Smartcast Modification

I've read Cakey's excellent article on increasing the range of the Smartcast, and am about to have a go with my RF15. However, in one of his threads Cakey mentioned that the length of the aerial is very important. I was thinking of using a telescopic 'FM radio' type aerial on the unit. Does anyone know if this would work or should I use a piece of wire and modelling tube as described by Cakey?

Sorry guys, I've just realised this should have been posted on the 'technique' forum. I'll not change things now, but won't make the same mistake next time.

A telescopic aerial will work but needs extending to the right length which means everytime you use it you have to measure the right length and if you knock it you start again,its a lot easier with a fixed wire ae

Thanks Cakey. What's the rough length needed for the aerial (American version), or is it simpler just to straighten out the spring? Also, if I don't straighten the spring in the receiver will this affect the ae length?

theres no rough length if you want it to work it has to be spot on
straighten the spring until it measures 3.06"
then make the overall length of the receiver 6.13"

sorry that I work in the old money

Cakey, if you're out there I promise this is the last question (I hope!).
I don't quite understand your last thread. Do you mean the aerial sticking out of the float is 3.06" and the aerial sticking out of the receiver is 6.13"? Sorry to be a pain but I know anything about electronics.

the floats aerial is measured from the printed circuit board (pcb)to the end of the spring
the reciever is measured from the pcb through the socket to the tip of the aerial
i.e.3"from pcb to socket socet and plug may = .5" so the external aerial would have to be 6.13-3.5 = 2.63"

measure from pcb to end of spring on float
on the reciever measure from pcb to socket,then measure plug and socket then whats left is the length of the external aerial you need to make
i.e. 3" from pcb to socket, .5" overall lenth of plug and socket so then take 3.5" from 6.13 which = 2.63

so good i done it twice...strange

If anyones interested I've just amended my rf10 to get the 'extra distance' and have done quite a bit of digging on tinternet.
I've used an extenable aerial from Maplins (?2.99) to increase the range of the ordinary rf10 unit with a rf40 (no mod) to approx' 100m. (provided there's no ripple)
I've cut another rf40 in half as per Cakey's excellent contribution (which got me started)and extended the half wave antenna to nearly, but not quite its full length. I then sealed the rf40 with epoxy resin and fitted an aerial cover to the length of 300 mm (with three turns left in the rf40)in the same manner Cakey did with his plastic tube and I've been out testing it this very night. I can get just over 300 metres with the maplins aerial set to the half wave length (345mm) of the 433mHz UK version. (This is easy to do) 690mm is just tooooo much and probably illegal.
I've modded an old PC microphone stand and fixed it to the front of my battered old microcat with velco to hold the modded rf40 still and it works a treat in open water. If I was snooping under trees it might fall off...hmmm
I've also just bought a 916.5mHz version from the USofA and am waiting for it to be delivered (for cheapness, ?95 with channel B RF45 and greyscale) and had a good look around as to what is legal and what is not at this wavelength in the UK. It appears that 916 to 917 mHz is for private TETRA broadcasting. TETRA being Terrestrial Trunked Radio. 916-917 falls in the MOD wavelength spectrum but there is an exception for transmitting in this particular band for private systems! (UK74)It appears it is legal to transmit in this band in the UK! Check it out for yourself! I'm no expert or ham and if anyone is I'd be very happy to hear from them. I'm going to use this at full wavelength 327mm (opps don't tell anyone) aerial length. (Although you have to allow for a particularly small ground plane, which is what the rf40/rf45 has. In other words you add on a bit of extra length to your antenna cause the thing its standing on is small....)
I've found that by using the Maplins aerial at full length on the rf10 it doesn't affect information at all until you start to get over 250m away then I lost the signal from the 300mm modded rf40 aerial. By dropping the aerial length to 345mm on the rf10 I managed over 300metre range with a perfect constant picture from the RF40. (I could just about see my microcat).
If you want I can take some photo's to see my efforts....
I'm going to install the Yank rf45 in the microcat rather than having it stuck to the front of my boat (although, if I say so myself... it does look rather good...)
Most of all thanks to Cakey for starting me off. I've discovered I own yet another anorak and have and am enjoying wearing it...
and I've learnt how to use a soldering iron. If only my shirts were so neat.

and how on earth do yer get a nickname?

back in the days of illegal cb radio and you had to have a handle so I was "the rig doctor" until my wife wasnt very well one day half way through making a cake,I sent her to bed and carried on but got caught by some visiting cbers so they changed my handle to cakemaker which got shorten to Cakey over the years

It all becomes clear.... Not all embarrasing then?
What sort of range do you get with the half wavelength aerial on the 916.5 version?

Thanks Cakey and Brian.
I had already bought an extendable 19" aerial from Maplins and had intended to use it, but now I'm not sure.

Brian, following your experiments do you think such an aerial is compatible with an American RF15 & RF40 (Channel 'A' I think), or would I be constantly fiddling with its length to try and get a signal? Also, I have no idea about full and half wavelengths. Does setting the antenna to "half wave length" simply mean extending it half way?

Any photos would be great. I am totally in the dark with all things electronic and any help would be most gratefully accepted.

The speed of a radio signal is the same as that of the speed of light. Both travel at 299,792,458 meters per second. This is a very useful number since the length of any radio signal can be determined by dividing the speed of the signal by the frequency of the signal.
this is then the wavelength (full)
half and quarter wavelengths are approx half and a quarter of full but another formulea is used to calculate the final figure depending on the media being used ,i.e.air then the cable etc
the advantages of quarter and half wave arials are that they reduce the size of the aerial needed i.e. the uk model smartcast needs 25.88 inches at full wave and only 6.4 at quarter wave


as to using a telescopic or not is up to you but Brian has got double the distance Ive ever had so it might be worth it

P.s. this page does it for you

Hi Tim,

what's your email address? I'll dig out some photo's and I've an extended piece of info that won't fit in here!

Having done a few calcs, if I were you I'd use a total aerial length of approx 13.5 inches on your bait boat and use the 19" extendable from Maplins on your rf15. I've used the exact same aerial on my rf10! Remember to solder the cut off aerial in the rf15 to a couple of bolts on the 2.5mm bolt that it sits on. If you don't you'll get noise on your screen....

Give it a go at 13.5 inches for 916.5mHz. That is a full wave transmission. Should be v strong. RF engineers allow for a small ground plane, which is what you're doing here. You can always trim it down a bit.....

I'll bet my bottom dollar you get 250-300m!

I'm Brian by the way, it took a bit of working out how to get a user name...bit slow sometimes.....

;-)

Cheers Brian.
I'm totally dumbfounded by the technical stuff, but hopefully you'll be able to answer a few questions via e-mail.
My address is duffield@tim10.freeserve.co.uk

I am off to the US shortly and wanted to buy a RF15 or RF20 but found out they all sell the onesd with a illegal frequency when used over here...doh! gutted

look above in Brian Newton's first post here..........