Testing and Reviewing LoRa Antennas

Part 2: Detailed antenna measurements

Mark Zachmann
Jun 17, 2020 · 6 min read

This is a continuation of the last article about measuring LoRa antennas. In this section I go through the impedance measurements (VSWR or Return Loss) for each antenna in gory detail.

The antennas being discussed

There is one more antenna (called Yagi):

The Yagi (beam) antenna

The beam covers the ISM band (900MHz) as well as some higher frequency bands. The label says 698–960MHz & 1710–2700Mhz.

FrSky 900MHz Moxon Zipp 9

The FrSky Zipp9

Looking at the traces on the back of the antenna it appears to be a dipole with an additional dipole beam that I assume adds some directionality/gain.

The FrSky Moxon Zipp 9

The return loss chart is very good. The 900Mhz dip is deep (so good match) and the rest of the range is appropriately unmatched, other than a strange dip at about 750MHz.

The manufacturer provides this very-nice claimed radiation pattern picture which shows the greatest gain upwards and broadside. I’ve never seen that but it makes sense.

FrSky 900MHz Moxon Zipp 9 Radiation Pattern

FrSky 900MHz Super 8 Antenna

FrSky Super8 Antenna

The impedance plot is good. Just like the Zipp9 it has a strange match area around 730MHz. Maybe these are artifacts of the short coax or the barrel adapter.

FrSky Super8 Vswr and Return Loss

There is a less-exciting radiation pattern provided by FrSky:

This is extremely uniform except along the X axis (to the left and right). Spherical (technically cylindrical) while retaining a good impedance match.

Linx 916-HW

Linx 915HW 5" center fed dipole

The impedance plot is classically pretty.

There’s a small dip near Wi-Fi (maybe caused by my active Wi-Fi field) and otherwise it’s a narrow spike in the frequency band.

Linx 916RH

Linx 916RH (2" tall)
Linx 916RH Helical quarter-wave whip

The impedance chart is very pretty. There’s a second moderate dip around 2GHz and that’s it. For a small quarter wave, the frequency range is fairly wide which suits the ISM band well.

Molex Flexible 102562

Molex 105262 Flexible Dipole

The pattern visible on the front of the antenna shows the trace.

The display here is very good. Nice low return loss from 860 to 928 and then out-of-band elsewhere. It’s a bit lower in frequency than I’d like but usable — later note: the U.Fl barrel connector seems to be introducing un-fixable errors in the measurements so don’t take this as gospel. For <$4 this is a steal in terms of impedance matching. The antenna ends in a U.Fl connector and so this test requires an SMA-U.Fl barrel connector of unknown effect.

The Molex Impedance Test Setup

Linx Monopole LTE

Linx LTE Monopole
Monopole Impedance/Return Loss

The impedance chart is pretty, but as expected the frequency range is lower than a typical 915MHz ISM antenna and it includes sub-bands for cell. I’m glad to be redoing these tests.

I don’t show those results here but without a ground plane this is a bad antenna since the impedance shift is substantial.

870–960 MHz Whip

The impedance chart is again very pretty, although tuned slightly low in frequency for my purposes with best match at 874MHz.

Siretta Echo1A

Siretta Echo1A Impedance chart

As you can see in the image, it kind of supports ISM bands but matches far better with the GSM/3G bands. I’ve used it when I need something to provide a load for U.Fl but. Their documentation shows a bigger dip in the ISM range (although it’s not clear) so it may have been testing error.

Phonetone 7/9dbi Outdoor Directional Yagi

Phonetone Outdoor Yagi

The impedance chart is fairly spectacular given the specification. Not great if you want to ignore some of the frequency bands but I’ll bet you could pull a few beams off to improve that : )

It shows a near 1.0 VSWR starting at 700MHz rising to 2 at 940MHz. I’m looking forward to measuring the gain of this beast.

915MHz whip

915MHz Whip — A

The whip seems to really be a bit higher in frequency.

915MHz Whip — B

Here’s the second sample of the 915MHz whip. I’ll just leave this here.

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