开云体育

At 12:03 am ((PST)) Thu Feb 8, 2007, Fraser wrote:

Please see my post on the internals of the DE31MS loop head.

Thanks for your excellent efforts, Fraser. I shall
download the picture in a moment... got it :-)

Do you know if the TG33 MW-only loop is
single-turn plus a series inductor too?

Sorry if I appeared to ignore or contradict your
earlier post: I receive the Digest, so I'm just
playing catch-up now.

I had overlooked the possibility of inductance in
series with the loop. Which is most remiss of
me, since I was recently looking at the reference
design for a receiver chip which used the same
technique to switch the ferrite rod aerial from
MW to LW. So no excuses ;-).

As you say, not the most efficient, however...
...I happen to have been looking at several
band-pass filter designs and one suggested
a Q of 30 for commercial bobbin-cored inductors
vs 100 for hand-wound ferrite toroids - and both
gave acceptable insertion loss in an aerial
preselector.

[On the other hand, I have seen bobbin inductors
condemned as having much lower Q, down into
single figures, so I guess "it all depends" - on the
method of measurement, too :-(.]

I suspect much better than 100 is possible with
a carefully sized and wound toroid. Alternatively,
Q in the region of 1000 is possible in an air-cored
solenoid - making a good padding coil for a fixed
location but rather poor luggage.

For a tuned loop a Q of 30 is a bit low but 100 is
quite reasonable. Remember that the higher the Q,
the more often a SWL will have to re-tune the aerial
while searching HF, at high Q it becomes tricky to
peak the loop on the receiver frequency and audio
sidebands can be clipped, and at extreme Q CW
signals will ring - and the tuning drift will probably
make it unusable.

Some designs include a switched or variable
Q-spoiler resistor across the tuned circuit to make
the loop more friendly to operate.

Better to have spare performance in hand (and
then be able to discard some) than be found
wanting, but no need to chase the ultimate and
find it unusable.

BTW, for those tempted to rebuild their loop,
be mindful that the cute little low-capacitance
mosfet has no internal gate static protection,
so a permanent RL shunt across the loop
terminals in case the external loop should
ever be disconnected could be a good idea.


Regards, LenW

--- In loopantennas@..., "Michael Stevenson"
<portstevos@...> wrote:

Yes, a different diameter wire will affect the frequency range but a

similiar diameter should give a similiar coverage range, the thing to
watch out for is if Degen designed the active element to compensate
for that metal telescopic rod support that goes horizontal through
it's midway point, getting rid of that metal support and then using
stiffer motor rewind wire means a support is no longer necessary but
it may change the tuning for the same diameter loop without the metal
support!

Will be an interesting experiment that I hope to carry out this

coming weekend!

Best wishes!

I untied the knots, desoldered one connector and slipped off that
telescoping element when I got my DE31, so I have no baseline, [I've
never seen a quadratic element with such a diagonal across it before
and assumed the telescope to be an engineering/marketing compromise]
I'm using #4 straws with a broken fishing rod tip inside... what I do
notice is directivity when the ant is a few feet within the window,
this is most evident when adjusting/rotating the ant to best receive
DRM signals... perhaps you may decide to check out the directivity of
the antenna with the metal telescoping element installed then compare
with your non-metallic spacer solution.


Best regards, Steve

Hi

I am in the process of getting materials for an 80-10 Loop Skywire. I
plan on setting this up in a Hex Shape to gain as much "Maximum
Enclosed Area". I was wondering if metal supports could be used for
this type of antenna? Also should the antenna be level (as much as
possible) or can it slope? The ground where I plan to set this up has
a 4-5 ft slope to it.

Any info would be appreciated.

73's

Bob

--- In loopantennas@..., Richards <jruing@...> wrote:

Can you give me an elementary explanation as to why or how
that would prevent one from replacing the wire loop with
another type or size loop? Can I not wire in, say, a bigger
loop and use it with the varactor inside the control unit?

THANKS /// RIchards ///
==============================================================

Marc wrote:

You can't . There is a varactor inside...

I beg to differ! Here's a clip from a post i made in the
ferriterodexperimenters group last may.
A picture is include in the photos section in my ferroids file.
Only difference is that it was made for the DE31:

I have performed further test on the Degen DE31 coupled to my
smallest ferrite
loop. Sensitivity is almost the same as the Palomar although the
noise rejection
isn't as good. The reason is more than likely that were dealing with
a single
ended input vs the balanced input the Palomar affords.

Here is an update of the Degen loop amplifier schematic. (courtesy of
the DRM
software radio forum)

The transistor is a 2SK544 MOSFET (Idss group E) with y21 = 11 mS,
Idss = 2.5 to
6 mA, very low Crss, get its datasheet here.

The tuning diode is a 1S149 or 1SV149 (equivalent) AM tuning diode,
get its
datasheet here.

