Blowing up a VLF converter
 

I was looking for an antenna for my LF/VLF converter.
The converter is from Jakson Harbor Press and uses a
SA602 chip to convert 10-400 khz up to 14.010-14.400.
It has 2 five pole L.P. filters (cutoff @ 500khz).

For $12, it can't be beat. Anyways, I've got it running
and everything that should be grounded is grounded. I've
got a antenna lead with an alligator clip on it and I'm
probing around, listening to WWVB. I try my 40m inverted
V (fed with ladder line & coax). I get a pretty good signal
on the "hot" side (the side that connects to the center of my
coax) but also I get the same signal from the ground side so
I left it there.

The path for the 40m antenna is radio/coax/coax coil/ladderline/
antenna. The converter is hooked to the junction where
the coil transitions to the ladder line. It's just a pl-259 with one
side of the ladder line going into the center pin and the other side
soldered to the shell. I figure I'll just go out and unhook the
converter's antenna clip when I use the 40m antenna.

Getting gutsy, I decided to see what would happen if I didn't
unhook the converter and transmitted into the 40m antenna
I tried 1/2 watt - no damage. I then tried different power levels
finally ending up with a 15.2w CW carrier. No damage!

I thought I'd blow my little converter. Anyone care to educate
me as to why it didn't blow? Would it have blown up if I had
hooked to the other side of the ladder line? Did the 2 five pole
low pass filters save it?
--
73 de Ken KGØWX - Flying Pigs #-1055
Elecraft K2 #4913

My money's on the filter.

Roy Lewallen, W7EL

Ken Bessler wrote:
I was looking for an antenna for my LF/VLF converter.
The converter is from Jakson Harbor Press and uses a
SA602 chip to convert 10-400 khz up to 14.010-14.400.
It has 2 five pole L.P. filters (cutoff @ 500khz).

For $12, it can't be beat. Anyways, I've got it running
and everything that should be grounded is grounded. I've
got a antenna lead with an alligator clip on it and I'm
probing around, listening to WWVB. I try my 40m inverted
V (fed with ladder line & coax). I get a pretty good signal
on the "hot" side (the side that connects to the center of my
coax) but also I get the same signal from the ground side so
I left it there.

The path for the 40m antenna is radio/coax/coax coil/ladderline/
antenna. The converter is hooked to the junction where
the coil transitions to the ladder line. It's just a pl-259 with one
side of the ladder line going into the center pin and the other side
soldered to the shell. I figure I'll just go out and unhook the
converter's antenna clip when I use the 40m antenna.

Getting gutsy, I decided to see what would happen if I didn't
unhook the converter and transmitted into the 40m antenna
I tried 1/2 watt - no damage. I then tried different power levels
finally ending up with a 15.2w CW carrier. No damage!

I thought I'd blow my little converter. Anyone care to educate
me as to why it didn't blow? Would it have blown up if I had
hooked to the other side of the ladder line? Did the 2 five pole
low pass filters save it?
--
73 de Ken KGØWX - Flying Pigs #-1055
Elecraft K2 #4913

In article ,
Roy Lewallen wrote:

I thought I'd blow my little converter. Anyone care to educate
me as to why it didn't blow? Would it have blown up if I had
hooked to the other side of the ladder line? Did the 2 five pole
low pass filters save it?

My money's on the filter.

Yeah, there would be quite a lot of attenuation... five poles, and the
40-meter signal is about four octaves above the filter's nominal cutoff.

I thought that the converter might possibly include a set of
anti-parallel diodes between the filter and the SA604 to provide some
additional strong-signal protection, but I don't see any. So, it must
be that the filter attenuation was sufficient to keep the SA602 input
levels below the danger threshold. I seem to recall that these little
Gilbert-cell active mixers are reasonably rugged.

In looking at the schematic, I do see one thing which concerns me.
The filter is a pi configuration, with a .01 uF cap to ground at
either end. The cap at the antenna end of the filter (C4) would tend
to shunt a lot of the 40-meter signal to ground, with L1 blocking much
of the rest.

Seems to me that there could be two bad effects from having this
circuit shunted across the antenna when the 40-meter transmitter is
keyed up. For one thing, it could present a low impedance at its
attachment point (depending on the length of the feedline from the
upconverter to the attachment) and might adversely affect the
transmitter. For another thing, if there's a significant amount of RF
power getting to the front of the filter, it'll be shunted to ground
through C4 (a little monolithic ceramic by the look of it) and losses
in C4 might be sufficiently high to cook it and let all of its magic
smoke out.

If C4 does pop, the converter would still work, but there'd be one
less pole of low-pass filtration.

It might not be a bad idea for the OP to check C4 to see if it shows
signs of overheating, and perhaps consider adding another inductor
between the antenna terminal and the C4/L1 junction. This would
convert the filter from a two-Pi to a three-L configuration, and
increase its antenna-side impedance at HF.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

As the filter represents a very high impedance above 500 Khz it should have
protected the converter.

"Ken Bessler" wrote in message
news:fXHPe.5152$ct5.5069@fed1read04...
I was looking for an antenna for my LF/VLF converter.
The converter is from Jakson Harbor Press and uses a
SA602 chip to convert 10-400 khz up to 14.010-14.400.
It has 2 five pole L.P. filters (cutoff @ 500khz).

