Total posts : 45366
Daniel mentioned removing the metal cover from a pot used in an RF attenuator. This is not a bad suggestion but there is more involved.
One thing which is often overlooked when constructing a RF attenuator is the need for adequate shielding. A “rats nest” circuit will make a decent antenna and if the power is high enough it can produce quite a distant signal even though it attenuates a thru signal. At VHF, designing and building a good attenuator is a tradeoff between shielding and introducing stray L and C, while at the same time preventing unwanted radiation.
At the least I suggest that the attenuator be placed in a metal enclosure connected to circuit ground in order to stop it from radiating a signal. Double sided PC board pieces soldered together was my choice, but any metal box of the right size will work. Keep all the leads as short as possible.
Also, don’t use just any resistors. I recommend carbon composition if you can get them. Metal film also works, but avoid the very common wire wound units. Too much inductance.
Without scaring anyone away from doing this, I hope I gave a bit of information which will be useful. Do a bit of homework and you will find it is not that difficult to build a good attenuator once you know some of the traps to avoid. You will find that it involves a bit more than just a couple of resistors, but it is not hard to do.
Neil
