DK3, Screwdriver Antenna

Here are the measurement results!

The DK3 is probably the best mobile antenna for hf. It is also well known as the screwdriver antenna. It works on all hf bands (10m-160m) without changing the whip. Well, the DK3 is not really  inconspicuously, but still better than some other hf mobile antennas (I think here of some radiator with inductivities large like a bucket).  I have bought this antenna in the online shop of W6AAQ for US$ 180 in 2001. Just have a look at www.hamradiotoys.com That is much cheaper than for example the HS-1800pro that costs about US$ 700 over here in Germany. In addition to that, the expensive competitor does not work on 160m and you should not put more than "only" 200W into it. You can carelessly empty your battery while transmitting with up to 500W using the DK3. Not that I have ever used so much transmitt power, but I have operated with up to 350W from Jersey Island. The antenna could handle it but a small resistor in my IC-706 burned because of hf in the headphone cable. One side of the headphone was muted. However, it is always good to know that you can get more for your money.

This antenna was delivered without a mobile whip. I have used a DV27long (about 2.6m for CB) and connected it to the DK3. There is a cable sticking out on the lower surface which is used for the remote tuning of the antenna. You just connect it to 12V and change the polarity to "screw" the sliding loading coil up or down. The antenna is screwed down for operation in 15m band and screwed up (about 1.5ft) for operation at 160m. I have to remove the upper part of the DV27 to use it on 10m and 12m. You can tune until the SWR is as low as 1:1, there must be anything wrong if  that doesn't work (look here at the measurement results).  You do not need an additional antenna tuner. The bandwidth is very low, especially on the low bands. You have to tune again every few kHz but it has the advantage that you can easily fade out noise. The QRM is much less than if you use a dipole. 

The whole antenna works as a quarter wave radiator. The body of the car is the ground. There was no mounting bracket delivered, but it came with a brass stud that you have to fasten (isolated with two plastic disks) to a mounting plate. You simply stick the antenna on that stud. On the one hand I don't want to drive always with that antenna but on the other hand I want to be QRV in less than a minute. Therefore I used the towing eye to fasten the mounting bracket (many thanks to Wolfgang, DL5YX, who helped me with that). I can easily take it off by just releasing two screws. 

Of course you can drive with it, maybe it's usual in the US but not here in Germany. People claim you as crazy if they see you with such an construction on your vehicle. I tested it up to 130 km/h (about 78mph). However, I prefer it to use it as a stand mobile. I have done more than 15,000 QSOs from 12 different DXCCs like 3A, ZB2, EA9, MU, MJ, HB0. It is very difficult to operate on 160m in countries like Monaco. I am in less than a minute QRV and ready for the pile up on all bands and often hear "thanks for band point". 

There was a screwdriver antenna shootout at the parking lot during the International DX Convention in California (DK3, High-Sierra, Hi-Q, Drill Motor and one other brand). The DK3 took the first place in DX contacts at the convention. Please be aware for the cheep "remakes" of that fantastic antenna. Make sure you buy the original DK3 antenna by W6AAQ.

MP1, Vertical-portabel Antenna

I have no possibility to set up a big hf antenna since I moved to Pforzheim. I have not a lot of time to be QRV anyway so I  decided to work with a small indoor antenna. I bought the MP1 in the USA where I used it for example from Cape Cod and Key West. It is a very small vertical antenna that works from 6m to 40m. For 80m is an additional coil necessary. You can tune the antenna by moving the sliding part up or down. . Mostly is it possible to get a SWR of 1:1.5 or better but that requires a good ground. It comes with a set of wire radials but it can be that these are not long enough, especially on 30m and 40m. I made some marks at the coil so I can tune it much faster. You should buy the MP2 if you don't like to tune it by hand. The MP2 works similar to the DK3 and has a built in motor for tuning.

This antenna is so very small that it fits into a briefcase. You do not have to look for a tie point to hang up a dipole or anything like that. You are QRV on many bands and you do not even need an antenna tuner. Sure, the efficiency is much smaller than from a dipole but I could work everything that I could hear. You get better results if you set it up on an open place rather than in the window like in my case.

An advantage to the other portable antennas is that you can operate with up to 150W on each band. You have a very nice and small equipment in connection with an IC-706.

Here the antenna in its individual parts. I have put a QSL card next to it so you can compare the size of each part. The wire to the right are the radials.

self made mobile antenna for 15m band

Here are the measurement results.

How short can an antenna be? There are some hf antennas on the market that are already pretty short and I think a radiator should have at least a tenth of a wave length. But I wanted to find out what you can expect from a hf antenna that is as short as 50cm (about 1.5ft). I decided to create such a short radiator for the 15m band. The coil would be almost as long as the whip for lower bands (based on the low diameter of only 7mm) and the dx conditions are not all the time that good on the higher bands. Therefore the 15m band is in the middle between. I have wound the coil using 0.5mm coated copper wire which didn't get warm by 50W of transmitt power. I have put the whip on a magnetic mount so I could also easily change the band if I would have different whips for each band.

The first few QSOs were convincingly, even to the US, Canada and of course EU. The bandwidth is narrow because of the shortens of the radiating part. There is a return loss of better than 10dB (SWR 1:2) in the range between 20.840 MHz to 21.080 MHz so it covers at least the CW range in the 15m band but not more. However, it is plenty enough for CW.

The antenna works as a shortened quarter wave radiator. It radiates less, the shorter the antenna is. Additionally the main lobe is not as flat as it should be for DX. A 5/8 wave length would help to make it better for DX but the size of the coil would be larger than the whole radiator.  

There are still lots of improvements to do. You could just put a ball on the top of the whip, that would increase the capacitive top load and the coil could become smaller. You also could increase the diameter of the coil which would make it shorter and the radiating part longer since the coil does not radiate a lot of power. It also would be better if the coil could be moved to the middle of the whip.

Well, for what is all that? I just want to find out how good such a short antenna can be. I also would like to create a very short hf antenna that can be mounted on the car and does not look so remarkably.