Motorola = Vertex

Jan 1, 2018 Motorola Solutions and Vertex Standard will join forces under the Motorola Solutions brand.
Vertex Standard models rebranded as Motorola Solutions: VX-260 Series, VX-450 Series, VX-2100 and VX-2200 mobiles, EVX-261 and EVX-S24

No word on the 6550 being released with a japanese manual


Yaesu Ft-101 E pricing 1977 – WOW a G Note?

When i got licensed back in the 70s the FT-101E was the popular radio until Kenwood released their excellent TS-820s (owner of both). The Yaesu was market leader because you were able to add a crystal and get on 11m for Freeband and 100w CB action.

The optional fan was the key item to add and most used the 4 pin Turner 3 or D104 mic.

You had a couple of choices of where to buy it : Hamtraders or VE Amatuer radio sales.

Canadian Yaesu Prices Apr.77

Hiker Go Kits for QRP Action in the Field

Here are some go kit ideas for qrp

I am still working on a tuner-less set up for the mtr3b set up but I did find the correct pelican box for it. I am looking at the St Louis series of antennas or will go with the Altoids L-Tuner. I am not kidding a couple of 9v work like a charm. About 2 watts output on 40 or 20m – no problemo. It was this or an icom 5100…icom lost

LMR qrp go kit.jpgsota kit

Learn How Transceiver work using the BITX40

This adds some effort by Goran VE6GPO to put a block diagram together that in conjunction with the schematic and the Ashhar’s description will give you some excellent information on how transceivers work.

42 years ago when i was licensed you had to know this stuff plus the morse code to get your ticket. I know that things have changed over the years but I am still excited when other hams start building stuff and figuring out how things work.

To really delve into this deeper you should buy one as they are cheap and support local labour efforts. Its amazing how you can make contacts with 5-7 watts with a dipole.

I will add the block diagram before the schematic. This block diagram is the key to understanding how the radio works.

BITX40 – Circuit Description

– Ashhar Farhan, VU2ESE

The original BITX was published on the Internet in the year 2003. In the last 13 years, it has grown to become one of the most popular rigs among radio amateurs around the world. The BITX40 board is this very classic now available as a fully tested board that is easy to hookup, modify and operate. You can read the original article that described the BITX at


Download the circuit diagrams »

What’s special about this version of the BITX?

  • Uses a 12 MHz IF and a Si5351 at 5 MHz as a rock solid local oscillator
  • The entire transceiver fits into a single large and easily accessible PCB
  • Though it works on 40 meters, it is easy to change coils and work it on other bands (details to be released soon)
  • It has a separate power line for the PA. By increasing the PA power voltage, the transmit power can be increased
  • The components supplied with the board will get you up on air without any special skill
  • Read the Wire Up to understand how it is hooked up

Development Notes

Almost all modes of radio communications share a natural principle that the receivers and transmitters use the same line-up of circuit blocks except that the signal direction is reversed. The CW direct conversion transceiver is the simplest illustration of this principle. A more complex example is the bidirectional SSB transceiver.

Bi-directional SSB transceivers have been quite common in amateur literature. A transceiver was described in the ARRL SSB Handbook using bipolar transistors. W7UDM’s design of bidirectional amplifier (as the basis of bidirectional transceiver) is referred to by Hayward and DeMaw in their book Solid State Design. The bidirectional circuitry is often complex and not approachable by the experimenter with modest capability.

The Raduino

The Raduino is a very powerful, hackable, easy to program board that comes loaded with the BITX40 software. The lower side OSCILLATORS connector has 16 pins. A 5 pin header that sits on it takes 12v, ground, and also provides the DDS output to be connected to the main board’s DDS connector. An 8 pin CONTROLS connector on the top connects to the tuning pot and future switches and controls. The tuning system is very precise and easy. The tuning pot covers 50 KHz of the band and the edge of the tuning pot’s range allow you to scan up and down the rest of the band in 10 KHz steps.

The broad band bi-directional amplifier

My interest in bidirectional transceivers arose after looking at an RC coupled bidirectional amplifier in the book Experimental Methods in RF Design (p. 6.61). An easily analyzed circuit that was simple and robust was required. It began its life as an ordinary broad-band amplifier:

There are some interesting things about this circuit:

  • The power gain, and the input and output impedances are all related to the resistor values and do not depend upon individual transistor characteristics. We only assume that the transistor gain is sufficiently high throughout the frequencies of our interest. The precise value of the transistor characteristics will only limit the upper frequency of usable bandwidth of such an amplifier. This is a useful property and it means that we can substitute one transistor for another. You can use 2N3904, BC547, 2N2222, etc. Just about any transistor will do!
  • The power gain is not a function of a particular transistor type. We use much lower gain than possible if the transistor was running flat out. But the gain is controlled at all frequencies for this amplifier. This means that this amplifier will be unconditionally stable (it won’t exhibit unusual gain at difference frequencies).

