Preferred Frequencies

Discussion on Frequencies

Note from Martin on Fly Quiet
Post a message in "The UK Flyers Frequency Chart" thread and a moderator will update this table and then delete your message (to keep the thread short). The reason for the list is to allow people to spread out when flying together or entering comps. Lets keep it down to the two (or three max) frequencies you would enter a comp on. Alternatives are good but too many makes this listing useless
Cheers Martin

List at 9th July 2005
Mike Stern	68 - 74
Gavin Stern	70 - 78
Steve Crowther	70 - 78 - 80
Jef Ott	74 - 76 - 80 - 84
Arthur Ott	74 - 76 - 80 - 84
Mac McComb	76 - 84 - 88
Richard Swindells	78
Nick Chitty	80
Tony Beckett	82
Mike Allton	82 - 84
Terry Adams	84 - 86
Martin Godden	84 - 86
Simon Whittick	84 - 86
Marc Trudeau	88
Peter Mitchell	90

January 2005
As a result of a query from Marc Trudeau, who has just moved to the UK, the following comments and list were posted on the F3K UK Register.
(Send your e-mail address to for spam free news about DLG in the UK).
There is also discussion going on at Richard Swindells Fly Quiet Forum.

Click below to go directly to the comments from these people.

Terry Adams
The Odd / Even "thing" is purely a BMFA recommendation and has been accepted as good practice for 25 years - it does work if local agreements do exist with cooperating power site clubs; however it is only a recommendation so as with me and the BIickley club near Dartford we will use all frequencies from 55 to 90.

A query from Mike Stern "Are odd Freqs generally not 'prefered' for gliders? Coz I quite like 77." brought this reply from Jef Ott
I will not fly if I have to use an adjacent frequency on my club field.

The problem with odds is that they are adjacent to two evens. To avoid adjacent flying, all odds (other than 55) wipe out both even adjacents, so less pilots can fly safely.

Example
72 74 77 80
72 74 76 78 80

If you cannot go "even" it will mean that your frequency will only be 10kHz away from (possibly) two other fliers.

In a competition scenario 6 or 7 transmitters may well be turned on at once, the harmonics produced by 'adjacent' frequencies may be more likely to cause interference.

In glider competitions even frequencies are generally preferred.

Tx signals can swamp receivers if Tx's on adjacent frequencies are much closer to the Rx than the dedicated Tx.

DLGers often spread themselves out over a wide distance and direct overflying of other's transmitters becomes almost inevitable.

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Peter Mitchell
As a club rule, we only use even frequencies at Tawney Hall. We only allow odd frequencies for guest's if the even number fliers either side of the odd number agree that the odd number can be used. Even then we think it is risky and if one of the even number fliers is not happy, then the odd frequency flier will not fly.

This is mostly aimed at Open/F3j and electric soarers where the potential for damage caused by a model suffering loss of control due to ' interference' is greater.

It could be said that this attitude is 'old hat' because it came about during the early days of 35mHz when Tx's then were not that accurate. However it is surprising, even now, how some Tx's and especially some Xtalls broadcast over a wide band and 'splatter' either side of their frequency. No one wants to have a dlg written off so we think it is a false economy for anyone interested in competition flying not to invest in a few even number frequency Xtals. It would take the cost of a lot of crystals to cover the loss of my Taboo or the Blaster.

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Marc Trudeau
This concern about use of adjacent odd and even frequencies on the same field with modern radios surprises me. We do this routinely in the US (20kHz spacing on 72MHz is the same percentage bandwidth as 10kHz spacing on 35MHz.) with no problems, except for the inexpensive single conversion receivers. (Good single conversions, like the JR 610 have no problem.)

The US Federal Communications Commission reallocated the channels in the 70s at the current spacing (half as far apart as they used to be), and required all TXes be replaced or modified to strictly meet the new narrow band spec, and it works! Furthermore, though the RX manufacturers will not guarantee it, the AMA has found all modern receivers are also narrow band, such that if everyone's using modern TXes and RXes, it's actually safe to have fields 2 miles apart, though the AMA requires 3 miles, in case someone's still using a very old receiver.

The radio manufacturers must be maintaining the same percentage bandwidth the world over. Are the fears here about operating on adjacent frequencies simply a holdover from problems many years ago, or have recent problems been reported?

Just curious.

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Mike Stern
I understand what you are saying and I will use 68 as my primary freq. But like Marc, I wonder if this is a some sort of hang over from technologically challenged times. I did not know about the American freq situation, but I have also been happy flying 10k apart, even years back in Zimbabwe, ever since the J series Futaba radios in fact.

