Hams living within cities and urban lots are often unable to erect a tower with a regular Yagi or Quad. Experiments with wires may require a lot of space so many Hams “ending” with a multiband vertical antenna. Regardless of wide availability of many types of such antennas the answer to the question “what antenna should I buy” is not simple. I tried many verticals from many manufacturers but I still cannot find an antenna with reasonable compromises – any antenna has its own weak points depending on poor engineering, use of cheap materials or bad fabrication.
Avoid a “no radial” vertical
A multiband vertical is always shortened on some bands and is “full sized” mostly only on 28 MHz. A non radial type which does not count on the mirror image building up the virtual half of the radiator seems to be more shortened than a usual vertical monopole using radials. This fact been fully confirmed by tests done with a Cushcraft R-7 which produced about 2 S units weaker signal than low mounted G5RV multiband dipole (path OK-W6)… No radial antennas may serve as emergency solution for those who has no access to the roof and must do all within own apartment… “Balcony Hams” may utilize advantages of such radiators using this antenna mounted on the balcony fence anchored to the wall by two non conducting ropes at angle of about 45 degrees. What a rocky way to the DX world!
Tuning problems
Antenna manufacturers mostly advertising their products as perfectly tuned, some providing tuning possibility by varying of the radiator length, rare exception are tunable traps (as I know the only is Hy-Gain DX-88). There is highly recommended to obtain a detailed manual before antenna purchase. The resonant frequency is strongly dependent on the antenna environment and grounding system (radials). You may find SWR graphs for CW, low phone and high phone tuning. I used the same antenna in my QTH with metal roof instead radials and a lot of different locations including rocky ones where is hard to bury any radial. I tried also elevated radials and different lengths of buried radials. All my tests confirmed that all antennas were pre-tuned to SSB band portions. If you hate SSB like me you may became disappointed with first results and tired with repeated up-down procedure required for proper adjustment.
Summary:
- Any antenna is pre-tuned to SSB band portions.
- Do not attempt to adjust the antenna without a good impedance analyzer (MFJ-259B recommended).
Cheap materials and poor fabrication
When purchasing a new antenna, take a look at the parts. If you find sharp edges or the tubing full of metal scraps, you need a bit of power to assemble two parts together, it is a sign of poor fabrication. Do not be blamed with “famous” product mark, a well known manufacturer may produce a poorly fabricated model.
Another problem is a cheap material used for construction. Some manufacturers using a thermoplastic material for trap coil forms. It may melt easily if applied power exceeds some 500-700 Watts (noted such problems on the Hy-Gain DX-88, do not be blamed if the traps looking very heavy – it is a plast only, inside you may find a coil wound of relatively thin wire and the encapsulated trap prevents any air exchange for sufficient cooling). If tubular capacitors used in traps, the dielectric insert may smoke up quickly if applied power exceeds the above mentioned level (noted such problems on the Cushcraft AP8-A). Select an antenna with heavy tubular air capacitors (without any plast dielectric insert). The capacitors should be well protected from moisture, dust and insects.
Pay attention to the clamps and screws used – the hardware should be always made of stainless steel. If you plan to buy an expedition antenna which should be assembled and disassembled many times, self-cutting screws may cause problems.
Ensure yourself about availability and quality of manufacturer’s customer support. I discovered a mistuned 18 MHz trap on my brand new AP8-A and asked for replacement. If I received no reply within 5 weeks, I decided to fix the trouble with own hands. Using the MFJ-259B, all went OK but some months later a gimmick capacitor burned out at 800 Watts regardless of the “full legal limit” power specification. Unfortunately, the warranty ceased.
Remember that applying of the legal limit power may become an “infernal” test. If your life is too short for QRP, use antennas with heavy traps where is easy a replacement with Teflon custom made coil form.
Results are disappointing. I could not find any 40 – 10 m vertical antenna covering also WARC bands. Some guys recommended the Butternut HF9-VX but I am afraid about open air-wound coils because I plan to use this antenna in the city with very aggressive atmosphere. I should try this one before starting development of my own construction.
