To: | [email protected] |
---|---|
Subject: | Re: LF: Re: Field Strength Meter - advice needed |
From: | Chris Osborn <[email protected]> |
Date: | Mon, 4 May 2009 07:23:06 +0000 (GMT) |
Dkim-signature: | v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.co.uk; s=s1024; t=1241421786; bh=yFzKZgOVI0WmKQI/LEZUPD5vq5T6rDqbYgaCs9l50y4=; h=Message-ID:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=Wenm9Lv0D0ttkr1ACg4habfGYtwuZAy9YGYebFpGk+aRrVQ4ItxhUKGdzgVL8VcPdviUdhT01d4ikSYLySxNKXdg0YxUHM/skwLrxU9KjwH6T1LkiLsSmwxglQozPuoqNaNtSy9Z4AhmIoImtom3Vaj+rr3V3fWWm9Qa+vleCu8= |
Domainkey-signature: | a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.co.uk; h=Message-ID:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=6H2rVKRdEu+X/1ynq+++oK+JFIbdFqtH4FcvUidewzYycVP3TDsc7f3K2ChSr51vNkmJEDsc3arvZMmr2f2lSTzwoOKB4fL2NxiQmG4ezh92ts/6LNJde+oybpP7uGXojbGsPGDODQJMBBdvg3H6komrGaXFb9S25c+GXB4HV4g=; |
Domainkey-status: | good (testing) |
In-reply-to: | <008001c9cc2c$084162e0$0900a8c0@AM> |
References: | <[email protected]> <008001c9cc2c$084162e0$0900a8c0@AM> |
Reply-to: | [email protected] |
Sender: | [email protected] |
Many thanks for the prompt suggestions Alan. I've spent ages trying to sort the problem and have now run out of ideas. I completely rebuilt the unit, even using a new ferrite rod. The front end tuning was very sharp and I subsequently added another RF tuning control (varicap + pot) to peak it up as it drifted. Also I've placed a 220 k resistor across the tuned circuit to lower the Q and flatten the response. I did the usual trick of blowing with a drinking straw on various components and the front end capacitors seemed to be the culprits hence the added RF amp tuning control. I'll try a BF981 as you suggest and also disconnect the front end and inject a signal. I'll hunt around for a BF960 as shown in the original circuit. Thanks again es 73 Chris XIZ From: Alan Melia <[email protected]> To: [email protected] Sent: Sunday, 3 May, 2009 21:00:26 Subject: LF: Re: Field Strength Meter - advice needed Hi Chris the following things occur to me to try 1 the 2N3819 is a juction fet not a mosfet (as with Dick original design) so is probably more likely to show changes in input (gate-source) current with temperature. The input current of a mostfet will be negligable. I cant remember what the original device was but if a 40673 for instance try a BF981 which are readily available. 2 At a lower level of probability the permiability of ferrite changes with temperature. I would not that to be anything like so great as problem though. I hope that helps to solve the problem. Alan G3NYK ----- Original Message ----- From: "Chris Osborn" <[email protected]> To: "LF Group" <[email protected]> Sent: Sunday, May 03, 2009 6:13 PM Subject: LF: Field Strength Meter - advice needed LF, I've just rebuilt PA0SE's field strength meter (LF Experimenters' Handbook), modified for use on the 500 kHz band. I've followed the published circuit as near as possible considering available components, the differences being: a) I have used a small variable capacitor instead of the published varicaps. b) I used a JFET 2N3819 in the front end instead of dual gate mosfets. c) Obviously I now use the MW coil of the ferrite rod instead of the published LW coil. I have made a decent Helmholtz coil which gives a stable magnetic field yet the field strength meter's output voltage is very dependent on temperature and can vary up to 30 %. I would be most grateful for any advice on curing this problem as I've spent hours trying to correct it. 73 Chris G3XIZ |
<Prev in Thread] | Current Thread | [Next in Thread> |
---|---|---|
|
Previous by Date: | Re: LF: Re: Mini Whip and local noise, Stewart Bryant |
---|---|
Next by Date: | Re: LF: Re: Field Strength Meter - advice needed, Chris Osborn |
Previous by Thread: | LF: Re: Field Strength Meter - advice needed, Alan Melia |
Next by Thread: | Re: LF: Re: Field Strength Meter - advice needed, Alan Melia |
Indexes: | [Date] [Thread] [Top] [All Lists] |