In order to make bidirectional amplifiers, we strap two such amplifiers together, back to back. By applying power to either of amplifiers, we can control the direction of amplification. This is the topology used in the signal chain of this transceiver. The diodes in the collectors prevent the switched-off transistor’s collector resistor (220 ohms) from loading the input of the other transistor. A close look will reveal that the AC feedback resistance consists of two 2.2K resistors in parallel, bringing the effective feedback resistance to 1.1K. All stages of amplification in this transceiver work this principle.

Diode mixers

The diode mixers are inherently broadband and bidirectional in nature. This is good and bad. It is good because the design is non-critical and putting 8 turns or 20 turns on the mixer transformer will not make much of a difference to the performance except at the edges of the entire spectrum of operation.

The badness is a little tougher to explain. Imagine that the output of a hypothetical mixer is being fed to the next stage that is not properly tuned to the output frequency. In such a case, the output of the mixer cannot be transferred to the next stage and it reflects back into the mixer. Ordinarily, if the mixer was a FET or a bipolar device, this reflected power just heats up the output coils. In case of diode ring mixers, you should remember that these devices are capable of taking input and outputs from any port (and these inputs and outputs can be from a large piece of HF spectrum), hence the mixer output at non-IF frequencies reflects back in the mixer and mixes up once more creating a terrible mess in terms of generating whistles, weird signals and distorting the original signal by stamping all over it.

A simple LC band pass filter that immediately follows the diode ring mixer will do a good job only at the frequencies it is tuned to. At other frequencies, it will offer reactive impedance that can cause the above mentioned problems. It is a requirement that the diode mixer’s input and output ports see the required 50 ohms termination at all the frequencies. In other words, they require proper broadband termination. Using broad-band amplifiers is a good and modest way of ensuring that. A diplexer and a hybrid coupling network is a better way, but it would be too complex for this design.

Circuit Description

Although simple, every effort was made to coax as much performance as was possible given the limitations of keeping the circuit simple and affordable.

The Receiver

The RF front-end uses a high performance 3 section band-pass filter for strong image and IF rejection. The three poles of filtering provide for a no-tune bandpass filter that needs no adjustment.

The 7 MHz bandpass filter. Each vertical division is 5 MHz

The RF Amps

An RF amplifier follows the RF band pass filter (Q1). There is 8mAs through the RF amplifier and the post-mix amplifiers to keep the signal handling capacity of the circuit above average. The Post-mix amplifier (Q2) does the job of keeping the crystal filter as well as the diode mixer properly terminated. The crispness of the receiver is more due to this stage than anything else. An improper post-mix amplifier easily degrades the crystal filter’s shape and introduces spurious signals and whistles from the diode mixer.

The Optional VCO

The BITX40 is supplied with the Raduino to make drift free, precise tuning easy. For the purists, a voltage controlled oscillator that covers 4.8 Mhz to 5 Mhz to cover the 7.0 Mhz to 7.2 MHz is an alternative. Just plug out the Raduino and solder the supplied yellow VFO coil. A varactor was chosen over a variable capacitor as it is easier to tune. Mounting a VFO capacitor properly is difficult. Good quality tuning capacitors are nolonger available. Those who like slower tuning rates with the VCO could use a multiturn 10K linear pot instead of a regular potentiometer. The VCO is fed via a broad-band amplifier into the doubly balanced mixer. The trimmer provides exact band covereage. This oscillator has low noise though it does drift a little like all analog oscillators. It settles down to a very imperceptible drift within 10 minutes of warm up. Tip: Turn the BITX40 on for a few minutes before actual use to avoid the warm up drift. The receiver withe the VCO takes just 90 mA current.

The Crystal filter

 The 12 Mhz crystal filter follows a Cohn topology. All the capacitors around it are 100pf. We use just 4 crystals to keep the ringing down and side-band suppression is 40 db. The receiver sounds exceptionally clean because of this crystal filter and the low noise oscillators.

BFO, Detector and Audio

The BFO is a plain RC coupled crystal oscillator with an emitter follower. The emitter follower has been biased to 6V to prevent limiting. The detector also doubles up as the modulator during transmit mode; hence it is properly terminated with an attenuator pad. It has no impact on the overall noise figure as there is enough gain before the detector. The Q13 audio pre-amplifier is a single stage audio amplifier. The 100pf capacitor across the base and collector provides for low frequency response. The receiver does not have an AGC. This is not a major short-coming. Manual gain control allows you to control the noise floor of the receiver and I personally find it very useful when searching for weak signals or turning it down to enjoy the local ragchew.