Tony Beckett
The three biggest HLG meetings last year (2004) BARCS Radioglide, Malvern High Summer event and the BMFA Nationals all required entries on even frequencies.

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Phil Haywood
We are having problems with shoot downs caused by 10kcs spacing on our local slopes. This is from the BMFA hand book We are silent flight and should follow recommendations. I have seen a new dual conversion PCM receiver lock up when the next channel was switched on.

1) Use of all frequencies at 10 kHz spacing

This is operated successfully by most clubs. It is not recommended for power clubs with sites near to known slope or thermal soaring sites and it is not recommended for clubs specialising in silent flight.

It is important that, as a safeguard, flyers regularly operating together on adjacent channels should perform an adjacent channel check every two or three months.

The check is quick and easy to do. Flyer A switches on transmitter (with aerial down), then switches on his receiver and stands about 4 metres from his model. Flyer B, on an adjacent channel, switches on transmitter (aerial up) and stands alongside flyer A. No interference should be noted on A’s model and it should be under the full control of A’s transmitter. The test is then repeated using B’s model and with his transmitter aerial down.

Any interference noted indicates possible tuning or crystal problems and must be investigated further. The test may save your model as it will give early warning of problems beginning in your radio equipment, usually well before they become bad enough to cause control problems in the air.

(2) Use of the Contest Band Plan

i.e. power flyers use the ‘odd’ channels and slope/thermal/electroflight flyers use the ‘even’ channels.

This system is recommended for all ‘silent flight’ clubs and all power clubs with sites near to known slope or thermal soaring sites. It is not recommended for clubs having separate power or glider flight lines on the same site.

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Nick Neve
One reason for maintaining 20 kHz spacing in the UK, is because in flying HLG the pilots with their transmitters are often spread about the field; no attempt being made to corral them into a group.

Inherent in the design of some modern FM receivers, which I will not explain here, is an effect that if such a receiver flies very close to the antenna of an adjacent (in frequency) transmitter when it is a considerably greater distance away from its own transmitter, then it may be "captured" by the adjacent transmitter with sometimes adverse consequences, commonly called a crash.

This is why pilots are normally asked to stay within a "box" when flying power and not to go some distance to retrieve their models with the transmitter in their hands.

It is all down to safety in the end. Until pressure of numbers, due to Jeff's efforts, mean we want to reconsider I suggest you stick to 20 kHz.

PS.
I am not convinced that you can apply a percentage approach to bandwidth when comparing the frequency separation used in the USA to the UK. A 20 Khz separation is many many times safer in decibel terms of comparative signal strength to signal rejection; decibels being based on a logarithmic scale rather than arithmetic.

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Terry Adams
We are up against several issues here so lets start at the beginning, I come from a position of some knowledge first having been an RF engineer in my early career and second having worked for Futaba (Model Avionics) in the period just after 35Mhz transition and saw them through many of these problems with Rx front end re-designs.

My other club; Bickley MFC Nr Dartford fly almost 100% power on all numbers, most guys are flying expensive models and from experience will pay the going rate for a good receiver, the club keeps a log of all incidents that can be related to frequency problems and the bottom line is we don’t really get any,

Our fundamental problem is what is a “good receiver” – a “good receiver” has several key features one is that it can reject adjacent frequencies i.e. +-10Khz, remember that is what is required to do by the modeller not regulations covering our equipment, regulations state only that the transmitter should not splatter all over the band.

Good receivers i.e. most historically known brand names (Futaba, JR, Mpx, Shultz) will do this with no problems a GWS priced at £18.50 will not and the owner will be shot down by adjacent channel interference.

It is much easier to make a transmitter to meet spec than an Rx

Second problem is 3rd order intermodulation product or 3IM, this is where 2 transmitted frequencies e.g. 65 and 67 are mixed in the Rx front end electronics and will internally produce a rogue signal on 69 which will shoot down the guy on 69, this effect also gives arise to what we used to know as channel 23 syndrome as these two Tx’s need not be adjacent but can easily be 10 numbers away e.g. 60 & 70 affecting 80

However the good news for us is this is the reason that dual conversion Rx’s were developed as they can reject this 100%

So there you go ! – all in a simplified format and easy to make sense of, but remember although these guidelines were made many years ago it is still going to be safer for a cheap Rx to be at 20Khz not at 10Khz although a Shulze will have no problems on 10 on the other hand a worthy dual conversion Rx should be able to handle any problem you can reasonably throw at it.

I guess we stick to evens giving us 20Khz spacing then buy good Rx’s and we will not see any thing to worry about.

From experience I know I will suffer from interference in the F3K launch environment using the old Mpx Pico Rx so that is the first one to put on the list of no-no’s

I hope this can settle a few worries and guide you the best way forwards.

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