a preproduction prototype which could not possibly account for the tolerances of the components used on the assembly line.<\/p>\n

Consider the figure at the beginning of this posting.\u00a0 It is a portion of the dial on a Hallicrafters S-38E \u2013 magnified somewhat.\u00a0 The full dial on the E model was big and bright.\u00a0 It extended across the front panel of the radio and presented frequency readout about as well as was possible.\u00a0 Nevertheless, there were real shortcomings.<\/p>\n

The figure is not only typical if communication receivers of the time but also living room console radios of an earlier period.\u00a0 Take the 31-meter band as an example.\u00a0 Broadcast stations were bunched roughly between 9400 kHz and 9800 kHz.\u00a0 At 5-kHz channel spacing, this resulted in roughly 80 channels.\u00a0 Of course, not all were in use at any given time, but still a smidgeon turn of the knob could traverse two or three stations.<\/p>\n

This situation was relieved somewhat on communication receivers by the addition of a bandspread \u2013 a separate tuning mechanism which could effectively magnify<\/i> a small portion of the main dial.\u00a0 The idea was to place the main tuning dial at the high end of the desired band and the bandspread at 0.\u00a0 Then, by tuning the bandspread toward the other end, lower frequencies could be tuned with greater separation.<\/p>\n

Since the bandspread could be used at any place within the tuning range of the radio, a separate dial became a problem, so it was usually annotated with a simple logging scale incremented linearly from 0 to 100.\u00a0 Thus, one had to compile a log-to-frequency conversion table or graph to interpret the frequency.\u00a0 More sophisticated receivers could display the 80- through 10-meter ham bands on the bandspread dials.<\/p>\n

\"\"<\/a><\/p>\n

As an example, I located some notes made in 1959 using the S-38E.\u00a0 The table shows the frequency, bandspread reading, station and country.\u00a0 Thirty-one meters was an easy match for the bandspread, as WWV on 10000 kHz was a steady marker which you could use to calibrate the bandspread with the main tuning.\u00a0 For all practical purposes, the band was bounded by the Voice of Spain on 9360 kHz and R. Budapest on 9833 kHz.\u00a0 For many years, Tel Aviv was an outlier on 9009 kHz.<\/p>\n

\"\"<\/a><\/p>\n

Alternately, one could construct a graph as shown below.\u00a0 Unfortunately, most inexpensive radios did not produce linear tuning, so you couldn\u2019t simply draw a straight line between two points on a graph and expect to interpolate the intermediate frequencies with accuracy.\u00a0 Instead, graphs were constructed laboriously by hand adding intermediate points for known frequencies.\u00a0 The figure shows the resulting parabolic function where the slope is greater on higher frequencies and gradually levels off as the bandspread is tuned lower.\u00a0 Notice that most of the activity was mashed between 40 and 60 on the bandspread, then compare this with the picture of the bandspread above.<\/p>\n

\"\"<\/a>On the S-38E a bandspread was something of an improvement, but not the complete answer.\u00a0 The problem only got worse as you went higher in frequency.\u00a0 At 19 and 16 meters the band compression became quite severe.<\/p>\n

Our esteemed leader, Thomas, occasionally uses a picture of the dial shown below as a lead figure of a posting.\u00a0 It is possibly an RCA Victor Model 110k console radio.\u00a0 When I see this, I think, who wouldn\u2019t give a king\u2019s ransom to own that radio in its fully restored condition?\u00a0 Note the 31-meter band has been magnified as its own separate band and appears in a near linear progression.\u00a0 Thirty-one meters was arguably the center of international shortwave broadcasting in the golden age.<\/p>\n

\"\"<\/a><\/p>\n

Have you ever wondered what the rest of that radio looks like?\u00a0 Here\u2019s one in sore need of some Pledge.\u00a0 Now imagine yourself, perhaps 11 or 12 years old, perched in front of it on your grandmother\u2019s needlepoint stool tweaking the dial.\u00a0 If you have experienced this, no explanation is necessary.\u00a0 If you haven\u2019t, none is possible.<\/p>\n

