Originally written and posted 8 July 1996.
Content last modified Saturday, 9 July 2016 .
External links last verified Tuesday, 1 February 2005.

Of Jesus and Sewers

The informal antenna survey

As i was saying, back in the day (oh, say May 1991… any day you want…) your intrepid D.J./Broadcast Engineer/Stereo Repair Technician set about doing an informal survey of the relative performance of a cross-section of indoor powered FM receiving antennae in relation to the T-shaped “folded dipole” (which is standard-issue with most mid-fi receivers), and that venerable reference, the rooftop antenna. The immediate motivation for the survey was the inability of a dedicated low-power FM listener and friend to get decent reception in his parents’ condemninium (sic, no rooftop receptors allowed) across the S.F. Bay in Fairfax, CA, U.S.A., a distance of, oh say, 43 km from the KALX (the desired station) tower, 3/4 high atop the Berkeley Hills.

The results surprise even this jaded techie: Can powered antennas receive weak FM signals better than yer basic plastic wire? NOOOOO! Can any indoor antenna receive weak FM signals as well as a rooftop? NOOOOO!(least not the ones i tested). Special shout-outs to The Soundwell (Berkeley, CA used stereo shoppe, 6 manufactured antennae loaned), Resistance Repair (Berkeley, CA home audio/video repair shoppe, ohsillyscope loaned), and the No Problem Household (Fairfax, CA, condemninium loaned). Here’s the Sonically Pure summary:

Antennas tested:

Most were tested in two locations: the author’s Sonically Oblique rented house in A-town (Albany CA U.S.A., 29 April 1991, clear, 22-25°C weather), representing a “city-grade” signal reeeeeal close to the KALX tower (oh, say 6km from de tower, >70 dBu-City Grade), and the No Problem condemninium in Fairfax, Hot Tub County, in fringeland, discussed above (<54 dBu).

Each antenna was tested with several different receivers: a Yamaha R300 and Marantz 2500 (both tweaked to the max, and having oscilloscope displays of signal strength, modulation, multipath, and all that other good stuff that you probably don’t care about, but that keeps me off the streets) in both locations, and additionally an old Scott 342B past its prime plus a malfunctioning (insensitive) Akai AA-R32 in Marin—possibly representative of what you use! Each antenna was adjusted for best results (no matter how impractical or ugly) and most were additionally tested in positions more representative of actual usage (crumpled up, strewn about, half-heartedly attached to the wall). Signal strength was measured (in dBf) from the oscilloscope display(s), and qualitative aural (via speakers and headphones) and visual (sillyscope) impressions were recorded for each of three representative local FM stations.

The chosen stations were: 1. KALX, Berkeley, a 500W non-commercial “alternative music”-formatted station on 90.7 MHz, using minimal audio processing[1]; 2. KYA-FM (now KYCY or who-knows-what…YEEEHAWWW!), San Francisco, a 50kW heavily-processed “oldies”-format station (back when these tests were run) at 93.3 MHz, whose San Leandro transmitter location provides extreme multipath problems at the Albany test location; 3. KDFC-FM, San Francisco, a 33kW moderately-processed commercial classical-formatted station on 102.1 MHz, difficult to receive well in many parts of the Bay Area.

Antenna Contender Profiles

Five categories of antennae were tested:

A. Dipoles

The dipoles were all variations on the T-shaped hunk of wire theme, some homemade, some manufactured. I tried three mounting positions of all dipoles: crumpled on the floor or dangling behind the receiver, held up limply (more of a “Y” than a “T”), and rigidly mounted with the top of the “T” quite straight and flat (wire not twisted). The latter is denoted as “Jesus-Mount” in this article.

T dipole mounting positions

Jesus-Mounting performed substantially better than limp- or crumple-mounting in all tests (but your results may vary). Note: best reception may not occur with the antenna flat against the wall (see “T” dipole tips fo mo info).

B. Freshly Homemade Goodness

The homemade gizmos were fabricated based upon inventive creations seen by stereo repair professionals, in order to test receiving antennae similar to what some of you use.

C. Unpowered (passive) Manufactured antennae

D. Powered (active) Manufactured antennae

E. Outdoor Rooftop

Time, money, and convenience limitations precluded extensive tests in this important category. The single representative is Antenna #13A, a Channel Master 4408G, self-installed on the roof of Sonic’s one-story rental padded cell in 1986. The antenna stands approx. 2m above the roofline, controlled by a Lance LC110A rotor system. An RMS balun feeds roughly 10m of Belden 9114 Duobond II-braid 75 ohm 18 AWG premium CATV coaxial cable. All connections were treated with Cramolin® and silicone weatherproofed during installation.

Raw Datapoints

Legend:

c=clean audio
a=average (v. slight multipath o.k.)
m=moderate multipath
s=severe multipath
u=unlistenable due to multipath
w=weak, noisy
i=inaudible
v=very (modifier for any attribute)

(the Akai AA-R32 has no sig. strength indication and could therefore not be plotted, but subjective impressions were included in the summary)

Reception of KALX in Albany data plot  Reception of KALX in Marin data plot  Reception of KYA in Albany data plot  Reception of KYA in Marin data plot  Reception of KDFC in Albany data plot  Reception of KDFC in Marin data plot 

The Envelope Please…

And the winner is……THE ROOFTOP ANTENNA!!, which obliterated all other contenders—nothing else was even close for cleanest, quietest signals for all three stations on both receivers. The message is clear: if you care at all about FM sound quality, settle for nothing less than a rooftop (if’n you can).

But what if you can’t put up a rooftop receptor? The indoor winner was THE 300 OHM FOLDED DIPOLE! (Jesus-Mount), which tied or beat all 7 factory indoor antennae. Ya haveta make sure it is truly a folded dipole and install it correctly, but at least you’re not wasting money on pretty but unproductive factory goods!

The best of the homemade fabrications was the coat hanger loop, which could not approach a good dipole but joined several other bargain-basement self-made creations in tieing most factory antennae, and all of these worked better than the Beam Box Model 6, including the Fairfax City Sewer! Most of the homemade antennae, and all the powered antennae, were fairly sensitive to human bodies roaming about (the rabbit ears and the better dipoles suffered least from motion in the ether ocean).

The clear loser was the Model 6 Beam Box. The Parsec refused to pull in KALX in Fairfax: it switched to KSJS whenever it was plugged into power! (KSJS has since moved to 90.5 MHz, so this wouldn’t happen today).

Some readers may be heartened to hear that the powered antennae provided a classic demonstration of the deceptive nature of relying on limited measured specifications to correlate with perceived sound quality. Looking back at the claims made on the Terk π box, the amplification of weak signals cannot be denied, but unfortunately, noise & distortion are amplified proportionally as well (for all powered antennae tested, not just the Terk). Sure, the signal strength meter reads nice & high, but in many cases the audible sound quality was inferior to one or more lower-reading passive designs (usually dipole variants). The remaining claims played out as follows:

Tested True

Tested False

Similar critiques apply to all the powered antennae.


[1]KALX used/uses? an Orban Optimod® 8100A, set near Orban’s suggested “audiophile” minimal-alteration settings.return
[2]M=tested in Marin only.return
[3]if one lives in fairyland, where the velocity of propagation is unity. Assuming a velocity factor of .82 for twinlead, the actual active length should have been 1.36m. It would be kind of you not to ask who made this antenna….return
[4]A=tested in Albany only.return
[5]The UHF results were sufficiently disappointing to not be included in these tests. Only the VHF section was fully tested.return

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