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Broad band antennas General discussion

Mel Farrer, K6KBE
 

As you have seen by the variants of the BBTD, etc., there is no special shape or size requirements within reason.  Orientation does not matter again within reason.  Bonnie has demonstrated a large number of possible configurations.  They all have one thing in common, they are a terminated and want to be a balanced antenna.  My work on modeling and building and testing a couple of the variants agrees with the premise that it is a broad band antenna.  Not that the performance is the same on all frequencies, but that one can use them without too much concern about match <2:1.  I have found that the antenna feedpoint impedance is complex, feedline length does make a difference, and yes, you need to rate the termination resistor for the full output of the transmitter if used on the lowest frequency. 

That being said, I have found the design to be a VERY useful antenna. Band jumping was never so much fun.  It will satisfy those in restricted space a VERY usable all band antenna. It also has a VERY nice attribute, being balanced, it less prone to RFI at the operating position. Remember to use a good CMC choke in any case. 

My work will continue with more elaborate testing as the weather improves.  If anyone has any questions about the actual antenna testing, please drop me a note, always glad to discuss results of testing Bonnie's design, Cheers,

Mel, K6KBE

Mel Farrer, K6KBE
 



More.

http://www.caddock.com/Online_catalog/current_sense/current.html

 

https://www.surplussales.com/Resistors/NonInductive/Res-NonInd_list.htm

 

http://www.kanthal.com/en/products/resistors-and-capacitors/bulk-ceramic-resistors/tubular-resistors/

 

http://www.ohmite.com/search.php?appl=Axial%20Lead&function=results&_vsrefdom=ppcbing&ex=yaquk0-13c8k9q-qldmmr&utm_source=bing&utm_medium=cpc&utm_campaign=Ohmite%20Mfg.%20Co.&utm_term=Non-Inductive%20Resistor&utm_content=Non-Inductive%20Resistor

 

10 ea 10K 2 W composition resistors in parallel = 1000 ohms @ 20 W

10 ea 12K 2 W  composition resistors in parallel = 1200 ohms @ 20 W


Mel, K6KBE


Mel Farrer, K6KBE
 

Also, depending on your installation configuration, it is wise to do a simple sweep test with 800 to 1500 ohm termination.  In doing the modelling, I found that with different conditions, there is no fixed termination value that is good for all..


Mel, K6KBE

Mel Farrer, K6KBE
 

Update, 

One thing I have observed, the antenna hears very well.  

When comparing the BBTD V with my dipoles or the Stepper antenna, disregarding polarity for the moment, the noise floor is 10 -15 dB lower while the signals are close to the same, meaning the S/N ratio is MUCH better..

Great news for noisy areas....  I think the key is the resistor termination while the antenna is still full size.  


Mel, K6KBE