Two executives at AIM-listed satellite operator Avanti Communications took advantage of a plummeting share price on Wednesday to raise their stakes in the company.The move came after the firm warned that annual revenues would be below market consensus forecasts due to the timing of certain contracts. Several major contracts in Africa that were expected to close before the end of the period are now due to be completed in the next financial year, Avanti explained."We believe some prudent re-basing of forecasts would be sensible until a track record of revenue delivery is firmly established," according to analysts at Jefferies following the trading update.By the close of trade, the stock had fallen by nearly 40% to 148.94p, compared with the closing price of 246.75p on Tuesday. The share price now stands around 57% lower than where it was last year.Chief Executive Officer David Williams, the co-founder who set up the company in 2000 along with Technical Director David Bestwick, bought 14,200 shares at 176p each, spending a total of £24,992.He now holds a total holding in Avanti of nearly 1.67m shares, equal to a 1.49% interest. He has additional shares held under the firm's long-term incentive plan which are subject to certain criteria.Non-Executive Director Paul Walsh meanwhile bought 10,000 shares at 161p each for £16,100, taking his interest to 140,000 (around 0.1%).Top Director BuysAvanti Communications Group (AVN) Director name: Mr David J WilliamsAmount purchased: 14,200 @ 176.00p Value: £24,992Avanti Communications Group (AVN) Director name: Mr Paul S WalshAmount purchased: 10,000 @ 161.00p Value: £16,100Top Director SellsCML Microsystems (CML) Director name: Mr Nigel G ClarkAmount sold: 15,000 @ 473.00p Value: £70,950