SOURCES; Lowband & PRC-127 Rubber Duckies
PS I haven't edited the spelling.
The most critical of these variables was radiation efficiency, frequency of operation, the real-world effects of the radio's own physical packaging, or electronic design, and all these combined with the extremely narrow band width that could be expected from an antenna that would be reduced in size to this great degree.
To explain, any shortened antenna will suffer a reduction in band width regardless of how much it has been shorted, the method used, or it's frequency of operation. These truths combined result in an extremely narrow window for operation of an antenna that has been reduced in size from a factor of about 5 to 1. So if you build an antenna to be resonant at 51 MHz in free space, or with a substitute counterpoise (radio case) it's resonance will change when it's actually installed on the radio. Being off resonance even slightly at these frequencies will result in drastically reduced radiation efficiency. When you combine this poor efficiency with the typically low power found on these type radios the result is a pretty much useless radio system.
The military's equipment used a similar short antenna/load coil system as commercial industry however they greatly improved on efficiency by making the load coil variable. Hence the antenna system could be adjusted to produce the best possible resonance. This is how it's done on such radios as the PRR-9, PRT-4, PRC-6, CPRC-26, even the PRC-68 [a side note, any of these radios will load a standard 2 mtr rubber duckie as their original antenna is nearly resonant at 2 mtrs]. In later years some commercial radio companies would follow the military's lead and replace their fixed load coils with variable ones. Though the antenna length was greatly reduced (over a full size 1/4 wave), and radiation efficiency increased, antennas were still too long & fragile to be of practical use while portable.
All these differing methods just confounded the efforts of the after market suppliers of antennas to try and produce a product that was useable among all these variables. Then we add to the dilemma the dozens of different antenna connection/mounting types, and the fact that not even one manufacturer could standardize on an antenna system in it's own product line. Motorola for instance started out with the simple high band 1/4 wave telescoping antenna & the fixed internal load coil on it's HT-200. They then went to a rubber helical type that was nearly 2 feet long on it's MH-70 (supposedly resonant). The more resent MT-500 used a rubber helical that was almost 1.5 ft long. These too used an internal coil to attempt resonance. As these last two attempts moved more of the radiating hardware to the outside of the radio they were an improvement, but they still suffered from efficiency problems associated with the fact that they could not be precisely turned to the operating frequency unless they were installed on the radio at the factory.
My first attempts to provide an efficient shortened antenna for use on these Lowband portables centered around making modifications to existing antennas. Usually old defunct CB radio varieties intended for vehicular use. They could be found at garage sales & flea markets for as little as a few cents, or even free. Of these, the all around best to work with were the short center loaded types. They offered several advantages over other designs which included smaller physical size & tough construction, better efficiency, slightly broader band width, & most important, ease of modification. The finished products in every case would greatly surpass the performance of the radio's own original equipment, or any after market/commercial antennas that were available.
Of the center loaded CB antennas, the best by far were those produced by Hygain/Hustler. They came in lengths from a 1.5 ft (Mini Twin Truckers), to around 4 ft. The heat shrink tubing could be easily removed from the load coil allowing for modification & easy replacement. And of the utmost importance, they all had what every commercial antenna lacked, that adjustable component needed to compensate for all those variables noted above. This by virtue of a set screw adjustable resonator (stinger for you CBers) so they could be put exactly on frequency regardless of the physical packaging of the radio they'd be used with.
The modifications could be very simple, or as complex as I deemed necessary. Sometimes I needed only to removing about 1/2 of the windings from the antenna's original load coil, then using a field strength meter to adjust it's resonator for maximum radiation. Other times elaborate mounting methods were explored, or the basic antenna was further shortened to a much smaller size than originally intended (for use on HT's). And believe it or not, in some cases no modifications were needed at all (details in Part II).
Some sort of flex at the antenna's base was always needed to absorb shock & prevent damage to the antenna & radio. Sometimes we simply used the spring that was originally affixed to the antenna. Other times we modified the springs from other antennas to work, but the best where those we made ourselves. Borrowing from the military's design that had been in use ever sense WW-II, we often stole the flexible goose neck type hardware from old desk lamps, cut it up, and fashioned the needed fixtures to approximate the effectiveness of the goose neck antenna bases used on the BC-1000, PRC-10, & PRC-25/77. It looked & worked Great!
