Reply by Bill Bowden ●April 3, 20072007-04-03
On Apr 2, 12:55 pm, John Popelish <jpopel...@rica.net> wrote:

> Bill Bowden wrote:
> > I measured the Qs of a couple ferrite rods, one with litz wire and the
> > other with solid wire of about the same AWG. Both Qs measure around 80
> > unloaded. I don't see any difference using litz wire.
> > I used a single loose turn of wire to couple a generator to the LC
> > circuit at 533KHz. The 3dB rolloff points occur at around 529KHz and
> > 536KHz for a bandwith of about 7 Khz and Q of 533/7 = 76.
>
> > The rod with the litz wire is loaded by the gate of a jfet, so I
> > believe there is no load, the other rod had no external loads
> > connected.
>
> > Not very impressive results, but the bandwidth seems reasonable, and
> > the audio quality is good using a little 2.5 inch speaker.
>
> Sounds pretty reasonable to me.  With that Q, I suspect the
> limit is more the ferrite than the wire type.
>
> How much of the rod's length is covered with the coil?
> Turns in the middle third produce higher Q than turns at the
> ends.
>
> Is the wire wrapped right on the rod, or over some sort of
> insulating tube?  Spacing the wire about a wire diameter or
> so from the rod can improve the Q at the upper end of the band.


The rod with litz wire is a original unit from a 1972 Radio Shack AM/
FM modle. The rod is 4.75 inch long by 3/8 diameter with a winding
length of about 1 inch (on a paper form) situated about 1/3 the way
from one end to allow fine tuning adjustment by sliding the winding
slightly up an down the rod.

The other rod with solid wire, I wound myself. It's a little shorter
at 4 inches (same diameter) and the winding is similar 1 inch long
situated in the middle of the rod on a similar paper form.

I'll run another test at the upper end of the band to see what happens
there and report results.

I etched the circuit board with a solid ground plane on one side to
avoid possible oscillation problems, but I found I need to space the
antenna rod about 1/2 inch away or more to avoid losing signal. This
makes the box size bigger than I planned, but I can live with it.
Guess it's not a good idea to use a solid ground plane with little AM
radios?

-Bill
Reply by Bill Bowden ●April 2, 20072007-04-02
On Mar 24, 7:16=C2=A0pm, John Popelish <jpopel...@rica.net> wrote:

> Bill Bowden wrote:
> > On Mar 24, 8:22 am, John Popelish <jpopel...@rica.net> wrote:
> >> Bill Bowden wrote:
> >>> How much improvement can I expect using Litz wire to wind a AM ferrite
> >>> Rod antenna as opposed to using solid copper wire?
> >>> Is it worth the trouble to obtain Litz wire, or can I expect almost
> >>> the same response at say 1 MHz using regular solid enamaled copper
> >>> wire?
> >> If you would like to see some comparative experimental data,
> >> Ben Tongue has performed some experiments and posted the
> >> data to his web site.http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.=

html

>
> > Thanks John,
>
> > Yes, it looks like Litz wire has a significant advantage. If I read
> > the results right, the unloaded Q factor at 943Khz is 141 using solid
> > copper wire verses a Q factor of 1030 using Litz wire.
> > That's quite a significant difference. Am I reading the results right?
>
> I think you are interpreting this correctly. =C2=A0Keep in mind
> that this is the Q of the coil, unloaded by any receiver
> circuit. =C2=A0If the circuit adds a significant load, the Q
> differences for a tuned antenna would be a smaller ratio
> different. =C2=A022 AWG is also pretty heavy wire for a typical
> antenna coil. =C2=A0With smaller wire, the Qs would be smaller
> but closer.
>


I measured the Qs of a couple ferrite rods, one with litz wire and the
other with solid wire of about the same AWG. Both Qs measure around 80
unloaded. I don't see any difference using litz wire.
I used a single loose turn of wire to couple a generator to the LC
circuit at 533KHz. The 3dB rolloff points occur at around 529KHz and
536KHz for a bandwith of about 7 Khz and Q of 533/7 =3D 76.

The rod with the litz wire is loaded by the gate of a jfet, so I
believe there is no load, the other rod had no external loads
connected.

Not very impressive results, but the bandwidth seems reasonable, and
the audio quality is good using a little 2.5 inch speaker.