The microphone amplifier has a DC bias for the mic. This is required for the electret microphone that is supplied with the kit. The common Personal Computer type of headset too need this bias voltage. If your microphone does not require any bias, then insert a 1uF in series with the microphone. The microphone amplifier is a simple single stage audio amplifier. It does not have any band pass shaping components as the SSB filter ahead will take care of it all. One 0.001uf at the microphone input and another at the modulator output provide bypass for any stray RF pickup.

The two diode balanced modulator has a simple balance control. The attenuator pad at the output was found necessary to properly terminate the diode modulator and keep the carrier leakage around the IF amplifier to a minimum.

Rest of the transmission circuitry is exactly the same as the receiver. There is an extra stage of amplification (Q13) to boost the very low level 7 MHz SSB signal from output of the bandpass filter to 1V level : enough to directly drive a driver stage.

Inductor data

The inductors used on the board as follows:

  • L1, L2, L3 : 6uh, 40 turns on T30-6 core
  • L4 : Only needed the analog VFO, 9uh, 50 turns on T30-6 core
  • L5 : just a jumper on the standard bitx40, you will have to an inductor of a few uh to pull the BFO down for upper-sideband
  • L6, L7 : 1.1 uh, 17 turns on T30-6 core
  • L8 : 10 turns on FT37-43
  • T1,T2,T4,T5,T6,T7 : 10 turns trifilar on FT 37-43 core

The L1,L2,L3,L4 need a wire gauge thin enough for the large number of turns. We use 36swg enamelled copper wire, you can use thinner wire if you have any. The rest of the transformers and inductors have use 28 swg.

Note: The L4 is not required with the Raduino or any other digital VFO. The L5 is needed only if you want to operate USB (to pull the BFO to the lower slope of the crystal filter).

Short Antennas for Mobile Operation September 1953 QST Article

Short Antennas for Mobile Operation
September 1953 QST Article

September 1953 QST

September 1953 QST Cover - RF CafeTable of Contents

Wax nostalgic about and learn from the history of early electronics. See articles from ARRL‘s QST, published December 1915 – present. All copyrights hereby acknowledged.

Here is a very in-depth and comprehensive discussion on antenna system design and evaluation for a mobile platform; i.e., a car or truck. As was common with QST articles of yore, there is a plethora of equations, sketches, graphs, and tables provided for reference. Radiation resistance, ground resistance, system impedance, antenna tuning, radiation efficiency, current distributions, and much more are introduced and explained. Even being six decades old, the information is as valuable today as it was then.

Short Antennas for Mobile Operation

Loading the Whip for Low Frequencies

By J. S. Belrose, VE3BLW

Many of those who have 75-meter mobile installations do not understand that if all of the power output from a mobile transmitter could be fed to a short whip, almost 100 per cent of it would be radiated. The problem in getting power into the antenna is definitely one of eliminating losses in the system. In this article, VE3BLW discusses the various points ill the antenna circuit where these losses are introduced and how they can be minimized.

Equivalent circuit of a short vertical radiator - RF Cafe

Fig. 1 – Equivalent circuit of a short vertical radiator.

Seventy-five-meter mobile radio operation is becoming quite popular both in Canada and in the United States. Many types of antennas have been used, such as simple base-loaded whips, center-loaded whips, top-loaded whips having disks, metal balls, or spoked wheels, and folded antennas. Several articles have been published in QST1, 2, 3 on low-frequency antennas for mobile use. However, the exact operation of a short vertical antenna is not too well understood by a good number of those using the antenna. I would like to try to explain clearly, on a mathematical basis, the operation and design considerations for a short antenna.

The fundamental frequency of a vertical radiator is the lowest frequency for which the reactance is zero at the customary feed point – between the lower end of the radiator and ground. At this frequency, the electrical length of the antenna is 90 degrees, or a quarter wavelength.

Vertical radiators which are short electrically have low radiation resistance and relatively high capacitive reactance. At frequencies near the operating frequency the antenna can be considered as being a lumped circuit which consists of a resistance and a capacitance in series, as shown in Fig. 1.

Here, Ra is the total antenna resistance, which includes principally the radiation resistance and the ground-loss resistance, and Xa is the capacitive reactance of the antenna at the operating frequency. It is clear that in order for this antenna to take power, the capacitive reactance of the antenna must be tuned out by a suitable inductor. The inductor introduces additional resistance, and the object in design is to obtain the highest practical ratio of radiation resistance to loss resistance.

