This is for operators stacking two OmniAngles on VHF/UHF who after the discontinued PAR SK kits. If you have a Rig Expert Stick Pro, it’s easy and fun!
Note: The photo below was the first ‘fit test’ and I swapped the 2m to the driver side (away from tree limbs on the passenger side) and moved the 222/430 to the passenger side. I also lowered the support arms so I can pull the pins and lower them without a ladder because to rotate requires them to be down obviously.
If you run PAR Electronics OmniAngle omnis on VHF/UHF and you’ve ever wanted to stack a pair of them for the extra gain (better take-off angle and less cloud warming), you’ve probably run into the same wall I did — PAR no longer sells their SK-series stacking kits. The antennas are available and they are excellent, but the precision phasing harnesses that tied a pair together are gone.
The good news: there’s nothing magic in those harnesses. They’re a textbook impedance-matching problem, and with the right coax and an antenna analyzer you can build your own that perform every bit as well as the originals. I just did exactly that for my rover — matched pairs of OA-144 (2m), OA-222 (1.25m), and OA-432 (70cm) — and this is how it went, including the parts where I learned something the amateur way, which in ham radio is the only way anyone learns anything.
The theory in one paragraph
Each OmniAngle is a 50-ohm antenna. Parallel two of them with a plain T and you get 25 ohms, which is a 2:1 SWR before you’ve even started — a great way to make your rig’s foldback circuit feel needed. The fix is to feed each antenna through a length of 75-ohm coax cut to three-quarters of a wavelength (3λ/4) at your design frequency. A 3λ/4 line is an impedance transformer that follows Z_in = Z₀² ÷ Z_load, so each 50-ohm antenna gets transformed to 75² ÷ 50 = 112.5 ohms at the junction. Two of those 112.5-ohm legs in parallel land at about 56 ohms — roughly 1.12:1 into a 50-ohm feedline. That’s the whole trick. The harness is just two matched 3λ/4 transformers tied together, doing quiet impedance math while you take the credit.
This is why the cable choice matters: you need genuine 75-ohm coax, not 50-ohm. I used Belden 1189A, a quad-shield 75-ohm cable with a published velocity factor of 0.83. It happens to be exactly the right impedance for this job, and the quad shield doesn’t hurt in a noisy mobile environment.
Tools and materials
- Belden 1189A 75-ohm coax (VF 0.83)
- Klein Tools Universal F Compression Connectors
- trueCABLE coax stripper and trueCABLE F-connector compression tool
- N-male-to-F-female adapters (one per antenna end — these mate the F-terminated coax to each antenna’s N-female jack)
- F-type 3-way splitter as the junction (see the note below — this matters)
- F-male-to-N-female adapter (to bring the splitter’s output port back out to your N feedline)
- An antenna analyzer that reads R and X and has a cable/stub mode. I used a RigExpert Stick Pro, which turned this from a faith-based exercise — cut, pray, measure with a grid-dip meter, argue with yourself about which harmonic you found — into a five-minute-per-leg job. Thirty years ago this was genuinely hard. Now it’s a podcast and a pair of side cutters.
- Permatex Ultra Black Gasket Maker (82180) for sealing the antenna element boots
- Scotch 2228 self-fusing rubber tape for the connectors
A word on that 3-way splitter: what you want at the junction is a passive device that simply parallels the three ports — center to center, shield to shield. Do not grab a powered or transformer-coupled TV splitter out of the junk drawer. Those have an internal matching transformer (and sometimes a DC block or amplifier) that will cheerfully undo every bit of the quarter-wave-transformer math you’re about to sweat over. A plain F junction is all you need; it just ties the two legs and the feedline together and otherwise minds its own business.
The design numbers
Because a rover covers a wide chunk of each band, I centered each harness between the weak-signal (FT8) frequency and the outermost FM simplex frequency rather than dead on the calling frequency. On 70cm that span is huge — 432.174 to 446.0 MHz — so I centered at 439 MHz to split the error evenly across the band. (That decision turned out to be exactly right; more on that at the end.)
| Band | Antennas | Design freq | Stacking distance | Stub-tuning target (design ÷ 3) |
|---|---|---|---|---|
| 2m | 2× OA-144 | 145.4 MHz | 54″ | 48.47 MHz |
| 1.25m | 2× OA-222 | 222.8 MHz | 35″ | 74.27 MHz |
| 70cm | 2× OA-432 | 439 MHz | 20″ | 146.33 MHz |
The stacking distances are PAR’s own numbers from the original SK kits — they’re set by the antenna pattern, not the coax, so I left them alone. The “stub target” column is the key to tuning, which I’ll explain next.
Cutting and tuning the legs
The clever part of building these with an analyzer is that you never have to trust a tape measure. Here’s why: a piece of coax that’s 3λ/4 at your design frequency is electrically a quarter wavelength at one-third that frequency. So if I put the Stick Pro in cable/stub mode with the far end open, the analyzer reports the frequency where the cable looks like a quarter-wave stub — and I just trim until that lands at design-frequency ÷ 3.
The workflow per leg:
- Cut the coax a couple inches long and put a compression connector on one end.
- Stub mode, far end open. Read the quarter-wave resonance.
- Too low means the cable is too long — shorten it to raise the frequency.
- Trim, re-measure, repeat until you hit the target.
The trim rate is wildly different by band, and this is the thing that bites people:
- 2m: about 1 MHz per inch. Forgiving. You can practically freehand it.
