This weekend I operated portable HF from the car, but I wanted to try out both a multi-band vertical and an EFHW. The advantage is both are quick, easy to deploy, and relatively cheap.
These can be made of purchased and much will depend on the power level required. The length of wire required can be calculated using the formula 141/f (in MHz) and this will provide the length in meters.
Use the lowest frequency required, so if you would like the antenna to operate from 7 to 28 MHz, use the formula for 7 MHz. If you use 7 MHz, the wire length should be just over 20m (a half wave on 7 MHz)
The EFHW transformer would often be described at 49:1 or 64:1, this ratio is required to transform the impedance from 4 to 5,000 Ohms to around 50. This provides a multi band antenna that requires no ATU. The antenna is easy to deploy out portable, as it can simply be run in a vertical or horizontal configuration.
If you would like to build your own, then have a look at this article
Here is a picture of my EFHW setup on a field day.
Telescopic Vertical antenna
The addition of an adjustable vertical antenna provides another easy-to-deploy multi-band antenna. The vertical will cover 14, 18, 21, 24 and 28 MHz
The vertical antenna is nothing more than a large telescopic whip antenna, that can be adjusted from full height around 5.6m to 50cm. The antenna are small, portable, and easy to transport. The whip antenna can be purchased online from eBay or Aliexpress. You will need to purchase a mounting plate and earth spike, so the antenna has something to connect to and you can attach your 50 Ohm coax.
Fully extended (5.6m) the antenna is resonant on 14 MHz, you can lower it down to achieve resonance on other lower bands.
I would also suggest using a 1:1 choke close to the feed point, this will stop the coax from radiating and improve the match of the antenna. Elevated antenna and radials would improve the performance further.
It’s also possible to buy a complete vertical kit for around £140 online (this would be £300 for ML&S), it includes the whip antenna and a loading coil.
So your options for the vertical are as follows.
1/Purchase a 5.6m whip, base, and ground spike for £60 (will cover 14 to 28 MHz)
2/ Purchase the PAC12 that includes whip and loading coils (will cover 7 to 28 MHz) for £140
Over the weekend I worked mostly on digital modes FT8 and completed around 250 QSO using Icom 7300 and 50w into the antennas described above.