Most people seem to think of photons as little bullets and this is often OK, when you are considering light (amongst the whole em spectrum). When challenged about the 'extent' of a photon, they will say "It's a wavelength long / wide / big" or some such arm waving statement. Because the wavelength of visible em is so short, it is possible to gloss over the details and, indeed, to visualise little bullets ('corpuscles', as they used to be called). Of course, there is an instant objection to the notion of a photon being just one wavelength long, on the grounds that a single cycle of a sinusoid (which is what you'd have if just one such photon were to be travelling through space in isolation) would have an infinitely wide spectrum, full of harmonics that would be detectable. We don't see these - ever, for photons of any wavelength. BUT, what about when we are dealing with low Radio Frequency em? Consider a photon with an 'extent' of just one wavelength. For a 200kHz transmission, that represents a wavelength of 1500m. Now take a very simple transmitter with, say, the collector of a transistor connected to a short wire. Take an equally simple receiver, with a short wire connected to the base of transistor. Separate them by 10m. The receiver will receive photons that the transmitter is sending it. These photons, if they were to have the proposed extent would have to extend from the transmitter to a region that is 100 times as far away as the receiver input or, they would somehow need to extend ('coiled up?' somehow) from within the transmitter to somewhere within the nearby receiver. This just has to be a nonsense model. In fact you just can't allow a photon to have any extent al all or there will be some circumstance like the above that spoils the model. The 'energy burst' model is also a problem if you consider the mechanism that generated any particular photon. All photons of a particular energy are assumed to be identical (there is only one parameter with which to describe them). That would imply that the systems that generated these little identical bursts of energy would all need to have identical characteristics. There will be a range of charge systems that can generate em of any given frequency but they would all need to generate a burst of em with the identical pulse shape. In the classical sense, that would mean that the resonances within any system would all need to have the same Q and to make the transition within exactly the same time interval. This is asking a lot, for all 2.23900000000eV transitions to be identical, whether they were the result of a single, discrete, atomic gas transition or a transition within a continuous energy band in a solid. The only way round this is for the transition time to be irrelevant and for the 'arrival' or 'departure' of a photon to be in the form of an impulse. Hence the spatial and temporal extent of a photon must be considered as zero. These 'little bullets' all have to be infinitely small. But that's the least of our problems with QM, when we try to force it to lie within our conventional ideas.