[Lowfer] [EXTERNAL]Re: Receiver protection
Howell, Laurence J
L.Howell at conocophillips.com
Tue Jul 10 14:04:15 EDT 2018
Its been a year of receiver and transceiver damage due to high RF voltages at the inputs.
Up to this year Ive had only desensing or similar artifacts, but I managed to destroy a U3S set up to transmit in parallel with my main 475kHz 5W EIRP Marconi (only around 100ft away), the U3S tuned also at 475kHz to a 30ft top loaded vertical.
I just didn't realize how many volts and total power was available at the end of the vertical - it burnt up the final and a number of surrounding components. Mr Tesla would have been proud.,,a total bin job
Secondly I burnt out the protection device on the front end of the TS870S - I first thought it was due to a lightning strike but again was due to RF from the MF Marconi power passing thru from a doublet on 10MHz again about 100ft away -
Ive ended up with a High pass filter in the front end of the TS870 which has eliminated the issue and dumps the MF to a few mV pd with little attenuation. So if you ever wondered why the 10KHz snapper goes dark at night, or did, it was I had to pull the coax out whilst transmitting on MF - but not now.
Just watch out on what can come out of a passive or active antenna in proximity or at some distance - it may cause you more issues than you think, inc active eprobes...
Ps this was the first such damage in nearly 45 years of tx ops, so its still a learning curve....old dogs and new tricks etc. I still have fond memories of old Racal active preselectors in front of my RA 1772 and 17Ls at my coast station op position.
Laurence KL7 L
-----Original Message-----
From: lowfer-bounces at mailman.qth.net <lowfer-bounces at mailman.qth.net> On Behalf Of Lee Hiers
Sent: Tuesday, July 10, 2018 9:45 AM
To: Discussion of the Lowfer (US, European, & UK) and MedFer bands <lowfer at mailman.qth.net>
Subject: [EXTERNAL]Re: [Lowfer] Receiver protection
I used to operate at a big 160 station for contests years ago - we ran two
rigs, so one RX always had a Beverage connected to it, even when the other
rig was transmitting (conservatively) at 1.5 kW. Never a problem. I would
think as long as you have about 40 dB isolation or better from the TX you
should be OK, and that's why you had no damage.
73 de Lee, AA4GA
On Tue, Jul 10, 2018 at 8:04 AM, N1BUG <paul at n1bug.com> wrote:
> Does anyone have ideas for receiver front end protection at LF and
> MF? I am worried about my TX signal damaging receivers.
>
> Of course the best idea is to disconnect the RX antenna from the
> receiver while transmitting. Any good solution while leaving it
> connected?
>
> Now I have a pair of back to back 1N4148 diodes across the receiver
> front end but I don't think this offers real protection because they
> allow too high voltage before conducting. Also there is a preamp
> after the didoes which can bring the RF to dangerous levels!
> (Somehow nothing was damaged during last winter operating this way... :)
>
> 73,
> Paul N1BUG
>
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