Thanks! It should be pretty good. I am going to try 5/8 inch diameter rod
material for a start, and see how that works out. There are 3-gang caps
available, with 400pF per section, so that should give a pretty good tuning
range if I use RF relays for switching. The other approach is to use
varactor diode tuning, but since these devices don't have as high a Q as air
spaced tuning capacitors so regeneration might be needed to regain the RF
selectivity that is lost. I have used the NTE-618 varactor in this
configuration, and it was actually pretty good. I need to pick up some nylon
male/female threaded spacers to isolate the tuning cap from the front panel
of the enclosure, since both the rotot and stator are connected to each
input of the differential amplifier. If the tuning cap isn't insulated, your
hand will act as an antenna when you try to tune the unit. An insulated
shaft extension is also required.

Pete

"RHF" wrote in message
...
On Feb 11, 2:01 am, "Pete KE9OA" wrote:
The longwave loophead is very good, although I haven't tried the tropical
band unit. I am in the process of designing a three band model that covers
longwave through the tropical range for one of the manufacturers in this
country. If anybody has any features they are looking for, please let me
know. It is early enough in the game to implement them right now.
I have experimented with multiple band windings on one ferrite rod, and
there are too many comprimises in the design. As an example, I encountered
self-resonance effects from interraction with the windings for the
different
ranges. This is the reason that Philips used separate LW/MW loopstick
antennas with the D2999. This is also the reason that the loop antenna
manufacturers in the USA are also using separate plug in loops.
The main thing that is holding me up with the tropical band unit right now
is that I have to wait until I get some samples of ferrite rod with a mu
of
400 or so. I've got some 900mu material, but with a permeability this
high,
only 16 turns center tapped, are needed for the required inductance. I
have
discovered that at least 40 turns are required in order to develop enough
magnetic current in the ferrite rod for adequate amplitude. With my
current
stock, the tropical band loopstick in about 10dB lower in output.
I am thinking about a rod diameter of between 1/2 inch to 3/4 of an inch.
It
seems that output amplitude has a relationship to the cross sectional area
of the ferrite itself.
An alternative to thie multiple head design would be to use a high Q
tuning
capacitor with a range of 14pF to 1500pF.
A 6:1 ball reduction drive would be used with this cap in order to make
tuning easier. I have built a couple of prototypes in the last couple of
weeks, using #36 x 14 strand Litz wire, and the results have been very
good.
This design seems to work fairly well, even without regeneration, but let
me
know if that is something you would like to see.

Pete

Pete [KE9OA],

Look forward to reading more about this Three-Band
LW/MW/TB Loop Antenna that you Designing.

keep us informed of the progress ~ RHF