In what follows, I propose to analyze the radiation efficiencies, bandwidths, and practical construction of base-loaded and center-loaded whip antennas. The expected range, for ground-wave propagation, is discussed, and it is shown mathematically that a better range is possible using 160 meters rather than 75 meters.

Definition of Radiation Efficiency

The total useful power radiated from an antenna can be considered as being that which would be dissipated in a fictitious resistance with the antenna current, at the point of reference, flowing through it. Normally, the current is measured at the base of the antenna, and therefore the radiation resistance is referred to the base of the antenna.

Pr = Ia2Rr watts,

where Pr = power radiated,

Ia = antenna current,

and Rr = radiation resistance.

The radiation efficiency of an antenna is the ratio of the radiation resistance to the total resistance of the antenna system.

radiation efficiency - RF Cafe

where Rr = radiation resistance,

Rg = ground-loss resistance,

and Rc = tuning-coil-loss resistance.

Under proper conditions, insulator-loss resistance and conductor-loss resistance can be neglected. Since the loss resistances are generally greater than the radiation resistance, for short antennas, careful design must be used to engineer a usable antenna system.

Radiation Resistance

The radiation resistance of a vertical antenna less than an electrical quarter wavelength is increased by top loading and by increasing the height. For short radiators, it can be shown that4

Rr = 0.01215A2 ohms,

where A = degree-ampere plot of current distribution on the antenna.

Current distribution on a short vertical antenna - RF Cafe

Fig. 2 – Current distribution on a short vertical antenna.

Consider the current distribution on a short vertical radiator. The current will be some value, I0 at the base of the antenna, and zero at the top of the radiator. If the antenna is very short – less than 30 degrees – the current distribution can be assumed to be linear. This is shown in Fig. 2.

For example, assume that

h = 110 inches (2.79 meters),

f = 3.81 Mc. (78.6 meters).

Then, Gv = electrical height of antenna in degrees

electrical height - RF Cafe

So current = RF Cafe

= 6.4 degree-amperes,

and Rr = 0.01215(6.4)2 = 0.5 ohm.

Current distribution on a sectionalized or center-loaded antenna - RF Cafe

Fig. 3 – Current distribution on a sectionalized or center-loaded antenna.

Now consider the effect of introducing a series loading coil, as shown in Fig. 3. If the inductance of the loading coil is zero, the current distribution will be curve (1), as shown in Fig. 3. This is obviously that of a simple base-loaded radiator, as shown in Fig. 2. As the inductance is increased from zero, the current distribution is modified to that of curve (2). At some value of inductance, L0, the input impedance of the antenna as seen between the base of the antenna and ground is a pure resistance with no reactive component. For this value of inductance, L0, we have the maximum current area on portion h2. This is shown as curve (3) of Fig. 3. For this condition, the current flowing through L0,

I1 = I0 cos G2,

where G2 = electrical height of h2 in degrees (similarly G1 = electrical height of h1)

For example, assume that

h1 = h2 = 55 inches (1.4 meters),

and G1 = G2 = 6.4 degrees (at 3.81 Mc.).

Hence, I1 = I0 cos 6.4° = 0.995 I0

Amperage equation - RF Cafe

= 9.57 degree-amperes,

and Rr = 0.01215 (9.57)2 = 1.11 ohms.

It is clear that a considerable increase in the radiation resistance is obtained by placing the inductance in the center portion of the radiator.

Ground-Loss Resistance

Current loop for a vertical radiator mounted on a car- RF CAfe

Fig. 4 – Current loop for a vertical radiator mounted on a car.

The current flowing at the base of the antenna must be returned to the base of the antenna by currents induced in the ground beneath the radiator. These currents must be collected by the car body and through the capacitance of the car body to the ground. Since the area of the car body is considerably less than a quarter wavelength, only a portion of these currents will be collected by the car frame itself, and the rest will be collected by ground currents flowing through the capacitance of the car to the ground. Since the ground is not lossless, quite a large loss resistance, Rg, is found. The current path is shown in Fig. 4.

In the past, writers have neglected this loss resistance. This resistance will be a function of the positioning of the radiator, the type of car on which the antenna is mounted, and to some extent on the ground beneath the radiator. A value of 10 to 12 ohms has been measured by the author for 8- to 16-foot antennas at 3.8 Mc.

Tuning-Coil-Loss Resistance

In order that a short antenna will take power, the capacitive reactance of the antenna must be tuned out by means of a suitable tuning coil. To estimate the inductance required, we need to know the capacitive reactance of the antenna at the operating frequency. The reactance of a short vertical antenna, such as shown in Fig. 2, is

tuning coil equation - RF Cafe

h = average height of radiator above ground,

a = average radius of radiator,

and Gv = electrical height of radiator.

