[TowerTalk] Modifying Comtek 4-square controller(relay unit) for a different band?

[Michael Tope]

Hi Jim,

Starting with version 5.0, EZNEC implements the capability to model 
lumped transformers, inductors, capacitors, and resistors. Thus, it 
should have capability to model the Collins 90deg hybrid. The only 
caveat is that the transformer model is ideal (K=1.0), so including the 
impact of flux leakage and core loss would have to be captured with 
additional components in an equivalent circuit model.

73,  Mike W4EF............

On 11/18/2021 6:12 PM, Lux, Jim wrote:
> On 11/18/21 12:58 PM, Tim Duffy wrote:
>> There is a reason DX Engineering/Comtek does not sell Comtek 4 square 
>> boxes above 14 MHz. The inductor and capacitor values are very low 
>> and losses can be a real problem. We are still trying - but it is not 
>> as easy as dividing down the values. Believe me - we tried.
>>
>> 73
>> Tim K3LR @ DX Engineering
>
>
> At some point, some other quad hybrid approach becomes more practical. 
> And harder as percentage BW increases.  I don't know that I would want 
> to build a Lange Coupler for 10 meters (although you might be able to 
> build on on flex substrate and coil it up?
>
> But there are other techniques that might lend themselves to coax. A 
> branch line coupler is made of 4 transmission lines, with impedance 
> 0.707*Z0.  If your Z0 is 71 ohms (maybe 75 ohms is close enough?) then 
> the lines are 50 ohm lines that are 1/4 wavelength long.
>
> Or a rat-race, with lines that are 1.414 * Z0 - again, 50 ohm Z0 would 
> use 71 ohm lines.
>
>
> https://www.microwaves101.com/encyclopedias/hybrid-couplers
>
> and various pages linked from there.  All kinds of cool ideas.
>
> The nice thing is that these are modelable in NEC (unlike the Collin 
> hybrid), since they're just transmission lines. (Yes, you can model 
> the Collin as an idealized 90 split, but you can't model the coupled 
> transformers and capacitors)
>
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