I don't like to get bogged down in math, and eham makes it difficult to post equations. So I'm going to go at this conceptually, which for me is easier to understand anyway.

To lower the Q of a L/R parallel circuit one needs to increase R.

No. That's just not right.

To lower the Q of an LR

**parallel** circuit one needs to

**decrease** R.

To lower the Q of an LR

**series** circuit one needs to

**increase** R.

The obvious way to do this is to increase the resistance of R.

No it isn't.

However as resistance increases, so does dissipation - and that problem is most severe at 28MHz since that is the band where the V-drop across L is max. Since the R component of a suppressor needs to have low self-inductance to function properly, suitable resistors are few. A workaround is to use resistance-wire for L.

Let's see where this goes.....

Even though its resistance is in series, by doing a series to parallel equivalent conversion one can see that it has the same effect that a parallel resistance has.

No it doesn't. It has a completely different effect. Series to parallel equivalent conversion is not valid in this case because the frequency changes, and so does the reactance.

Here's proof:

Consider a conventional suppressor consisting of a coil of very high conductivity (very high Q coil) in parallel with a resistor of very low inductance.

At "high" (parasitic) frequencies the inductor has quite high XL and very low R. Not much RF current can pass through it because of the XL, so most of the RF current has to go through the resistor - which is so lossy a parasitic can't start.

At "low" (desired) frequencies the inductor has very low XL and very low R. RF currents can pass right through it with very low loss. Only a tiny bit of the RF current has to go through the resistor and be dissipated, because the XL and R of the coil are very low.

Now consider an unconventional suppressor consisting of a coil of resistance wire (low Q coil) in parallel with a resistor of low inductance.

At "high" (parasitic) frequencies the inductor has quite high XL and considerable R. Not much RF current can pass through it because of the XL, so most of the RF current has to go through the resistor - which is so lossy a parasitic can't start. So it "works" in the sense that the parasitic problem is solved.

At "low" (desired) frequencies the inductor has very low XL but considerable R. RF currents can pass through it, but there is considerable loss due to the R. Not only that, but more of the RF current has to go through the resistor and be dissipated, because while the XL of the coil is low the R isn't.

If we take the limiting case (DC), the unconventional suppressor dissipates more than the conventional, because the resistance wire has more loss right down to f equals zero.

IOW, what we want in a parasitic suppressor is a coil that has as high Q as possible and a resistor with as little reactance as possible. The ideal would be a coil of pure L and a resistor of pure R.

Intentionally making the coil resistive is the absolute wrong approach because the coil will then dissipate more, not less, desired-frequency RF.

Now of course we can't get ideal parts. But we can come close by using large copper wire or strap for the coil, and the lowest inductance resistors available.

Remember that if a parasitic suppressor works, the parasitic never starts. All the heat dissipated in a parasitic suppressor is either DC or desired RF. Therefore it makes sense for the suppressor to have as low loss at the desired frequency as possible.

73 de Jim, N2EY