\"\"<\/a>

Source:\u00a0 https:\/\/www.liveauctioneers.com\/<\/a><\/p><\/div>\n

So, as it turns out, I have tempered my earlier conviction that a digital frequency readout is necessarily better than a classic dial.\u00a0 Not to say you can easily pry the PL-880 with 10-Hz resolution from my cold, stiff hands, but I have come to realize that intrigue and mystery of shortwave listening rested in the uncertainty of knowing exactly what frequency you were on.\u00a0 There was always the possibility that the elusive Nibi Nibi Islands<\/a> lay somewhere near the shadow cast by the dial pointer.\u00a0 It was a land of enchantment, and once you left its borders, you could never return again.<\/p>\n","protected":false},"excerpt":{"rendered":"

– Recollections of Bob Colegrove In the late \u201860s, I worked as a mechanical assembler at Communications, Electronics Inc. (CEI) in Rockville, Maryland (acquired by Watkins-Johnson Company).\u00a0 We produced military-grade receivers, mainly for the military (whom else?).\u00a0 These covered the spectrum from VLF through microwave.\u00a0 It was the early days of electronic digital readouts.\u00a0 There […]<\/p>\n","protected":false},"author":15,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[3,305,288,7566,26,43],"tags":[10732,11022,4091,1302],"class_list":["post-65188","post","type-post","status-publish","format-standard","hentry","category-news","category-nostalgia","category-radio-history","category-radio-memories","category-radios","category-shortwave-radio","tag-bobs-radio-corner","tag-radio-dials","tag-radio-history","tag-radio-nostalgia"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/pn3uc-gXq","jetpack-related-posts":[{"id":63601,"url":"https:\/\/swling.com\/blog\/2025\/08\/bobs-radio-corner-illuminating-radios\/","url_meta":{"origin":65188,"position":0},"title":"Bob’s Radio Corner: Illuminating Radios","author":"Thomas","date":"August 10, 2025","format":false,"excerpt":"The Book Lamp; or Shedding Some Light on a Radio Illuminated by Bob Colegrove There was a time in this writer\u2019s memory when radios were well lit \u2013 well, at least the ones with glass tubes.\u00a0 Tubes emitted a warm glow which made the radio come alive, generated some heat\u2026","rel":"","context":"In "Accessories"","block_context":{"text":"Accessories","link":"https:\/\/swling.com\/blog\/category\/accessories\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/08\/Fig-6-PL-990-scaled.jpeg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/08\/Fig-6-PL-990-scaled.jpeg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/08\/Fig-6-PL-990-scaled.jpeg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/08\/Fig-6-PL-990-scaled.jpeg?resize=700%2C400&ssl=1 2x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/08\/Fig-6-PL-990-scaled.jpeg?resize=1050%2C600&ssl=1 3x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/08\/Fig-6-PL-990-scaled.jpeg?resize=1400%2C800&ssl=1 4x"},"classes":[]},{"id":33222,"url":"https:\/\/swling.com\/blog\/2018\/07\/boat-anchor-tuesday-national-hro-50t\/","url_meta":{"origin":65188,"position":1},"title":"Boat Anchor Tuesday: National HRO-50T","author":"Thomas","date":"July 17, 2018","format":false,"excerpt":"Many thanks to SWLing Post contributor,\u00a0Price Kagey, who shares the following photo for Boat Anchor Tuesday and writes: \"My wonderful HRO-50T. I have replaced all tubes and now need to start on capacitors and resistors.\" What a beautiful radio, Price!\u00a0 Once you've re-capped and replaced the resistors in this girl,\u2026","rel":"","context":"In "Boat Anchors"","block_context":{"text":"Boat Anchors","link":"https:\/\/swling.com\/blog\/category\/boat-anchors-2\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2018\/07\/National-HRO-50T.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2018\/07\/National-HRO-50T.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2018\/07\/National-HRO-50T.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2018\/07\/National-HRO-50T.jpg?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":59212,"url":"https:\/\/swling.com\/blog\/2024\/03\/why-schenectady\/","url_meta":{"origin":65188,"position":2},"title":"Why Schenectady?","author":"Thomas","date":"March 12, 2024","format":false,"excerpt":"Many thanks to\u00a0SWLing Post\u00a0contributor,\u00a0Bill Meara\u00a0who writes: Thomas: SWLing Post readers might like this one. Ramakrishnan sent me the Smithsonian article. It is very nice, and helps answer -- I think -- the question about why so many old SW radio dials have \"Schenectady\" on them. Steinmetz seems like a great\u2026","rel":"","context":"In "News"","block_context":{"text":"News","link":"https:\/\/swling.com\/blog\/category\/news\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2017\/12\/General-Electric-Vintage-Radio-Dial.