Antennas as short as 1 ft were made for use on larger HT's like the FM-2 (slightly smaller than a BC-611), and as long as 2-3 ft for use on the GE & Motorola Draggie Talkies. Adjustment was simple, though a little more difficult than setting up a vehicular antenna where a SWR meter could be used. When making an antenna for use on a portable there is no way to make a connection between the radio & the antenna for taking SWR measurements that will not adversely affect the system's resonance, or result in false readings caused by the extra hardware that's been temporarily connected to the system (not to inter into the SWR debate). So a field strength meter is the only option.
To adjust the antenna/radio combination, the radio with antenna affixed is situated in a position free of obstructions that can be exactly repeated. i.e. if you have a need to move the radio to make modifications, you want to be able to put it back in exactly the same place for the next check. A field strength meter is then placed as far away as possible yet remaining visible from the radio's location, it too must remain stationary so as to not mess up repeated measurements. An FS meter built to accept either a remote antenna, or external meter movement, is great for this application as then the RF sensing portion of the meter can be remotely located while the meter movement itself is setting next to you.
The antenna's resonator ("stinger", or whatever else is used to make fine adjustments) is placed in the center of it's travel. Key down the radio & take an initial reading on the FS meter. Move the resonator to it's minimum & maximum settings taking FS readings at each extreme. If the FS reading went up at the resonator's maximum setting the antenna most like too short. Likewise, if the FS reading went up at the resonators lowest extreme then the antenna is most likely too long. In either case spreading, and or compressing the turns in the load coil may get you closer to your goal. If not, and your antenna was too long, great, now begin removing windings one turn at a time until a max FS reading is achieved. If you remove one too many turns simply compensate with an adjustment of the resonator.
Another method that would get the antenna in the ball park, or at least let you know where it was basically resonant while saving some wear & tear on your radio involves the use of a signal generator. Connect the antenna to the signal generator & advance it's frequency while watching the FS meter. When the max FS reading is found, simply look at the Signal generator's frequency & you'll see where the antenna is approximately resonant. Final adjustment of the antenna must still be made on the radio it will be used with.
These same procedures may also be used for bands other than 6 meters, and with other antenna types. Base loaded, Top loaded, and fiberglass whips may all be used in much the same way, but each suffers from it's own draw back. Base loaded types while they are typically very damage resistant tend to be slightly less efficient than the top or center loaded breed. Additionally, only the very high quality types will allow you to gain access to the load coil, even then you may destroy it trying.
Fiberglass whips (usually top loaded) are very efficient, and do allow modification but they are stiff as a board thus poorly suited for use on most portables (they will however make great mobile antennas). Center loaded antennas are generally very tough, have good efficiency, and are the easiest to modify.
If you have an HT that uses an internal load coil, you can use a duckie that was intended for use on 2 meters (or the high band VHF spectrum). This is because most early HT's had an original antenna that was actually intended for use at these frequencies (telescoping 1/4 wave). You may have only one obstacle however. The internal load coil may not be suitable, and if it's the fixed type, you can bet it's not (especially if you have changed the radio's original frequency). If you have an adjustable internal load coil, you need go no further, this will tune about any type antenna you screw to the radio. It will not however be as effective as one that is actually resonant. In fact, it will be just a little better than keying into a light bulb. Compare the effectiveness of the PRC-68 when it's 6" antenna is used (advertised 300 yard range which is actually closer to 100 yards), and it's longer rubber helical (about 1.5 ft) with it's approx 1 mile range (usually a little better).
If your HT has a fixed internal load coil you still have an option. You can replace this fixed load coil with an adjustable one. An original coil may still be available from the manufacturer (many producers of lowband HT's replaced the fixed coil with an adjustable one towards the end of production). Alternately I have robbed the coils from old 49 MHz radios and used them in my HT's combined with a rubber duckie antenna similar to those used on the PRC-127 (see "Sources" column below). It worked reasonably will.
But of the options available, the best is an antenna that is actually resonant at the frequency in use. For instance, the internal load coil/PRC-127 combo noted above worked well up to about one mile (talking to a like radio). When the internal load coil was removed, and a resonant 10" commercial antenna was installed, this range was more than doubled.
