Preamp

[lew247]

Does anyone have a circuit for a preamp that will work from about 2 to 30 Mhz?
I live in the middle of Manchester, cant get an aerial outside so I'm stuck to a pice of wire inside the attic, which is worse than useless,
I'm going to make an atu using a varicap but it will definately need a preamp which will go inbetween the atu and reciever (Elektor SDR)
Ideally a circuit thats easy to make, has a veroboard layout already (but not essential) and cheap.
No complicated coil winding please, I have no toroids and really my fingers dont work well enough to try winding them or my eyes to see what I'm doing.

If anyone has one they dont want and wanna get rid of it I may be willing to buy it instead of making one, but again cant be dear.

[dcwuk]

There is a kit here http://www.wsplc.co.uk/acatalog/Kits_Ramsey.html
SA-7 Ramsey Broadband RF Pre-amp Kit.
Can you improve your aerial in any way how long is it?
Have you earthed your receiver?
Have you considered a loop aerial at all?
HF Pre amps do work to a point but in general all they do is amplify everything you are receiving including the noise they do not seem to winkle the signals out.
rgds
dcw

[JOHN,YORK]

Lew.
Before you start spending a lot of money on a kit,here is a very simple circuit that might be of interest to you:-

AM/FM/SW ACTIVE AERIAL,MPF102

There are various sites with this circuit on it.

Regards,John.

[mikecharlie]

I would have thought that a pre-amp, for HF would be one of the worst things that could be introduced to ' recieve better signals' ....as dcwuk says, they amplify the noise as well as the signal........everything just sounds louder........


Considering how we all know HF has with background noises etc......its more about wheedling the signal OUT of the noise .


I havent ever used one for HF, but from what Ive seen that it does to VHF in some cases, it can cause more problems that it solves.
I have had usefull success by using one for UHF ( 430 ish and above) though.

[JOHN,YORK]

Lew,
As you have said that you are going to make yourself an ATU,would it not be a better solution to build a preselector.Then you would only amplify a small portion of RF around your tuned signal.As DCWUK and M/C have said,you will leave your receiver wide open to all interference by using a RF amp.
The circuit that I gave you should not cost more than £5.All the parts can be got from Maplin.Use that as a guide to see if a RF amp is any good for you,if not,you should be able to convert it into a amplified preselector.

Regards,John.

[lew247]

Sorry for the delay in replying, been buys with my new toy an android phone and learning how to mod it - great fun

JOHN,YORK there is no link in your post, so I cant check out what you said.
However your right, preselector is what I need, I just need to find a decent circuit for one, its one of the hardest things to find.

[JOHN,YORK]

Lew,
The info was in the previous message,all you have to do is search for:-

AM/FM/SW ACTIVE AERIAL,MPF102


Regards,John.

[lew247]

Thanks for that, I thought you had tried to put a link in but it didnt work
found it now though

Dont suppose anyone looking at this has any circuit diagrams for a preselector?

I've actually made an amplified loop and it works brilliantly now, only problem is it could do with a preselector.

[DX-Digger]

Try to get one with variable gain as Direct conversion receivers as used in SDR's tend to suffer from image rejection if the front end is overloaded! Not sure if the elektor sdr has tuned filters for whatever band they are used on so if you are getting a very strong out of band signal say on 7.5MHz and you are trying to capture signals on 7.0MHz to 7.05MHz say your front end will be desensed making the wanted signals even weaker!

So variable gain would be better if you really really must use one , and as already pointed out pre-amps on HF amplify noise as well. I would try to improve your antenna rather than use a pre-amp!

Having said that SDR recievers are great fun I use SDR-radio with mine love the data mode decoder!

HTH Mark

[crusty]

The Lowe PR-150 (if you can find one s/h) is worth looking at.
http://www.universal-radio.com/catalog/ ... pr150.html

[lew247]

Very nice piece of kit, but at £248 on ebay 2nd hand I'll be passing on that
I'll probably try and build one if I can find a decent circuit, it should be pretty easy to make and could be made compact if I used radial inductors instead of large coils where you guess the inductance.