For $12, it can't be beat. Anyways, I've got it running
and everything that should be grounded is grounded. I've
got a antenna lead with an alligator clip on it and I'm
probing around, listening to WWVB. I try my 40m inverted
V (fed with ladder line & coax). I get a pretty good signal
on the "hot" side (the side that connects to the center of my
coax) but also I get the same signal from the ground side so
I left it there.

The path for the 40m antenna is radio/coax/coax coil/ladderline/
antenna. The converter is hooked to the junction where
the coil transitions to the ladder line. It's just a pl-259 with one
side of the ladder line going into the center pin and the other side
soldered to the shell. I figure I'll just go out and unhook the
converter's antenna clip when I use the 40m antenna.

Getting gutsy, I decided to see what would happen if I didn't
unhook the converter and transmitted into the 40m antenna
I tried 1/2 watt - no damage. I then tried different power levels
finally ending up with a 15.2w CW carrier. No damage!

I thought I'd blow my little converter. Anyone care to educate
me as to why it didn't blow? Would it have blown up if I had
hooked to the other side of the ladder line? Did the 2 five pole
low pass filters save it?
--
73 de Ken KGØWX - Flying Pigs #-1055
Elecraft K2 #4913

Ken Bressler, KG0WX wrote:
"I was looking for an antenna for my LF/VLF converter."

Over the 10-400 KHz frequency range, there are propagation variations
between night and day. A tuned loop antenna of the type often used in MW
broadcast radios also works in other frequency ranges including your
converter input.

The tuned loop is small in terms of wavelength, yet it can improve
signal to noise ratio from its frequency selectivity and from its
directional characteristics. It can be an air-core type or be wound on a
ferrite rod.

I won`t speculate why ken hasn`t destroyed his converter with his HF
transmitter.

Best regards, Richard Harrison, KB5WZI

"Fred W4JLE" wrote in message
...
As the filter represents a very high impedance above 500 Khz it should
have
protected the converter.


Thanks everyone for the advice - I did check for overheating
and I did check to see if the addition of the converter changed
either SWR or performance of my dipole. Seems OK so far.

Thanks for the education!

73 de Ken KGØWX - Flying Pigs #-1055
Elecraft K2 #4913

Dear Dave Platt - AE6EO
You must be looking at the schematic of the converter. Where is the
schematic to be found?
Thanks, Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Dave Platt" wrote in message
...
In article ,
Roy Lewallen wrote:

I thought I'd blow my little converter. Anyone care to educate
me as to why it didn't blow? Would it have blown up if I had
hooked to the other side of the ladder line? Did the 2 five pole
low pass filters save it?

My money's on the filter.

Yeah, there would be quite a lot of attenuation... five poles, and the
40-meter signal is about four octaves above the filter's nominal cutoff.

I thought that the converter might possibly include a set of
anti-parallel diodes between the filter and the SA604 to provide some
additional strong-signal protection, but I don't see any. So, it must
be that the filter attenuation was sufficient to keep the SA602 input
levels below the danger threshold. I seem to recall that these little
Gilbert-cell active mixers are reasonably rugged.

In looking at the schematic, I do see one thing which concerns me.
The filter is a pi configuration, with a .01 uF cap to ground at
either end. The cap at the antenna end of the filter (C4) would tend
to shunt a lot of the 40-meter signal to ground, with L1 blocking much
of the rest.

Seems to me that there could be two bad effects from having this
circuit shunted across the antenna when the 40-meter transmitter is
keyed up. For one thing, it could present a low impedance at its
attachment point (depending on the length of the feedline from the
upconverter to the attachment) and might adversely affect the
transmitter. For another thing, if there's a significant amount of RF
power getting to the front of the filter, it'll be shunted to ground
through C4 (a little monolithic ceramic by the look of it) and losses
in C4 might be sufficiently high to cook it and let all of its magic
smoke out.

If C4 does pop, the converter would still work, but there'd be one
less pole of low-pass filtration.

It might not be a bad idea for the OP to check C4 to see if it shows
signs of overheating, and perhaps consider adding another inductor
between the antenna terminal and the C4/L1 junction. This would
convert the filter from a two-Pi to a three-L configuration, and
increase its antenna-side impedance at HF.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dear Dave Platt - AE6EO
You must be looking at the schematic of the converter. Where is the
schematic to be found?

The manufacturer's page for this kit can be found at

http://jacksonharbor.home.att.net/lfconv.htm

You can download the manual and/or the schematic.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dear Dave Platt - AE6EO:
Thanks. I should have thought of that.
Back when Navy VLF stations were still using CW, one could receive great
practice by listening. I used a crystal oscillator and a simple filter to
modulate the oscillator with VLF.
73, Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Dave Platt" wrote in message
...
Dear Dave Platt - AE6EO
You must be looking at the schematic of the converter. Where is the
schematic to be found?

The manufacturer's page for this kit can be found at

http://jacksonharbor.home.att.net/lfconv.htm

You can download the manual and/or the schematic.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!