Another Custom Version of the TFT EAS 930A
AM, FM and Weather Band Monitor
Above is the original project showing the factory EAS-930 and below it my version of the EAS-1. Note the awkward screwdriver adjustments needed to
change frequency on the factory model and the improved tuning method using BCD pushbutton switches on the EAS-1.
I liked the first modification of the EAS-930 so much that I decided to build another one, but a little better than the EAS-1. The EAS-2 will have more
flexibility in tuning and show the signal conditions more effectively.
Instead of the pushbutton BCD tuning switches, we now have rotary switches that select the actual frequency digits.
Below are some pics of the beginning layout. For this version, I am using rotary switches that will be wired for BCD translation.
If you are familiar with some of the older MacKay Dymek receivers, then you'll recognize the individual digit switching arrangement.
I've also added LED indicators to show the 'carrier-only' and 'audio demod' conditions, along with a 'level set' control for each of the three bands.
More soon, during Oct/Nov., 2012.
These views were taken during the check to make sure all the controls, meters and switches will
actually fit on the front panel as dictated by my layout of the front panel decal.
As before, I had to make my own meter faces. Below are shown the only tools
needed to accomplish that, once you have designed and printed the
meter decals. There is more info about that on the EAS-1 page.
The meters mounted, along with all the switches and pots. Note the 5-gang, 10-position
rotary switches which are wired as BCD translators for the AM "KHz", FM "MHz" and WX
channels "1 thru 7" selection.
This is a test of the wiring for the LED indicators for signal strength indication, mode and carrier/data re-broadcast suitability. This independent and constant signal
strength and condition monitoring is (of course) not necessary for the average, and casual, listener. But, for re-broadcast use, whether "in-studio" or via STL (studio
transmitter link), the source signal's condition must always be known, prior to mixing the signal to the On-Air transmitter - for obvious reasons.
This system is not only mandated by the FCC for commercial broadcasters, but also a great source of information for organizations such as ARES, CERT, SKYWARN,
WXspots and other civilian, government and commercial use.
Note that under the actual antenna feed signal level indicators (u V), there are indicators for "carrier only" and usable demodulated audio. There are separate detector
circuits that sense constant carriers for the three bands; AM, wide FM and narrow FM (red LED)) and if any usable audio is demodulated from those carriers (yellow
LED). The signal strength digital meters are calibrated against the analog S-meter for 50 u V at S-9. For instant visual recognition: Red = AM, Green = FM, and Blue =
Weather. The band switch selects which of the three bands are fed to the line feed and the second analog meter indicates the 600 Ohm audio line feed to the monitor
line. There is also a monitor level control for the user to hear the signal through the internal speaker, or an external studio monitor, or headphones.
For emergency conditions, the power line is also monitored (120 VAC / 12 VDC) as "Stnby/Ready" and "Operate" indicators.
| Digital to BCD Truth Chart
DIGIT Binary Switch Section
1 2 4 8
3 X X
5 X X
6 X X
7 X X X
9 X X
| SWITCH SECTION JUMPER WIRING
WAFER #1 BCD-1 1-3-5-7-9
WAFER #2 BCD-2 2-3-6-7
WAFER #3 BCD-4 4-5-6-7
WAFER #4 BCD-8 8-9
For reference, if you want to wire your own (4-pole) 10-position rotary switches as BCD translators, here's the data:
(Note: use a 5-pole switch if you want to incorporate a digital display or indicator, but not necessary if you have the digits printed on the panel decal)
--- or ---
This can also be done with a single section, 10-position, rotary switch by using diode
logic. It will require 15 diodes (like a 914 or 4148). But the radio requires 7 switches for
the 7 digits, so I elected to use the hard-wired method for the sake of time.