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Laurence & All: It would be interesting
to take one of those Array Solutions Receiver Front End Protectors
and replace the pair of isolation transformers in
it with something that is optimized for 100kHz to 1MHz service. The
above-mentioned product is rated for use down to 500 kHz, but I would be
concerned about the IMD performance of those transformers in normal service and
the nearby AM broadcast band signal levels....
I have been thinking of ordering one of these units
for placement after my LF converter, as I run a +23dBm LO and DBM
(Level 23 RAY6 from Mini Circuits). If a
mixer diode fails, my IF receiver would see + 23dBm at 3.000 MHz. I built
a version
of W1VDs 500kHz variable high-Q preselector
that covers 3.2 to 3.5 MHz, which offers some protection to my IF
receiver, but the
saturated 1:1 transformer seems like a more
elegant solution....
Not all receivers have push-pull 2N5109 front ends.
The kind of power levels discussed are a potential overload-damage hazard,
especially outside the the LF/MF frequency range. I have an FT-847 with a
dead preamp stage from accidently leaving the radio connected to my 2M yagi with
my 144.3 CW beacon running 20 feet away. 10mw on the rx input killed
it.... The TS-2000 is known to be worse for rx overload damage at VHF/UHF.
Some of the HEMT devices used for preamps have -10 dBm danger zones and will
likely expire at levels above 0dBM.....so it is worthwhile to determine the safe
operating limits of a receiver's front end active device.....
73, Mike wa3tts
----- Original Message -----
Sent: Thursday, October 15, 2015 1:26
AM
Subject: Re: LF: PA0RDT antenna near a
TX? Front end OK?
Chris Mike JNT et al - So this piqued my measurement interest
This evening running circa 2W ERP at 137kHz 1Kw from Decca 5501, I
measured the following:-
Ve7sl clone 10ft diameter screened mag loop burhans amp at 50ft from
500ft circumference tx loop gave plus 13.2dBm into terminated 75ohms W
and G SPM30 (oerrr!) - this is normally connected via a 6dB pad to an Icom R75
without issue to date.
Amp appears to have a lot of "head room"
And -8.4dBm from an LF engineering L400b probe at 150ft or so
Interesting
Laurence KL7L WE2XPQ
Wspr 2 136kHz till dawn
Laurence, Chris & All: I did a test
with my eprobe which is about 30 feet away from my HF elevated ground plane
that has 65 ft radials a few years back. With 100W output on 40 meters. I
was getting 1mw of RF power from the eprobe into a Boonton RF voltmeter. I
was using a 1 inch wide by 12 inch long brass strip as the eprobe
antenna at the time. I would assume the eprobe may be able to generate
more power than that at higher nearby transmitter power
levels. Suitable overload protection for a receiver front end would
appear to be prudent.....
73, Mike wa3tts
----- Original Message -----
Sent: Wednesday, October 14, 2015
2:56 PM
Subject: RE: LF: PA0RDT antenna near
a TX? Front end OK?
Chris I run up to 1Kw on 136kHz and up to
400W on 475kHz and "alive" Eprobes (L400 and PA0RDT variants)
about 100-150ft away up at 30ft plus and not blown them up. They
don't like it much of course and produce unwanted products during Tx but
that not surprising. Only FET failure to date has been down
in Oklahoma from a nearby lightning
strike. Laurence KL7L et al
> > > If I mount my PA0RDT clone on my mast stub,
about 50 feet from my LF > TX'ing aerial, is it likely to be damaged
if powered on when TX'ing? > > Thanks. > Best
regards, > Chris mailto:[email protected]>
>
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