We are currently installing this sweet little transmitter:
Nautel NV-5 FM transmitter
Like its big brother, the NV-40 at WVPS, the NV-5 is a very cool transmitter. I am a born skeptic, things like touchscreen displays tend to make me a little nervous, especially on a transmitter connected to a 350 feet tall steel tower right next to the transmitter building. That is the one major difference between WVPS and this site; at Mount Mansfield there are many things between the transmitter and antenna, but in this place, not so much. Even so, Nautel makes a good product, so troubles are not expected.
The ground strap, AC power, remote control, and composite audio connections were all made without difficulty. The result, new transmitter on the air:
Nautel NV-5 FM transmitter GUI
This unit is analog only, but the information on the spectral display is still useful. The GUI uses Linux with a touch screen, which is a neat feature.
Nautel NV-5 FM transmitter controller board
In case the front panel GUI goes out, all transmitter controls can be accessed via push buttons on the remote control interface, which is the small board to the right. The main controller board is on the left.
This is one of the possibilities that has been bantered about as a solution for the “AM problem.” The theory goes as such; former TV channels 5 and 6 (76 – 88 MHz), which are not suitable for DTV would be an ideal place for the existing AM stations to move. That represents a 12 MHz chunk of spectrum, which is much more than the current 1.16 MHz spectrum the current AM broadcasting service takes up (.54 to 1.7 Mhz). An added benefit is that the VHF spectrum does not have the skywave “problem” that the MF spectrum does, thus many more stations could be licensed to the service. Everyone would benefit, and AM stations would get a new lease on life in the FM band. The number of stations would increase by several fold, including LPFM, non-commercial, and translators. AM stations would no longer be burdened with expensive directional arrays or substandard audio quality.
It seems almost too good to be true…
The FCC reportedly promised “take a hard look” at this idea back in 2008. Four years later, one wonders what has become of it.
A quick search of the existing TV stations licensed to channels 5 and 6 reveals the flaw in this theory. The FCC has re-licensed many full powered and Low Powered DTV stations to channels 5 and 6 since 2008.
List of full power channel 5 stations:
Call Sign
Service
Status
City
State
Fac ID
ERP (kw)
HAAT (m)
Licensee
WOI-DT
DT
LIC
AMES
IA
8661
13.9
566
CAPITAL COMMUNICATIONS COMPANY, INC.
WGVK
DT
LIC
KALAMAZOO
MI
24783
10
169
GRAND VALLEY STATE UNIVERSITY
WBKP
DT
LIC
CALUMET
MI
76001
6.4
301
LAKE SUPERIOR COMMUNITY BROADCASTING CORPORATION
KXLF-TV
DT
LIC
BUTTE
MT
35959
10
588
KXLF COMMUNICATIONS, INC.
KXGN-TV
DT
LIC
GLENDIVE
MT
24287
1
152.4
GLENDIVE BROADCASTING CORP.
KHAS-TV
DT
LIC
HASTINGS
NE
48003
45
217
HOAK MEDIA OF NEBRASKA LICENSE, LLC
WLMB
DT
LIC
TOLEDO
OH
17076
10
155
DOMINION BROADCASTING, INC.
KOBI
DT
LIC
MEDFORD
OR
8260
6.35
823
CALIFORNIA OREGON BROADCASTING, INC.
KIVV-TV
DT
LIC
LEAD
SD
34348
9.2
561
KEVN, INC.
WTVF
DT
LIC
NASHVILLE
TN
36504
22
425
NEWSCHANNEL 5 NETWORK, LLC
WMC-TV
DT
LIC
MEMPHIS
TN
19184
34.5
308
WMC LICENSE SUBSIDIARY, LLC
KCWX
DT
LIC
FREDERICKSBURG
TX
24316
23.7
412
CORRIDOR TELEVISION, L.L.P.
WCYB-TV
DT
LIC
BRISTOL
VA
2455
29.9
743
BLUESTONE LICENSE HOLDINGS INC.
