[Lowfer] modified Amrad E probe

Tue Dec 14 09:40:43 EST 2010

Jay - if two J310's are used I'm guessing the total current goes to 60mA or will each have 15mA?  I see the link the arrl site on the AMRAD probe is now broken - does anyone have the link to the original that still operates with the cct diagram?

I have both IP2 and 3 issues in AK so Ill have a go with your design once Ive fixed the dang puter up there.

The K9AY beats the existing probe on s/n by a couple of dBs both on 137 and 500.

Good conditions long haul to Eu MF to OK last night with PA0A making it on WSPR for an hour or two around 0200Z or so. 

Laurence KL7UK/5

-----Original Message-----
From: lowfer-bounces at mailman.qth.net [mailto:lowfer-bounces at mailman.qth.net] On Behalf Of Zack Widup
Sent: Tuesday, December 14, 2010 8:26 AM
To: Discussion of the Lowfer (US, European, &amp, UK) and MedFer bands
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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