CBWI September 1996 The New DF 10000 Low Pass Filter by RF Limited
Yup a 10,000 watt low pass filter. Most of you don't need anything quite this heavy duty, but it's a pleasure to see some new serious equipment coming down the pike. There are some out there that could use this gem. There are some that could use a 50,000 watt version. But believe it or not that's not the most impressive specification this unit offers.
RF Limited has three models to choose from, the DF-4000 a 4KW PEP unit, the DF-7000 a 7KW PEP unit, and the DF-10000 a 10KW PEP unit. All are rated half of their PEP rating for DC. That's only were the specifications differ. All other specs. are identical.
DF Series Low Pass Filter Specifications
Above is the from the specification sheet supplied with the unit. To the right is the graph of frequency verses attenuation. After removing the 19 screws I peeked under the cover and found some of the best workmanship I've seen in a long time.
All the connections are secure. This is were most failures occur in filters. A connection problem may not be obvious to the operator making it a more undesirable problem. One bad connection could cause the filter to allow the harmonic emissions along with the fundamental frequency to pass right through.
Continued interference after installing a filter leads you to believe it could be one of a hundred other problems and not the filter because your match and signal strength are OK. There isn't much to go wrong with them beyond connections. The coils are heavy gauge copper and all insulators are Teflon including the SO-239 connectors.
Everything is screwed together or soldered. No pop rivets in these units! The two specifications that impress me are the cutoff frequency of 32Mhz and the attenuation of 70 - 100db above 38Mhz. The low pass filters I've encountered, Nye Viking, Barker & Williamson, Para Dynamics, and the old CPI, have cutoff frequencies from 45Mhz to 50Mhz.
This is very close to the lst harmonic of CB and the bottom of the TV frequencies. And the above mentioned filters had attenuation figures from 60db to 80db at 54Mhz. As you can see the DF series filters are at approximately l00db at 5OMhz. The DF filters have a ground connection with a wing nut to connect the filter to earth ground.
None of the other filters have this connection even though it makes sense to ground the filter to bleed off the unwanted emissions. Under an actual use test I replace a RF Limited DF-2000, which has decent specs., there was no interference on channels, 2, 4, 5, or 7. Without the filter Channel 2 was a washout, 4 had a few lines, 5 was terrible and 7 had intermittent interference.
The DF-2000 improved everything but 5 had a few lines and 2 became blurred with interference. Adding the earth ground did show a slight improvement. I'm impressed, the DF-10000 is the best I've seen. The manufacturers suggested list price is a little inflated but I'll include that for reference.
The DF-4000 MSRP is $219.95, the DF-7000 is $249.95, and the DF-10000 is $299.95. In real life you can expect to pay about 2/3rds of suggested retail. BCB will make them available for a limited time by special order at a reduced amount.