----- Original Message -----
From: "Boye Christensen" <oz7c@cool.dk>
To: "Mike Tubby" <mike@tubby.org>
Cc: <info@transmittersrus.com>
Sent: Sunday, March 11, 2012 1:48 PM
Subject: Re: [Amps] 6kW Coax
There is another way to do it convert it down and up
Use of 50 Ohm coax
Take 2 x 50 Ohm in paralell = 25 Ohm 1/4 Labda this gives 12.5 Ohm connect
then toghter 6.25 Ohm
then 3 x 50Ohm = 17.Ohm 1/4 lambda back to 53 Ohm ?
7 pice of 1/4 wave of 50 Ohm coax
73 Boye
total lenght app 1 Meter
> ----- Original Message -----
> From: "Mike Tubby" <mike@tubby.org>
> To: "David Shapiro" <info@transmittersrus.com>
> Cc: <amps@contesting.com>
> Sent: Sunday, March 11, 2012 10:06 AM
> Subject: Re: [Amps] 6kW Coax
>
>
>> Dave,
>>
>> Some thoughts:
>>
>> 1. your design really should be a full Wilkinson combiner, the output of
>> each LPF should have a 100R across to the output of the other LPF so
>> that you have circa 30dB of isolation between the transmitters -
>> consider what happens if of half fails
>>
>> 2. you "coax 70-75 ohms" needs to be 70.71 ohms of the system is matched
>> to 50R with a decent return loss
>>
>> 3. at the power levels you're aiming for any loss of very important...
>> recall that 0.1dB loss is 11% and at your power levels that's a lot of
>> heat
>>
>> 4. if you really do need to use a final combiner made from coax at this
>> power level then, as pointed out by others, you're looking for 7/8ths or
>> bigger
>>
>> 5. alternatives for your application that are worth considering are:
>>
>> a) a six port Gysel combiner (rather than the two three port ones
>> you have now)
>>
>> b) a further two port Gysel combiner cascaded after your LPFs
>>
>> c) a Rat Race combiner which has some advantages:
>>
>> * doubles up on the coax (you can use a slightly smaller coax)
>> * provides isolation between the two transmitters
>> * can be built using 75R coax (lengths 0.25, 0.25, 0.25, 0.75)
>> or 50R coax (0.153, 0.153, 0.153, 0.653)
>>
>> using 50R coax you might have success with LDF7-50A
>>
>>
>> Personally, if I was attempting this project I would tend towards the
>> KISS approach - you would probably get as much overall transmitter
>> output from:
>>
>> 5 x 2500W FM pallets -> 5-port Gysel -> single LPF
>>
>> and avoid a significant amount of combining losses and system complexity.
>>
>>
>> Mike
>>
>>
>>
>>
>>
>> On 10/03/2012 16:35, David Shapiro wrote:
>>> Hi Carl,
>>>
>>> Yes, it seems so.
>>>
>>> I have just fired off a mail to Allied Cable to see what they suggest.
>>>
>>> Thanks.
>>>
>>> Dave G4ZOW
>>>
>>>
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>>
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