QRZ'd and greetings from Tampa, Florida.
My interest in amateur radio for the last 40 years has been VHF and UHF operating.
My first HF station was first on-the-air December 30, 2013!
Previously I worked HF contest stations for W4DFU (University of Florida,1982) and W4HSO (ARRL Field Day).
HF Antenna - "Long" Inverted L
I find the Long Inverted L antenna together with the SGC-231 tuner/antenna coupler to be an ideal backyard HF station.
It is oriented E-W and fed at the west end of the downward part of the "L" at about 4 ft above elevation.
The secret is a non-resonant antenna length and excellent grounding/counterpoise system at the feedpoint (with longest ground counter poise located below horizontal antenna wire and grounding conductor bonded to household grounding electrode and cold water pipe).
EZNEC plots support my on-air findings with low angles/multi-lobes for 10-20m for DX, and more (cardiod upward) NVIS pattern for 30-160m. Note: NVIS daytime coverage on 40m is solid 400-500m operating radius, while NVIS evening coverage on 60m-160m out to 800-900m. 30m coverage is mixed DX and NVIS.
Polarization is mixed horizontal and vertical.
The system as described below is very effective on ALL HF frequencies 1.8 to 54 MHz (including 60m).
Dimensions for my "Long" Inverted L antenna as follows:
Grounding Electrode: 5/8 inch x 8 foot galvanized rod, driven 7 foot 9 inches into soil adjacent to one of the vertical supports.
Ground counterpoise (located below horizontal radiator): 62 ft - buried 3-4 inches, 12 AWG one end bonded to grounding electrode, the opposite end is open.
Vertical ground conductor: 4 ft, 6 in, 12 AWG, one end bonded to grounding electrode, the other connected to SGC-231 grounding lug (see grounding below).
Vertical radiator: 8 ft 6 in, 12 AWG, one end connected to SGC-231 via grounding relay, the other connected to horizontal conductor at 13 ft elevation.
Horizontal radiator: 57 ft, 12 AWG, ceramic porcelin insulators, supported by 2-4x4x16ft poles pressure treated, painted and anchored with a poured concrete footing.
Antenna Length: I believe the ideal non-resonantlength would be about 71 ft total, 57 ft horizontal, and 14 ft vertical, at elevation of 14 to 18 ft. The vertical length/elevation should be selected by the operator to give optimal vertical pattern response for 6m (0.5L to 3/4L), or 10m set for (0.25L to 0.5L).
SGC Elevation: SGC recommends a maximum elevation of about 5 ft above the ground surface, and I have found better tuning results with an elevation of 2-4.5 ft with different antenna/grounding configurations including a sloper.
SGC Enclosure: The SGC tuner must be housed within a suitable NEMA rated non-conductive enclosure as shown for protection and the antenna lead protected (high voltage potential) from accidental contact (see CANTEX, 24"x24"). These are available from Lowes, Home Depot or local electrical supplier.
Antenna Conductor: The antenna was constructed using #12 AWG copper, THWN/THHN 19 mil insulated wire due to short length and limited sag. In the future, I may consider replacing the copper conductor with an insulated copper plated steel stranded wire of same diameter.
Antenna Conductor Insulated: I believe the benefit of an horizontal insulated antenna conductor helps minimize static charge build-up and helps reduce overall system noise especially below 60 MHz and HF.
Antenna Lightning protection: The antenna must be grounded when there is lightning probability or static discharge/induced currents that could damage the SGC231 tuner. This is accomplished by using a relay located at the SGC 231 antenna connection which grounds the antenna and isolates the SGC231 when 12VDC bias is removed. The relay has not affected tuning or signal radiation as might be suspected. The SGC231 coaxial feeder is further protected using a shunt 600V gas discharge arrestor (see L-COM) which passes DC bias and bonded to the service entrance electrode just prior to entering the radio operating location.
Antenna Grounding: Later I added a grounding conductor bonding the antenna electrode to the home service entrance electrode and cold water pipe without any measureable increase in system noise or signal pattern distortion. This was done to minimize any voltage potential (lightning flash-over) developed from the antenna to radio system power ground. Additional tests have shown excellent results when bonding to a cold water well-head pipe (if galvanized steel) if no other grounding radials are readily available. Use the proper methods of attaching to either grounding electrode or cold water pipe (rated bronze nut or clamp). Review NEC electrical standards prior to connection if you aren't sure.
SGC-231 antenna coupler, SGC DC Bias Tee, Antenna Grounding relay, Fair-rite clamp-on common mode RFI (ferrite) suppressors, mounted within Cantex NEMA non-conductive enclosure. Feed coaxial cable is LMR400-DB.
Antenna DX directional pattern:
The "Long" Inverted L seems to favor E-NE, and E-SE directions (Especially Central Europe and Central Asia) for 20, 17, 15, 12m and this is supported by the EZNEC plots.
I plan to add a 2nd inverted L or sloper oriented at 90 degrees (N-S) to the first to fill a percieved signal void (switched by relay).
The station is an ICOM IC 7410 normally operated at about 80 W PEP.
UHF and 6m repeaters
Repeaters shown in the photo below are Motorola Micor vintage (replaceable discrete components but very reliable, 1970's).
The repeaters are part of a radio system covering the TAMPA BAY area including St. Petersburg and Clearwater.
They are networked (Allstar, Echolink and DSTAR) into the KC1AR (Naples, FL) and KA9RIX (arsrepeaters.com, Clearwater, FL) repeater system (VHF and UHF) with coverage extending from Tampa to nearly Ft. Lauderdale along the west coast of Florida.
The six meter FM repeater used mainly for DX with highpower (330W, using 2-8560AS Eimac PA) and groundplane antenna (DB-201) at 200ft. The 6m repeater output is 51.64 MHz/PL 141.3 Hz, primary receiver at 51.14 MHz/PL 141.3 Hz, secondary receiver at 51.14 MHz/PL 71.3 Hz.
I have included analytical measurements of the DB212 antenna for those interested in the "hairpin" design used in many DB antenna designs (Note the approximate 50 ohm input impedance of the single loop).
If 6m is open, please QRZ'd.
Ciao and 73's,
DB212 hair-pin dipole antenna response shown below.
7231161 Last modified: 2016-04-10 17:21:49, 7868 bytes
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