Topband: 'Hairpin' matching
The excellent web site for calculating matching network values should have been: http://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html not the one I posted yesterday. 73, Tom G3OLB _ Topband Reflector
Re: Topband: Hairpin Matching Coil Questions - "Shunt"?
Thankyou Charlie. I got those Q numbers from http://www.m0ukd.com/Calculators/air_core_inductor_calculator/ Maybe a decimal point was left out. Jim, I thought something was misleading you somewhere. Be careful with online calculators. The one in the link uses pi out to 39 places (which might give the impression of accuracy), but omits many far more critical, important, parameters. It is a very rough guess that might be a mile off, even though the publisher implies accuracy. They would be better off to just use "3.1" for Pi, and add in some more important things. One way to evaluate an inductor calculator for design omissions is to see if it asks for: 1.) Insulation thickness and type 2.) Turns spacing 3.) Form material 4.) Conductor size 5.) Form length 6.) Form diameter That one grossly fails. It doesn't ask for several important things. To check the calculator for function, start taking a large coil up higher in frequency. If you get weird results like progressively increasing Q that goes over 1000 for normal good conductors, extreme inductance values (like values near whole Henries at HF and higher), the calculator is likely just junk. That one completely fails. It obviously does not consider turn-to-turn capacitance, skin effect, materials, or internal resonances, because I can "make" door bell wire inductors with Q's in the thousands and almost a Henry of inductance on 50 MHz!! Since it doesn't ask for enough things and obviously ignores many important traits of inductors, it is unreliable. It might work in some cases by pure luck, but who knows when it could be trusted!! Things like that can send you down the wrong path, and cause you to start giving out wrong numbers. 73 Tom _ Topband Reflector
Topband: 'Hairpin' matching
Just to add a comment on this thread: I do not use an inductor to match my inverted 'L', just a capacitor from coax centre/bottom of wire to the radial point. Further I do not use big wide space 'toast-rack' Cs, but tiny ceramic ones rated at 6.3KV which will handle very decent amounts of power and are readily available over here. They seem to handle the high currents at the bottom of the quarter wave 'L' quite happily. I measure the impedance at resonance of the antenna without any matching network, then use www.sandiego.edu/~ekim/e194rfs01/jwmatcher2.html to calculate the L-network values needed. Fit the parallel capacitor then lengthen the antenna slightly to bring it back to the required frequency. This provides the inductance necessary for the L-network. Needless to say, your MFJ, or Palstar ZM-30 in my case, antenna analyser will probably give you the wrong sign for the reactive part of the antenna's impedance. This had me going for a long time before I realised the problem! Check this by moving the analyser frequency LF from resonance and the impedance should show -jX (capacitive). Moving the analyser HF from resonance should show inductive reactance (+jX). My inverted 'L' needs 1600pF to give me 50 + j0. I have also made switched L-networks to successfully resonate the same antenna on some other bands. 73 Tom G3OLB _ Topband Reflector
Re: Topband: Hairpin Matching Coil Questions - "Shunt"?
Thankyou Charlie. I got those Q numbers from http://www.m0ukd.com/Calculators/air_core_inductor_calculator/ Maybe a decimal point was left out. Thanks Tom -- Jim K9TF _ Topband Reflector
Re: Topband: 75 ohm coax to twisted pair Adaptors
Hope this will be of some interest for those using twisted pair instead of coax. The company I work for is manufacuring all kinds of 75 Ohm / UTP balun adapters and surge protection units. The one I am using for my phased biderectional flags is "УПВ-МВ" http://www.elsy.com.ua/ru/pasivnie-priemnikiperedatchiki-kanal-c-1_15_66_61.html Sorry the site is in Russian only. The surge protection units - http://www.elsy.com.ua/ru/videonablyudenie-zashchita-ot-visokovoltnih-navodok-c-1_27.html If someone is intersted, please contact me directly. Среда, 18 сентября 2013, 15:33 -07:00 от "Bruce" : >Yes Jim, and that is what I do, sell transformers. Just trying to locate >some cable and let others know adaptors are available. > >Thanks, it's always good to find maybe a better adaptor source and more >resaonable price. > >73 >Bruce-K1FZ > > > >- Original Message - >From: "Jim Brown" < j...@audiosystemsgroup.com > >To: < topband@contesting.com > >Sent: Wednesday, September 18, 2013 12:03 PM >Subject: Re: Topband: 75 ohm coax to twisted pair Adaptors > > >> On 9/18/2013 2:47 PM, Bruce wrote: >>> Found these for a friend who is thinking about going to twisted pair. >> >> To connect what to what? Why? >> >> If it's for RX and the ends are unbalanced (that is, one side grounded), >> he'll need some form of transformer or other circuitry to make a balanced >> connection. >> >> There are female F to male PL259 adapters (most I've seen are el-cheapo), >> and I've seen female F to RCA, and female F to 2-ckt (T-S) 1/8-in male. I >> think Fry's stocks them. >> >> 73, Jim K9YC >> >> >> >> >> _ >> Topband Reflector >> > >_ >Topband Reflector -- 73, Victor Goncharsky US5WE/K1WE (UW5W in VHF contests) UARL Technical Committee DXCC card checker in Ukraine(160 meters). _ Topband Reflector
Re: Topband: Hairpin Matching Coil Questions
Hi Jim, I'm glad to hear you (and others) liked our L-network inverted-L tuner design. All the info I have is posted in the Topband thread. I thought I had more info and pictures, but I guess I'll have to take some new photos sometime. I suppose if you made the elevated radials long, then you could adjust the current balance with series variable capacitors. You could use a simple clamp-on meter like W8JI has on his site to measure the relative current, perhaps.I didn't bother with that myself, I was just careful to keep the radial lengths the same length and height. 73, Mike www.w0btu.com On Tue, Sep 17, 2013 at 5:44 PM, Jim F. wrote: > Hi Mike, > I read with interest your two capacitor tuner and it may be just what is > needed here to tune out the reactance of 3 TB raised radials when they go > up after the leaves leave. > > I wonder if an individual capacitor for each radial would be better ? > > Please send me the info on your system. > _ Topband Reflector
