[ARC5] Navy LM Use

[Bill Cromwell]

On 05/23/2013 05:23 AM, Christopher Bowne wrote:
> Here's another challenge...try to figure out the approximate frequency the
> ART-13 is set to by zooming on the picture and attempting to read the dials and
> band switch settings, using an ART-13 calibration book you might have on hand.
> The estimated frequency should be pretty close.  My ART-13 did not have an
> original calibration book, and I use a copy of one sent to me a long time ago by
> Walt, KJ4KV.   The actual frequencies set using the numbers of the copied table
> are pretty much right on the money.
>
>
>
>
> ________________________________
> From: Jason W6IEE <w6iee.73 at gmail.com>
> To: arc5 at mailman.qth.net
> Sent: Wed, May 22, 2013 11:31:20 PM
> Subject: Re: [ARC5] Navy LM Use
>

Hi Jason,

I don't have an ART-13 so I have no idea about the dial markings (which 
I can't read from the blurry photo anyway). Since it has a "calibration" 
book I assume it has logging scales and a bandswitch or bandswitches. 
It's not difficult to make a cal book or a tuning chart for an LM, a 
RAK/RAL, or any radio with "logging" scales. I have three LMs here and 
each has the cal book with matching serial number. I suspect that they 
wouldn't be very far off if I swapped the books. Some day maybe I'll 
test for that.

I made the tuning charts/graphs I use here with my RAK and SW-3 by 
driving a digital frequency counter with a signal generator so that I 
can exactly record the dial numbers for a string of frequencies. That 
information is entered into a spread sheet which then generates points 
in between by interpolation/extrapolation - just as the cal books that 
shipped with the LMs and probably with the ART-13s. My observations 
about doing that show the tuning curves are not a straight line but are 
very close to that over most of the tuning range. The curve bends a 
little more at the ends and at the very ends it bends sharply. For each 
increment of the tuning range (for one chart I plotted every 1 kc for a 
reality check) you can determine the amount of frequency change per 
graduation mark on the dial. That number will change gradually as you 
move across the covered spectrum. You use the rate of change for each 
'increment' to plot the intermediate points.

You will get operational satisfaction entering 10kc, 50 kc, and even 100 
kc cal points into your spread sheet against log scale readings and then 
letting the spreadsheet generate a smoothed curve overlaid with a grid. 
I use mine in the low light of my shack to preset my radios (with 
logging scales) to the desired frequency or in reverse to read the 
frequency of a found signal. All of this assumes that we do not have to 
set our radios to the nearest tenth of one milliHerz! That kind of 
nonsense is for the very weak signal (QRSS/WSPR) fellows, God bless 
their pea-pickin hearts. But just as an example - with my RAK the 
coarsest dial readings are for the highest frequency band and each one 
kc is divided by approximately 3 and a half dial marks. That varies a 
little and varies smoothly across the one thousand dial marks. That 
suggests that presetting within 300 cycles should be rather easy. The 
marks are far enough apart to guesstimate half and maybe quarters of a 
mark. certainly getting within 300 cycles is plenty good enough for ham 
communications on CW, AM, and SSB. For CW and SSB you might want a small 
touchup to get the note you want on CW or to clarify the audio on SSB. 
The RAK isn't any good for phone anyway but you can zero beat an AM 
station and then disable the BFO or oscillating detector. The same 
approach applies to that ART-13.

73,

Bill  KU8H