We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissible in your locale.

Author Topic: FMUser CP100 elliptical circular antenna (CZH) - anyone have this?  (Read 1385 times)

Offline chanito

  • Full Member
  • ***
  • Posts: 217
  • S.Texas
  • RF Exposeur
    • View Profile
    • Email
screwed with one for 4 hours today and could not get it down lower than 2:1 SWR best case and only on the lowest part of the band. Also, how the heck does it mount? The diagram shows it stuck on top of a pole in line with the pole. Never seen a CP antenna mounted like that. I stuck it on sideways like it looks like it is really supposed to be, but not geed results.
PCR-1000, PCR-1500, RSP1A, RSP1, VR-120D, HDT-1, Accurian HD, Royal 3000
Caras HF-315, Belar LP-1A, SuperAntenna MP-1, RatShack 20-043 discone, MLA-30, 100' wire

Offline redhat

  • DX Legend
  • ******
  • Posts: 1591
  • USA
  • Music is my drug.
    • View Profile
    • Email
Re: FMUser CP100 elliptical circular antenna (CZH) - anyone have this?
« Reply #1 on: November 15, 2020, 0249 UTC »
I've built a number of them over the years as emergency antennas for stations.  The length of the elements sets the resonant frequency, the position of the arms adjust the match.  The two do interact.  It should be mounted with the feedpoint straight up.  Also proximity to its mounting structure and size of such will also affect the match and center frequency.  Usually the match was around 1.2:1 or so.

A sweepable analyzer of some sort will make life a lot easier.  I now use a return loss bridge and a service monitor so I can see the adjustments in real time.  Doing it the old way with an exciter and a wattmeter was always a maddening experience.

« Last Edit: November 15, 2020, 0254 UTC by redhat »
Somewhere under the stars...
Airspy HF+, MLA-30/Mini-whip/Chi-Town Loop
Please send QSL's and reception reports to xfmshortwave [at] proton [d0t] me


HFUnderground T-Shirt
HFUnderground Garden Flag
by MitchellTimeDesigns