Modification of the Ramsey FR1 kit for use as a 30 MHz WFM IF for Gunn
Figure 1 - The
fully-modified (except for the addition of the 2nd IF filter) Ramsey
FR1 FM receiver. Click on the image for a larger
One of the more popular modes of operation on the
10 and 24 GHz microwave bands is Wideband FM using Gunn
transceivers. Because frequency modulation is very easy to
accomplish using Gunn oscillators, this mode is a
natural choice with these devices - and using wideband FM with a
relatively wide 300 kHz bandwidth (the same standard as
is used on FM Broadcast Bands) makes it
easier to find and track signals when the frequency stability of one or
both ends of the 10/24 GHz link may be suspect.
Traditionally, a 30 MHz Intermediate Frequency (IF) is utilized,
implying a difference 30 MHz between the Gunn oscillator frequencies of
the two stations in QSO. Why is 30 MHz used instead of a
seemingly more-obvious choice of 88 MHz or some other frequency in or
the FM Broadcast band where receivers are extremely common? While
it may seem natural to want to use
readily-available receivers designed for wideband FM, it's a simple
that in most areas it is difficult to fund a span of 2-6 MHz or so of
the FM broadcast band in which one may track a drifting signal that
does not already have a high-powered FM broadcast station in it:
This is especially true for those operators atop mountains that are
likely to be line-of-sight with a high-powered broadcast station that
may be some distance away - or right next door!
It should be noted that no matter how well one attempts to
shield their receive system, it is nearly impossible to minimize
ingress of FM broadcast signals to allow a weak signal being received
via the Gunn transceiver to be received even when the converted IF is
atop a frequency of an active FM broadcast station.
30 MHz, on the other hand, is a relatively low frequency (simplifying
design) and more within the design range of the Gunn transceiver's
receive mixer diode and it is very unlikely that one will encounter a
signal in the 30 MHz area that is likely to cause an ingress
problem. An obvious problem with this frequency range is that
there is little equipment to be found capable of receiving
wideband FM signals around 30 MHz - a notable exception being the Icom
IC-706 - which is not particularly cheap, portable or low-powered.
While it is practical to construct a homebrew 30 MHz WFM receiver, it
is also possible to modify a readily-available kit receiver to work as
a 30 MHz WFM IF receiver, and one of the more easily-available
receivers is the relatively inexpensive Ramsey FR1.
Figure 2 - Details of
the modifications of the VCO that allow tuning through 30 MHz. Top: The new inductor,
L1. Center: The 68
capacitor added to the bottom of the board across L1. Bottom: The schematic
of the modifications. Click on an image for a larger
In addition to operation at 30 MHz this page contains additional
modifications that can improve the performance of the FR1. Note
that these additional modifications are intended to improve various
performance aspects of the receiver and are not absolutely necessary
for 30 MHz WFM operation. About the FR1:
The FR1 (or "FR1C") is a "bare-bones" wideband FM receiver intended for
use as a broadcast band FM receiver amd as such, certain design
decisions were made to keep it simple and its price down: It
contains a voltage-tuned
local oscillator that mixes the input signal down to 10.7 MHz where is
filtered through a 300 kHz wide ceramic bandpass filter and then
demodulated. As it is, it is a fairly easy matter to simply
modify the local oscillator to provide tuning around 30 MHz - but a few
additional modifications are required to provide optimal performance.
Being a bare-bones receiver, the FR1 does NOT
have any input filtering at all: Without such filtering, the
receiver responds to image
signals with sensitivity equal to that of the desired signal.
Within the FM broadcast band, this lack of filtering may not be noticed
as FM signals are typically very much stronger than those that would
appear at the image frequency: When high-side
LO injection is used, the image responses land at a frequency of twice
the IF above the desired frequency (e.g. 21.4 MHz) and are within
band, but when weaker signals are used, this lack of filtering can
degrade performance somewhat due to "Image Noise" - not to mention
making the receiver somewhat more susceptible to spurious responses.
Constructing the FR1:
Even though the ultimate use of the FR1 will be as a 30 MHz wideband FM
receiver, it is recommended that it first be built as originally
designed to allow testing using FM broadcast-band signals!
Once the unit
is verified to work properly,
the unit may then be modified to operate at 30 MHz, but keeping in mind
that the receiver will eventually be modified,
there are a few changes that should be made while constructing the unit.