Latest Update: Latest measurements made by our forum member Funkerberg
(thanks!), indicate that L1 = 10 uH and C2 = 10 nF which yields a low-
Q series
resonant circuit for mediumwave at the drain of the FET, more or less
shortening
mediumwave signals to ground.
C1 = 10 nF, it acts as an RF short.

Assuming a lossless RF decoupling circuit in the battery box, the RF
voltage
gain for shortwave signals with a receiver load of 500 Ohms is about
0.9, it
falls to about 0.36 if a receiver with an input impedance of 50 Ohms
is
connected. However, more signal power is transferred in case of the
50 Ohm
receiver since the impedance mismatch is smaller.
If maximum sensitivity is desired on a receiver with a 50 Ohm input,
a 2:1
impedance transformer could be used to transform the loop amplifier's
output
impedance (100 Ohms, established by R1) to the receiver's input
impedance.
Similarily, a 1:4 impedance transformer could be used to transform
the loop
amplifier's output impedance to a high impedance receiver input in
case maximum
sensitivity is desired.
Link to Schematic:

attachmentid=15616&d=1130372787

John

Hi Len,

Please see my ost on the internals of the DE31MS loop head.

The MW position utilses a bulk inductor to increase the the effective
loop inductance. This may explain the odd ratio results with this loop
when compared to the TG33 MW only version ?

Fraser

At 21:32:04 +0000 Wed, 07 Feb 2007, Len Warner wrote:

If you want to turn the DE31 into a MW loop,
bear in mind that the fet drain load is a broad trap
- 100R//10uH in series with 10nF/100R -

Oops!

Should read "- 100R//10uH in series with 10nF -"

In other words, the amplifier output load is
100R paralleled by 10uH, in series with 10nF.

And that acts as a broadly-tuned series trap
roughly centred on MW BCB, to prevent your
SWL radio's front end being swamped by
MW broadcasters while you are DXing.

See the DE31 schematic, de31_loop_amp.jpg


in a post by Roland dk8cb, 27-10-2005, 00:26,
#10 in thread: "Degen DE31 active loop" at
DRM Software Radio Forums > DRM Software Radio - User Forums > Antennas


or Google <dk8cb Roland de31_loop_amp.jpg>
follow the link and scroll down just over 1/2 page to post #10.

There's a good discussion in that thread which eventually
gets the design worked out. Several excellent photos too.

From tuning range calculations on the circuit and loop size,
I deduce that:
DE31 tunes SW 3.9 - 22 MHz with 1 turn & 1SV149
DE31-A tunes SW high 3.6 - 22 MHz with 1 turn & 1SV149
and SW low 1.8 - 4.5 MHz with SV149//2200pF
TG33 tunes MW 520 - 1720 kHz with 7 turns & 1SV149

Like the DE31, the DE34MS tunes SW 3.9 - 22 MHz
so it is reasonable to assume that is also 1 turn & 1SV149
but it also has a MW range 531 - 1602 kHz so perhaps
the loop is switchable between 1 and 7 turns.

The DE34MS's SW range is exact same as the DE31,
giving a max/min ratio 5.64 which suggests the stray
capacitance is minimal - in fact, it would take an
above-spec 1SV149 to achieve it. Perhaps the tuned
peak does not actually reach 22 MHz, or perhaps
one is expected to "squeeze" the loop into a narrower
diamond, lowering its inductance, to get there.

However, DE34MS's MW range is less than the TG33,
a ratio of only 3.02 versus 3.31, and both of these are
much less than the SW ratio. The drop from 5.64 can
be explained simply by the self-capacitance of a
bundled winding compared to a single turn, but why
the DE34MS's MW range starts higher than the TG33
(531 vs 520) but finishes lower (1602 vs 1720) isn't
explained just by extra stray capacitance: that would
_reduce_ both values.

So there is still something to explain about the MW
loops. Does DE34MS perhaps have one less turn
than TG33 plus some band-setting fixed capacitance
or is there a previously unsuspected band-setting fixed
capacitor in the TG33 which is different in the DE34MS?


Regards, LenW

Hi Richards,

Just make it out of PVC pipe like I did. With 2 meters on a side,
two turns about four inches apart would be 16 meters, which is
within the range of size that Wellbrook recommends. Of course, if
you like BCB DXing or LW, you could go longer.

Rob

--- In loopantennas@..., Richards <jruing@...> wrote:

Gee ... you make it sound pretty flexible. I am now working
on a couple of things:

First - moving to a new qth - very upsetting - I HATE
that feeling of being unsettled and living out of boxes;

Second - I am conjuring up images of how I might
make a relatively small loop, maybe two-meters-on-a-side,
that I could mount out back on a pole or just off the corner
of my deck;

Third - inventing some huge lie to tell the neighbors so
they do not realize what it is.


