ON7EQ HF Mobile

As I am traveling a lot by car around Europe, I like to operate on HF to keep contact with the friends in ON-land.

The rig is the Icom IC-706MkII(G) (now upgraded to  IC-7200), doing FB job with it's handy separable front panel, which I mounted on a hinged support plate (so that access to the storage compartment on dashboard is still possible!)

For the antenna, I have been looking for a solution which was meeting following requirements:

very efficient and good performance (I operate mostly on skeds)
no HF-operation required while driving, only while parked (skeds ...)
very quick deployment time (in less than 1 minute QRV!)
at least 20m and 40m band (contacts within Europe)
the Icom IC-706MkII(G) has no built-in ATU : so operation on both band must be possible with decent SWR!
very easy to mount on mobile
possibility to use antenna for fixed operation (holiday, camping, ...)
cheap ! (actual cost <25 EUR)

I  imagined a  solution around a tiltable antenna made from a glassfibre fishing rod.

the fishing rod : I used a 6m long rod (cost = 11,-EUR), from which the top section is not used (because not hollow at it's extremity). Some sources claim that carbon fibre rods are not OK.
the antenna is a flexible wire, insulated (section 4mm²), operating as quarterwave on 20m (my lenght = 4m70). This wire is inside the fishing rod, it is kept straight by a rubber band + small nylon rope at the top + cap where it is permanently attached. When antenna is retracted, the wire is pulled out the antenna base (drill a hole in the cap) and put inside the car.  The SWR <1.5 on complete band.
for 40m a loading coil is inserted at the antenna base. First tried to simply insert a coil in the feed, found antenna resonating,  but SWR very poor (impedance much too low, about 12 ohms). How to adapt this ? Put the 'feed' side of the loading coil at ground level, then searched for 50 Ohm impedance along the coil. This works fine, SWR <1.5 on 40m phone band (7.040 - 7.100). See further for coil construction details....
See pics for the tilt support construction. Only one butterfly nut keeps it down or up.
All electrical connections are made with 'faston' type connectors. Apply grease/vaseline to avoid oxydation.
Do not forget to provide proper RF ground (I used a copper braid to a bolt of the car roof rails). It is essential to have a good RF-ground (don't rely on 'zero ohms' indication of your multimeter) if you don't want to have a 'hot' microphone and poor SWR/bandwidth !

Suggested procedure for adjusting the antenna :

first determine the lenght wire for 20m band. Start with a lenght of 5.10m, then cut till best SWR at 14.175 (this will be close to 1.2 or 1.3) For me, this was at about 4m70. Once this is adjusted, you can  permanently arrange the wire with the rubber band (strong elastic).
then work on 40m band: first put the coil inline and adjust number of turns for resonance (lowest SWR, probably high about 1:4 or 1:5). Then ground the feed side of coil, and look for 50 Ohm feedpoint (approx 2 turns from cold side - test with a needle through wire insulation and then solder permanently). Once this is OK, the coil will have to be slightly re-adjusted. If necessary, spread the windings to look for resonance on desired QRG. Once all OK, fix everything with PVC glue.
you can work with an antenna analyser, or if your TRX is able to work out-of-band, this is quite handy to fine-tune at low power. The IC-706 has a handy 'SWR Graph' analyser function. If you want to construct a very nicely looking coil, think of first making a 'prototype'...
Results :  This antenna works really well mobile on 20m and 40m bands, despite the fact that  some sources claim that 'base loaded antenna's are not efficient'. Made several S9+40 dB QSO's on 40m, distance 300  kms ....  and some nice DX as well (on 20m band HS0/IK4MRH = Thailand, Pukhet Island, and on 40m ZL4IR Ed, both with  'true 5N' reports! 
For portable use, it can be used on a small pole or metal tube, lenght approx 60cm, driven into the ground. Base of antenna elevated approx 10cm from ground. You really will need a ground plane: tested with 3 radial wires 0.75mm² section (insulated), length each 4m50 (not too critical), simply put on the ground in a "star". .  SWR was exactly same for 20m and 40m as on the car. This ground system should be quite OK for 'continental' QSO's.... but don't expect DX !
Next generation ?  These fishing rods exist in lenghts up to 12m (manufactured by Spiderbeam) ! Thinking of a full size 1/4 wave on 40m and 5/8 on 20m !?

Mobile mount, driving (horizontal) position


The mobile mount / horizontal position.

The red butterfly nut keeps the swivel plate down.

The mobile mount, tilted, operating on 20m

(straight feed)

The 40m band loading coil, which is clipsed on the the rod when required.

Wound on PVC tube 50mm OD, 19 turns of 4mm² wire.(same as ant)

Feedpoint (red wire) 2 turns from 'cold side'.

Even after hours of operation, this coil doesn't heat up (100w SSB) at all.

Operating /M in Bretagne at CAP FREHEL (Côtes d'Armor/22)