Eddystone EA12

[MichaelR]

Hi,

Has anybody experience of the EA12. According to the manual S9 of the S meter represents 54db uV which would give represent an input of about 500 microvolts . Modern radio equipment in general has S9 specified as an input the order of 50microvolts .

Mike

[Herald1360]

According to this reference, the modern standard was agreed in 1981.

http://en.wikipedia.org/wiki/S_meter

The EA12 somewhat predates this, I think, so its S meter calibration would be whatever Stratton & Co wanted it to be......

[neon indicator]

Most S meters in my experience are what ever the manufacturer wanted it to be (or even the user). Many (most?) are driven from a basic diode detector driving the AGC line. A very few modern ones have a logarithmic output from RSSI pin on an IC and are calibrated in dB steps of 6dB. Most are nothing like 6dB steps over the whole range

Originally S1 meant not usable and S9 meant perfect, so nndB over 9 was originally meaningless. Sadly you still hear people say you are 5 and 9 but I can't make out your call

[Skywave]

54 dB above 1 µV = 500 µV: agreed; the EA12 calls this S9: agreed.

On the basis of 6 dB per S-unit, my arithmetic produces S1 as 2 µV and, therefore, S0 as 1µV. However, I would have expected S1 to be 1µV, making S9 correspond to 250 µV.

Over the years, Eddystone appeared to have been rather inconsistent in their S-meter calibrations. For example, the S-meter for the 888A (which is used with other models) has a calibration of 4 dB per S-unit. But then over the years I've come across many features in Eddystone radios that have caused me to pause and think "Hmm; that's strange: why did they do that?"

This link is relevant:
http://www.seed-solutions.com/gregor...eterBlues.htm#

Al.

[Junk Box Nick]

Once I'd got my first dedicated amateur bands receiver way back when - the first I had owned with an S-meter - I remember getting quite worked up over the 'poor' meter readings. I had a decent (resonant length) aerial and a tuner/matching unit, yet the the DX that was supposedly 5 & 9 plus whatever with everyone else sometimes barely flicked the meter. I tried adjusting it, which of course was just self deception to make me feel better.

I began to think the receiver was deaf but it seemed that it required someone next door with 400w PEP to make it end stop. I could hear stations that I couldn't with the previous much simpler receivers which I eventually realised was the acid test.

[MichaelR]

Everything you say is very true and for the "thinking" beginner it raises many doubts over the receiver.

Al you are correct as usual in your thoughts , at least in setting the "S" meter with the EA12 you do supposedly have to terminate the Ax input with a 75ohm resistor and then adjust to S0. This assumes that the noise floor is 1microvolt I suppose.

Mike

[Station X]

Well nowadays the noise level on 80 metres is S7 before you start.

[ms660]

Yes I have to agree about S Meters, in a lot of cases they are configured to make everything look the best, reminds me of level meters on HI Fi etc, we used to call them idiot lights..years ago I was chief tech for sony of canada and every week we would get the usual quota of audio nutters in saying the could hear a half db drop in this and that, I usualy replied with a lecture on logarithmic volume controls and fletcher munsen curves..usually got rid of em.
Cheers.

[ms660]

Yes Graham...it's about S9 where I am and top band is a wipeout...3.3kv power line is only 30 feet away!

Lawrence.

[Skywave]

Originally Posted by MichaelR

. . . in setting the "S" meter with the EA12 you do supposedly have to terminate the Ax input with a 75ohm resistor and then adjust to S0. This assumes that the noise floor is 1microvolt I suppose.

Mike

And it also assumes that that noise level is constant between the various switched bands - which of course, it won't be. (I note that the S-meter 'set zero' is at the rear of the cabinet). But let's be fair to the designers; this concept of using an S-meter to measure the strength of received signals at the aerial socket is not what the designers had in mind: it's really there for comparative signal strength measurement by using the magnitude of the AGC voltage.

And that consideration, using the AGC voltage to control the S-meter, leads me to the following thought. Since the EA12 provides a low impedance IF output at 100 kHz, (which produces about 100 mV for a 2uV input signal), it may be possible to use this output as a signal source for driving an outboard amplifier & rectifier arrangement to operate an external signal strength meter. This, of course, will not require the AGC to be switched on, which for reception of CW and SSB (the two most common forms of communication on the Amateur bands these days) is required: therefore, a much better arrangement on that basis alone, on the grounds of improved linearity over the AGC-source method. Agreed, the IF and RF gain controls will still change the resultant meter reading, but with the use of a calibrated signal generator, a series of calibration charts or graphs could be drawn to allow for this, (and changing sensitivity between switched bands), thus enabling received signal strengths to be accurately measured.

Sounds too easy. There has to be a snag / over-sight in there somewhere!

Al.

[MichaelR]

Originally Posted by Station X

Well nowadays the noise level on 80 metres is S7 before you start.

Very true Graham ( or S2 on the EA12 .. )..... Lately I have been using a sloping doublet here which keeps the noise down low, signals are also low but much more readable which is what really matters.Spend most of my time on 40 meters now.

Very interesting comment Al and feasible, I am not too bothered about S meter readings to be frank it just "threw " me at first when I started to do some sensitivity checks on the receiver.

Mike