For example, let us calculate the reactance of the base-loaded antenna shown in Fig. 5.

Fig. 5 – Vertical radi­ator mounted on a car.

height equation - RF Cafe

a = 0.125 inch,

impedance equation - RF Cafe

and Gv = 12.8° (at 3.81 Mc.) (Add 5 per cent for spurious end effects.)

reactance equation - RF Cafe

A tuning coil of 73.4 μh. is required to supply an equivalent positive reactance at 3.81 Mc.

If the coil has a Q-factor of 300, then

resistance equation - RF Cafe

Now consider the sectionalized antenna, as shown in Fig. 3. Firstly, we calculate the reactance of the top portion. From this we subtract the lumped reactance of the loading coil, and finally the input reactance of the antenna is calculated by assuming the lower portion an opened-out transmission line, terminated in the resultant reactance of the loading coil and the top section. If the antenna is resonated so that the base reactance is zero, it can be shown that the reactance of the inductor required is

jXL0 = jZ0 (cotan G1 – tan G2) ohms,

where Z0 = characteristic impedance of antenna (as before),

G1 = electrical length of top portion of antenna,

and G2 = electrical length of bottom portion of antenna.

For example, suppose we have the antenna system of Fig. 6.

height formula - RF Cafe

a = 0.125 inch,

Z0 = 418 ohms (as before),

and G1 = G2 = 6.4° (at 3.81 Mc.)

(Add 5 per cent for spurious end effects.)

jXL0 = j418 (cotan 6.71° – tan 6.71°)

= j3500 ohms, or 146.3 μh. at 3.81 Mc.

If a coil with a Q-factor of 300 is used, the coil-loss resistance,

coil resistance - RF Cafe

Bandwidth of Antenna System

Center-loaded whip mounted on a car - RF Cafe

Fig. 6 – Center-loaded whip mounted on a car.

For frequencies near resonance, the antenna may be considered as a lumped circuit with a Q-factor of

"Q" equatino - RF Cafe

where Rt = total antenna resistance.

The operating bandwidth of the antenna is therefore approximately

bandwidth equation - RF Cafe

For the vertical base-loaded whip described,

Rt = Rr + Rg + Rc = 0.5 + 10 + 5.85 = 16.35 ohms.

For the center-loaded antenna described,

delta frequency - RF Cafe

It must be remembered that a bandwidth of 5 kc. is required for double-sideband a.m. ‘phone operation. The bandwidth of both antennas described above is adequate. However, the proximity of near-by metal objects can cause considerable detuning of the circuit. Also, very little shift in operating frequency can be allowed without retuning the antenna.

Theoretical Radiation Efficiency

The radiation efficiency of an antenna was shown to be the radiation resistance divided by the total resistance, or

radiation efficiency (1) - RF Cafe

For the 110-inch base-loaded whip,

radiation efficiency (2) - RF CafeFor the 110-inch center-loaded whip,

radiation efficiency (3) - RF CafeIt is clear that a small but worthwhile improvement is obtained by center-loading the antenna.

However, this is gained at the expense of reduced operating bandwidth, and increased mechanical-construction problems.

Determination of the Optimum Location of the Loading Coil

Graph showing optimum location for loading coil - RF Cafe

Fig. 7 – Graph showing optimum location for loading coil.

Suppose we have a 16-foot whip antenna. The antenna is bumper-mounted, the base insulator being 2 feet from the ground. The average radius of the radiator is 0.18 inch. We decide to load this antenna by introducing a loading coil in series with the antenna, and would like to know where this coil should be placed for maximum radiation efficiency. If we choose a coil Q-factor

of 300, and a ground resistance of 10 ohms, the graph in Fig. 7 shows the calculated variation of radiation efficiency with the ratio h2/h1. The ratio h2/h1 = 0 is, of course, the case of a base-loaded antenna. It is seen that the best location for the coil is approximately in the center of the radiator (or h2/h1 = 1). The curve for no ground-loss resistance is also shown. It is noted how the optimum location of the coil is shifted toward the feed point as the ground-loss resistance is reduced.

Field Measurements of Radiation Resistance

The actual measurement of radiation resistance of an antenna at 3.81 Mc. is difficult, and involves equipment not normally available to the average amateur. However, to show that measurements. can be taken to prove the theory we have developed, I think a short discussion of the principles involved would be in order.

