The new expanded 36MHz frequency allocation with both odd and even frequencies cleared for use by the SMA and MAAA has placed stringent new demands upon the 36MHz frequency control system. The main problem is the fact that the band now extends for 600kHz which means that fourteen pairs of transmitters spaced 450 or 460kHz apart can now transmit simultaneously. Theory predicts and practical tests have confirmed (also field experience, see QFI June/July) that there exists the potential for interference in single conversion receivers if two transmitters spaced 450 or 460kHz apart are allowed to transmit simultaneously. Dual conversion receivers using a 10.7MHz first I.F. frequency are immune to this type of interference. An additional consideration is the fact that the odd frequencies are available for shared use by boating clubs. Thus in some areas it may not be possible for aircraft clubs to open both sets of odd and even slots. As a result of the foregoing model clubs are now faced with a bewildering array of choices when deciding upon their frequency policy and setting up their frequency control system. There is however no cause for alarm for the Silvertone Issue 4 Keyboard can handle all of these situations in a simple and practical manner. If the safety gate is not removed, a key cannot be inserted into that slot and therefore a transmitter on that frequency cannot be operated on your club field. The Club remains in control at all times. The key to a successful outcome is therefore in the correct setting up of the keyboard. The above considerations do not apply to the 27, 29 or 40MHz bands as all of these bands are less than 450kHz wide. The following list summarises the frequency policy options available.
A recent MAAA ruling recommends all slots be opened even for single conversion receivers. Silvertone does not recommend this practise and stands by the above policy.
(a) Model Aircraft Clubs allowing single and dual conversion receivers. This policy is applied in most model aircraft clubs. In this case open all slots between and including 601 and 645. Slots 646 to 659 are left closed. Channels 646 - 659 use the paired slots on the No.1 board.
(b) Model Aircraft Clubs adopting an exclusive dual conversion receiver policy. Open all 59 slots on the board. In this case it is recommended by Silvertone that single conversion receivers should not operate on this field, especially AM single conversion receivers which do not have the advantage of capture effect to mask the intermodulation problem..
(c) Boating Clubs. Should open only the odd numbered slots 601, 603, 605 etc. The same rules concerning single or dual conversion receivers apply.
(d) Conservative Model Aircraft Clubs. Some clubs choose to only allow odd or even channels on their field. In this case open the appropriate odd or even slots as required. Again the same rules apply regarding single or dual conversion receivers.
NOTE: It is important to understand that if there is even one single conversion receiver in the club or visiting the club then the high numbered slots 646 - 659 on the No. 2 board should be left closed and the paired slots on the No. 1 board used instead. The simultaneous operation of two transmitters 450 or 460kHz apart is therefore not possible. Silvertone recommends that the only time all slots should be opened is when a club decides upon an exclusive dual conversion receiver policy with both odd and even frequencies cleared for use.
As you can see from the above operation on 36MHz is no longer the simple matter it once was. However if the recommendations offered above are adhered to, then operation on 36MHz is quite safe and in practise as easy as it ever was. In fact even better than it was for once the correct procedures are in place, some of the mysterious glitches that showed up from time to time tend to vanish. For most frequencies it is still only a matter of slipping your key into the board and go fly. There are only a few frequencies that require additional care and even these are simple once the board is correctly set up. The alternative is to restrict the band to less than 450kHz wide, a totally unnecessary and wasteful exercise.
Silvertone Issue 4 Keyboard (0.1" = 1kHz standard). The 1" (small blue) key can only be used as a guard key under the existing MAAA ruling. The new 25mm metric keys (yellow) must not be used in Issue 4 keyboards.
1) Hold a club meeting to decide upon which frequency allocation policy will be adopted by the club. (Eg. Single conversion (odd and even), dual conversion receivers only (odd and even), 20kHz boating (odd), 20 kHz exclusive aircraft (even) etc.) The Issue 4 Keyboard can cater for all of these systems. These policies are listed in more detail in the introduction..
2) Using a square jewellers file, open the safety gates on the appropriate slots for the frequency spacing system decided upon by your club and listed in detail above.
(3) Issue or ensure that all club members have the correct key for their R/C system. The Silvertone Issue 4 Keyboard features a dual row of numbers on the slots 601- 614 on the No. 1 board, the standard row of black numbers and a second shorter row of red numbers (646-659). The lower row of black numbers are for standard Blue 2" keys. The window in the Blue key is placed to show the black lettering. As a result keys bearing the numbers 646 - 659 will not show the correct number in the window when using the paired slots. A nice touch to the Silvertone system has been the introduction of a modified RED key with the window in the correct location to show the RED numbers on the paired slots. (Fig 2) These modified keys should be issued to modellers using the 646 -659 slots wherever possible.
(4) Place the 1" guard key in the "G" slot on one of the boards. This key must stay in one of the two boards at all times. If a 2" key is to be placed in 630 then the guard key moves across to the "G" slot on the No. 2 board. If a 2" key is to be placed in the 631 slot then the guard key is moved to the "G" slot on board No. 1. Two 1" keys are provided with each board, with one as a spare. (Fig 1)
(5) All keys should be marked with the operatorís name and the channel number (625, 639 etc). The channel number should be in numbers approximately the same size as the number which appears in the key window and located on the key as per Fig 2.
(6) In operation the Issue 4 keyboard works in the normal way. Before switching on a transmitter the operator checks the keyboard to ensure that there is a clear slot for his key and that his key is for a valid frequency. (ie. That the safety gate has been removed) When the key has been plugged into the keyboard and a check has been made to ascertain that the number in the window matches the number on the key, then and only then may the transmitter be switched ON.
(7) Some clubs have found that when using the paired slots there exists the possibility of 645 being available on the No. 2 board and 646 being available on the No. 1 board. This places two transmitters only 10kHz apart. If 645 and 646 are used in your club then the second (spare) guard key can be used as a guard key for the 645/646 combination. The more elegant solution being to recommend not using 646 in your club. As this is one of the new even frequencies there is less likelihood of this frequency already being in use.
Note: A recent ruling by the MAAA recommends that in clubs not using paired slots, a second lock-out key may be inserted into the opposing 450/460kHz slot by fliers who wish to operate conservatively. To ascertain the correct slot, add or subtract 45 to the channel number. (eg 601 + 45 = 646)