To my knowledge, despite all the dire warnings, nobody has actually
"fried" an Si4734 chip by directly connecting any antenna in place of
the stock loopstick. Graham Maynard's original FSL article gave a
severe warning not to try directly connecting an FSL this way
(surmising that the signal overload would surely burn up the chip), but
even Graham never mentioned an actual chip failure due to such a
Those in the group over a year ago may recall Jim Kearman's "Hoop Loop"
project, where he directly connected a 20" diameter air core loop to a
PL-380 in place of the stock loopstick, apparently suffering no ill
effects. Although the hard-wired connection to a 20" external loop
seemed kind of unwieldy to me for transportation reasons, I figured
that if the Si4734 chip varactor could survive such a test it could
probably survive direct connection to a moderately-sized FSL,
was verified in my own test. Of course, nobody really wants to "fry" an
Si4734 chip to find out exactly what the component's maximum signal
handling level is.
After directly connecting the small (12 rod) FSL to a PL-380 I ran an
LW signal "Shootout" test against a (hard-wired) 7.5" LW loopstick
PL-380, the same type of radio that was sent to Rob, Kevin and Patrick
(in France). The hard-wired FSL had superior RSSI and S/N readings on
every fringe LW signal, but the 7.5" loopstick was able to match it
station-for-station, at a slightly lower signal level. This wasn't the
result I was looking for-- the hard-wired FSL cost about $150 to
construct, while the 7.5" LW loopstick cost about $25. I figured that
the hard-wired FSL needed to at least receive a few stations that the
7.5" LW loopstick couldn't, in order to justify the steep cost of
construction-- but it couldn't do this. Accordingly,
the hard-wired FSL
was dismantled, and the parts recycled into the inductively-coupled
6.5" Longwave FSL used for the recent Oregon Beach DXpedition. This
inductively-coupled FSL had performance that seemed to border on
science fiction, providing inductive coupling boosts to a stock PL-380
that allowed reception of many stations thaty were completely inaudible
on the 7.5" LW loopstick PL-380. When used together with the latter
model, it provided reception of a 1,000 watt LW beacon in the South
Pacific at over 5,000 miles from the Oregon beach site.
From: Rick Robinson <w4dst@...
To: ultralightdx <ultralightdx@...
Sent: Sun, Aug 7, 2011 10:25 am
Subject: [ultralightdx] Re: DSP noise
I'd like to know what caused the signal level to "fry" the Si4734.
That's very interesting that this could/would happen but if within
proximity to one of those European megawatt transmitters, I'm sure it's
possible if you aren't careful. If it were extremely static sensitive,
I'd have fried mine long ago. :>)
If you remember Stephen's tests last year underneath a transmitting
antenna, he was in as large an RF field as anyone would want to be in
and reported no damage to his radio. I duplicated his tests with my G8
and PL-310 within 100 feet of my local WHKP tower on 1450kHz while they
were running daylight power. About the only thing I learned, other
the field strength pinned the signal level at the max
on both radios,
was that there was an image on 1360kHz, 90kHz below the WHKP frequency.
From this I deduced that the DSP IF was around 45kHz which was
by a post from Scott at Silicon Labs.
I see from your pictures that a second version of the antenna has a
tuning capacitor. Do you remember what your signal levels were with
direct coupling and inductive coupling? I wonder if perhaps the
internal ferrite bar tends to increase the field strength from the
inductively coupled FSL over the directly coupled version. Possibly
step up transformer action between the 2 could account for the
difference. Just thinking out loud.
On 8/7/2011 12:04 PM, D1028Gary@...
> The hard-wired FSL was reasonably sensitive on
both LW and MW, and
> despite dire warnings from Graham Maynard and others, the signal
> provided by the hard-wired FSL did not "fry" the Si4734's internal