The surface-wave field intensity (that is, for grounded radiators) from a short radiator can be expressed in terms of radiated power, distance, and propagation factor for the ground between the transmitter and receiver by the following expressions:

power, resistance - RF Cafe

where F0 = unattenuated field strength at one mile in millivolts-per-meter,

k = propagation factor to take account of ground conductivity, dielectric constant of the ground, and diffraction due to curvature of the earth,

d = distance in miles,

F = field strength received at distance d, and

Pr = power radiated.

Graph showing variation of ground-wave field intensity - RF Cafe

Fig. 8 – Graph showing variation of ground-wave field intensity with distance for poor to good ground. σ = ground conductivity, Frequency = 3.8 Mc. Ground dielectric constant ξ = 15.

The first step necessary in order actually to measure the radiation resistance of the antenna is to determine how the ground influences the electric field. To determine this, we must make several measurements of the field strength at distances out to at least 10 miles from the transmitter. In this way a graph showing field strength against distance can be plotted. Comparison with a set of theoretical curves, as shown in Fig. 8, after Norton,5 is then made. In Fig. 8, several curves are shown ranging from poor ground (σ = 2 X 1014) to good ground (σ = 15 X 1014). The propagation factor, k, is the ratio, at distance d, of the unattenuated or inverse-distance field strength, divided by the actual field strength predicted by the curve for a particular ground conductivity.

Once the power radiated is found, then the radiation resistance,

radiation rsistance - RF Cafe

where Ia = base current. This is obvious, since the actual power radiated can be considered as being the real power dissipated in a fictitious radiation resistance.

Measurements on an Actual Antenna

A sectionalized 16-foot antenna was built.

h1 = 6.86 feet,

h2 = 9.29 feet,

a = 0.18 inch, and

f = 3.81 Mc.

The antenna was bumper-mounted on a 1940 Dodge sedan, the base being 272 feet above the ground. Suppose we design a suitable coil so that the input impedance at 3.81 Mc. is a pure resistance.

characeristic impedance - RF Cafe

L-section match - RF Cafe

Fig. 9 – L-section match.

A coil 2 inches in diameter was wound with 66 turns of No. 14 enameled wire. The inductance was found to be 97.6 μh. with a coil Q-factor of 170. This was installed. The resonant frequency was found to be 3.81 Mc. with an input resistance of 29.7 ohms. This was measured with a General Radio r.f. bridge type 916-A, an Eddystone receiver type 750, and an A.V.O. signal generator. The equipment was battery-operated and isolated from ground.

To calculate the radiation resistance, refer to Fig. 3. Substituting in appropriate values,

antenna current - RF CafeTherefore, the ground-loss resistance must be

ground resistance - RF Cafe

Antenna characteristics chart - RF CafeTo check the calculated figures, the field intensity was measured 0.284 miles from the antenna using a Stoddart field-intensity meter type NM-20-A. Preliminary measurements indicated a ground conductivity of 10 X 10-14

The results are as follows:

f = 3.81 Mc.,

F = 3.5 mv./m.,

d = 0.284 miles,

k = 2.06 (see Fig. 8 where a = 10 X 10-14), and

Ia = 0.185 amperes.


F0 = Fkd = 3.5(2.06)(0.284) = 2.04 mv/m,

power, resistance formulas - RF CafeThe agreement of measured with calculated values for radiation resistance is better than normally experimentally obtained due to the many parameters involved. It is noted that the radiated power is 0.121 watt. The power input to the antenna was supplied by a single Type 6AQ5 tube and is

Pin = (0.185)2 29.7 = 1.01 watts.

This corresponds to a radiation efficiency of 12%.

Tuning and Matching Center-Loaded Whips

Adjusting antenna to resonance - RF Cafe

Fig. 10 – Adjusting antenna to resonance.

A method of matching the antenna to the transmitter will now be considered, and a method outlined by which the antenna can be tuned using a g.d.o. and an s.w.r. detector (equipment normally owned by the average amateur).

Firstly, let us consider what matching involves. If we consider the 16-foot antenna just discussed, the input impedance at resonance was a pure resistance equal to 29.7 ohms. We must transform this low value to 50 ohms so that the antenna can be fed with standard coaxial cable (RG-8/U or RG-58/U). This can be done with an L-section matching unit as shown in Fig. 9.

L-section equation - RF Cafe

Substituting values,

reactance formula - RF CafeNow the inductance, L, can be artificially obtained by adding just a small amount more inductance to L0 the center-loading coil, than needed for resonance, thus making the antenna input impedance inductive. An exact match to 50 ohms can be obtained by adjusting the condenser, C, and the center-loading inductance, L0.

Matching antenna - RF Cafe

Fig. 11 – Matching antenna.

