May 2014
M T W T F S S
« Apr   Jun »
 1234
567891011
12131415161718
19202122232425
262728293031  

Archives

Categories

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 odd-ball 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 1960’s and early 1970’s 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.  Often times, 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, north east 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 type things by scraping, rather than dumping them in the woods.  While there is not a lot of scrap value to this unit, it can become an attractive nuisance 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.

Be Sociable, Share!

7 comments to The Shively 6710 Antenna

  • 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”!

  • H-pol and v-pol radiation from elements of this general design have different physical locations in space. Axial ratio can be fairly poor in some directions.

    Here is a link to a NEC analysis of the net H&V radiation patterns of four types of FM transmit elements…

    http://s10.postimg.org/8h5bijofd/FM_Elements.gif

  • In addition to v-pol radiation being better able to serve car radios using vertical receive antennas, v-pol can produce somewhat larger coverage areas within a given contour with some types of terrain.

    The clip below shows this using a Longley-Rice analysis of an FM station with equal ERP in h-pol and v-pol (single transmit antenna).

    http://s29.postimg.org/4jpxm0ekn/H_pol_vs_V_pol_FM_Coverage_Hilly_Terrain.jpg

  • Jim Seaman

    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.

  • bill.frahm

    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?

  • 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 http://rfry.org – which might be of general interest.

    http://s13.postimg.org/kwl628vwn/Sidemount_FM_vs_CBR_Pattern_Example.jpg

  • 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 .

    http://www.necrat.us/955cleveland.html is the antenna.

Leave a Reply

 

 

 

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

Axiom


A pessimist sees the glass as half empty. An optimist sees the glass as half full. The engineer sees the glass as twice the size it needs to be.

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin

The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is hard business. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.
~Rudyard Kipling

Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19

...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner

Free counters!