|[AMRadio] BC-610 on 160|
rbethman at comcast.net
Tue Nov 5 14:31:48 EST 2013
I haven't had any harmonic issues with either of my BC-610s.
I do run a low pass filter on the immediate output. One is a Bud LP
filter, the other is a B&W LP filter.
I've only had one instance of a squawk of interference, and it happened
while using an Apache. It got into a cordless phone a few blocks away.
The Apache is rather noted for several issues.
When they get put back on air again, I'll be controlling frequency with
an HP-3336B Frequency Synthesizer feeding the crystal jack of the Tuning
The Den/Shack has spent a bit over three years as a living space for
family members and was silent to allow them some modicum of private space.
They departed in July, and the XYL decided to undertake a significant
renovation of this Den/Shack. It isn't quite done, and looks more like
early next year before I can begin my work of getting the Shack back to
I'm looking forward to getting back to operating. I have really missed it.
I used to operate 40mtr AM in the mornings. The group that used to
operate there sort of fell apart with the loss of WC3K in 2002. It
really hit us all hard.
So it is going to be almost starting from scratch once more.
I do know at least one coax must be replaced due to those furry tailed
rats called squirrels that decided that the coax was a snack. I do have
new coax, and will run it when the inside gets its arrangement set in place.
I'll run on 80, 40, and 20 as time goes by. I really don't have the
space to try running 160. I have enough issues running on 75/80. There
is a lot to be done to rebuild an operating position from the ground
up. The "old" operating bench gave up the ghost and even with a metal
frame, became an old sway backed horse.
Right now there is just a bit more to the renovation to be done before
the XYL will let me begin recovering my area. It isn't a small room, it
is 27 ft by 24 ft. I'll have about 12 ft by 27 ft for everything.
The operating bench will be either 10 ft or 12 ft in length.
There would be a better chance of starting sooner, except for a wedding
to attend the end of the month. It does feel more normal now that the
extra family isn't here now. We have begun getting things back to normal.
Bob - N0DGN
On 11/5/2013 1:51 PM, JAMES HANLON wrote:
> If I were trying to attenuate my second harmonic, in this case from a BC-610 operating on 160 but in general for any transmitter with a second harmonic problem, I would use a "Half Wave Filter." I'm looking at my Editors and Engineers Radio Handbook, 15th Edition, page 387 where they are described. The "Half Wave Filter," which was also described in the Nov-Dec 1949 GE Ham News, is simple and "presents the same value of impedance at its input terminals as appears as load across its output terminals." This type of filter will give an attenuation of about 30 dB to the second harmonic, 48 dB to the third harmonic, 60 dB to the fourth harmonic, 67 dB to the fifth harmonic and so on, increasing at a rate of 30 dB per octave.
> The schematic of the filter is two pi-sections in cascade, each section in a shielded box with a shield in between each section. The top of each pi section is an inductance, and the side legs are capacitances. For 160 meter and for a 52 ohm characteristic impedance, the capacitors are 1700 picofarads (all four of them) and the coils are 4.2 microhenry. The coil is described as 22 turns of #16 enamel wire, 1" diameter, 2" long. The coil should be checked and adjusted for resonance at the operating frequency when paralleled with one of the capacitors. Transmitting type ceramic capacitors are recommended for high power operation. Silver mica or small ceramic caps are OK for lower power.
> I use Half Wave Filters made up for 80, 40, and 20 meters with my Collins 32RA8 to keep its harmonics in check. They seem to work well.
> Jim Hanlon, W8KGI
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