To close, when you see
those old CB antennas at garage sales, flea markets, Hamfest etc,
don't stick your nose up at them. If they are cheep, buy um! Every
part of it regardless of it's size will someday be useful. And the
older it is, the better. And if your lucky, each hamfest might
yield a bundle or two of them in the dumpsters at the end of the
fest. There is only one exception, stay away from all the Oriental
imports! They are all, without exception, JUNK! All my 2, 6, &
10 meter antennas are made from old junk CB antennas (base,
mobile, and portable), as well as some expedient antennas for my
PRC-25, -47, -70, & -74, but
those are another story.
By far the most common
connection used on our military radios to affix the portable whip
antenna is a front panel 3/8 x 24 threaded base/mount. 3/8 x
24 has been the industry standard thread for mobile antennas ever
sense an need for a portable/mobile antenna was first perceived
back in the 1930's. This universal thread is used on antennas for
every conceivable application to include Commercial, Ham, CB,
& Military, MF, HF & VHF alike. As a result, we have over
60 years worth of junk from hundreds of sources to obtain our
[Brooke's note: when you click on the AB-591 spring base
photo notice that there's a skinny finger below the
threads. It's there to activate a switch in the
PRC-25/PRC-77 (and other) radio telling the radio that a 3
meter (9') whip antenna is installed so the proper
matching circuit is selected (depending on if in the low
or hi band). My Tape Whip
Adapter allows using mil antennas on civilian
antenna bases. The TWA web page has a table of
antenna, base and radio thread sizes)]
With the PRC-25 class
radios (including the PRC-77, SEM-35
etc) you will realize an antenna system that while not nearly as
long as the standard AT-271 is still considerably more efficient
than the short tape antenna. For instance, I once used a
PRC-25 for a talk-in radio at an indoor hamfest. The short tape
antenna was good for little more than talking to the parking lot,
but the ceiling of the building was too low to allow the use of
the AT-271. A 4 foot center loaded CB antenna was substituted for
the AT-271 resulting in an antenna that was 4.5 feet long vice 9
ft, and an increase in range of over a mile over that of the tape
Years ago, with my first PRC-10, I had none of it's original accessories excepting a handset. I didn't even have the AB-129 rubber spring/base (itself a very useful item for various applications)! A standard antenna spring was used as found on many CB mobile mounts combined with a series of different antennas lengths dependent on the application. i.e. a 2ft center loaded antenna was used for short range/portable work, and a 9 ft whip for stationary/longer range. All were screwed into the same spring which was affixed to the radio's long whip connection. It was all an excellent alternative until the original antennas came along, and still finds application today.
But fear not! The fix is very simple and may cost you absolutely nothing. Simply swap the AT-271 for the CB antenna of your choice & desired length, and it will work. Even on the HF bands! As the radio's automatic antenna tuner was designed to work with an antenna of about 9 ft, and as the CB antenna is an electrical 9 ft, the radio doesn't know, or care if the antenna is actually only a couple feet long.
Some caution, and common sense should be exercise however. While the radio may tune a two foot antenna, it would not be wise to try and use it thusly on 75 meters. In all cases it's advisable to use the longest antenna that is practical for the application. Also, as it is possible that the radio's tuner might see the antenna's load coil as a trap instead of a resonant part of the antenna, it's probably best to use an antenna that has it's load located as high up on it's length as possible. What this means is if you try to use a center loaded antenna, the tuner may only see the lower half of this antenna (where the load begins) and try to tune this portion alone. This may be as little as 1 ft or less on some center loaded antennas. So it's best to use one of the top loaded fiberglass types with this radio.
I've use a 3 ft top loaded fiberglass antenna for use at 51 MHz to great effect. While the radio did tune this same 3 ft antenna on the HF bands, it would not be advisable to use anything less than 4ft (better 5 ft) on the lower frequencies.