Omit the SCA output circuit consisting of J3, R14, Q3, R18 and
C22. The SCA signal output is not required and the presence of
the Q3 circuit causes a slight amount of re-radiation of the 10.7 MHz
IF signal and somewhat worsens spurious responses. If you intend
to add the 30 MHz bandpass filter described below,
may be conveniently utilized as the RF input connector
to the added filter - but do not mount J3 until you install the filter.
Connect the 10 uF capacitor that
would have been used
as C22 (from the SCA circuit that was NOT constructed) across pins 1
and 8 of U2, the audio amplifier. This increases the audio gain
of the receiver significantly. It may be easiest to install this
capacitor on the bottom of the board. The "+" (positive) lead
of the capacitor is connected to pin 1.
Omit R9, the 10k
resistor. This disables AFC - which we don't want to use in this
Add a 0.001 (1000 pF) capacitor from pin 3 of U2 (the LM386 audio
amplifier) to ground
(either pin 2 or pin 4) at U2, on the bottom of the
board. The addition of
this capacitor will prevent extraneous response by U2 to RF (such as
from a nearby 2m or 70cm transmitter) as well as minimize spurious
response of the receiver.
Do not mount the 9-volt battery holder/clip hardware as we won't
be running the receiver from a 9 volt battery
Tune up and test this receiver as described in the Ramsey
instructions. The adjustment of L2 is the only critical one and
is best done using a weaker signal. Because it is an IF
adjustment, its adjustment does not need to be changed with the change
frequency if properly adjusted in the first place. If
MHz FM signal generator and AC-voltmeter or oscilloscope are available,
L2 may be
"fine-tuned" for lowest distortion and highest audio output - a
procedure best done at low volume level.
Modifying the FR1 for operation at 30 MHz:
Once proper operation of the FR1 has been verified on the FM broadcast
band, we can now modify its VCO so that it can receive signals at 30
MHz using high side injection - that is, with the local
oscillator at 10.7 MHz above the receive
This involves a few simple modifications that are detailed in Figure 2:
Change C14 (100 pF) to a 1000 pF (0.001 uF) unit.
Replace L1 with a tunable inductor of 0.11-0.16 uH range.
It may also be possible to
increase the inductance of the existing coil - either by adding turns
existing unit or by the addition of a few turns of an outboard
"air-core" inductor that is tuned by compressing/stretching the
turns. (The addition of the air-core inductor may be done on the
bottom-side of the board, or on the top side of the board provided a
slight board modification is done involving adding additional holes and
isolating an additional pad on the "ground" side of L1. Comment:
used is of about the same diameter as the original, but
has 5.5 turns instead of 2.5 turns.
Parallel L1 with a 68 pF capacitor on the bottom of the
board as shown in the picture and on the schematic. Use only an NPO, dipped
silver mica or polystryrene type for best frequency stability!
Change R10 (2.2k) to 1k, or simply parallel R10 with another 2.2k
resistor. This is done to slightly increase tuning range using
The goal of these modifications is to shift the local oscillator
frequency such that it tunes from approximately 38.7 to 42.7 MHz,
correlating with a tuning range (using High-Side
injection) of approximately
28 to 32 MHz - a range of about 4 MHz. Note that the exact range
isn't important: A tuning width of 3-6 MHz (or from +-1.5 MHz to
+-3 MHz) is adequate.
Figure 3 - Details of
the 30 MHz bandpass filter. Top:
bug" on a piece of circuit board material. Note that
the new "input" uses the "SCA Out" connector (J3) and the board is
grounded and secured using existing holes in the circuit board. Center-top: Version of the
wound using air-core inductors. Center-bottom:
Passband response of the air-core filter. Bottom:
of the filter. Click on an image for a larger
After the above modifications have been made, set the tuning
potentiometer (R12) to 3.33 volts on the wiper and adjust L1 for a
oscillator frequency of 40.7 MHz, +- 100 kHz or so, corresponding
with a receive
frequency of 30 MHz. For checking/setting the local oscillator
it is probably easiest to use a general-coverage receiver or a scanner
to find the local oscillator, taking care to assure that one is really
hearing the LO and not a spurious response of the receiver. For
verification of proper operation, a signal generator or even an HF rig
tuned to the top of 10 meters can be used to generate a signal in lieu
of fancy test equipment.
The following modifications are
not absolutely necessary for WFM operation of the FR1 on 30 MHz, but
they may be done to improve its overall performance.
