[Premium-Rx] FS: HF RECEIVER MULTICOUPLER (FROMDRAKE7-LINESTATION)

[Jack Smith]

A few years ago, I built a variety of 6 dB and 3 dB hybrid couplers and 
measured key parameters including some with 25 and 75 ohm terminations 
as well as short circuit and open circuit. Info can be found at 
http://www.cliftonlaboratories.com/6_db_hybrid_combiner.htm

Jack K8ZOA


On 4/29/2012 2:27 PM, Michael O'Beirne wrote:
> Thanks Clemens
>
> Many thanks for the email.
>
> I don't have the knowledge or software to emulate your grapgs, but I have
> noticed with my old HP8640B and th Racal 9301A RF mVmeter, that the output
> port-to-port isolation seems to be critically dependent on the input port
> impedance.
>
> I have also measured quite a few nominal dummy loads and the DC resistance
> varies quite widely from about 48 to 53 ohms (with a Fluke 25).  My thought
> to improve matters is to stick the DL on the end of a very good 10dB fixed
> attenuator from R&S.
>
> I have a CA612 in as new condition (via Pat) and also the same circuit.  You
> will probably know that he had to modify his one to achieve that superb
> isolation.
>
> I suspect for higher frequencies that you could make a combiner for a fixed
> frequency from coax at little cost but quite a lot of effort.
>
> 73s
> Michael
> G8MOB
>
> ----- Original Message -----
> From: "Clemens Paul"<cpaul at gmx.net>
> To: "Michael O'Beirne"<michaelob666 at ntlworld.com>
> Sent: Sunday, April 29, 2012 6:25 PM
> Subject: Re: [Premium-Rx] FS: HF RECEIVER MULTICOUPLER
> (FROMDRAKE7-LINESTATION)
>
>
>> Hello Michael,
>>
>> thanks for your interesting email,too.
>>
>> Star Splitter
>>
>> I was also surprised at the measured 6dB isolation.
>> So I've drawn a circuit diagram and done a simulation
>> with spice,see attachment.
>> If you have a voltage of 1V at port 1 you get 0.667V after R1 (blue line
>> in
>> the simulation,see att.) and 0.5V over R5 (red line).
>> You can also calculate the voltage division by hand,paralleling and adding
>> the different resistors,  which is a bit more cumbersome and one easily
>> can make calculation errors (at least I did at the first try),but you get
>> the same result.
>> I've also done a simulation with RFSim which also calculates 6dB isolation
>> using power.
>> Anyway, I found it a good exercise for me. :-)
>>
>> Hybrids
>>
>> I've measured my two HP 8721A directional bridges which are 6dB
>> combiners/splitters,and my MSC ZFS-2-6,a 3dB design,see att.
>> You can see different curves.
>> The best curve (bottom) is from one of the 8721As with a very good HP 50
>> Ohm termination from the 8407A VNA system.
>> Next best is the other HP bridge,also with the good resistor.
>> The next two curves are with the better HP bridge and two of the the
>> common
>> HP 50 Ohm resistors  which were widely used to terminate unused
>> spectrum analyzer ports.
>> The top (i.e.worst) curve is from the 3dB MSC combiner with the good
>> resistor
>> as termination.
>>
>> Racal CA612
>>
>> I have got a circuit diagram of this amazing combiner from Pat,G3YFGK,
>> who you know well.
>> Pat has measured a port to port isolation of 88dB.
>> I wish I had also the combiner itself not only the diagram!
>>
>> 73
>> Clemens
>> DL4RAJ
>>
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