For the most part, resonant(or even non-resonant) whips for backpack portable use on the HF bands do not exist on the commercial market, and only very few(& prohibitively expensive) versions were produced for the military. But a very nice one can be built, and as with most of the hardware needed in this series of articles, your next local hamfest will most likely yield everything you need. I'll begin this part of the series with the construction details for a nearly universal resonant whip antenna suitable for use on very wide variety of HF portables. I'll close with just a few of it's possible applications.
marketed a very popular HF mobile antenna system to hams for many
years. The system consisted of the same basic mast section
combined with a separate coil & resonator for the band of
choice. These load coils were/are available for all the ham bands
between 160(rather rare) and 10 meters, in both standard &
high power/heavy duty versions. For our purpose the standard
version is more desirable as we don't need the high power option,
it is lighter in weight, has a little less bulk, is far more
common, & is cheaper. Of the highest priority are the 75/80
& 40 meter coils, but if others surface and they are cheep,
get them too because if nothing else they'll provide the hardware
for other projects. Don't bother with the 15 or 10 meter
coils, they are pretty much
useless(except for the hardware).
Many of these coils when found, especially the larger 75 & 160 meter versions, will have cracked end caps, or loose threaded ends(where the mast and resonator screw on), but that's ok this will just make them even cheaper. This damage was most likely caused by harsh mobile use, and is in almost every case is easily fixed with more than ample strength for our application. All the metal used in these coils in chrome plated brass, you need simply to take a Dremel & grind away the chrome plating and effect the needed repairs by soldering. Don't have a Dremel you say? SHAME ON YOU, buy one! And a good supply of the high speed cut off disk. I know for a fact that they(or a reasonable facsimile) are available all over the world. I purchased my second one at a Woolworth store in Malaga Spain, and my third one at a hobby shop in Naples Italy, and my fourth one at the PX in Augsburg Germany.
The resonator(stinger) used on the lower frequency versions of these coils is a bit stiff for my liking(which accounts for the damage inflected on many of them). Also the original base fitting dose not allow for much travel/adjustment. The fix for this is easy & will allow the antenna to be used in a wider variety of applications with less probability of damage. The thread used for the fitting on this end of the coil is also a standard used on nearly all US built antennas, 1/4 x 20. You can simply replace the original fitting, & resonator, with one removed from a common CB type base loaded antenna(resonator cut to length with a Dremel or grinder). Choose a fitting that is hollow clear through. To allow greater adjustment/travel of the resonator take a 1/8" drill bit and drill down through the center of the load coils top fitting the full length of the drill bit(even into the plastic form of the coil). This will allow several inches of possible adjustment to the resonator(stainless steal 'stinger') rather than the previously had 1".
After you have gathered the needed coils, and a suitable spring, the next step is to construct a mast. The original Hustler/Hygain mast will work but it's too long & heavy for convenient use. Besides, why buy one when you can make a better one?. The options are endless, and limited only by your imagination and skill with simple hand tools.
#1, Take a couple old CB type top loaded fiberglass whips, strip one of it's heat shrink and wire(save the wire). Cut it down to about a 2ft length(it's length is not significant & can be just about anything you are comfortable with). Take the second whip & remove it's 3/8 x 24 fitting(if you don't have a supply already scavenged). Affix this fitting to the cut off end of the 2ft mast you've already prepared. Connect the two ends of the mast with a piece of the copper wire saved from the original winding(most effective will be a slow winding with about 2 inches or more between turns). Now recover your new mast section with some heat shrink tubing which will most likely be your highest investment in the entire project(aside from the Dremel I made you buy).What we want is a stud with about 1/2 inch of threads to mate with the load coil(or spring/base), and 3/4 to 1 inch of shank to fit the mast section. The diameter of this shank portion is dependant on the mast section you wish to use & the method by which you wish to attach it. Your preference may be a simple & 'permanent' force fit requiring a few mild whacks with a mallet and no further work. This will work just fine for any mast section type you use, and might even be preferred for the last mast section options outline below. But for the AT-271 modification, you may opt for the 'serviceable' method which will require a snug fit of the fitting combined with a small roll pin for final attachment, this method will allow you to service your antenna in the event you damage it in the future.
