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Author Topic: LF receiver input protection. Is this sound??  (Read 937 times)

2E0ILY

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LF receiver input protection. Is this sound??
« on: September 12, 2018, 04:20:20 AM »


RX protection sought for either a Kenwood TS-590 or a Red Pitaya
functioning as an SDR for the LF 136kHz band. Change over relay box
for the antenna has a 60 Amp automotive relay grounding the RX line
and changing to switching the antenna to the amp with a Russian high
power co-axial relay 500mS before TX starts. In case of an unforeseen
whoopsie an automotive 5W festoon bulb would be in series with RX
antenna input prior to two back to back 6A10 diodes? The festoon bulb
is long enough not to sustain an arc over (I have tested on full power with
one side of the bulb to ground). I don't believe the inductance of the
bulb is significant "down there" frequency wise. But I am unsure about
the effect of the big diodes...


Amp is a 1kW Class D FET amp, is this a sound scheme? The TX side of things has a
separate exciter and the SDR or TS-590 function solely as a receiver
but sharing the TX antenna. Thanks.
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Best regards, Chris Wilson.

G3RZP

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RE: LF receiver input protection. Is this sound??
« Reply #1 on: September 12, 2018, 09:36:01 AM »

I am a bit dubious about using a 6A10. With over 100pF of capacity and a relatively long trr (500nS), I feel you would do better with a rectifier meant for SMPS use at higher frequencies than the 60Hz which what the 6A10 is characterised at.
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G4AON

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RE: LF receiver input protection. Is this sound??
« Reply #2 on: September 12, 2018, 10:29:41 PM »

Could you use a separate RX antenna? If you have enough room in your garden, an active antenna could avoid the worry over the effectiveness of relays, etc.

I don't operate below 160m, but have a vertically polarised active antenna mounted about 60 feet from a short vertical for 160m. Even without turning it off on TX, the ADC clipping/overload LED on my SDR doesn't light while TXing on 160m.

The circuit of the active antenna, and the dc injection/TX disconnection box, is at:
https://www.qsl.net/g4aon/pa0rdt_aa/

While I use the "belt and braces" approach of a series lamp and back to back diodes myself... If you check the peak to peak Voltage across the commonly use back to back pair of diodes, while increasing the output of a signal generator feeding them, you will find a lot more signal level than you expect.

73 Dave
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W9IQ

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RE: LF receiver input protection. Is this sound??
« Reply #3 on: September 12, 2018, 11:06:57 PM »

Take a look at the Vishay 15ETX06 for the protection diodes. 600 PIV, trr = 18 ns, IF=15A, IFM=30A, CT=20 pF, LS=8 nH, isolated case and reasonable cost.

- Glenn W9IQ
« Last Edit: September 12, 2018, 11:17:05 PM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

G3RZP

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RE: LF receiver input protection. Is this sound??
« Reply #4 on: September 13, 2018, 03:28:57 AM »

Glenn,

I'd say those are a far better bet than the 6A10......
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2E0ILY

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RE: LF receiver input protection. Is this sound??
« Reply #5 on: September 13, 2018, 03:59:12 AM »

Thanks for the replies, I have the space for a separate RX antenna but the resonated top loaded vertical easily surpasses experiments I have done with the active mini whips for RX. I have never had much luck with those here, but fully understand others get great results.

I have looked at the data on the super fast diodes and see what a huge difference there is! Hopefully the festoon bulb in front of them will assist as well. I am not sure what voltage the amp produces prior to the outside matching transformer and big loading coil, probably near to the peak voltage of those diodes. I have ordered 4 of them and will use these super fast rectifier ones as suggested, thanks for info and putting me straight!
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Best regards, Chris Wilson.

G3RZP

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RE: LF receiver input protection. Is this sound??
« Reply #6 on: September 13, 2018, 10:05:37 AM »

FWIW, a 2 turn 1 metre square loop loop 70 feet away from my 160m vertical at 400 watts had about 80v rms across the tuning capacitor. So I used an E88CC/6DJ8 twin triode as a push pull cathode follower: the tx signal drove it into grid current, which damped the tuned circuit and reduced the volts on the cathode follower grid. But I still switched the antenna feed line to the receiver.
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2E0ILY

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RE: LF receiver input protection. Is this sound??
« Reply #7 on: September 14, 2018, 06:17:17 AM »

FWIW, a 2 turn 1 metre square loop loop 70 feet away from my 160m vertical at 400 watts had about 80v rms across the tuning capacitor. So I used an E88CC/6DJ8 twin triode as a push pull cathode follower: the tx signal drove it into grid current, which damped the tuned circuit and reduced the volts on the cathode follower grid. But I still switched the antenna feed line to the receiver.


OK, thanks again Peter :)
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Best regards, Chris Wilson.
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