WDTV
DT
LIC
WESTON
WV
70592
10
240
WITHERS BROADCASTING COMPANY OF WEST VIRGINIA
WIWN
DT
LIC
FOND DU LAC
WI
60571
9
338
WWAZ LICENSE, LLC
List of Low Power Channel 5 stations (analog):
Call Sign
Service
Status
City
State
Fac ID
ERP (kw)
HAAT (m)
Licensee
KSCT-LP
TX
LIC
SITKA
AK
15348
0.049
0
DAN ETULAIN
K05KF
TX
LIC
DILLINGHAM
AK
792
0.16
0
ALASKA CORP OF SEVENTH DAY ADVENTIST
KRDN-LP
TX
LIC
REDDING
CA
127179
0.6
0
KM COMMUNICATIONS, INC.
W05CO
TX
LIC
SARASOTA
FL
66995
3
0
THREE ANGELS BROADCASTING NETWORK, INC.
W05CJ
TX
LIC
KEY WEST
FL
125642
0.59
0
JAMES J. CHLADEK
DKHHB-LP
TX
LIC
HILO
HI
126233
3
0
KHHB, LLC
WIKY-LP
TX
LIC
EVANSVILLE, ETC.
IN
61036
0.14
0
ROBERTS BROADCASTING COMPANY OF EVANSVILLE, IN, LLC
Looking through this data, particularly the digital licenses which were granted since 2009, one an only assume that the FCC has, by de facto, nixed this idea if it ever considered it at all.
Zorch is a term used to describe an over voltage or over current condition that usually leads to catastrophic failure, e.g. the power supply was zorched by lightning. There is also a quality to radio signals that defy and exceed theoretical definitions for service contours or power density. That is quality defined as:
Zorch (adj): The ability of an RF signal to be received in unlikely locations; outside of predicted service contour, in steel structures, underground facilities, tunnels, etc.
It brings to mind the saying, “antennas are not amplifiers and amplifiers are not antennas.”
ERI circularly polarized 2 bay antenna
During the earlier stages of FM broadcasting, there was a notion that costs could be reduced by increasing antenna gain and reducing transmitter size. While theoretically, ERP (Effective Radiated Power) is ERP, broadcasters soon learned that high gain antenna, low TPO (Transmitter Power Output) installations lacked building penetration and had other reception issues. Realizing that there is a trade off between antenna bays, transmitter power output especially in difficult reception areas, a great debate occurred and continues on what the optimal system is. The answer is, it depends on the receiving environment.
Where this technical detail can be really important is with lower powered FM stations; Class A and LPFMs to be exact. They are already battling against bigger stations that have tens or even hundreds of times more power. Certainly an LP-100 station has it’s work cut out for it. The choice of antenna is perhaps one of the most important technical decisions to be made. Choosing the right balance of antenna type, antenna gain, antenna height and transmitter power output can greatly influence reception reliability and thus coverage area.
A good study of this quality can be had by looking at various LPFM installations:
Station ERP (watts)
Antenna Type
Antenna Gain (power)
TPO (watts)*
Coefficient of Zorch
100
1 bay vertical
0.92
127
0.1
100
1 bay circular
0.46
253
0.4
100
2 bay vertical full
1.98
58
0.15
100
2 bay vertical half
1.40
83
0.2
100
2 bay circular full
0.99
118
0.5
100
2 bay circular half
0.70
166
0.7
100
3 bay circular full
1.52
77
0.46
100
3 bay circular half
1.01
115
0.52
*Includes 100 feet of 1/2 inch foam transmission line, Andrew LDF4-50A, loss of 0.661 dB at 100 MHz, or 0.859 power gain.
Stations should try to get the transmitting antenna as high up as permitted without reducing ERP. In other words, the FCC allows 100 watts ERP with 98 feet Height Above Average Terrain (HAAT) radiation center in their current LPFM rules. Being lower in height will reduce the coverage area. Going over 98 feet HAAT will cause the station’s power to be reduced, which will lower the coefficient of zorch accordingly. Therefore, getting as close to 98 feet HAAT, which is different than 98 feet above ground level in many places, will net the best performance.