A 30 MHz bandpass filter:
For best performance it is recommended that a 30 MHz bandpass
filter be added to the receiver to remove "image noise" from the
receiver input. Note, however, that the addition of this filter
is most efficacious
if there is amplifier gain prior to the bandpass filter
- such as the use of a low-noise MMIC preamplifier on the mixer output
of the Gunn transceiver: Without such preamplification, the
receiver's intrinsic sensitivity may not be adequate to be able to
detect the thermal noise of the Gunn transceiver's mixer diode and thus
it may not be able to "hear" the image noise in the first place. (This
optimal weak signal performance may be had with the
installation of the MMIC preamplifier at the Gunn transceiver itself.
Details of this filter are shown in Figure
3: The components
of the filter are mounted "dead bug" on a small scrap of circuit board
material (either single or double-sided.) As it turns out, it is
possible to wire the "SCA Output" connector (J3) as the bandpass
filter's input (note in the picture how the center conductor of J3
is bent straight out and connects to the input of the filter) and
mount the filter in the "empty" portion of the
circuit board where the 9 volt battery would have original gone.
The original Antenna Input connector (J1) should be removed and a
short piece of small-diameter coax cable (such as RG-174) is used to
connect the output of the bandpass filter to where J1 (the "Antenna"
connector) was originally connected.
To properly tune this filter it is necessary to use a sweep
generator with diode detector and oscilloscope, a network analyzer, or
a spectrum analyzer with either a noise generator or tracking
generator. The two inductors are adjusted to yield a flat
bandpass of at least +-2 MHz (at the 3dB points) centered at 30 MHz,
(see the center-bottom picture in Figure 3) dropping by
at least 20 dB at 40 MHz with the insertion loss being
between 4 and 6 dB
at 30 MHz. In the "image passband" (above 49 MHz) this
filter should provide well over 40 dB of attenuation - more than
necessary to provide highly effective rejection of image noise as well
as minimizing spurious responses in the FM broadcast band. The
dB of attenuation at the image frequency and
5 dB of insertion loss within 1.5 MHz of 30 MHz.
your own coils for the bandpass filter:
While the prototype 30 MHz bandpass filter used some slug-tuned coils
from a junk box, it is practical to simply wind some air-core coils
work equally well as long as one keeps in mind that they are
mechanically rather fragile - See the center-top picture in Figure
Suitable coils are wound using 9 turns of #22 enameled
wire on the shank of a 1/4" drill bit. If you look carefully at
the picture you might notice that the two coils are wound in opposite
directions: This is done so that the ends of the coils are easily
oriented such that they face the "input/output" terminals on one side
and the other ends face the "100pF-22pF-100pF" junction in the
middle. Note also that the coils are very slightly elevated above
the ground plane to minimize interaction between the body of the coil
and the ground plane.
In initial testing, the close-wound 9-turn coils (in
their original "un-stretched" state where
all of the turns are against each other) resulted in a filter with a
center frequency of
about 27 MHz. As can be seen in the center-top picture in Figure 3, the coils were
spread slightly to lower the inductance, thus moving up the center
frequency slightly. With a bit of tweaking while using a tracking
generator, spectrum analyzer, or some other means for "sweeping" the
frequency response it is possible to "fine-tune" the bandpass to the
Once the filter is tuned, it is important to make sure
that the coils can't move or stretch/compress and detune the
filter. If the filter has already been mounted to the receiver's
circuit board, one source of coil movement (the flexing of the
input/output leads and subsequent moving of associated components) has
already been eliminated. To make the filter
even more rugged, it is suggested that the coils themselves be
stabilized with RTV (silicone adhesive) to prevent movement. If
this is done, it is recommended that the filter be tuned up first
make sure that it will tune
properly) and then flow RTV over, under, and through the coils, and
then re-check tuning before and after the RTV cures.
Improving the input preamplifier:
Figure 4 - Top:
The replacement of R5 with the network consisting of two resistors and
one capacitor. Bottom:
Added components are indicated with arrows. Click on an image for a larger
It is possible to improve the input preamplifier somewhat over the
original with the addition of a few components. While the
original preamplifier works, its gain is somewhat excessive for our
purposes and the input impedance is not well-controlled. The
described modification will increase the stability of this amplifier,
reduce the gain somewhat, and provide a consistent input impedance to
better-terminate the bandpass filter.
The modifications, depicted in Figure 4, are as
Remove R5, the 10k resistor.
