Return to KLUBNL.PL main page

[Top] [All Lists]

LF: RE: Re: Can I match 2 frequencies with one loading coil?

To: <[email protected]>
Subject: LF: RE: Re: Can I match 2 frequencies with one loading coil?
From: "Clemens Paul" <[email protected]>
Date: Fri, 29 Jun 2018 18:26:40 +0200
In-reply-to: <[email protected]>
References: <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Thread-index: AdQPL5K4BmtC/ckjQtyJuKXIrBY3VgAlX98A
Hi Mark and Chris,

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


>-----Original Message-----
>From: [email protected] 
>[mailto:[email protected]] On Behalf Of Mark
>Sent: Friday, June 29, 2018 12:27 AM
>To: [email protected]
>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:[email protected]>  
>Sent: Thursday, June 28, 2018 8:32 PM
>To: LineOne <mailto:[email protected]>  
>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.     
>On 28 June 2018 at 20:04, Chris Wilson <[email protected]> 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:[email protected]

<Prev in Thread] Current Thread [Next in Thread>