First, resonate the antenna by a. g.d.o. as shown in Fig. 10. Power is coupled into the antenna from a 50-ohm transformer. In my case the output tank circuit is a pi-tank. See Fig. 11 for set-up. Adjust the condenser, C, in small increasing steps, resonating each time by adjusting the center-loading coil for maximum current. For some value of C near 690 μμf the antenna will draw maximum current and show no detuning effects at the transmitter end. An s.w.r. detector will also indicate a minimum s.w.r. for this adjustment.

(Note: L and C of Fig. 9 can be reversed. A small coil could be used instead of condenser C. The coil should have an inductance of 2.45 μh. – i.e., 60.6 ohms. The antenna must be tuned slightly capacitive. That is, resonate the antenna alone as before, and subtract turns from L0 to resonate again after introducing the small matching coil. This method has certain advantages, and its use should be considered.)


Adding more capacitance - RF Cafe

Fig. 12 – Adding more capacitance.

In conclusion, I hope that I have made clear the factors involved in antenna design and also the considerations in matching the antenna to 50 or 70 ohms so that it can be fed with standard coaxial cable. It is shown that some improvement can be obtained by center loading – a gain of 1.5 in power – but this may not always be worthwhile since the mechanical problem of fixing a good high-Q coil in the center of the whip is difficult. The diameter-to-length ratio of the coil should be 2/1 if possible.

The placement of a spoked-wheel-type disk, as shown in Fig. 12, could be used to provide a substantial reduction in the size of the loading coil required. For example, a 1-foot-diameter ring of No. 12 with eight spokes has a capacitance equivalent to the length of the radiator h1 for the experimental 16-foot antenna discussed. However, it is felt by the author that such means are not adaptable to mobile antennas, since cumbersome structures like this are rather sorry-looking sights after striking a tree branch at 50 miles per hour.

Choosing the Optimum Frequency Let us consider whether it would be better to use 1.9 Mc. rather than 3.8 Mc. At first thought, one might say not, since the antenna efficiency will be much lower. However, the lower ground-wave propagation factor overcompensates for this. The variation of the propagation factor with frequency and distance is shown in Fig. 11 for good ground (σ – = 10 X 10-14)

If we assume a transmitter power of 50 watts, an antenna as shown in Fig. 5, coil Q-factors of 300, and ground-loss resistance of 10 ohms, the results for transmission over 10, 30, and 50 miles are shown in the accompanying tables.

Graph showing variation of propagation factor - RF Cafe

Fig. 13 – Graph showing variation of propagation factor, k, with frequency and distance for good ground (i.e., conductivity σ = 10 X 10-14, and dielectric constant ξ = 15). Distance d is in miles.

It is seen that at all distances the received field strength is better at 1.9 Mc. than at 3.8 Mc. It is also interesting to note that the atmospheric noise level goes through a broad minimum near 2 Mc., which is another factor in favor of using 1.9 Mc. The field strength required to communicate varies with the time of day, season, frequency, and location. For frequencies near 1.9 Mc., approximately 0.5 μv./m. is required at noon for radiotelephone communication in Ontario. Many times that is required at night – 30 μv./m. at 8 P.M. in the summer, and 100 μv./m. at the same time in the winter. These estimates were taken from graphs given in Laport.6

It would be interesting if a few amateurs decided that 75-meter ‘phone is too crowded and moved down to 160 meters. I will bet a lot more would soon move down after comparing cross-channel transmissions at distances up to 50 miles. This, of course, is so only if there is no sky wave, such as a summer day. Normally low-power mobile operators on the low-frequency amateur bands communicate by ground wave.


1 Oberlies, “Installing a Practical 75-Meter Mobile Antenna,” QST, Dec., 1949.

2 Swafford, “Improved Coax Feed for Low-Frequency Mobile Antennas,” QST, Dec., 1951.

3 Wrigley, “Folded and Loaded Antennas,” QST, April, 1953.

4 Laport, Radio Antenna Engineering, p. 23, McGraw-Hill (1952).

5 Norton, “The Calculation of Ground-Wave Field Intensities Over a Finitely-Conducting Spherical Earth,” Proc. I.R.E., 29, 623 (1941).

6 Laport, Loc. cit., p. 542-555.



Mobile HF UHV VHF ANtenna Placement

I heard someone get TOLD for not understanding how antennas work in the mobile. It is very simple once you understand the following diagrams. This is something that is not taught in the typical ham class. You need a copy of the ARRL Mobile Handbook from the 50s to fully appreciate some of the cutting edge research done.