Replace R5 with a small circuit consisting of a 470 ohm resistor
in series with a 3.3k resistor that is paralleled with a 0.01 uF
capacitor: The network of 3 components should fit where R5
originally was installed.
On the bottom of the board, add a 1k resistor between Q2's base
and emitter (e.g. the ground.)
The original data sheet for the ULN2111 shows
capacitor from the output of the quadrature tuning network (L2)
pin 9 - and that is the way that the FR1 is, in fact, wired. The
data sheet for the pin-compatible Motorola MC1357's that better
may be usually obtained by using pin 10 instead of pin 9. Why is
used, then? Apparently, in some situations, some sort of overload
distortion could occur - particularly at higher deviations at lower
frequencies. At 10.7 MHz and using 75 kHz deviation, this isn't
an issue so one can benefit by making the following modification:
Sever the trace between C1 and pin 9.
Connect a small jumper from the severed end of C1 to pin 10.
Note that you may have to re-tweak the discriminator transformer
(L2) slightly for highest audio output with an FM signal input at 10.7
What "better" performance is gained by doing this? The audio
slightly higher, the limiting sensitivity is better, and the audio
distortion on the received signal is lower.
On the FR1, the single 10.7 MHz ceramic IF filter (FL1) is placed
between the mixer and Q1, a simple IF amplifier. While the output
impedance of the mixer, an NE/SA602 is fairly high and a reasonable
match to the 330 ohm in/out impedance of the filter, the input
impedance to Q1, the IF amplifier is not. The result of this
significant mismatch is that the bandpass response of FL1 has
This deficiency may be easily remedied as follows:
Locate the trace between the base of Q1 and the output of FL1 and
sever it. Note that R4, Q1's bias resistor (47k) will still be
connected to the output of FL1.
Bridge the severed trace with a 220 ohm resistor. Q1 will
once again get its bias through the added resistor. This added resistor may be seen in the
upper-right corner of the lower picture in Figure 5.
slightly lower overall IF gain, no
appreciable change in sensitivity was noted on the receiver: This
especially true if the "Discriminator Modification" (above) is also
The FR1 has only a single 10.7 MHz ceramic filter with a bandwidth of
somewhere in the range of 280 to 350 kHz. Typically, these
filters have a stopband rejection of only 30-40 dB in the range of 9-12
MHz: Outside this range, they can have a number of odd responses
with less rejection: It is these other responses that can
contribute to spurious responses of the receiver.
Practically speaking, with no other signals likely to be present
nearby, a single bandpass filter is adequate - but the presence of just
the one filter and its lack of good ultimate off-frequency rejection
can contribute to the presence and energy of miscellaneous spurious
responses. Because the LO itself is very strong (80 dB or so
above the weakest detectable signals) it is understandable how even a
very low-level mixing can appear on-frequency at 10.7 MHz.
Fortunately, it is pretty easy to add a second filter to this
receiver. Because these filters are rather ubiquitous, they are
(less than $2.00 each in single quantities) or they may be found for
free in junked FM receivers. For best performance it is
that the filters be placed in different stages rather than simply
cascaded - and the second filter is easily added between Q1 and U1 and
is done as follows and are shown in the pictures in Figure 5:
Figure 5 - Top and
bottom views of the circuit board with the added ceramic IF filter. Click
a larger version.
Do the "Improved IF filter matching" modification above.
Remove R6, the 470 ohm resistor.
Drill three holes just "above" where R6 had been installed (see
Figure 5) with
the holes spaced the same as the three leads of the ceramic
These holes are centered approximately over the "square" on the
silkscreen denoting the position of R6. The "left-most" hole
in the circuit board trace coming from pin 4 of U1 while the other 2
holes will be into "blank" board with no traces.
After drilling the three holes, sever the trace that goes from
pin 4 to R6 between the position for R6 and the new hole that
was drilled. The idea is to disconnect the pin 4 of U1 from R6
but still allow it to connect to the new filter.
Insert the new bandpass filter into the three holes. One
lead of the filter should be soldered to the trace that was just
severed and now be connected to pin 4.
Using a small piece of wire (from a trimmed component lead)
connect the center pin of the new filter to the ground pad at pin 7 of
Using another small piece of wire, connect the remaining lead of
the filter to end of R6, on the other side of the now-severed trace.
Install R6, the 470 ohm resistor, on the bottom side of the board
across pins 4 and 6 as seen in the bottom image of Figure 5.
