LEO/Amateur Satellite Quadrifilar Helix Antenna (QFHA):
Frequently Asked Questions

Here, we address frequently asked questions concerning our Amateur Satellite antennas, which have been posed by visitors. Our intention is for these inquiries and answers to assist other enthusiasts with similar interests and concerns. If you need further information or if there are additional queries left unanswered, please don't hesitate to View Details or contact us directly via phone or email. We are delighted to provide a thoughtful and impartial response.

' Why choose a Quadrifilar Helix over other omnidirectional satellite antennas?

There exists a variety of omnidirectional antenna types suitable for satellite communications including Monopoles (Verticals), Dipoles, Turnstiles, Loops, Egg-Beaters, Spirals, and Circular Arrays. Among these, the Quadrifilar Helix Antenna (QFHA) is favored due to its benefits. Unlike linearly polarized antennas that may necessitate adjustments during a satellite pass, circularly polarized antennas, such as those mentioned, allow operators to enjoy QSO without constant technical considerations.

Among circularly polarized options, Turnstiles, Egg-beaters, Lindenblads, and Quadrifilar Helices are the most utilized structures. Basic forms of the first two offer a gain of 0 dBic. Their enhancements often require additional elements like radials or a ground plane to achieve a gain that typically ranges from +3 dBic to +5 dBic. In contrast, a Quadrifilar Helix, being a phased array, naturally manages the exclusion of lower hemisphere radiation, yielding comparable gains without added complexity, typically around +3 dBic to +5 dBic as well.

Notably, the QFH maintains a more stable axial ratio during off-zenith angles thanks to its symmetry and compact dimensions. Thus, overall, Turnstile, Egg-beater, and Quadrifilar Helix antennas can be engineered to provide similar levels of performance. Therefore, all three remain excellent options for satellite communications. Our -531 and -328 series QFHs are designed with discreet aesthetics to facilitate Amateur Satellite operations, especially in communities with restrictions.

The Lindenblad presents an ideal construction in free space, with optimal performance during low elevation angles; however, real-world conditions, including atmospheric effects and ground reflections, diminish its effectiveness when averaged across most satellite passes. Thus, the aforementioned [CP] structures often outperform the Lindenblad in practical applications.

' Is the 50-Watt rating of QFHAs the maximum power allowed?

Our QFHAs are rated at 50 Watts, which is a robust power level for most Low Earth Orbit (LEO) satellites. Notably, the design of the -531 series antennas demonstrates significant tolerance; for instance, the VHF model can handle intermittent operations reaching up to 100 Watts, while UHF models may operate briefly up to 75 Watts without issue.

' Is RHCP (Right Hand Circular Polarization) the optimal choice for most Amateur satellites and the ISS?

Historically, popular OSCAR operations used VHF LHCP for uplinks and UHF RHCP for downlinks, currently referred to as our "default" pairing. Nevertheless, a variety of satellite designs have emerged, complicating the decision due to differing polarization methods. Some satellites are linearly polarized, while others can alter their polarization during an orbit. The ARISS (Amateur Radio on International Space Station) website indicates that their VHF antennas are vertically polarized.

Given the variability of satellites and their polarization types, the "ideal" choice is multifaceted. However, a practical approach is to choose a Circularly Polarized antenna (either RHCP or LHCP), which will perform decently across most satellite passes and minimize atmospheric influences. Thus, we generally recommend our default pairing strategy of VHF LHCP and UHF RHCP.

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' Can QFHAs be mounted at elevated heights?

Yes, although we advise users to weigh practical considerations: elevating a ground satellite antenna enhances its field of view, prolonging the duration of satellite passes. However, elevation also subjects antennas to increased wind and environmental challenges. Therefore, the optimal height accommodates safety concerns and geographical factors while ensuring a clear horizon and sky view.

Best practice recommends positioning the UHF antenna at least two feet away from the VHF antenna, with the orientation between the two designed to be perpendicular to the most likely satellite path. This helps minimize any potential obstructions caused by the VHF antenna.

' What distinguishes the UC-AMSAT-KITP from the UC-AMSAT-KITP-531 kits?

The difference between these two kits is minimal; the key distinction lies in the UHF antenna configuration. The -KITP-531, being the latest iteration, is our preferential recommendation, as the original kit will eventually be phased out. Noteworthy improvements include the new UHF element (UC--531), which boasts +1dB better performance compared to the older UC--328. The UC--328 was compact yet still provided over +3 dBic gain across the Amateur UHF band. As many users also utilize the VHF model, the benefit of a compact UHF antenna became less significant, prompting us to develop a full QFH version matching the performance standard of the VHF UC--531 model, hence naming the new kit UC-AMSAT-KITP-531.

In the future, we plan to phase out both the original UC-AMSAT-KITP (a pair of passive QFHs) and the UC-AMSAT-KIT (-531 VHF + Mini -UHF QFH with an integrated LNA) coinciding with the release of TX/RX LNAs for VHF and UHF later this year in Q4.