An easy way to validate this and to aid in antenna tuning is the Field Strength Meter and it will help you see the antenna pattern.

heathkit pm2

antenna placementantenna placement2

Portable QRP Field Bag for Field Ops – Mountain Bike Travel Radio

If you want to travel small and light and work some DX here is a list of my portable cw go -kit.

  • MTR3B Mountain Topper
  • American Morse DCP Paddle
  • EF-MTR 40M/30M/20M EndFedZ antenna 1.5:1 VSWR on all three bands. No tuner needed
  • 50 feet of 550 Paracord – I actually have a super light version
  • Pelican 1020 Case
  • RG-316 BNC male to SO-239 patch cord
  • PL-259 to BNC male adapter (Connects between the above two jumper cables).
  • RCA to BNC female adaptor for antenna
  • Headphones
  • ARRL MINILOG, Notebook and pen with a clipboard
  • Several 9 volt batteries. Power out is about 2 watts @9v
  • Li-on battery at 11.6V for almost 5 watts output – option for extended use
  • 4.0mm x 1.7mm DC power plug cable with a 9v battery connector
  • 4.0mm x 1.7mm DC power plug cable with a Anderson Pole connector
  • Ham 73 mobile app for logging
  • Portable Tuner – Elecraft T1, MFJ antenna tuners – various models

– Required if using non-resonant antennas. I also use the Packtenna kit and am waiting for my antenna wire order to arrive. I will have resonators for 100w and lightweight versions for 5 watts.

This will all fit in a small carry bag or molle pouches and is TSA/CBSA friendly

I need to re configure my patch cords as I want a simple RCA to bnc for the T1 tuner and another rca to pl-259 for the mfj qrp tuner

The radio is super sensitive and has a very tight audio making cw a breeze. Several memories make sending cq while pouring a thermos coffee a joy to operate.

I find the headphones work great and no need for the JBL external speaker.

The 9v alkalines are great and support more than enough daily fun and lots of contacts can be made at 2 watts on cw. I am looking at some higher current 9v niMH

I ran a very slimmed down go-kit (minimalist 1 battery, earbuds, hand key) to take when mountain biking and the results were fantastic. I use the Pelican box and then a sandwich baggy in my backpack/water bag. This is lighter than my FT-817 but then its CW only.

I am making a small hand code key so I dont have the bulk of the paddles. I tried a 3D version and the action was horrible. I may have to just resort to the hacksaw blade version.

I made a super small 9:1 balun and the swr is very good on 40m and 20m and with some #26 wire its easier to pack  and less bulky.

WE may have to rename the go-kit MBTR for the minimalist version but if you are flying out on business you can pack a few extra things in your carry on.

If you are operating hotel/motel portable then duck tape and or clips will help get the antenna from the curtains to the door in a zig zag fashion. Hey it works! Also get a high floor room half way up and ask for a balcony and if a window can open then the water bottle can be attached to the longwire and extended out the window.

Clansman PRC-320 LSB Modification

The UK Clansman PRC-320 is a USB only radio. Based on band conditions the ability to work 40m/60m and 80m is important.

But, you need LSB. If you are buying the radio from a UK stockist then have them do the mod and test the kit before shipping out. They will add a LSB toggle and then the radio is complete.

The link is here

This mod is not that easy so I strongly recommend that you get a technician that has done many of these to do it up. Taking the radio apart is half the battle


Radio Direction Finding – 1992 IRMA CSTI-1000

I worked for a local start up back in 1992 as Chief Engineer – Hardware and this is what we came up with. It started with some patents and technology transfer with the Department of Communication (Federal Government).

All radios were from the local ham supplier and a Single Board Computer (check out the specs for a good laugh) from a supplier in the back of Circuit Cellar Magazine.

Everything was pretty much COTS except for the controller board. It worked well and we had the initial Proof of Concept in Mexico. We placed these on 3 hilltops and had some great success with radio direction finding.

We also used the Traffic Study or Channel Occupancy tool which helped provide insights in signal occupancy.

Now, I am “full circle” and engaged once again in a project but its now SDR, MP3, WiLAN and message bus technology.

I spent a whole day doing up the photography for the brochure which to this day I still recall how many packs of Polaroids I went through. I also used the Instant 35mm film for proofing. Today, I could just use my Smartphone.

A typical use case would be where the radio inspector would have interference complaints. He could get the location, an audio recording with freq, time and date stamp and even activate the radio and inform the interfering station over the air that he is under investigation.

Another popular example was to track channel usage and apply that to the current spectrum management policies.

As old school as it is the IRMA would actually still work today as an effective tool.

The receiver was the Icom 7000 and yes the modem was 2400 baud.  The Discone was the AH-7000 as a switched alternate.