[600MRG] SID - Sudden Ionospheric Distrubances

Wed Apr 4 20:05:23 EDT 2018

On 4 Apr 2018 at 18:32, Dave Riley wrote:

> How low to go is the question here.. The SDR-IQ goes down to low audio...
> 
> I see this RAK as the ultimate BPF throughout it's range... Why have
> AGC? The thing can take about +40 or so...a 150 db dynamic range is
> not so shabby.. Intermod??

I've never, ever experienced any. I used one for several years to receive the Navy VLF 
stations. I also used an RAL (the HF version) as my main and only station receiver for at 
least 12 years before switching to something more modern.

And the researcher I mentioned earlier used many RAKs. He never, apparently, 
experienced any intermod either.

They are a TRF with two 6D6 (equivalent to the 6K7) RF amps, a 6D6 regen detector and 
two stages of audio. There is a sixth tube, a 41 (equivalent to the 6K6) configured as a 
switchable output limiter, which the manual calls an "AVC" but it isn't.

Go here and take a look:

http://www.w7ekb.com/glowbugs/BA/index.html

The audio gain runs wide open all the time, and the "gain" control is an RF gain control.

There were two things about them (and the RAL) I didn't like: 1) no direct frequency readout: 
dials are 0 - 10 and 0 - 100 (but there is no backlash either), and 2) they weigh nearly 80 lbs 
and are ....um....rather large....(!!!)

Stability, sensitivity, and selectivity are more than adequate. At MF/LF/VLF the RAK exhibits 
"single-signal" selectivity, in fact. The "other side of zero beat" simply isn't there.

Power supply requirements are VERY minimal: 180 VDC at 35 mA, 90 VDC regulated at 1 
mA (for the detector), and 6.2 VAC at 2 amps.

I also have two RBAs, but those are even larger. And an R-389, several RBLs and some 
SRR-11s. I sold my last SP-600-VLF-31 and have none now.

Oh. I also have some Stoddart "Noise Meters" which cover our range....and more.

http://online.sfsu.edu/hl/src.html

I suspect that these days one could couple a cheap eBay frequency counter to the detector 
stage of the RAK and get a close-to-accurate readout.

Ken W7EKB

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