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2017\/12\/General-Electric-Vintage-Radio-Dial.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2017\/12\/General-Electric-Vintage-Radio-Dial.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2017\/12\/General-Electric-Vintage-Radio-Dial.jpg?resize=700%2C400&ssl=1 2x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2017\/12\/General-Electric-Vintage-Radio-Dial.jpg?resize=1050%2C600&ssl=1 3x"},"classes":[]},{"id":64316,"url":"https:\/\/swling.com\/blog\/2025\/10\/bobs-radio-corner-shortwave-multiplex\/","url_meta":{"origin":65188,"position":3},"title":"Bob’s Radio Corner: Shortwave Multiplex?","author":"Thomas","date":"October 19, 2025","format":false,"excerpt":"Reported by Bob Colegrove Incurable DXers are always looking for new challenges.\u00a0 So it was, I recently did some scanning between 42 and 45 meters (~6600 to 7000 kHz).\u00a0 Trenton Military on 6754 kHz and the MARS net on 6913 kHz are regulars here, as are a selection of pirates\u2026","rel":"","context":"In "News"","block_context":{"text":"News","link":"https:\/\/swling.com\/blog\/category\/news\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/10\/Fig.-1.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/10\/Fig.-1.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/10\/Fig.-1.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/10\/Fig.-1.jpg?resize=700%2C400&ssl=1 2x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/10\/Fig.-1.jpg?resize=1050%2C600&ssl=1 3x"},"classes":[]},{"id":63472,"url":"https:\/\/swling.com\/blog\/2025\/07\/mark-dials-into-nostalgia-with-the-lego-retro-radio\/","url_meta":{"origin":65188,"position":4},"title":"Mark Dials Into Nostalgia with the Lego Retro Radio","author":"Thomas","date":"July 27, 2025","format":false,"excerpt":"Many thanks to SWLing Post contributor, Mark Hirst, who writes: Thomas, You might remember that a year or so ago, Lego released a retro radio set aimed at the 18+ age group. I had an opportunity to visit a Lego shop recently because a company away day meeting was set\u2026","rel":"","context":"In "Kits"","block_context":{"text":"Kits","link":"https:\/\/swling.com\/blog\/category\/kits\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/07\/Lego-Radio.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/07\/Lego-Radio.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/07\/Lego-Radio.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/07\/Lego-Radio.jpg?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":63931,"url":"https:\/\/swling.com\/blog\/2025\/09\/bobs-radio-corner-uncle-clayton-and-his-national-nc-188\/","url_meta":{"origin":65188,"position":5},"title":"Bob’s Radio Corner: Uncle Clayton and His National NC-188","author":"Thomas","date":"September 14, 2025","format":false,"excerpt":"As recalled by Bob Colegrove Uncle Clayton was my very first SWLing buddy.\u00a0 In the late \u201850s there was no Internet \u2013 very few ways for SWLs to interact with one another.\u00a0 There were clubs that published mimeograph bulletins every month or so.\u00a0 These were mailed to SWLs across the\u2026","rel":"","context":"In "News"","block_context":{"text":"News","link":"https:\/\/swling.com\/blog\/category\/news\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/09\/Fig-5-NC-109.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/09\/Fig-5-NC-109.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2025\/09\/Fig-5-NC-109.jpg?resize=525%2C300&ssl=1 1.5x"},"classes":[]}],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/posts\/65188","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/users\/15"}],"replies":[{"embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/comments?post=65188"}],"version-history":[{"count":2,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/posts\/65188\/revisions"}],"predecessor-version":[{"id":65197,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/posts\/65188\/revisions\/65197"}],"wp:attachment":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/media?parent=65188"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/categories?post=65188"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/tags?post=65188"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}