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
>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?
>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.
>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]