The Shively 6710 Antenna

Shively 6710-1 FM antenna
Shively 6710-1 FM antenna

Perhaps that is one Shively Antenna that you haven’t heard of. They were an oddball combination of a horizontally polarized antenna with an adjustable vertical element. This design allowed the station to adjust the ratio of horizontal to vertical power from a range of 1:1 to about 4:1 (H:V).  Why would this be a desirable feature?

Back in the early days of FM broadcasting, almost all stations had horizontally polarized antennas.  This system worked remarkably well, stations could broadcast at moderate power levels over fairly long, line-of-sight (or mostly line-of-sight) paths.  Most FM receivers were stationary units installed in people’s homes often with outdoor antennas.

It was not until the late 1960s and early 1970s that FM radio receivers became a stock option in most low and mid-cost automobiles.  It was then that a slight problem with FM broadcasting was discovered;  car antennas are vertically polarized.  People driving around in their new machines found that the FM reception was not all that great.  Stations began adding a vertical component to their signal to help improve the mobile reception situation.

I found this Shively Brochure in a file cabinet drawer at the WFLY transmitter site.  This model antenna was ordered and installed by that station in 1970.  It had a 3:1 horizontal-to-vertical ratio.  Why not install a fully circularly polarized antenna?  Because often that necessitated installing a new, more powerful transmitter.   Every watt of power taken from the horizontal plane and added to the vertical plane reduced the ERP by that much and had to be made up with more transmitter power output.  Oftentimes, the ratio of H:V power would be adjusted to take up whatever headroom there was in the transmitter and the station would run that way until the next transmitter replacement cycle.

I found the remains of this antenna in the woods, northeast of the tower.

Shively 6710 antenna section
Shively 6710 antenna section

This section looks pretty well destroyed.  It is probably better to dispose of these types of things by scraping, them rather than dumping them in the woods.  While there is not a lot of scrap value to this unit, it can become attractive nuisance to copper thieves and other vandals if it is left laying about.

It is a strange-looking piece of kit, a sort of make-do until the situation could be fully rectified.  I think this antenna was in service until 1986 or 87 when it was replaced with a circularly polarized ERI.

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8 thoughts on “The Shively 6710 Antenna”

  1. The use of circular polarization in FM broadcasting pre dated the use of CP antennas in Analog TV broadcasting by 20+ years. CP does not really push your service contour out that much farther. It does seem to fill in weak reception areas better. I have a copy of Broadcast Engineering Magazine dated Nov 1975. The FCC seemed too be in more of an inquisitive, uncertain mood about CP, while the TV broadcasters were saying “go for it”!

  2. Paul, that antenna was in storage on the second floor of the FLY-mitter building when I arrived as the chief. I think it was a 4-bay with partial radomes. There was an older ERI rototiller in service on the mast which was damaged during maintenance activities sometime in 1985. We had the tower crew reinstall the Shively on one of the tower legs to get us back on, while we placed an emergency order for a new ERI which arrived a month or so later. The Shiveley was kept up on the tower as a backup. The remains of the old ERI were lying in the weeds up there long after I left the station.

  3. Have observed some interesting differences between a panel CBR and side mount ERI/Dielectric/Jampro antennas from the same site. Penetration into a couple canyons (around 70 and 90 miles out) is really different. While the signals from the CBR panel slowly fades away with not much multipath, the side mounts can be heard deeper into the canyons but is too multipathed up to listen to. What am I observing?

  4. Bill – Probably this is related to the differences in axial ratio from non-panel “sidemounts” relative to the CBR.

    The link below compares NEC2D patterns of sidemount on a large face tower with the measured patterns of a Harris CBR on a large face tower.

    As probably expected, the H- & V-pol patterns from the sidemount don’t track each other very well, and have >20 dB nulls in some directions (different for H&V).

    The CBR pattern was measured on a calibrated, far field test range using a spinning transmit dipole to illuminate the CBR. So that measured pattern shows axial ratios for all polarization planes, not just for H&V. Its quite low.

    The sidemount patterns in the clip below were taken from Paper 6 at – which might be of general interest.

  5. I am almost certain that ERI was replaced again in the late 1990’s when I visited the site with Roger Brace. The old antenna had had some bad lightning damage, and while I was there, he was switching back over to the Continental after it too had been repaired from the same storm. I seem to recall him showing me the blown pieces from the interbay feedline on the bench there, and mentioning the antenna being replaced.

    I’ve seen a few odd ball Shively designs in my time touring these sites. There is a station in Cleveland which as a Shively 6013 antenna. It’s like a cross between a Lindenblad style antenna and their 6016 panel. I’ve never been able to cross reference this model on their website or archives . is the antenna.

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