From: "Clemens Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>
References: <A905714CEEED4F84A38B62B60939952A@MPC>
In-Reply-To: <A905714CEEED4F84A38B62B60939952A@MPC>
Date: Fri, 29 Jun 2018 18:26:40 +0200
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Subject: LF: RE: Re: Can I match 2 frequencies with one loading coil?
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Hi Mark and Chris,

on http://www.waniewski.de/LW/Lakihegy/lakihegy_lw_1en.htm
you can download a pdf file with a schematic etc. 
of a 135.6kHz & 540kHz 100kW/150kW diplexer
Maybe that's a starting point for Chris' own design.
For download cklick on
http://www.waniewski.de/Pdf/1E-8920-810-DO_documentation%20diplexer%20Lakihegy.pdf

73
Clemens
DL4RAJ 

>-----Original Message-----
>From: owner-rsgb_lf_group@blacksheep.org 
>[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Mark
>Sent: Friday, June 29, 2018 12:27 AM
>To: rsgb_lf_group@blacksheep.org
>Subject: LF: Re: Can I match 2 frequencies with one loading coil?
>
> 
>Hi All
>The technique used for MF  broadcast systems to combine 2 or 
>more transmitters into a single antenna is valid here.
>This is not a '1 loading coil' solution, but is relatively 
>easy to implement as there is no interaction between legs.
>Build a parallel tuned circuit for each frequency you want to 
>use. These are referred to as rejectors.
>The 2 rejectors are joined at the antenna driving point each 
>leg goes to the  equipment.  ie the MF Rx  is passed through 
>the LF rejector  to the antenna and vice versa
>Each rejector will have a very high impedance at its resonant 
>frequency but  have a  series reactance  that is manageable at 
>the  pass freq.
>You then add this series reactance at the pass frequency to 
>the driving point impedance (it helps if you  can measure this 
>and  consider in series reactance format)
>The pass reactance is easily calculated for the rejector. You 
>can then match each leg at the  wanted frequency with no 
>significant  interaction between the  legs of  combiner / diplexer
>Many broadcast antennas at MF are electrically short and often 
>it is helpful to add a  pre-match  element at the driving 
>point  a shunt C or series L or whatever  minimises the 
>subsequent matching requirements on both legs. Matching is 
>commonly done with Pi or T matching sections for ease of 
>adjustment and improved harmonic rejection, although a simple 
>L match would suffice on receive.
> 
>This technique allows transmitters at very high powers 
>(50-100kW or so) on 2  or more  frequencies to use one 
>antenna. It will work on receive just as well enabling a  
>proper 50 j0 ohm resistive  match ( if that is actually needed 
>)  for n frequencies, you need n-1 rejectors in series  for 
>each leg before the matching section
> 
>If you decide to try this on Transmit, watch out for the  
>increased 'circulating currents' in the rejectors due to the 
>passed transmission. Currents and voltages in the C and L of a 
>rejector are larger than the  expected current in the 
>equivalent  pass reactance.
> 
>Mark GM4ISM
> 
> 
> 
> 
>From: Andy Talbot <mailto:andy.g4jnt@gmail.com>  
>Sent: Thursday, June 28, 2018 8:32 PM
>To: LineOne <mailto:rsgb_lf_group@blacksheep.org>  
>Subject: Re: LF: Can I match 2 frequencies with one loading coil?
> 
>Try this, but you'll have to adjust iteratively: 
>Bands referred to as LF and MF
> 
>First make your LF loading coil so it resonates the antenna as 
>it stands.    Now make an MF loading coil.  The problem is 
>that t=when both are connected to the antenna teh lower value 
>MF one shunts teh LF.  So add series C to the MF one to make a 
>series tuned circuit, increasing the L to keep the system at 
>resonance.   The net effect now, at LF will be an increased 
>value of X shunting it.  As your additional C reduces and L 
>increases, the residual at LF across the LF coil goes up.    
>Now adjust teh LF colil to bring it to resonance, then go back 
>and redo the MF L or C.  Iterating between teh two until they both go.
> 
>I'ts a complicated setup, with two frequencies and three 
>variables to play with - so an infinite set of values to end 
>up with, but if I were doing it, I'd make up a spreadsheet and 
>play around with values until a workable solution that 
>resonated both antennas was found and looked OK.  Once 
>resonated you can bring them to a match if needed.   But on Rx 
>just resonating them ought to suffice
> 
>Or use a circuit analysis prog.     
> 
>Andy 
>www.g4jnt.com
>
> 
> 
>On 28 June 2018 at 20:04, Chris Wilson <dead.fets@gmail.com> wrote:
>
>
>
>
>	Hello Mal,
>	
>	Thanks Mal and Stefan, but Mal, I want to listen to and 
>decode both bands
>	at the same time on 2 different receivers, sharing the 
>one antenna. I
>	tried  shorting out the loading coil but LF reception 
>is much poorer.
>	Not  sure how much of an effect no loading coil has at 
>MF ,but suspect
>	a loading coil to resonate would be pretty helpful?
>	
>	Thursday, June 28, 2018, 7:55:55 PM, you wrote:
>	
>	> I use aircore loading and matching
>	> Use 2 coils and SW between them for desired band
>	> G3KEV
>	
>	
>	
>	
>	
>	
>	
>	-- 
>	Best regards,
>	Chris                            mailto:dead.fets@gmail.com
>	
>	
>	
>
> 
>