As jwenting and Voitcus have suggested in the comments, this cable is not attached to the jeep, so the other picture of the jeep you referred to is not relevant.
See below, a magnified and enhanced image of the critical section of this photo, which appears to show clearly that the cable in question runs behind the shoulder of the soldier on the left side of the jeep. Based on the cable's trajectory in the picture, juxtaposed with the position of the jeep, its point of fixture appears of necessity to be in the ground behind the jeep, near its left hand rear side.
The faint line that appears to show that the cable runs in front of the soldier's shoulder is in fact the shadow of the pennant mounted on the front of jeep, cast by the sun shining from the upper right hand side of the picture, as is visible in the original picture: Note shadow of the jeep's rear right corner, and the shadow of the beard of the soldier on the right, veering off to the rear left of the picture, proving that the sun was shining from the upper right, and also creating the shadow of the pennant, which is cast on exactly the same point where in the image, the cable intersects with the soldier's shoulder. (The shadows are quite shallow and the sunlight on the soldiers appears to be quite direct, so the picture was probably taken near noon time.)
In addition, the cable in question, although very long, is apparently quite taut, showing no sagging or bending - indicating that is it is secured somewhere further up towards the upper right, outside the scope of the picture. If it was a long, extended whip antenna,for a radio possibly mounted on the far left rear of the jeep, it would be mounted vertically and be shorter, as in the other picture (that orientation aids propagation of the RF) And, it would usually sag and droop when extended to such a length and angle.
Also, it has neither the correct angle nor the correct structure for a ground mounted antenna, which would be vertical, not angled, and normally thicker. The other candidate would be a wire antenna used for a dipole antenna, but they are generally strung horizontally and held by non conductive vertical supports.
Since that cable is fixed, fairly thick and taut, the most likely candidate is that's it's a guy-wire supporting an antenna or observation tower of some sort. I don't know how thick a cable to hold a balloon needs to be, but I did some research and didn't find anywhere that balloons were used in Operation Horev.
See All about Vertical Antennas, one of numerous sources: Wire and vertical antennas are very popular with amateur radio operators and the HF frequencies used by hams were the most commonly used then for military operations, (as they were in WW2) before modern technology allowed military operations to switch to VHF and UHF, which can do with much more compact, portable and easier to manage hardware. See Radio-Communications Theory:
High-frequency (HF) communication was first made practical in the
1920's when the first actual radio system was installed in Europe.
The desire to go to higher frequencies was caused by the need for
longer range, higher capacity circuits. Until HF came about,
transatlantic communication was by cable or mail. World War II had a
profound impact on the use of the radio-frequency spectrum. Military
leaders realized higher capacity communications were needed.
Naturally, the solution was to go to even higher frequency bands.
During the early part of the war, a system called radar was developed.
The development of components and equipment to operate at the higher
radar frequencies led to the development of higher frequency radio
Here is picture of an HF vertical "antenna farm": Note structure of the antennas and the supporting guy wires.
Contrast with a simple HF dipole - note the horizontal orientation and plastic insulator:
Problems with this analysis:
- Based on the image, the guy wire would have been anchored very close
to the shore, in unstable, water-logged gravel and sand: Not a good place for an anchor. This might be a serious
problem for my answer, although perhaps there is some boulder or
rocky structure along the shoreline, its view obstructed by the jeep,
that was suitable for an anchor.
- Now that Pradeep's answer has been posted, perhaps there is another
problem: The second picture in that answer shows a very similar
looking long, rigid antenna, mounted on the right side, very close to the rear of the jeep, pointed at about a 60 degree angle. The object in our picture might be a
similar sort antenna mounted on the rear left side. The trajectory
of the cable in question would likely support this. As for antenna
design theory, in combat situations, ad-hoc implementations were
often used even if they were less than optimal in terms of RF
engineering. The important thing was that it got the required job
done, and was amenable to mobile combat use.