-Bill


>
>
> > Quote from website:
>
> > " Solid wire instead of litz?: =C2=A0Keep in mind that the work describ=

ed

> > here used close-wound 125/46 litz wire. =C2=A0If one duplicates 'Coil a=

nd

> > Former B' in Table 2, except using 22 ga. solid copper wire (having
> > the same diameter) as 125/46 litz, the Q values drop to about 1/6 of
> > the values achieved with the litz wire. =C2=A0The cause is the large
> > proximity effect resistive losses in the solid wire. =C2=A0The proximity
> > effect, but not the skin effect loss may be much reduced if the wires
> > are space-wound. =C2=A0New trade-offs now must be considered: Same wire
> > diameter, and therefore a longer solenoid, or a smaller wire diameter
> > and the same overall length? =C2=A0If one wishes to use solid wire, it
> > should probably be wound directly on the ferrite, not on a former.
> > The overall Q will still be much less than when using litz, but the
> > loss from the high (tan =CE=B4) dielectric of the ferrite will be pretty
> > well swamped out because of the now higher losses from the skin and
> > proximity effect losses. =C2=A0The Q values, using a close-wound soleno=

id

> > of 22 ga. solid copper wire on a polyethylene former, as in 'Coil and
> > Former' B in Table 2 are: 520 kHz: 130, 943 kHz: 141 and 1710 kHz: 150
> > when using the "best core". =C2=A0The Q drops only 3, 3, and 5 points
> > respectively if the "worst core" is used. "
>
> > -Bill- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -
Reply by John Popelish ●April 2, 20072007-04-02
Bill Bowden wrote:


> I measured the Qs of a couple ferrite rods, one with litz wire and the
> other with solid wire of about the same AWG. Both Qs measure around 80
> unloaded. I don't see any difference using litz wire.
> I used a single loose turn of wire to couple a generator to the LC
> circuit at 533KHz. The 3dB rolloff points occur at around 529KHz and
> 536KHz for a bandwith of about 7 Khz and Q of 533/7 = 76.
> 
> The rod with the litz wire is loaded by the gate of a jfet, so I
> believe there is no load, the other rod had no external loads
> connected.
> 
> Not very impressive results, but the bandwidth seems reasonable, and
> the audio quality is good using a little 2.5 inch speaker.


Sounds pretty reasonable to me.  With that Q, I suspect the 
limit is more the ferrite than the wire type.

How much of the rod's length is covered with the coil? 
Turns in the middle third produce higher Q than turns at the 
ends.

Is the wire wrapped right on the rod, or over some sort of 
insulating tube?  Spacing the wire about a wire diameter or 
so from the rod can improve the Q at the upper end of the band.
Reply by Rich Grise ●March 28, 20072007-03-28
On Tue, 27 Mar 2007 15:33:53 -0700, John Larkin wrote:

> On Tue, 27 Mar 2007 13:01:12 -0300, YD <ydtechHAT@techie.com> wrote:
>>Late at night, by candle light, John Larkin
>>>On Mon, 26 Mar 2007 22:27:55 GMT, Rich Grise <rich@example.net> wrote:
>>>>On Sun, 25 Mar 2007 22:40:34 -0700, Bill Bowden wrote:
>>>>> On Mar 25, 5:35 pm, John  Larkin
>>>>>> On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddr...@att.net>
>>>>>> >On Mar 24, 8:22 am, John Popelish <jpopel...@rica.net> wrote:
>>>>>> >> Bill Bowden wrote:
>>>>>> >> > How much improvement can I expect using Litz wire to wind a AM ferrite
>>>>>> >> > Rod antenna as opposed to using solid copper wire?
>>>>>>
>>>>>> >> > Is it worth the trouble to obtain Litz wire, or can I expect almost
>>>>>> >> > the same response at say 1 MHz using regular solid enamaled copper
>>>>>> >> > wire?
>>>>>>
>>>>>> >> If you would like to see some comparative experimental data,
>>>>>> >> Ben Tongue has performed some experiments and posted the
>>>>>> >> data to his web site.http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html
>>>>>>
>>>>>> >Yes, it looks like Litz wire has a significant advantage. If I read
>>>>>> >the results right, the unloaded Q factor at 943Khz is 141 using solid
>>>>>> >copper wire verses a Q factor of 1030 using Litz wire.
>>>>>> >That's quite a significant difference. Am I reading the results right?
>>>>>>
>>>>>> In a superhet, high Q will make it that much harder to track the LO,
>>>>>> so you may well lose signal with a q=1000 rod. Why do you want a high
>>>>>> antenna Q? In the AM band, gain is cheap and s/n is dominated by
>>>>>> ambient noise, so it won't matter much.
>>>>> 
>>>>> It's just a little portable AM radio I've been wanting to build for
>>>>> years. I took a radio class in 7th grade 50 years ago and never got
>>>>> around to finishing the superhet design. But I got an A anyway. We
>>>>> used tubes in those days.
>>>>> 
>>>>> I'm using the Signetics NE602 balanced modulator IC that produces
>>>>> about 13dB gain. The antenna rod is buffered with a JFET so there is
>>>>> minimal load on the antenna rod yielding another 12 to 18 dB. The
>>>>> front end is pretty hot.
>>>>> 
>>>>> But as you say, the bandwidth is narrow with a high Q coil, so I'm
>>>>> using a switch to short a couple turns on the antenna rod to load the
>>>>> antenna for local strong stations. Local/DX select.
>>>>> 
>>>>> The biggest problem is separating a distant station 40KHz away from a
>>>>> strong local 50KW station 5 miles up the road.
>>>>
>>>>I've read somewhere that the idea is to build the selectivity into the 
>>>>IF part.
>>>
>>>Yes, but you have to be careful that nothing overloads in the
>>>front-end, or in the first IF stage, from that 50 KW monster. A decent
>>>antanna Q helps some. Fets are really good for avoiding nonlinearity.
>>>
>>>So, low-gain jfets or mosfets in the front end and maybe the first IF,
>>>and pile up selectivity and gain in later IF stages. Manual stage gain
>>>pots, rather than AGC, would be fun.
>>
>>Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away.
>>Great for RFI immunity testing.
> 
> We look up at this beast from our back window. Something like 22
> megawatts of AM, FM, TV, and HDTV...
> 
> http://en.wikipedia.org/wiki/Sutro_Tower
> 
> and we're in a wooden building... no shielding at all. All the scope
> traces are fuzzy.
> 