#2, As has been noted, the AT-271 9ft long sectional antenna is without exception the most common military antenna ever produced (it's been in use for over 50 years). As a result there are many around that have been damaged, some beyond practical repair. Most of the damage to these antennas has been to the top few sections which is perfect for us as we only require the bottom two or so. The possible uses for these remaining bottom sections, and the methods you may utilize them will again present several options.(special note, the PRC-74's original antenna is a modification of the AT-271 with the second mast section being replaced by a band switched load coil)
Option 2a, If you only wish to use the first section of the old AT-271 alone you may simply run a 3/8 x 24 tap into it's end and insert a standard threaded stud(usually used between a spring & antenna mount). If you don't have a 3/8 x 24 tap, or a threaded stud, and don't wish to buy either, you may proceed to Option 2b and make them yourself.(While one section of the AT-271 will work, I recommend using both of the first two sections)
Option 2b, If you wish to use two sections of the old AT-271, or one of the alternate mast ideas below, you must make the needed fitting that will allow mounting of the load coil to the top of AT-271 section. Or, if one of the other mast ideas are used, two fittings will be needed(one for each end).
Our efforts are again made simpler by the military's choice of threads as 3/8 x 24 is not only an industry standard for antennas, but it is also a standard SAE thread(often called 3/8" fine). You'll need to go to your local hardware store and purchase a 3/8 x 24 bolt that's made from as soft a material as possible(brass would be best, aluminum nice, mild steel will work). The bolt should have an unthreaded shank(portion between the bolt's head & the threads) of at least 1.5". While your at the hardware store also buy a matching nut of hardened steel.
The first step is to cut off the bolt's head taking care to save as much of the unthreaded shank as possible. Then chuck the bolt(shank first) into your Poorboy's Lathe(power hand drill). Screw the nut down firmly on the bolt as far as it will go. This nut will serve the multiple purpose of premeasuring & protecting the half inch of threads you need to keep intact, and help in the next two steps.
The bolt with it's head removed is now chucked in your drill shank first, and a nut is screwed down on it as far as it will go. With the drill running, hold a hack saw blade against the threaded portion of the bolt to be removed using the nut as a fence(reciprocate the blade slowly to keep it's teeth clear of shavings). Once you've cut off the unneeded portion of the threads, remove the nut. This may alone clean up the ragged edge of the cut threads well enough to allow use. If not, clean them up with a couple touches of a fine file(again while the drill is running).
The next step is to turn down the shank of the bolt to fit the mast section. First put the nut back on the bolt(it will prevent you from messing up the threads & provide a guide for the turning process). Then loosen the chuck and reposition the bolt so as to leave about 1 inch between the face of the nut & the drill's chuck. With the drill running, use a file, just as you previously did with the hack saw blade, to turn down this 1" portion of the bolt to the size needed to fit the mast section. Once you have the bolt turned down to the desired size, remove the nut(remove it now or you may be sorry!). The last step is to cut off the unwanted portion of the bolt using the hack saw blade just as you already did with the threads.
Your fitting should now be pretty much finished, but if you screwed up, that's ok, we can fix it. If you didn't get the fitting turned down enough, you can put it back in the drill threads first and turn it down some more, but take care as you'll not have much left for the chuck to grasp & you may mess up the threads. If you turned the fitting down too much you have two options(DO NOT crush the end of the mast section!). First is to use a old Gun Smiths trick, with a center punch 'stipple' the shank of the fitting(make a bunch of little dents in it). Each little dent creates a tiny crater with swelled edges effectively enlarging the diameter of the shank. If the shank is still too small for this trick to work, you can shim it with a strand or two of fine copper wire.
[Note the TWA2 Antenna Adapter has 5/16-24 female threads to accept the military antennas & AB-591 and 3/8-24 male threads to mate with common ham and CB antenna bases.]
To restore the
internal spring tension feature of the AT-271 all you'll need is a
small role pin obtained from your local hardware or automotive
parts store, & a drill bit to fit it(a small brass or mild
steel pin will also work).
Step #1, Drill a hole about 1.5" from the top end of the #2 mast section just large enough to fit the role pin. This hole will be in the brass section of the mast but far enough from the end to still allow insertion of the 3/8 x 24 fitting without interference.
Step #2, Fashion a small wire loop. The loop should be large enough to freely accept the role pin, yet small enough to still pass through the
trunk of the #2 mast section.
Step #3, Measure the needed length of the string that's attached to the internal spring of the #1 mast section. This will be about 2-3" shorter than the distance between the role pin hole in the #2 mast section and it's bottom end. Tie the end of the string to the small loop you have made.
