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Show all reviews of the Palomar LF Converter VLF-A
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of the Palomar LF Converter VLF-A.
Mar 8, 2013 19:57
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Palomar VLF Converter and its Use with Flex Radios
Time owned: 3 to 6 months
Review of Palomar VLF-B Converter and its Use with Flex Radios
U.S. hams should soon get their first permanent longwave allocation since 1912. Even now experimentally licensed stations are active in RF’s “basement” and can be heard on various modes with simple receivers. One thing is certain, longwave hams will transmit with inefficient antennas and low power. They will utilize a full arsenal of sophisticated weak signal modes including WSPR and QRSS. You’ll want top notch receiving equipment to get the most out of this new allocation.
Few ham receivers hear well below 540 kHz. My Flex-5000 transceiver is perhaps the worst. It picks up absolutely nothing below 530 KHz except a cacophony of broadcast artifacts. What a waste! Flex radios otherwise provide cutting edge technology for weak signal reception. Flex, for instance, offers lab quality stability and frequency accuracy to <1 Hz. Its fantastic panadaptor is useful for analyzing longwave digital signals.
Flex owners have discussed ways to improve LF performance. Low pass and band pass filters hold promise, but it’s hard to predict their effectiveness in any specific location. I’ve gone with another approach which is to use a converter to move longwave signals up to a range where my receiver excels.
Good low frequency reception is mostly about rejecting unwanted noise from a myriad of natural and man-made sources. Virtually all receivers and antennas have plenty of sensitivity. The conversion itself can introduce problems related to intermod and overload by nearby high-powered stations.
I opted for the venerable $89.00 Palomar VLF-B converter which arrived within a few days from K1EL Systems. Its specs say it transforms the 10 kHz-500 kHz band to 4.010 MHz-4.500 MHz by mixing incoming longwave signals with RF from its 4 MHz crystal controlled oscillator. With most receivers one would simply ignore the preceding “4” from the readout to get the actual listening frequency. I was concerned that the converter wouldn’t cover around 505 kHz where some ham activity takes place. But you can easily hear through the lower portion of the AM broadcast band.
I noted just one or two trivial instances of weak spurious AM BCB signals intruding on reception. At last, hams, NDBs, WWVB and even European LW AM broadcasts popped out from the background as I tuned my Flex. Digital ELF stations from thousands of miles away can be heard almost down to direct current. My antenna is hardly ideal: a DX Engineering 43’ HF ham vertical in a St. Louis suburb.
Twelve years ago QST, in reviewing an earlier version of the Palomar converter, wrote that oscillator error produced readouts that were 7 kHz off. My new converter is off by 318 Hz across the receiving range. Unfortunately it has no trimmer for correcting that. The manufacturer tells me that replacing capacitor C1 in my unit with one of 10 pF should move it close to the proper frequency.
TRANSMITTING INTO ANY CONVERTER CAN DESTROY THE CONVERTER. Refer to the manual to assure that you connect the Palomar properly. At first I used Flex-5000’s RX1 input which is a simple receive-only BNC connection. I eliminated the 318 Hz frequency error with the Flex RIT.
The Flex-5000 provides a more elegant way to connect a converter through the transverter (XVTR) input. Clicking on XVTRs brings up the XVTR Setup Form where the LO Offset should be set to -4.000. That removes the preceding “4” so the readout shows WWVB, for instance, at 0.060.000 rather than at 4.060.000. I corrected for my Palomar’s oscillator error by entering -0.318 in the LO Error box. The converter selection button on the Flex “Front Console” can even be relabeled to read “VLF” if desired. After a few other simple form settings the Palomar is fully integrated into the transceiver.
The sturdy Palomar VLF-B consists of a three stage low-pass filter, crystal LO, and a 1496 mixer chip. I counted about 15 capacitors and 13 resistors, none of them SMD. With its LM7809 voltage regulator, the simple converter is remarkably drift-free. No schematic is provided in the 4-page manual. The front panel switch turns the converter on or off and bypasses it when turned off.
The VLF-B brought the longwave performance of my Flex-5000 to life. However a converter is actually a minor component in a low frequency receiving system. Important too are antenna type and placement, feed line, man-made noise sources including lighting and power lines, and proximity of powerful broadcast stations.
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