Doesn't it have a pattern something like this? 
("side" view): http://www.marcspages.co.uk/tech/antgain2.gif

IOW, aren't you kind of "in the shadow"?

Cheers!
Rich
Reply by YD ●March 28, 20072007-03-28
Late at night, by candle light, "Bill Bowden" <wrongaddress@att.net>
penned this immortal opus:

<schnipp-schnapp>


>On Mar 27, 8:01 am, YD <ydtech...@techie.com> wrote:
>>
>> Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away.
>> Great for RFI immunity testing.
>>
>
>Is that KOGO clear channel (600Khz) in San Diego?
>Up here in LA area, we have clear channel KFI on 640KHz.
>They both carry Coast to Coast with Art Bell, George Noory,
>etc. Some of the stuff is pretty good, but I stay away from the remote
>viewing, flying saucers, "out of body experiences" and shadow people
>stuff. Some of the callers ghost stories are very original. I like
>good story tellers, even if it's BS.
>
>-Bill
>


Nope, it's Radio Gaucha in southern Brazil. When they installed it
about 15 years back you could hear it on the telephone! Great for
soccer fans but a pain for everybody else. Then they had some crews
running around placing filters and what-not all over town and it's
pretty much under control now. It still gets in if you're not careful
and crystal radios are a waste of time.

- YD.

-- 
Remove HAT if replying by mail.
Reply by Bill Bowden ●March 28, 20072007-03-28
On Mar 27, 8:01 am, YD <ydtech...@techie.com> wrote:

> Late at night, by candle light, John Larkin
> <jjlar...@highNOTlandTHIStechnologyPART.com> penned this immortal
> opus:
>
>
>
> >On Mon, 26 Mar 2007 22:27:55 GMT, Rich Grise <r...@example.net> wrote:
>
> >>On Sun, 25 Mar 2007 22:40:34 -0700, Bill Bowden wrote:
> >>> On Mar 25, 5:35 pm, John  Larkin
> >>>> On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddr...@att.net>
> >>>> >On Mar 24, 8:22 am, John Popelish <jpopel...@rica.net> wrote:
> >>>> >> Bill Bowden wrote:
> >>>> >> > How much improvement can I expect using Litz wire to wind a AM ferrite
> >>>> >> > Rod antenna as opposed to using solid copper wire?
>
> >>>> >> > Is it worth the trouble to obtain Litz wire, or can I expect almost
> >>>> >> > the same response at say 1 MHz using regular solid enamaled copper
> >>>> >> > wire?
>
> >>>> >> If you would like to see some comparative experimental data,
> >>>> >> Ben Tongue has performed some experiments and posted the
> >>>> >> data to his web site.http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html
>
> >>>> >Yes, it looks like Litz wire has a significant advantage. If I read
> >>>> >the results right, the unloaded Q factor at 943Khz is 141 using solid
> >>>> >copper wire verses a Q factor of 1030 using Litz wire.
> >>>> >That's quite a significant difference. Am I reading the results right?
>
> >>>> In a superhet, high Q will make it that much harder to track the LO,
> >>>> so you may well lose signal with a q=1000 rod. Why do you want a high
> >>>> antenna Q? In the AM band, gain is cheap and s/n is dominated by
> >>>> ambient noise, so it won't matter much.
>
> >>> It's just a little portable AM radio I've been wanting to build for
> >>> years. I took a radio class in 7th grade 50 years ago and never got
> >>> around to finishing the superhet design. But I got an A anyway. We
> >>> used tubes in those days.
>
> >>> I'm using the Signetics NE602 balanced modulator IC that produces
> >>> about 13dB gain. The antenna rod is buffered with a JFET so there is
> >>> minimal load on the antenna rod yielding another 12 to 18 dB. The
> >>> front end is pretty hot.
>
> >>> But as you say, the bandwidth is narrow with a high Q coil, so I'm
> >>> using a switch to short a couple turns on the antenna rod to load the
> >>> antenna for local strong stations. Local/DX select.
>
> >>> The biggest problem is separating a distant station 40KHz away from a
> >>> strong local 50KW station 5 miles up the road.
>
> >>I've read somewhere that the idea is to build the selectivity into the
> >>IF part.
>
> >Yes, but you have to be careful that nothing overloads in the
> >front-end, or in the first IF stage, from that 50 KW monster. A decent
> >antanna Q helps some. Fets are really good for avoiding nonlinearity.
>
> >So, low-gain jfets or mosfets in the front end and maybe the first IF,
> >and pile up selectivity and gain in later IF stages. Manual stage gain
> >pots, rather than AGC, would be fun.
>
> >John
>
> Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away.
> Great for RFI immunity testing.
>


Is that KOGO clear channel (600Khz) in San Diego?
Up here in LA area, we have clear channel KFI on 640KHz.
They both carry Coast to Coast with Art Bell, George Noory,
etc. Some of the stuff is pretty good, but I stay away from the remote
viewing, flying saucers, "out of body experiences" and shadow people
stuff. Some of the callers ghost stories are very original. I like
good story tellers, even if it's BS.

-Bill


> - YD.
>
> --
> Remove HAT if replying by mail.
Reply by john jardine ●March 27, 20072007-03-27
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:oc6j03hprt40skqs7ohh0gns5i1uvjf6e5@4ax.com...

> On Tue, 27 Mar 2007 13:01:12 -0300, YD <ydtechHAT@techie.com> wrote:

[...]

> >Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away.
> >Great for RFI immunity testing.
> >
> >- YD.
>
>
> We look up at this beast from our back window. Something like 22
> megawatts of AM, FM, TV, and HDTV...
>
> http://en.wikipedia.org/wiki/Sutro_Tower
>
>
> and we're in a wooden building... no shielding at all. All the scope
> traces are fuzzy.
>
> John


Ugh!.
Thought I had it bad with an interfering 10uV of line scan noise from the PC
monitor a few feet away. Even considered seeing if the LCD types were any
better.  Clearly I'm living on easy street.

How on earth do you cope when designing low level stuff stuff, a screened
room any worth?.



-- 
Posted via a free Usenet account from http://www.teranews.com
Reply by John Larkin ●March 27, 20072007-03-27
On Tue, 27 Mar 2007 13:01:12 -0300, YD <ydtechHAT@techie.com> wrote:


