[Lowfer] modified Amrad E probe

[jrusgrove at comcast.net]

Zack

>Does this circuit use two J310's in parallel, or just one J310?

One J310 will work ... or two J310 in parallel for slightly better IP2 and IP3 performance.

> Also, the transformer in the original article was 17 bifilar turns.
> This says "38T bifilar." Is that the same as 19 bifilar turns wound as
> described in the original article?

Twist up a length of bifilar and wind 38 turns of the bifilar on the core. There will be a total of 
76 turns on the core if one were counting turns of the individual wires. Bifilar, trifilar, 
quadrafilar are always treated as if it were a single strand of wire for turns counting purposes.

Note that the transformer and resistor change are to improve the low frequency response below 10 
kHz. If you're not interested in this frequency range there's no need to make those changes. The 
J310 or pair of J310s are a low cost substitutes for the CP666 FET and provide decent performance. 
If you live close to broadcast stations you might consider one of the e probes that uses an FET 
input stage followed by a push pull totem pole output.

At this location I have the following broadcast stations (all line of sight) to contend with:

WSNG 610 kHz 3 miles 1 kW

WTIC 1080 kHz 11 miles 50 kW

WJMJ 88.9 kHz 2000' 5 kW

With either the single J310 or pair there are no noticeable IP2 or IP3 products at this distance. 
Based on field strength measurements I'd *guess* that this e probe would be okay somewhat closer to 
a 50 kW station. Multiple high power stations nearby would make the IP2 / IP3 problem worse. This 
all assumes a 1 meter whip and that the antenna is mounted a *reasonable* height above ground. 
Raising the antenna increases signal strength - it is difficult at best to divorce the connecting 
feedline from acting as part of the antenna.

Jay







----- Original Message ----- 
From: "Zack Widup" <w9sz.zack at gmail.com>
To: "Discussion of the Lowfer (US, European, &amp,UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Tuesday, December 14, 2010 1:24 AM
Subject: Re: [Lowfer] modified Amrad E probe


> I'm a bit confused. Does this circuit use two J310's in parallel, or
> just one J310?
>
> Also, the transformer in the original article was 17 bifilar turns.
> This says "38T bifilar." Is that the same as 19 bifilar turns wound as
> described in the original article?
>
> 73, Zack W9SZ
>
>
> On 12/13/10, jrusgrove at comcast.net <jrusgrove at comcast.net> wrote:
>> Interested parties can find a schematic at
>> http://www.w1vd.com/modifiedeprobe.pdf .
>>
>> Jay
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