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Re: [Fwd: Primstar dishes at 10 Ghz? (again)]



Hi Tom et.al.

>> Has anyone had any luck at all using a Primstar dish and feed, and/or the
>> electronics at the feed (I assume LNB) on 10 Ghz?  Some of these are

I don't know about the Primestar setup, but they are all alike I guess.
There are literally hundreds of different dish/lnb/mount combinations
available here in Europe, although it seems that the market has cooled 
down a bit in anticipation of the new DVB era...

>> the IF the LNBs put out, 70 Mhz like a big dish?  There are two LNBs, and

As Tom pointed out, the IF is approximately in L-band. The nominal IF now-
adays is 950 MHz to 2150 MHz. Some IF's go even below this...

>> two coax feeds from them, one for vertical polarization and one for
>> horizontal.  The whole feed can be rotated manually to align the

There are LNB's avalable with integrated V/H reception capability. Usually
there are two LNA's ( switchable ) with a common mixer and IF, but therea
are also models with full V/H dual reception capability with dual IF out and
all ( nice sources of cheap P-HEMT's and the like ! ). 

>> feed close enough to the P3d 10 Ghz freq to work?  How about to the

Most feeds I have seen are still quite usable at 10451 MHz and also 10368
MHz. I have actually used a totally unmodified commercial Ku-band scalar
choke feed successfully for 10368 MHz EME ( see my homepage ). The only 
thing I did was add a section of waveguide with a set of screws for 
matching. I equally well could have modified the probe length ( the
feed had an integrated servo driven polarisation control ). I made the
servo control box with a simple 555 timer and a calibrated potentiometer
to read polarisation angle directly. ( On my subsequent 3.4 GHz EME rig
I antually tuned the probe lenth on a commercial 3.8 - 4.2 GHz feed to
bring the resonant frequency down to 3.4 GHz with excellent results 
- see my homepage ).

Tom said:

>(a) There are some of the K-band front ends that have a 10.000 GHz LO, 
>done with a free-running DRO (Dielectric Resonant Oscillator). The DROs
>have pretty good frequency stability -- typically better than 1 MHz: this
>is adequate for the high-speed digital applications for which they were
>intended, but not for SSB! One mod that can work is to drill/tap the lid
>of the DRO cavity box for the 1/4"-32 threads of an SMA "bullet" connector.
>A "nude" SMA connector is threaded into the hole and its lead serves
>as a probe that can injection lock the DRO to the harmonic of a lower
>frequency stable source (like 1 GHz).

I have tried this almost exactly as Tom describes. Both injection locking
and harmonic injection ( needs more power though ) are possible.
I have also modified DRO resonators with different methods to resonate lower
or higher for different applications ( ATV mostly ). To raise the frequency,
you need to reduce the cavity volume. How you do this is by a mechanical
procedure with a diamond abrasive mini drill tool or equivalent. 
To reduce the frequency you can need to increase the volume. This can be
achieved by gluing anything with suitable dielectric properties and high
Q directly onto the dielectric resonator. You can use small circular low
capacitance chip caps with the solder contacts removed ( with a hot soldering
iron ). I have even glued pieces of other resonators onto each other to 
achieve the desired frequency ! There might be better glue availabe, but
I stuck ( couldn't avoid the pun !!! ) with cyanoacrylite as it seems to
work and not have too high dielectric losses. The same stuff I have used
for gluing down teflon too.

What I have done a couple of times is remove the DRO completely and
use the oscillator FET as an amplifier or multiplier. As some after-
thought I suggest that the FET and all surrounding components are 
removed completely and the the external final frequency LO is fed 
directly to the mixer with a piece of low diameter coax. The reason
I suggest this is that arranging adeqauate grounding and building
suitable structures around the DRO FET to prevent it from oscillating
arbitrarily is not something for the faint hearted !!!

The most common LO frequencies I have seen are 9.75, 10.0, 10.3, 10.7,
and 11.0 GHz. Undoubtedly others are available too. It's just good to
know that there is a variety. The tuning range isn't usually very big,
but using the volumetry modification concept you can make these resonators
go more or less where you like. You just have to be careful that the 
the oscillator keeps running smoothly - this often requires the oscillator
cover to be put in place.

My P3D rx ( see my homepage ) uses the oscillator transistor as a 
straight buffer for my 10018 MHz LO. The IF is broad band, so by using
my FRG-9600 at 350 MHz as an IF, I can also listen to 10368 MHz with the
same antenna/converter. 

The IF took some modification too, to get coverage and adequate gain
at 70 cm. Until now I have been using 23 cm as an IF as this does not
require any modification. 