>Late at night, by candle light, John Larkin
><jjlarkin@highNOTlandTHIStechnologyPART.com> penned this immortal
>opus:
>
>>On Mon, 26 Mar 2007 22:27:55 GMT, Rich Grise <rich@example.net> wrote:
>>
>>>On Sun, 25 Mar 2007 22:40:34 -0700, Bill Bowden wrote:
>>>> On Mar 25, 5:35 pm, John  Larkin
>>>>> On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddr...@att.net>
>>>>> >On Mar 24, 8:22 am, John Popelish <jpopel...@rica.net> wrote:
>>>>> >> Bill Bowden wrote:
>>>>> >> > How much improvement can I expect using Litz wire to wind a AM ferrite
>>>>> >> > Rod antenna as opposed to using solid copper wire?
>>>>>
>>>>> >> > Is it worth the trouble to obtain Litz wire, or can I expect almost
>>>>> >> > the same response at say 1 MHz using regular solid enamaled copper
>>>>> >> > wire?
>>>>>
>>>>> >> If you would like to see some comparative experimental data,
>>>>> >> Ben Tongue has performed some experiments and posted the
>>>>> >> data to his web site.http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html
>>>>>
>>>>> >Yes, it looks like Litz wire has a significant advantage. If I read
>>>>> >the results right, the unloaded Q factor at 943Khz is 141 using solid
>>>>> >copper wire verses a Q factor of 1030 using Litz wire.
>>>>> >That's quite a significant difference. Am I reading the results right?
>>>>>
>>>>> In a superhet, high Q will make it that much harder to track the LO,
>>>>> so you may well lose signal with a q=1000 rod. Why do you want a high
>>>>> antenna Q? In the AM band, gain is cheap and s/n is dominated by
>>>>> ambient noise, so it won't matter much.
>>>> 
>>>> It's just a little portable AM radio I've been wanting to build for
>>>> years. I took a radio class in 7th grade 50 years ago and never got
>>>> around to finishing the superhet design. But I got an A anyway. We
>>>> used tubes in those days.
>>>> 
>>>> I'm using the Signetics NE602 balanced modulator IC that produces
>>>> about 13dB gain. The antenna rod is buffered with a JFET so there is
>>>> minimal load on the antenna rod yielding another 12 to 18 dB. The
>>>> front end is pretty hot.
>>>> 
>>>> But as you say, the bandwidth is narrow with a high Q coil, so I'm
>>>> using a switch to short a couple turns on the antenna rod to load the
>>>> antenna for local strong stations. Local/DX select.
>>>> 
>>>> The biggest problem is separating a distant station 40KHz away from a
>>>> strong local 50KW station 5 miles up the road.
>>>
>>>I've read somewhere that the idea is to build the selectivity into the 
>>>IF part.
>>>
>>
>>Yes, but you have to be careful that nothing overloads in the
>>front-end, or in the first IF stage, from that 50 KW monster. A decent
>>antanna Q helps some. Fets are really good for avoiding nonlinearity.
>>
>>So, low-gain jfets or mosfets in the front end and maybe the first IF,
>>and pile up selectivity and gain in later IF stages. Manual stage gain
>>pots, rather than AGC, would be fun.
>>
>>John
>>
>
>Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away.
>Great for RFI immunity testing.
>
>- YD.



We look up at this beast from our back window. Something like 22
megawatts of AM, FM, TV, and HDTV...

http://en.wikipedia.org/wiki/Sutro_Tower


and we're in a wooden building... no shielding at all. All the scope
traces are fuzzy.

John
Reply by YD ●March 27, 20072007-03-27
Late at night, by candle light, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> penned this immortal
opus:


>On Mon, 26 Mar 2007 22:27:55 GMT, Rich Grise <rich@example.net> wrote:
>
>>On Sun, 25 Mar 2007 22:40:34 -0700, Bill Bowden wrote:
>>> On Mar 25, 5:35 pm, John  Larkin
>>>> On 24 Mar 2007 18:53:56 -0700, "Bill Bowden" <wrongaddr...@att.net>
>>>> >On Mar 24, 8:22 am, John Popelish <jpopel...@rica.net> wrote:
>>>> >> Bill Bowden wrote:
>>>> >> > How much improvement can I expect using Litz wire to wind a AM ferrite
>>>> >> > Rod antenna as opposed to using solid copper wire?
>>>>
>>>> >> > Is it worth the trouble to obtain Litz wire, or can I expect almost
>>>> >> > the same response at say 1 MHz using regular solid enamaled copper
>>>> >> > wire?
>>>>
>>>> >> If you would like to see some comparative experimental data,
>>>> >> Ben Tongue has performed some experiments and posted the
>>>> >> data to his web site.http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html
>>>>
>>>> >Yes, it looks like Litz wire has a significant advantage. If I read
>>>> >the results right, the unloaded Q factor at 943Khz is 141 using solid
>>>> >copper wire verses a Q factor of 1030 using Litz wire.
>>>> >That's quite a significant difference. Am I reading the results right?
>>>>
>>>> In a superhet, high Q will make it that much harder to track the LO,
>>>> so you may well lose signal with a q=1000 rod. Why do you want a high
>>>> antenna Q? In the AM band, gain is cheap and s/n is dominated by
>>>> ambient noise, so it won't matter much.
>>> 
>>> It's just a little portable AM radio I've been wanting to build for
>>> years. I took a radio class in 7th grade 50 years ago and never got
>>> around to finishing the superhet design. But I got an A anyway. We
>>> used tubes in those days.
>>> 
>>> I'm using the Signetics NE602 balanced modulator IC that produces
>>> about 13dB gain. The antenna rod is buffered with a JFET so there is
>>> minimal load on the antenna rod yielding another 12 to 18 dB. The
>>> front end is pretty hot.
>>> 
>>> But as you say, the bandwidth is narrow with a high Q coil, so I'm
>>> using a switch to short a couple turns on the antenna rod to load the
>>> antenna for local strong stations. Local/DX select.
>>> 
>>> The biggest problem is separating a distant station 40KHz away from a
>>> strong local 50KW station 5 miles up the road.
>>
>>I've read somewhere that the idea is to build the selectivity into the 
>>IF part.
>>
>
>Yes, but you have to be careful that nothing overloads in the
>front-end, or in the first IF stage, from that 50 KW monster. A decent
>antanna Q helps some. Fets are really good for avoiding nonlinearity.
>
>So, low-gain jfets or mosfets in the front end and maybe the first IF,
>and pile up selectivity and gain in later IF stages. Manual stage gain
>pots, rather than AGC, would be fun.
>
>John
>


