preselector schematics, bord layouts ect

[nay27uk]

Hi does anyone have a schematic, bord layout, parts list and instructions please for me to build a SW preselector that will cover 525KHz - 30Mhz

Thanks will also post this in for sale and wanted section

[bon beanie]

Hi dont know if this link is any good to ya?
http://www.mds975.co.uk/Content/aerials2.html

Not tried any these myself yet, but probably something to do in the winter.

[JOHN,YORK]

You do seem to be a busy bee,broomstick last week,now a preselector this week.I hope that it is the passive one that you want,because it is a coil and capacitor,no amplication,simple.
A similar article was in this forum by Mike Charlie 01/09/2009,under the heading of HIDDEN LONGWIRE.He has used 4 coils,but there is nothing to stop you from using a tapped coil.You can see it in his diagram.

Regards,John.

PS...
Have you given the active aerial a miss,or is that on hold.

[nay27uk]

Hi john. well the active antenna is on hold as I have been doing some thinking and I alredy recive loads of static at an S5-S10 constanly so I think the noise is coming in fine. I am now just wanting to peak the actual signals somwhat and thought a preselector was the way to go. I think the passive one is the way to go and found full instructions on the internet of one that used a plastic tube with windings on it and taps at various points, however it was unclear on what tap whent to what pole on the switch.

this was the one I found, although I think it is more of an ATU rather than prescaler

http://www.mds975.co.uk/Content/aerials2.html

[mikecharlie]

Hi Nay


This circuit can be built from a polycon varicon capacitor from a old bust household radio, and the best way for the coils is to just snaffle some pre-wound inductors (see picture) from an old bust VCR, CRT TV etc.......the inductors are very close to the colour cose values .
I found a fairly wide range on inductor inside these old things and save SO much bother trying to wind your own from wire.

A bit of care is needed though, so you dont confuse them with resistors as the colour code is almost identical.

Trial and error is required to find out what value of inductor matches best your aerial and frequency range.

These passive preselectors are very usefull, they really do help to tune out noise and peak the signal as required.

[nay27uk]

Hi Nay


This circuit can be built from a polycon varicon capacitor from a old bust household radio, and the best way for the coils is to just snaffle some pre-wound inductors (see picture) from an old bust VCR, CRT TV etc.......the inductors are very close to the colour cose values .
I found a fairly wide range on inductor inside these old things and save SO much bother trying to wind your own from wire.

A bit of care is needed though, so you dont confuse them with resistors as the colour code is almost identical.

Trial and error is required to find out what value of inductor matches best your aerial and frequency range.

These passive preselectors are very usefull, they really do help to tune out noise and peak the signal as required.

cheers for this charli I seen this the otherday when looking through the forum and think I am going to biuld it, I do know what chokes are I have about 500 1uh ones here I bulk ordered off ebay when I made my FM Transmitter.

I also found this website that modifies the said circuit http://www.bobsamerica.com/mfj-956.html.

I will buy the chokes to the exact values as stated on the scheatic so will have to wait till wednesday now. I also found this on ebay http://cgi.ebay.co.uk/Minature-AM-Tunin ... 27b312501d but I am unsure it will work as the schematic states a 365Pf variable capacitor but the ones out of an old radio I.E the one on ebay above states its only
Antenna capacitance 3.0 - 141.6pF
Oscillator capacitance 4.0 - 59.2pF

so I am unsure as what to buy for the cap

[JOHN,YORK]

N27 and MC.
This circuit is not really a preselector,it is more of an atu.I do not think that the values are too important.I think a tapped wound coil would be better,then you can play around with it.For example,if you were to wind it on a ferrite rod,you could move the rod in and out of the coil to vary the inductance.I used a similar set up years ago for MW and low HF.A wire from the aerial socket to a coil of 20-30 turns wrapped around a ferrite rod,then 3-4 metres of wire on the other end of the coil.Then slowly move the rod in and out of the coil for best signal.Give it a try,you will be surprised.

Regards,John.

[nay27uk]

thanks john will remember that and give that a go as well, cheers for all your input

[pioneer]

Here is a pre-selector circuit based on a FET , the gain that the fet produces is really only there to overcome the losses in the rest of the circuit. the capaitor VC1 is a 250 pf are 'GANGED', the frequency range is from 7 mhz to 30 mhz but with a higher value capacitor it should be able to tune lower in frequency.

http://i925.photobucket.com/albums/ad10 ... o30mhz.jpg


Mark 163 CT 20 / FB 20 GW0WVL

[crusty]

OT but I just had a look on fleabay for an FRT-7700.. Nearly fell off my chair.

[nay27uk]

Here is a pre-selector circuit based on a FET , the gain that the fet produces is really only there to overcome the losses in the rest of the circuit. the capaitor VC1 is a 250 pf are 'GANGED', the frequency range is from 7 mhz to 30 mhz but with a higher value capacitor it should be able to tune lower in frequency.

http://i925.photobucket.com/albums/ad10 ... o30mhz.jpg


Mark 163 CT 20 / FB 20 GW0WVL

Cheers for this pioneer it looks a nice circuit and easy to build to, however when you say to alter the caps for more frequency coverage what cap would I need to cover from LW through MW right up to 30MHz SW

[pioneer]

A bit of trial and error would be needed but going on the circuit already, VC1 the 250 pf gives a frequency down to 7 mhz, so possibly try 400-500 pf, easiest way to try this would be to just ' tac ' on in parralel a couple of fixed capacitors and see where it takes you. one good thing about this circuit is that its fully variable and tunes continuosly via the variable capacitor.

here is a image of the pre-selector showing the layout.


http://i925.photobucket.com/albums/ad10 ... dimage.jpg


Mark

[nay27uk]

nice one thanks loads for that. I was thinking 500Pf like you say though I will used some fixed ones to start

[nay27uk]

OK I bit the bullit and actualy purchased one It was as cheep to buy a redy made one than it would to make one.

Now all I need is a user manual for it, please see my other thread here for info http://www.transmission1.co.uk/forum/vi ... 33#p115233