As it turns out, U1 terminates the new filter fairly well with about
350 ohms or so. The "output" of Q1 isn't quite as good a match,
but it isn't severe enough of a mismatch to cause appreciable ripple on
the added filter.
One noted change was that the no-signal noise (the
"hiss") was notably quieter - probably due to less thermal noise
reaching the discriminator than before from the FR1's preamp and IF
amplifier, causing this noise to be below the limiter threshold:
If an antenna (or an operating Gunn transceiver) is
connected to the FR1 with these modifications, much of the "hiss" will
return - especially if the Gunn transceiver has an onboard MMIC IF amp.
Another notable change was a significant diminution of receiver
spurious response: The main spurious response (at about 31.8 MHz)
is significantly reduced by the addition of the filter, no doubt due to
less "blow-by" through the filter. Even though the filtering adds
a couple of extra dB of loss in the IF,
no decrease in ultimate sensitivity was noted (provided that the
Discriminator Operation" modification mentioned above was done) and
tuning seemed to be "crisper" (due to "steeper" sides of the filtering
resulting in a better shape factor) - especially with stronger signals.
In testing with the above modifications, this receiver seems to have
a sensitivity of 10-15 uV for a signal with 12 dB SINAD
measured in a 3 kHz audio bandwidth with 20 kHz deviation) at 30
In the original Ramsey notes, a sensitivity of about 1 uV was claimed -
a value that is probably optimistic (especially considering that the
thermal noise alone in a 350 kHz bandwidth with a 3 dB noise figure and
an antenna noise temperature of 300K would be over 1/3 of a microvolt
alone) and certainly would not represent a
signal of good quieting.
One minor problem with this receiver in its unmodified state is that it
has somewhat of a
tendency for spurious response - particularly at frequencies near
multiples of the 10.7 MHz IF. Fortunately, there are no such
significant responses within 1.5 MHz of the 30 MHz center
frequency. The worst response in the unit that I constructed
occurred at about 31.8 MHz - but it was completely overridden by a
signal of about 30 uV. As mentioned above, the addition of a
second 10.7 MHz bandpass filter significantly reduces the
of an "S-Meter":
One further modification to this receiver would be the addition of a
signal strength meter using an LM3089 or
LM3189: This modification may be described at a later date on
Less common at 10 and 24 GHz is so-called "narrow FM"
operation. Unlike VHF/UHF operation, however, this is not the
traditional +-5 kHz deviation in a 15 kHz IF bandwidth, but rather a
+-15 kHz deviation using an IF bandwidth of 30-50 kHz.
By replacing the existing IF bandpass filter with a
narrower-bandwidth version (or simply placing it in series with the
signal path - something that can be done with a selector switch or by
using switching diodes) one can obtain superior (6-10 dB) weak-signal
performance. The disadvantage of this narrower bandwidth is that
tuning of the 10/24 GHz units is far more touchy and is really only
practical if an AFC circuit is used to compensate for
Unfortunately, these narrower filters are relatively rare and
somewhat expensive ($5-$20 each, depending on the model and
source.) It is possible that a few of these filters may be
obtained via surplus channels: Contact me if you are really
Originally, the FR1 has a rudimentary AFC, but in the above
instructions, I recommend not installing R9 - effectively
disabling the AFC. Why is this done? In the original FR1
operation, the tuning range of receiver is over 20 MHz - more than
enough to cover the entire FM broadcast band. In converting to 30
MHz, the tuning range is much more limited - typically in the range of
3-6 MHz. This also means that the AFC lock-in range is also more
restricted as well.
One can experiment with having R9 installed - but note that having
an AFC on 10/24 GHz may be a two-edged sword: While it is nice to
have the receiver automatically tracking the signal, with AFC, the
received signal will suddenly disappear when it gets out of the
AFC circuit's tracking range rather than gradually drift out when no
AFC is being used. In many ways, having a gradual warning of
drifting is preferable because you, as the operator, are more likely
to know what happened to the signal and has had time to re-tweak the
tuning. If the signal abruptly disappears, on the other hand, you
may not know if it simply drifted out of AFC range, or if something
else happened. If AFC is desired, it should be possible to
implement it - but the
user should know the potential pitfalls of its operation.