Ack, I have a 200 kW 600 kHz transmitter just over a kilometer away.
Great for RFI immunity testing.

- YD.

-- 
Remove HAT if replying by mail.
Reply by Bill Bowden ●March 27, 20072007-03-27
On Mar 26, 7:07 am, "Anthony Fremont" <spam-...@nowhere.com> wrote:

> Bill Bowden wrote:
> > On Mar 25, 5:35 pm, John  Larkin
> >> In a superhet, high Q will make it that much harder to track the LO,
> >> so you may well lose signal with a q=1000 rod. Why do you want a high
> >> antenna Q? In the AM band, gain is cheap and s/n is dominated by
> >> ambient noise, so it won't matter much.
>
> >> John
>
> > It's just a little portable AM radio I've been wanting to build for
> > years. I took a radio class in 7th grade 50 years ago and never got
> > around to finishing the superhet design. But I got an A anyway. We
> > used tubes in those days.
>
> > I'm using the Signetics NE602 balanced modulator IC that produces
> > about 13dB gain. The antenna rod is buffered with a JFET so there is
> > minimal load on the antenna rod yielding another 12 to 18 dB. The
> > front end is pretty hot.
>
> I take it this is connected to pins 1 and 2?  How did you do your oscillator
> on 6 and 7?
>


The oscillator is the Hartly version with a tapped coil. Pin 7 goes to
the tap through a 0.1uF cap. Pin 6 goes to the high side of the coil
through another 0.1uF cap. Low side of coil goes to ground and tuning
cap goes across the coil.

But, I had to rewind the oscillator coil because the tap on the
regular (red slug) coils is too close to one end for good oscillation.
I put the tap about 1/3 the way up and used a resistor (1K) in series
to get it about right.


> > But as you say, the bandwidth is narrow with a high Q coil, so I'm
> > using a switch to short a couple turns on the antenna rod to load the
> > antenna for local strong stations. Local/DX select.
>
> > The biggest problem is separating a distant station 40KHz away from a
> > strong local 50KW station 5 miles up the road.
>
> What are you using as an IF filter and AM detector?


I have 2 IF stages planned, but just using one right now. It just uses
the normal (black slug) coil with a 2K secondary to drive the
detector. The detector is a Schottky diode that feeds the gate of a
JFET. There is a 2 Meg resistor from gate to +V to bias the diode at a
few microamps and a 1000pF cap from gate to ground to filter out the
RF. Audio comes off the source of the JFET.

I'm not sure exactly how this works, but it does the best job of all
the other configurations I tried. The audio is good from a weak
station. I have an article about using a zero bias JFET so that no
diode is needed, but I haven't tried that one.


> I've been tinkering
> around trying to build a 10MHz WWV receiver and I have an NE602 that I'm
> injecting my "PIC locked" 9.545MHz LO into (pin 6) and using a 10MHz tank
> circuit ( 2.8uH and ~100pF) as a preselector with the antenna coupled to the
> coil.  I only have that much done so far, but it's time to do some filtering
> and detection and I'm not sure what direction to take on that.  Just playing
> around, nothing critical.
>
> I always wanted to build a crystal set using an oatmeal box sized coil form
> with a sliding tap.  Maybe when my daughter gets a little older she'll wind
> it for me.  ;-)


-Bill