[Lowfer] modified Amrad E probe

Tue Dec 14 09:50:39 EST 2010

Zack

J310s in the plastic case are fine. Optimum idling current is found by adjusting the bias while 
making an IP2 measurement ... but for general work 20 - 25 mA for a single FET and around 40 mA for 
a pair is a good starting point (assuming a 13 volt supply). See Steve's measurements from last 
week.

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 9:26 AM
Subject: Re: [Lowfer] modified Amrad E probe

> Thanks for all the info, Jay!
>
> I have J310's in the TO-92 plastic case. Is the voltage and current in
> this circuit set to the same values as the original circuit? Does the
> TO-92 case sufficiently transfer the heat from the device?  I do have
> a few U310's in small metal cans.
>
> I have three AM stations in the vicinity: WDWS on 1400 kHz and WILL on
> 580 kHz, both about 3 miles away, and a weather/travel info station on
> 530 kHz about half a mile away. The weather station has never given me
> problems but I have had some intermod problems in the past with one
> circuit from WILL on my loop antenna.
>
> On 12/14/10, jrusgrove at comcast.net <jrusgrove at comcast.net> wrote:
>> 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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