Several Blog postings ago I spent a bit of time on S Meters for your homebrew rigs. What I didn't cover was some possibilities for meter displays.
It was one of those slow day things several years ago where it was too hot in the garage Lab/Shop and my idle mind turned to possible Meter Scales.
I tripped over my prior work the other day which caused this circling back. What suddenly struck me is the possibility of a multiple meter face showing SWR, Signal Strength and Power supply status. Now that would be a lot of info packed into a small panel space.
In all cases it would be a "bar type" scale. There are some detailed considerations however, behind each of the scales and that in turn drives the mathematics behind each scale.
In the top scale this is not suitable for an S Meter but OK for a Voltage reading. S Meters somewhere in the background have a log function hiding in the woodpile. The middle scale shows that log depiction.
But it is the very bottom scale that looks like a real S Meter. We see by the spacing that the tick marks are log based and typically S9 is the on the air reference point -- you know, it is a contest and the guy at the other end says you are 5X9 but can't make out your call sign.
So, behind the simple bar graph is the math equations but also the sensors that provide the math inputs. For the S Meter you can read a voltage on an Analog input pin and convert that into the length of the horizontal bar.
For the battery level a voltage reading across a resistor would provide the source voltage to an analog pin. That would not be read directly, but the sample voltage is converted (in analog) to the battery status. Example: a 0.5 Volts sample would register as 10 VDC based on the math you provide.
For SWR a sample collected via a snoop loop consisting of 1 turn of wire passed through the final coil of the W3NQN LPF and connected to a diode to provide a negative voltage. This is where you take that voltage and match that to an external SWR bridge so that you can develop a scaling factor as input for the Arduino. You might have to invoke the abs(Vin) math function to get it to play right but that is half the fun.
The Weird and Strange
Long before the invasion of the Far East Ham Radio manufacturers stuff was built here in the USA which spawned a lot of unusual rigs to hit the marketplace. Likely Blog Readers have not seen these before, but they do exist.
The example above comes from World Radio Laboratories and the fertile mind of Leo Meyerson. It is a dual band 80/40M 100-watt SSB Transceiver in a really small package. Likely the intended market was for Mobile Operation. The tuning range was not full band but covers the SSB range for the then known phone bands. The DB84 had some unique IF type transformers that were band pass filters.
The Crystal Filter was on 5.2 MHz which offers the possibility if liberated from the rig to form an 80/20M rig and with a 9MHz VFO and the same BFO frequency would place the rig on 20M USB and 80M LSB. There is a pair of 6HF5's in the final and so capable of more than 100 watts. Weird indeed was the use of a 12BY7 as a Receiver Mixer stage.
This is a bare bones rig but shows some really clever circuitry including a push pull knob that is the band switch.
Another barebone radio not often seen is from Atlas Radio. I have no clue as to why you would do this but essentially the Atlas 210 Transceiver was broken up into two boxes with one being a receiver and the second box a trans-citer that could be either a 15 watt or 100-watt radio.
Weird and strange are two good words to describe why any radio manufacturer would think there is a market for such radios. These would never compete with a TR-4 or FT-101.
73's
Pete N6QW