[TMC] TMC receive whip antenna

[John Vendely]

Hi Glenn,

It wouldn't be too hard to make your own replacement transformer similar 
to those used in the VRA series whip antennas.  The transformer spec 
drawings for all the various types are in K4OZY's fabulous TMC website, 
and you can deduce the impedance ratios from them.  For example, the 
2-32 Mc VRA-6 transformer is simply a broadband autotransformer with the 
feedline tap at 70 ohms, and the top of the transformer (antenna 
connection) at 300 ohms, so a 4:1 impedance ratio would be a good choice 
for a 75 ohm feedline using CATV coax.  Use a good-sized ferrite core 
and wire gauge to prevent transformer burnout from inevitable nearby 
lightning hits.  The typical Minicircuits RF transformer will not last 
long in this application.  Connect a gas discharge tube or air spark gap 
from antenna connection to a decent ground.

These are broadband antennas and so obviously don't present a stable 
impedance to the feedline.  They are compromise designs, as the manuals 
stress, and the impedance varies widely.  They have their limitations.  
But they are useful antennas and work quite well for their intended 
purpose.  If you must have a good match and more consistent output 
level, some form of active antenna would be a better choice.

73,

John K9WT

On 9/1/2021 8:15 AM, GLEN SWIDERSKI wrote:
> Hope everyone is having a good day today! Im wondering if anyone has information on building one of the TMC passive whip antennas for HF? I need something for my R390a that I wont have to interfere with my ham station and can still swl without moving things around. Im guessing the hard part is the matching transformer Any help would be appreciated
> 73
> Glenn
> W7gs
> ______________________________________________________________
> TMC mailing list
> Home: http://mailman.qth.net/mailman/listinfo/tmc
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:TMC at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html