Note also that the AFC on this receiver affects only
the receiver's operation: On the fancy, commercial Gunn
Transceiver units (such as the ARR) the AFC does not affect the
30 MHz IF receiver's tuning (which is, in fact, often crystal
controlled and cannot be adjusted) but rather the AFC adjusts the Gunn
oscillator's frequency - which means that the transmit frequency is
tracked as well. When this is done, the user on the other end
must be aware that AFC is being used and shut his/her AFC off or else
they may "fight" each other: If configured properly, the "other"
person (without AFC) also benefits as the AFC keeps the stations locked
to each other - no matter who is drifting.
Another point of concern has to do with AFC polarity: Because
the Gunn Oscillator's frequency may be either above or below that of
the other station's frequency, this affects AFC operation in that if
the polarity of the AFC circuit is set improperly, it will always "push
away" a received signal rather than lock onto it. Of course, this
does not happen if the AFC is only used in the 30 MHz receiver's LO
(rather than on the Gunn oscillator) but also note that in this case
the "other" person in the QSO does not benefit directly from the AFC
The Ramsey documentation suggests powering of the receiver with a 9
volt battery - but it is strongly recommended that a 12 volt supply,
regulated down to 9-10 volts, be used instead with the use of a
3-terminal regulator such as a 7809 or a simple transistor-Zener
regulator. The use of a regulated supply will improve the
stability of the receiver as its tuning will drift as battery voltage
drops, but the use of a "stiffer" supply will improve stability of the
receiver as the current consumed by the audio amplifier would
"modulate" the power supply voltage: Such supply voltage
modulation will cause distortion or feedback to occur in the audio or,
even worse, an annoying frequency drift in response to audio -
particularly if a weak 9 volt battery were used.
Note that ONLY "-4" version of the
amplifier (U2) is rated for operation above 12 volts: Do not
operate the LM386-1, LM386-3, or un-suffixed versions above 12 volts!
U1, the FM audio detector in the FR1C, is
shown as being a ULN2111. This is the same as the:
MC1357P. The more commonly-available (but also
made by Motorola.
MP5071 - a compatible variant often found in older
NTE708 - This may may be found as a replacement item
online or (possibly) at your local electronics store.
comments on Gunn transceivers:
of a MMIC preamplifier at the Gunn transceiver's mixer diode:
Additional details of the MMIC circuit will be added here in the
It was mentioned above that better receiver system performance may
obtained by installing a MMIC preamplifier directly on the Gunn
transceiver module itself to amplify the signal from the detector
diode. A good choice for this MMIC is the MAR-6 (a.k.a. the
MSA0685) MMIC which may be obtained from DownEast Microwave. This
MMIC has a fairly low noise figure (under 3 dB) and moderately high
(about 20 dB at 30 MHz) and is useful for overcoming cable losses
between the Gunn transceiver and the IF receiver. An added
benefit is that it also offers some protection to
the fragile mixer diode, protecting it from static discharges that
might enter through the IF line connecting to the receiver.
This MMIC consumes only about 16 mA and one typically constructs the
(very simple) circuit on a small piece of circuit board mounted
directly on the Gunn transceiver right at the mixer diode connection.
The use of a MMIC preamplifier on a Gunn oscillator without
a mixer diode:
It was recently noted that there are some surplus Gunn units on the
market that do not have a mixer diode, but these units
were still used as microwave motion detectors - a task that implicitly requires
a means of detection. After some puzzlement, Ron Jones, K7RJ,
determined that the Gunn diode itself was being used as the
detector diode: This feat is possible only because there is
relatively heavy coupling between the Gunn oscillator cavity and the
feedhorn (e.g. a very large iris) and through careful decoupling of the
power supply and the detected signal.
In some very crude testing, Ron determined that this "dual use" of
the Gunn diode also worked at IF as well. In his tests Ron did not
make any attempt to optimize either the Gunn diode's power supply
decoupling or IF signal coupling/matching but was able
to make successful QSOs over a distance of a dozen miles. While
it is expected that the ultimate sensitivity of this detector scheme is
less than that of the "traditional" mixer diode, it is also strongly
suspected that Ron's first attempts to couple the received signals from
the Gunn diode working as a detector could be greatly improved upon -
notably through proper impedance matching and low-noise amplification-
using a MMIC.
At the present time, further experimentation to determine an
optimal means of coupling to the "Gunn diode as a detector" has not
The reader is solely responsible
for the modifications made to the
FR1 and there are no guarantees that the receiver and/or
modifications described will be suitable for your applications.
This page is not meant as a
product endorsement of Ramsey's products, but rather as a resource to
direct interested parties to a potential source of equipment for the