Step #4, Prepare a 2ft length of stiff small gage wire(the wire from a wire welder 'Mig' will be perfect). Fashion a VERY SMALL hook in the end of the wire. Insert the 'fish wire' through the trunk of the #2 mast section (bottom to top)leaving about 1" of the hook end exposed. Now hook the wire loop of the string and pull it through the #2 section stopping just at the hole you've drilled for the roll pin. Insert the roll pin through it's drilled hole, and the string's wire loop(still being held by the fish wire). You can now unhook the 'fish wire'(best done by simply pushing it back down through the mast section the same way it came in).
Step #5, Place the end of the roll pin against a hard surface and give it's other end a tap or two with your center much. The idea is to flare the end if the role pin just enough that it will not readily pass through it's hole. Push the flared end of the role pin in to where it just contacts the hole. With your Dremel, cut off the excess roll pin on the other side, then flare this end.
Step #6, the 3/8 x 24 fitting you've made can now be installed on the mast you've just finished. If you can never foresee a need to remove the fitting it can be affixed as noted above. If you wish to be able to remove it in the event of future repairs or modification, you can attach it with a role pin. If this is the case, insert the fitting into the mast and drill through them both at the same time. Your center punch, and Dremel will complete the process just as above. But don't flare the ends of the roll pin too much, if you have a good snug fit you may not need to flare it at all.
The possibilities are endless! I've used MS & AB mast sections as used on the RC-292, and AB-15 antenna systems. Fittings & adapters can be easily made from the ends of the many damaged sections that can be found*. These will allow elevated use of your basic antenna while operating in the semifixed station mode. They will also allow the use of your load coil alone on host of standard military vehicular antenna mounts. A special caution is needed on these type of mast sections. NEVER use anything but your hands to assemble them. NO PLIERS! Always use a silicone based grease on the threads before assembly. If you do not heed these warnings you will have a permanent whip antenna system as you will not be able to get them appart. *[Fair Radio also stocks an M-422 adapter ( Stock # 2A168-422) that goes from the male end of these mast sections to a male 3/8 x 24 stud. A military item, it was designed to allow the use of standard AB & MS mast sections as an expediant replacement for the AT-271]
Aluminum sections can be easily made useing the same basic 3/8 x 24 fitting construction details as explained above, and tubing robbed from old base Ham or CB antennas.
A very attractive option is to use automotive steel break line. This is readily available from all automotive parts stores in various lengths & diameters. Just fabricate 2 of the 3/8 x 24 fittings as outline above for a tight force fit with a mallet into each end of the tubing. Covering the completed mast section with some dark colored heat shrink tubing will give an extremely professional appearance & may prevent you from getting the crap knocked out of you via an RF shock.
Basic adjustment of this antenna can be carried out with an FS meter in the same fashion as outlined previously in this series. If the radio to be used has an internal antenna tuner(like the PRC-74) you may not need to adjust the antenna at all. Just having it in the ball park will be fine because if your using a radio capable of multiple frequencies(even if they are located in the same band) you will quickly exceed the antenna's narrow bandwidth. But if you do wish to align the antenna for peek performance, you should first load the radio into a fixed 50 ohm load before attaching & aligning the whip.
If you will be using a radio that does not have an internal tuner, you will need to get the antenna as close to the operating frequency as possible. There were many HF backpack sets that while they had provision for use with a whip antenna, had no externally accessible means of adjusting it. Some used a primitive external antenna tuner that was a part of the antenna's mount apparatus to fine tune the system. Some of these included the Hallicrafters/OPS TR-9, SBT-18, SBT-20 etc, Motorola SA-200 series, Galaxy Comm-2, and a host of early SGC, Racal, Stoner & Spilsbury Products. A simple tapped coil(toroid) & some adjustable capacitance would probably fill the bill, and it's size could be kept to a minimum.
Mounts for all these type radios were simple, and generally included variations on the same few themes. Some used the hasp type fasteners found on all military portables sense WW-II(like what holds the case halves of a PRC-6 together, or an RT-70 to it's AM-65). Others use studs that are similar to those used on mics to hang them up on the dash of your car etc. And some used fasteners similar to those that hold the tube covers on aircraft command sets. In nearly every case, the needed hardware can be found in a well stocked junk box(or in my case, Junk Warehouse #1, #2, or #3).
