EMRFD Message Archive 10387
Message Date From Subject 10387 2014-10-26 10:33:58 Weddig, Henning-C... AW: [emrfd] Losses in Diplexer? Steve,
a "loaded Q "of 10 seems a bit too mcuh for me!
The Problem ist that the L in the series arm gets large ( 3978 nH) whicle the parallel resonantor- L gets very small (38 nH)
To get a low Insertion loss the unloaded Q´s of the components should be large, I guess at least ten times the loaded Q.
You do not state whiczh type of coilsd You use.. SMD inductors surely will be insufficient due to their low Q.
And think about the self capacitance of the series L!
I would recoomend to use a loaed Q of about 3!
Von: 'Steve VK2SJA' firstname.lastname@example.org [emrfd] [mailto:email@example.com]
Gesendet: So 26.10.2014 08:51
Betreff: [emrfd] Losses in Diplexer?
Newbie again. Seems like every time I get stuck and need to cry "Help!"
it's about losses. This time in a Bridge-Tee Diplexer I built for 20Mhz.
Built one at Q1 - too wide. Needs to be Q10. Then built Q10 version and it
is exactly where it should be in frequency and just a little over 2Mhz
wide. Very pleased with myself, I have it under control.
Except that I have a 6dB insertion loss. This article says that with good
quality components I should be looking at 0.5dB or less!
I used the following online calculator:-
And then manually verified the answers against the equations in the paper
I played around with it trying a few things and did manage to get the loss
down to 4.5dB but its still a long way to 0.5dB
So questions. Is 0.5dB truly a realistic home-brew target before I go
knocking myself out. And can someone suggest where the common losses
occur. As the circuit has so few parts is it in the capacitors used?
Brown, round, disc-ceramic, Modern. One side NPO the other not. If so what
type of capacitors should I be using here?
10391 2014-10-27 05:07:54 i7swx Re: AW: [emrfd] Losses in Diplexer? Hi Steve,a Q of 10 is too high as you will have a narrowbandwidth.I use a Q=1, the components are the same one for serial and parallel tuned circuits. I do get between 0.2 or lees to 0.5 dB loss as second as the circuits are tuned. You may use commercial inductance values near the required ones, i.e. for 8,215MHz, you need L=0.969uH and a C= 388pF, you can use a 1uH and adjust C.With these values you should be lower than -0.5dB loss73GianI7SWX 10406 2014-11-01 21:06:55 kerrypwr Re: AW: [emrfd] Losses in Diplexer? Q=10 is workable at frequencies up to about 10 or perhaps 15 MHz; at your 20 MHz it might be better, as others said, to drop the design Q to somewhere in the 1 - 5 range.
Common "Jaycar" ceramics are usually reasonable Q; as Henning said, the inductors might be the problem.
Try #2 (red) iron-powder for the inductors.
The Q=10 diplexer in this 5 MHz mixer/amplifier/diplexer module has 0.4 dB loss;
10415 2014-11-05 09:33:16 Steve VK2SJA Re: AW: [emrfd] Losses in Diplexer? Another big thank-you to all who replied.
I re-calculated for Q=6 and rebuilt the filter. I now have about -2dB IL
for about 4Mhz of BW. So at least I'm now heading in the right direction.
I'm already using a T50-2 red toroid for the larger inductance value. The
small inductance I made as an air core coil at 5mm diameter.
The breakthrough came when I realized that the air core coil for best "Q"
needed to have the coil loops spaced apart to reduce capacitive effects (I
assume). The need for a "Q-Meter" has now become obvious. So that's the
This process has also clearly highlighted why one should NOT use 50 ohm
resistors that exhibit significant inductive properties.
> Q=10 is workable at frequencies up to about 10 or perhaps 15 MHz; at your
> 20 MHz it might be better, as others said, to drop the design Q to
> somewhere in the 1 - 5 range.
> Common "Jaycar" ceramics are usually reasonable Q; as Henning said, the
> inductors might be the problem.
> Try #2 (red) iron-powder for the inductors.
> The Q=10 diplexer in this 5 MHz mixer/amplifier/diplexer module has 0.4 dB
> http://i57.tinypic.com/fummjd.jpg http://i57.tinypic.com/fummjd.jpg
> Kerry VK2TIL.
10418 2014-11-05 11:27:48 kerrypwr Re: AW: [emrfd] Losses in Diplexer? Loss of 2dB still seems high.
You may have the reason in your comment about coil turns-spacing; the coil may be getting into its self-resonance region, esp. at the fairly high frequency of 20 MHz.
Your DSA-815TG can be used to determine Q; it's really just an RF signal generator and a sensitive detector.
We lost a wonderful resource when Wes took his website down; one of the gems was his paper "The Two Faces Of Q". It describes simple practical methods of determining Q.
I have a copy; PM me if you would like it.
I could put it in the Files section here if that's OK with Wes.
10419 2014-11-05 12:35:31 blumu Re: AW: [emrfd] Losses in Diplexer? ----- Original Message ----- From:Kerry VK2TIL´
. . . "The Two Faces Of Q".
. . . I could put it in the Files section here if that's OK with Wes.
. . .
It would be great if this were possible.
10420 2014-11-05 14:33:01 kerrypwr Re: AW: [emrfd] Losses in Diplexer? I would do it if Wes or Roger give the OK.