In another concept of the P3D rx I used a commercial GPS DRO oscillator
( from Matsushita ) phase locked to a suitable crystal. The tuning range
of the GPS DRO is smack in the the middle of 10451 - 7 * LO giving an
IF on the 6 m band...

By locking the DRO to  1485.714285714 MHz and multiplying this LO by
six you get  8914.285714286 MHz, which is the LO signal taken to the
mixer of the modified LNB. The downconverted L-signal I then mix with 
a sample of the 1485.71428714 MHz GPS LO to further down convert to
6 m. You must take care to have a narrow 1.485 MHz LO filter for this
concept though to maintain reasonable image rejection. 

Just food for thought !

Further, Tom said:

>(b) I know of one group at a University in Japan who modified 11.7 GHz
>units down to the 10.7 GHz Radio Astronomy allocation to serve as the 
>front-ends for an array (I seem to recall it was 12x12, i.e. 144 elements)
>that was used for imaging the radio sun. The LNA packages they used had
>a strip-line microwave bandpass filter between the LNA and the mixer.
>After a lot of hacks at lengthening the filter elements to accommodate the 
>~10% frequency change, they found that it was MUCH simpler to
>dielectrically
>load the filter by putting an appropriate sized slab of Teflon on top of
>it. As I recall the numbers, with this mod more than 90% of the units
>achieved < 100K system temperatures.

Done this too. It works !!! This is how I modified my latest LNB for P3D.
I loaded the band pass filter with a slab of teflon onto the filter and 
another piece onto the mixer. Ah, the mixer. You get either the FET mixer
or the diode mixer. And the diode mixer may have one or two diodes. The 
one I had in my P3D rx is of the dual diode variety based on the 3 dB
coupler design. Loading the coupler with a slab of teflon brought up the
gain a couple of dB. Haven't the sofisticated noise temperature test 
equipment available, but the noise temperature is low judging by the
sensitivity to pointing the horn at different sources. Haven't measured
the sky/ground difference yet as I only just got the PSU to work. This
DC stuff gives me the creeps... The P3D rx is now fully integrated into
a diecast box with the LO, PSU ( + 8 V ... + 14 V in, -20 V and + 15 V 
out ) and modified LNB within and the circular depolarizer externally to
this, between the box and the feedhorn. 

The circular depolarizer is 
simply a section of circular waveguide with a quarter wave delay line
of rexolite ( polystyrene ) at a 45 degree angle. ( actually the de-
polariser was for LHCP at first, but is I modified it for RHCP by 
redrilling the flange holes to allow rotation of the waveguide by
90 degrees ... ).

>(c) I know Michael and the Helsinki group have played with similar 
>packages as well, in part because of their love of microwaves, and in part
>in anticipation of their X-band package flying on P3D. Perhaps they can
>be enticed into announcing their results to the world!

I have modified maybe 15 different types of commercial LNB's for different
ham and amateur radio astronomy purposes ( Tom, have you realized how
easy these things are for making a demonstration mini-VLBI by injection
locking the DRO's of the two LNB LO's together or driving them with an
external common LO ? ).

The problem here is that we are emerging the era of fully intergrated
and production sealed LNB's where all the circuitry is on one small
piece of PCB and the enclosures cannot be entered non-destructively.
Some modern designs simply will not be stable once the enclosure has
been opened. I have been collecting the older variety of LNB's that
still use good old screws. The noise temperatures are somewhat higher,
but take a look at the ERP of P3D ! Who cares !

>(d) The (typically) 900-1600 MHz IF section in these units have a LOT of
>discrete L/C components. Modifying them will be a challenge! It might
>be worth considering using 23 cm (1269 or 1296) MHz as a convenient IF.
>With P3D, you will only be using the TX side of your transverter since
>23 cm is only an uplink (as stipulated in the International Radio Regs).
>A good place to use the RX side of the transverter would be as a way to
>save having to do a lot of hacking on the IF stages in the front-end
>packages for the Primestar and/or DSS dishes.

That's right. Though some of the more modern ones have one or two IF
MMIC's with the band limiting achieved with fairly straight forward
filtering easily modified.

Also the flange is standard, so you can fit other waveguide pieces
together with the commercial TVRO equipment. As the 12 GHz radio link
band has become obsolete, there is a lot of surplus out there that is
flange compatible ( I have scrounged isolators, circulators, filters, 
multipliers, couplers, detectors, Gunn oscillators and waveguide to 
SMA transitions that use the same flange - used some of this stuff
on my 10 GHz EME rig ).

Cheers - Michael


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