I will keep you posted on my progress... or lack thereof...
Thanks for the nice replies. //// Richards ////
=========================================================

Rob Moore wrote:

Hi Richards,

Sarcasm notwithstanding, if it was me, based on what I've found

out

abut the ALA-100 so far, I'd go with that.

A picture of the DE31MS head unit was requested.

Your wish is my command.....

I have uploaded a picture of my TG34/DE31MS loop head unit with it's
secret exposed !

The picture is in an album named "DE31MS"

Enjoy :-)

Fraser

For thise who are interested.....

I own the DE31(SW), TG33(MW) and TG34(MW&SW)loops

I have just dismantled my TG34(DE31MS)loop head.

It contains, amongst other things the Varicap(varactor)diode, the FET
and an inductor.

The loop element consists of just ONE turn. All conductors in the
insulated element are connected together in parallel to form a
conductor of larger cross section.

The TG34 uses a similar technique for banding the loop to that of the
AOR WL500 (I have the schematic). To increase the effective
inductance of the loop and lower it's resonant frequency, a bulk
inductor is placed in series with the loop element. The MW/SW switch
just inserts the inductor into the loop element circuit. You can
effectively mess with the loop tuning by changing the bulk
inductance. This will not make for the most efficient of loops
however !

Hope this helps a little :-)

Fraser

You can make a large 1 turn loop, or a smaller multi-turn loop.<<<

Or both, since you supply the wire. Can the head unit at the antenna
be easily disconnected and connected to another loop? Or, how about
an arrangement where the small multi-turn loop is bypassed with a
switch so that the coax then continues to a large loop elsewhere in
the back yard. Would that work? If so, then how about multiple
configurations of loops attached to a remote multi-antenna coax
switch where the common comes back to the shack from several loops
through the head unit.
Dave


--- In loopantennas@..., "Rob Moore" <rmoore5@...> wrote:

Hi Richards,

Sarcasm notwithstanding, if it was me, based on what I've found out
abut the ALA-100 so far, I'd go with that. It's flexible, fairly
sensitive and potentially very quiet. You can make a large 1 turn
loop, or a smaller multi-turn loop. It's compact enough so that

you

can bring it, a roll of wire and your portable radio on a trip and
be set up and ready to go in a half an hour or so. What else is
there to say?

Regards,
Rob

--- In loopantennas@..., Richards <jruing@> wrote:

(Rob -- Read this as ooooozing with feigned sarcasm:)

Oh... yeah... you offer a little sympathy...
or is it empathy... whatever...

Still I lament the lack of solid advice !! ;-)

OK - so I poke some fun, but just knowing someone appreciates
the difficulty of my dilemma helps me know I am at least
considering the right notions.

I will certainly let you know what I do.

/////////////////// THANKS -- Richards //////////////

Rob Moore wrote:

Hi Richards,

I know the quandry you're in. Let us know what you try.

At 12:49 am ((PST)) Wed Feb 7, 2007, Michael Stevenson wrote:

Yes, a different diameter wire will affect the frequency range

The wire diameter doesn't make much difference to the
tuning range for a single turn but it will affect the Q:
bigger gauge will have lower resistance hence higher Q

but a similiar diameter should give a similiar coverage range,

The loop diameter and number of turns are the main
determinants of the tuning inductance. Wire diameter
(and turn spacing for multiple turns) determines stray
capacitance, which impairs both Q and tuning range.

the thing to watch out for is if Degen designed the active element to compensate for that metal telescopic rod support that goes horizontal through it's midway point,

I doubt that the horizontal telescopic stretcher has a
very large effect, as it is doesn't complete a circuit and
is orthogonal to the electric field. There is probably a
tiny increase in the stray capacitance but this is a
high-capacity resonant circuit so I don't think the effect
would be noticeable. If it bothers you, replace the metal
stretcher with a couple of bamboo skewers or chopsticks,
with a tubular joiner for portability.

getting rid of that metal support and then using stiffer motor rewind wire means a support is no longer necessary but it may change the tuning for the same diameter loop without the metal support!

I don't think the tuning compensation would be larger
than the probable production variations in varactor
characteristics or tuning voltage inverter output.

However, the DE31 uses lap-screened audio coax
(inner and shield in parallel) so the "motor rewind wire"
would have to be a very stout gauge to match that
diameter (and Q) - and would be a bit difficult to pack
away, should you ever want to.

What's in the DE31MS I don't yet know and it may be
that motor or magnet wire might equal it - but be liable
to breakage. Whatever you use, make sure it is plain
copper rather than tinned copper.

Will be an interesting experiment that I hope to carry out this coming weekend!