If a singular polarization (horizontal or vertical) is desired, vertical polarization should be chosen, as most mobile reception is by a vertical whip antenna. For best reception performance, a circularly polarized antenna will work best, as receiver antenna orientation will not effect the signal reception. A circularly polarized antenna has better building penetration and multi-path characteristics. The FM broadcast circularly polarized antenna in not a true circularly polarized antenna, it is actually unpolarized.
The use of a multi-bay antenna has the effect of focusing the RF radiation outward, perpendicular to the element stack, thus limiting the radiation directly up or down from the antenna. This is more pronounced with one half wave spaced antennas, which may be an environmental consideration in heavily populated areas.
Thus, the best coefficient of zorch for an LPFM station would be a circularly polarized, 1/2 wave spaced, 2 bay antenna. This antenna would have some gain over a single bay antenna, take up less room on a tower than a full wave spaced antenna, offer good RF protection performance for the general public living and working under the antenna, reduce wasted upward radiation and offer good building penetration for the ERP. It would require a slightly larger transmitter and more electricity, but that trade off is well worth the effort.
A piece of vintage gear from the late 1970’s, the Optimod 8000 was and still is a good sounding box. I have often thought that these processors would make an excellent internet audio processor using the test jacks on the back of the unit. The audio on these jacks is unbalanced and has 75 µS pre emphasis. It would be easy enough to make a de-emphasis network and create balanced audio with a 10K:600 ohm transformer. Some experimentation may be required with the transformer primary impedance value. Orban notes that not less then 1 MΩ impedance should be connected to the test jacks. For the internet station looking to copy the “FM radio” sound, this unit would do the job nicely.
The 75 µS de-emphasis network would look something like this:
75 microsecond de-emphasis network, unbalanced to balanced audio conversion
In this case, the values for the de-emphasis network are fairly critical, therefore 1% or better tolerances for the resistors and capacitors is required.
Even better, an LPFM or some other radio station on a budget could acquire one of these for relatively little on eBay or somewhere else. With a little TLC, most of these units can be rebuilt and put back into service. I would recommend that some type of limiter be used in front of it, such as a Texar Audio Prism or CRL SEP-800.
Some classical music stations prefer these units. I have noticed that they have a nice, mellow, open sound. Not at all fatiguing and yet still offer a nice easy 10 dB gain reduction. There is also a modification that can slow down the release time on the gain reduction. More gain reduction, AKA compression, can be had with something else in front of the unit.
The best part about these units, there is no rebooting, no processor lock ups, software glitches or any of that non-sense. Additionally, a quick look at the front of the unit shows very few user controls, making it almost impossible to screw up and sound bad. They are well built and so long as the electrolytic capacitors are changed out, fairly bullet proof. Other processors, not so much.
Optimod 8000A under test
This is an Optimod 8000A that I decided to put through its paces.
Really, how much more do you need? I recorded this on the camera microphone using a replica table radio, seen near the end of the video on the right hand side of the frame.
I used the Technics SL-1200 MKII turntable through an ATI P100 turntable preamp into the Optimod. The Optimod is feeding a BE FX-30 exciter running 15 watts into a dummy load. The Optimod is running about 5-7 dB gain reduction, which is enough in my mind. The BE FX-30 is still just about the best sounding analog exciter every made.
Rechipped Optimod 8000A, TL071 opamp
This unit has been re-capped and re-chipped at one point. The re-chipping follows the Orban recommendation; the 4558 and 1556 opamps are replaced by TL071CP and TL072CP respectively, and the uA 709 and 301A opamps are left in the unit. A good thing to remember, the uA709 and 301A opamps can be replaced by TLO71cP opamps in the event of failure. The Texas Instruments TL0 series opamps are very good and readily available.
Optmod 8000A input and limiter board
Overall, this unit is in good condition, however, like many such units, it is missing its brown “Optimod” cover, which goes over the input/output controls.
Manual is available at the Orban ftp site: ftp.orban.com.