- 1.25m: about 2 MHz per inch. Pay attention.
- 70cm: about 8 MHz per inch. Respect it, or it will teach you respect.
On 2m and 1.25m this is relaxing work — take an inch off, then quarter-inch nibbles, sneak up on it. My pairs matched to within tens of kilohertz with no drama and no casualties.
70cm is a different animal. My first leg, I took what I generously called a “conservative” cut and sailed right past the target — the resonance leapt over 20 MHz on a 2.5-inch snip, like the coax had been waiting all day for the chance. That piece is now a future jumper, which is the polite ham term for “expensive mistake I refuse to throw away.” On the second attempt I treated 8 MHz/inch as scripture: one-inch cuts only while I was 12+ MHz out, quarter-inch bites inside 5 MHz, and eighth-inch slivers for the last 2 MHz. It came in dead on. If you build the 70cm pair, start small and measure every single cut. Coax, famously, does not grow back, no matter how sternly you look at it.
The single most important rule across all three bands: match the two legs to each other, not to the textbook length. Tiny differences in how the cable seats in each connector show up as electrical-length differences a tape measure can’t see. So I tuned leg one, wrote down its final resonance, and trimmed leg two to that same number. A matched pair beats two “perfect” legs every time.
Verifying with a dummy load
After tuning, I checked each leg as a real transformer: 50-ohm load on the antenna end, analyzer on the other end, swept at the design frequency. A good 3λ/4 leg should read close to 112.5 ohms, resistive, with reactance near zero.
In practice mine read a bit high — about 118 ohms on 2m and 130 on 222 — with reactance essentially at zero (0.02–0.18 ohms). That’s not an error. The transformation is Z₀²/Z_load, so a real cable running a hair above 75 ohms or a dummy load a hair under 50 will nudge the number up. What matters is that the reactance is near zero (the leg is behaving as a clean transformer) and that both legs read the same — the load is a constant, so any offset is identical on both.
The 70cm gotcha worth knowing about
When I went to verify the 70cm legs, I got a huge reactance — around −55 ohms — and went through the full five stages of grief in about four seconds, briefly convinced I’d ruined both legs. The culprit wasn’t the harness at all. My dummy load wears a PL-259 (UHF) connector, and I was mating it through a string of adapters that would make a plumber wince. UHF connectors are not constant-impedance; they get genuinely lumpy above 300 MHz, so at 432 that whole adapter chain was acting like its own reactive stub hanging off the leg and editorializing on my measurement. The resistance still read in family with the other bands, which was the tell — only the reactance was garbage.
The fix was to stop chasing the absolute number and switch to a pure relative comparison: measure both legs through the identical fixture and confirm they read the same. They did, within whatever resolution those PL-259s can be bothered to provide, and the stub-resonance readings had already matched to 30 kHz anyway. Lesson learned: buy a 1-watt precision 50-ohm termination with an N connector. A clean N-male load reads like a true 50-ohm dot at 70cm instead of a reactive mess with opinions, and it costs less than the coax you’ll waste arguing with the alternative.
Putting them on the air
This is where it all pays off. Connected to the actual stacked OA-432 pair, the harness swept 1.25:1 at 438.8 MHz, rising to 1.87:1 at 432.174 and 1.89:1 at 446.0. Best match at center, soft symmetric edges — and those near-identical edge numbers are the proof that the 439-MHz centering decision was correct. If the center had been off, one band edge would have been noticeably worse than the other. At 1.87:1 you’re only giving up about 0.4 dB to mismatch loss, which is invisible on the air.
Expect your on-antenna numbers to differ from the bench readings — once you stack two antennas, mutual coupling shifts each element’s driving-point impedance, so the system match won’t be the textbook 1.12:1. Anything from roughly 1.2 to 1.7:1 across a band is a healthy stacked pair. Only go hunting if something reads worse than about 2:1.
Weatherproofing
This is a rover, so everything sees highway wind and weather. I sealed the antenna element boots with Permatex Ultra Black Gasket Maker (82180) — it stays flexible and grips the rubber socks well. For the coax connections I used Scotch 2228, a self-fusing rubber mastic tape: stretch it as you wrap with good overlap, run it onto the cable jacket on both sides, and orient the overlaps to shed water downward. I went with self-fusing tape over butyl putty deliberately — on a setup that gets handled and stowed, 2228 peels off far cleaner than a gummy butyl seal when you eventually need to break a connection.
One reminder: weatherproof after you’ve verified everything, so you’re not peeling open a sealed joint to retune — ask me how I know, except don’t, because I was smart enough to learn that one from somebody else’s blog. And let the connectors carry their own mechanical load — the seal is for keeping water out, not for holding your antenna farm together at 70 mph.
Final thoughts
What I like about this project is that by the end, none of it was guesswork. You tune to electrical length instead of trusting velocity-factor math, you match the legs to each other rather than to a number in a manual, and you let the symmetric band edges confirm your design center. Three matched, verified harnesses, built from the transformer equation up, for the price of some 75-ohm coax and a handful of connectors.
The 70cm pair fought me the whole way — that 8-MHz-per-inch knife edge is no joke, and it has no sense of humor about your sense of humor — but it came in just as tight as the rest. If PAR’s kits are gone and you’ve got a pair of OmniAngles waiting to be stacked, don’t let the missing harness stop you. Cut some Belden, fire up the analyzer, accept that you’ll sacrifice one piece of coax to the gods of 70cm, and build your own.
73 — N5ZY