When you have taken it apart, let us know what's inside.
(Were it not for curiosity, I would have advised you not to
modify the loop head - keep the original "for best" and
for travel and make a substitute homebrew loop head:
all you need is a low input capacitance low voltage fet, a
15V rated varactor and a few Rs and Cs from the junkbox.)


Regards, LenW

[I wish people who wanted reasoned argument
wouldn't make it more difficult by top-posting
and disrupting the logic of the thread ;-) ]

Marc wrote:

You can't . There is a varactor inside...

At 12:28 am ((PST)) Wed Feb 7, 2007, Richards wrote:

Can you give me an elementary explanation as to why or how
that would prevent one from replacing the wire loop with
another type or size loop?

It doesn't. However, if the loop is multi-turn as I
suspect it has to be on MW (unless Degen have
used a _lot_ of varactor diodes) and, as a corollary
of this, range switching involves varying the number
of active turns, then doing so may turn out to be a
difficult-to-reverse modification because of the
likelihood of messing up the wire or its protective
jacket in the process.

Tricky too, if you want to preserve the dual-range
nature of the loop without further surgery on the
electronics, as there is little scope for increasing
the size of the HF turn while preserving its tuning
range since its tuning capacitor is determined.
So you would have to have a dual-diameter double
loop, which will be a less convenient, less portable
arrangement than the original product.

If you want to modify a Degen aerial to use a larger
loop it would seem sensible to _either_:-

a) Modify the TG33 MW model to use less but larger
turns than the seven I suspect it contains; _or_

b) Modify the DE31 by changing the varactor diode
to one with a similar capacitance ratio but much
smaller value. You could also turn it into a DE31-A
clone dual-HF-range loop with a switched additional
fixed tuning capacitor. I estimate the DE31-A uses
2200pF in parallel with its large-value varactor but you
would need to use something smaller in proportion.

[If you want to turn the DE31 into a MW loop,
bear in mind that the fet drain load is a broad trap
- 100R//10uH in series with 10nF/100R - stop band
centred at 700kHz by my reckoning, but the feed line
capacitance is in parallel and I have no idea of its
value or effect. You would need to modify this trap,
perhaps by removing or changing the inductor.]

It seems to me a sensible idea use the schematic
to make 2 or 3 single range loop heads to be plugged
(or switched) interchangeably into one control unit.

Can I not wire in, say, a bigger loop and use it with
the varactor inside the control unit?

No, in the same way as you cannot shave
"the present king of France's beard", because
there is no "varactor inside the control unit".


Regards, LenW

I thought i had this antenna installed correctly,its in the window but
when i power up the antenna i hear no difference than when its powered
off,anybody else have this same issue??

Yes, a different diameter wire will affect the frequency range but a similiar diameter should give a similiar coverage range, the thing to watch out for is if Degen designed the active element to compensate for that metal telescopic rod support that goes horizontal through it's midway point, getting rid of that metal support and then using stiffer motor rewind wire means a support is no longer necessary but it may change the tuning for the same diameter loop without the metal support!

Will be an interesting experiment that I hope to carry out this coming weekend!

Best wishes!

Michael S

Can you give me an elementary explanation as to why or how
that would prevent one from replacing the wire loop with
another type or size loop? Can I not wire in, say, a bigger
loop and use it with the varactor inside the control unit?

THANKS /// RIchards ///
==============================================================

Marc wrote:

Ohhh... that sounds interesting.

////////// Richards //////////
====================================================

Michael Stevenson wrote:
I will also experiment by replacing the origional
loop element with different types and diameter wiring!

Michael Stevenson schreef:

I will also experiment by replacing the origional loop element with different types and diameter wiring!

You can't . There is a varactor inside...

Marc

Gee ... you make it sound pretty flexible. I am now working
on a couple of things:

First - moving to a new qth - very upsetting - I HATE
that feeling of being unsettled and living out of boxes;

Second - I am conjuring up images of how I might
make a relatively small loop, maybe two-meters-on-a-side,
that I could mount out back on a pole or just off the corner
of my deck;

Third - inventing some huge lie to tell the neighbors so
they do not realize what it is.


I will keep you posted on my progress... or lack thereof...
Thanks for the nice replies. //// Richards ////
=========================================================

Rob Moore wrote:

Yep, I will try this out and hear what happens and will report my findings to this group in due course. I will also experiment by replacing the origional loop element with different types and diameter wiring!

Best wishes!

Michael S

Hi Richards,

Sarcasm notwithstanding, if it was me, based on what I've found out
abut the ALA-100 so far, I'd go with that. It's flexible, fairly
sensitive and potentially very quiet. You can make a large 1 turn
loop, or a smaller multi-turn loop. It's compact enough so that you
can bring it, a roll of wire and your portable radio on a trip and
be set up and ready to go in a half an hour or so. What else is
there to say?

Regards,
Rob