Electronics > RF, Microwave, Ham Radio

DIY RF EMC Biconic Antenna

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piotekp90:
I recently opened up my Tekbox TBMA1 antenna and this is what it looks like inside:


dazz1:

--- Quote from: piotekp90 on January 02, 2024, 01:52:17 pm ---I recently opened up my Tekbox TBMA1 antenna and this is what it looks like inside:

--- End quote ---

That is interesting.  It appears to be similar to the Ethernet matching network I rescued from a dead motherboard.  When I tested it, the performance was decidedly mediocre so I started looking for another solution. 
You can see the results of my R&D here:  https://www.eevblog.com/forum/rf-microwave/correctly-calculating-impedance-of-a-biconical-antenna-and-impedance-matching/
My results do not necessarily apply to the Tekbox solution.  That could only be confirmed/denied by testing the Tekbox balun.

 I took a completely different path.  One of the key problems I had with a twisted pair design is the difficulty in sourcing wire with the required and known insulator properties.  This is needed to obtain the correct impedance.   The problem of impedance matching a twisted pair was compounded by on-line twisted pair impedance calculators that produce the wrong answers.   That is why I switched to using coax cable.

Coax requires physically large toroids.  The combination has a measured -20dB bandwidth of 20MHz to 300MHz. I think that is close to the limit achievable with coax/toroid approach.   I am about to change tack to look at a different coax/ferrite topology.  First I need some parts.

Kean:

--- Quote from: piotekp90 on January 02, 2024, 01:52:17 pm ---I recently opened up my Tekbox TBMA1 antenna and this is what it looks like inside:

--- End quote ---

This got me curious, so I took the cover off my Aaronia Bicolog 30100.  https://aaronia.com/en/emv-antenne-bicolog-30100

Unfortunately there isn't much to see without some difficult desoldering which I'm worried could be destructive.
I can't even see the type of conductor used through the ferrites, but they are somewhat compliant.

T3sl4co1l:
Probably the same basic design:



The twisted pairs are Zo = 100R, two in parallel is 50R at the port.  Notice the far ends are grounded oppositely, making one an inverting 1:1 autoformer, and the other a straight pass-thru (delay).  The latter doesn't need any choking but I had the binoc cores so I figured why not. The former drops the full input voltage so needs choking accordingly.  The output in series is therefore 200R, a reasonable match to the, in this case wire frame bowtie, but bicons are similar of course.

Tim

dazz1:
Hi
I have formed the view that emc antenna performance is largely defined by the balun, which is also the item with the least info, test data results and possibly the weakest link in antenna design. 

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