Transceivers - how to select an appropriate antenna?
Shortening an antenna from its ideal length is not a problem providing you accept and possibly counter the limitations that shortening brings. Here are some words from this site that tell you the story: -


  A shortened dipole is simply a dipole antenna that has been shortened.
  Since it is shorter than its resonant length, it will not be resonant
  and will exhibit both resistance and reactance at the feed point.
  Shortened antennas tend to have a capacitive reactance and therefore
  need an inductance to cancel the capacitance and bring the antenna
  back to resonance. Normally the resistive impedance also drops as the
  antenna is shortened, so additional impedance transformation will be
  needed to effectively match the antenna.
  
  A shortened dipole will act similar to a full sized resonant dipole in
  many ways. The effect of ground will still be important, current will
  be maximum in the center and very close to zero at the ends with
  maximum voltage at the ends and minimum in the center. If the antenna
  is center fed, it will still be balanced, with equal voltage and
  current distributions on both legs.
  
  From the principle of conservation of energy, we know that if we can
  feed energy into an antenna, it will radiate. We also know that with a
  suitable matching network, we can feed power into nearly anything,
  including a shortened dipole.


The article goes on to demonstrate how the impedance of the antenna becomes reactive and how the idealized "50 ohm" input resistance becomes significantly less when shortening is done excessively.

Here is another excellent site that explains you can make an antenna from any length.

In short, any length works providing you can get the power into it that you require for transmission. Reciprocity means that a badly shortened antenna works just as "inefficiently" as a transmitter and receiver. There is no silver bullet of length - optimum is quarter, half and full wave antennas but don't let this stop you running the antenna at significantly shorter lengths.

One caution - if you are wanting to transmit several hundred milli-watts or above, not having an ideal antenna (proper length or compensated by matching networks) you may damage your transmitter output stage.