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## [AMPS] L-Net calculations: Am I doing something wrong?

 To: [AMPS] L-Net calculations: Am I doing something wrong? w6ru@lightspeed.net (Terry Gaiser) Tue, 16 Feb 1999 16:30:26 -0800
 ``` Rich Measures wrote: > > > > >Jon, > >I tried this idea with a YC-156 tube I have been experimenting with to > >try to get it to play on 10 meters....its Cout is about 36PF. This is > >the idea of a series inductor between the tube and C1 ??? To step down > >the plate load X... so that you would need more C, less Xc at C1 ??? > >Talk about laying an egg! > > ? What happened? Nothing ! Made no difference. W6RU > > >I would sure like to talk to someone that has > >done this successfully if they exist. > > > ? 36pF of Cout should pose no problem for a conventional tank - > Provided the anode current is max. and C-tune has a minimum of <10pF. // > It seems to me that those who propose using an L-match between the anode > and C-tune, fail to consider that the added L also decreases the anode > vhf-resonance. This could be problematic, depending on where the > RF-grounded screen (or grounded-grid in cath. driven config.) resonance > happens to fall. > > - later, Terry > > > >Jon Ogden wrote: > >> > >> OK, > >> > >> In order to match the high impedance of the 4-1000A to a lower impedance > >> so that I have better loaded Q in my tank circuit, I decided to take the > >> advice many people had given me and that is to make an L-network to step > >> the impedance down to a more workable level. This L-network would > >> consist of the output capacitance of the tube as the shunt (parallel) > >> element and a small inductor as the series element. > >> > >> OK, so at 5KV, the 4-1000A's plate impedance is 4600 Ohms = R1 (from > >> Eimac Specs) > >> The Cplate of the 4-1000A is 7.6 pF (from the ARRL handbook) > >> > >> Let's choose L (the series inductor) to be 1 uH (a suggested value by > >> others). > >> > >> What secondary impedance do we obtain? > >> > >> OK: > >> > >> In an L-net Q=R1/Xp > >> > >> At 28 MHz: Xp=1/(2*pi*28E6*7.6E-12)= 747.91 Ohms > >> > >> Therefore Q=4600/747.91 = 6.15 > >> > >> R2 = Xs/Q (R2 = output impedance) > >> > >> At 28 MHz: Xs=2*pi*28E6*1E-6 = 175.9 Ohms > >> > >> R2 = 175.9/6.15 = 28.6 Ohms > >> > >> Now 28.6 Ohms is unrealistically small in order to properly get a good > >> match with realistic components. > >> > >> OK, so what would a good R2 be? Let's try for 2500 Ohms as this will > >> give decent Qs with the component values I have for the tank circuit. > >> > >> Therefore: > >> > >> Q is still 6.15 since neither R1 nor Xp have changed. > >> > >> Xs = R2*Q = 2500*6.15 = 15375 Ohms > >> > >> At 28 MHz: Ls = Xs/(2*pi*28E6) = 15375/(2*pi*28E6) = 87.4 uH > >> > >> This won't work either since it is a HUGE coil. > >> > >> OK, what gives? Am I missing something here or doing a calculation > >> wrong? > >> > >> Everyone says they've seen this "trick" done in the ARRL handbook and > >> other texts. Can someone be specific as to what handbook (what year)? I > >> sure can't find it yet in the 1999 issue or in my 1989 issue. > >> > >> This idea won't work unless I am totally missing the concept of how to do > >> this. > >> > >> So what am I missing or what have I misunderstood that folks have > >> suggested? > >> > >> 73, > >> > >> Jon > >> KE9NA > >> > >> ------------------------------------- > >> Jon Ogden > >> KE9NA > >> > >> http://www.qsl.net/ke9na <--- CHECK IT OUT! It's been updated!!!!! > >> > >> "A life lived in fear is a life half lived." > >> > >> -- > >> FAQ on WWW: http://www.contesting.com/ampfaq.html > >> Submissions: amps@contesting.com > >> Administrative requests: amps-REQUEST@contesting.com > >> Problems: owner-amps@contesting.com > >> Search: http://www.contesting.com/km9p/search.htm > > > >-- > >FAQ on WWW: http://www.contesting.com/ampfaq.html > >Submissions: amps@contesting.com > >Administrative requests: amps-REQUEST@contesting.com > >Problems: owner-amps@contesting.com > >Search: http://www.contesting.com/km9p/search.htm > > > > Rich... > > R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures > > -- > FAQ on WWW: http://www.contesting.com/ampfaq.html > Submissions: amps@contesting.com > Administrative requests: amps-REQUEST@contesting.com > Problems: owner-amps@contesting.com > Search: http://www.contesting.com/km9p/search.htm -- FAQ on WWW: http://www.contesting.com/ampfaq.html Submissions: amps@contesting.com Administrative requests: amps-REQUEST@contesting.com Problems: owner-amps@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
 Current Thread [AMPS] L-Net calculations: Am I doing something wrong?, Jon Ogden [AMPS] L-Net calculations: Am I doing something wrong?, Terry Gaiser [AMPS] L-Net calculations: Am I doing something wrong?, Jon Ogden [AMPS] L-Net calculations: Am I doing something wrong?, Rich Measures [AMPS] L-Net calculations: Am I doing something wrong?, Terry Gaiser <= [AMPS] L-Net calculations: Am I doing something wrong?, Jon Ogden [AMPS] L-Net calculations: Am I doing something wrong?, Rich Measures [AMPS] L-Net calculations: Am I doing something wrong?, Jon Ogden [AMPS] L-Net calculations: Am I doing something wrong?, Rich Measures [AMPS] L-Net calculations: Am I doing something wrong?, Peter Chadwick [AMPS] L-Net calculations: Am I doing something wrong?, Rich Measures [AMPS] L-Net calculations: Am I doing something wrong?, Peter Chadwick [AMPS] L-Net calculations: Am I doing something wrong?, Jon Ogden [AMPS] L-Net calculations: Am I doing something wrong?, Rich Measures [AMPS] L-Net calculations: Am I doing something wrong?, Jon Ogden