The original rubber spring/base for the PRC-74 is identical to the one used on the PRC-10 family radios (AB-129) which is far more common. The only difference is that the spring for the 74 has a wire screwed to it's base to allow connection to the radio's antenna binding post. You can simply make the needed jumper by soldering a 3/8" lug to the end of a piece of wire which is then secured by screwing the AB-129 down on top of it.
If you do not have the original side mount antenna bracket you can make one without too much trouble. You'll need some sheet metal (aluminum, or mild steel) and a couple hasp fasteners robbed from a 40-50's vintage military radio. Try to use those as supplied on the RT-70, late BC-1000 etc as they use dual external springs which will yeild a little move travel, and are not quite as critical about where you locate their matching hooks.
Your side mount will be made in two pieces that should over lap about 1/2" when in place. Take note of the variant PRC-74 you have! 2-12mc versions are about 1 inch shorter than 2-18mc versions. Hence you want to make the two pieces of the side plate longer that is needed for the 2-18mc version (PRC-74B) so that it may still be used on an earlier PRC-74. The hasp fastener is screwed to the lower half of the mount bracket, and it's hook is attached to the upper. Multiple screw/mount holes for the hook will allow use of the finished mount on various versions of the PRC-74 (& other radios). When cinched down, the hasp fastener squeezes the two sections of the mount together, each end of which is hooked over the edge of the top & bottom of the radio. Several Para-Military radios use a similar method for the mounting of their whip antennas.
The antenna will really shine as a Semi-Fixed Station antenna where you will be operating while stationary for a relatively short period of time, and possibly a little more range is desirable. The distance between the mount device and the base of the load coil will have little effect on the resonant frequency of the antenna. I/E, you can have a mast that's 2ft long for backpack use, or 2-4 ft for moving/vehicular use, or one that's 10ft or more for fixed station use, with very little or no effect on the resonant frequency of the antenna.
The above will hold true until the length of the mast itself, or the combined physical length of the mast & coil, approach the resonant length of the frequency in use. For instance, if your operating on 10 meters where about 8 ft is resonant, you can't use a length of mast that could itself stand alone as an antenna then top that with a load coil/resonator which is also resonant. In this case you'd end up with an end feed 1/2 wave antenna which would present a very high impedance.
If you have opted to make adapters that will allow the connection of your load coil to standard military MS/AB type mast sections, your in business! You can stack as many of these mast sections as you feel comfortable with, with your load coil at their top. The vehicular mount may be the super common AB-15, or the AB-652 (better for longer HF antennas). Elevated operation might even be had using the components of the RC-292. Even standard civilian ball & spring mounts can be used if you've purchased one of the military adapters (or made one of your own).
I have used this system at many a hamfest on such radio's as the GRC-9, PRC-47, PRC-74, PRC-70, Syncal 30, even a few converted HF/AM 20 watt marine radios. Today I keep a bundle of these mast sections in my Old Power Wagon just for this purpose. One of my first mobile experiences with a GRC-9 was checking in on the 75 mtr East Coast Military Radio Users Net with it mounted in the back of my old Chevy van. The antenna was an 50's vintage Webster Band Spanner (more on it later) being elevated 6 ft (2ea MS mast sections), secured by an AB-652 base. From southern Missouri (I was parked in a friend's front yard) to the east coast on a 5 watt AM radio operating into an antenna that had a total length of about 12ft, it was GREAT!
I should explain the design of these old Webster antennas before proceeding, they are basically a very long hollow load coil, about 3ft long with a 1 inch diameter (dependant on the particular model). It had an even longer, very stiff resonator(stainless steel whip). Band/frequency changes were effected by sliding this whip up/down the entire length of the hollow load coil wherein it made internal contact to the windings of the coil. Thusly the antenna could be tuned for operation between 2 & 30mc(dependant on the model).
Bob's problem lay in that he was trying to use the antenna as it was intended, as a base loaded antenna that just had an unusually long base load. As we know, base loaded antennas are not very efficient. My solution was simple, use it as a center loaded antenna! Simply inserting as little as 1.5ft of mast between the bottom of the Webster and the mount transformed it from a poor base loaded dummy load into a fabulous center loaded performer. When Bob saw the transformation of that old antenna he'd been playing with for all those years he tried to shame me into giving it back. I still have it after almost 20 years!
Though long out of production these old Websters can still be found with some regularity at Hamfest today. If you find one, it's cost will run from between $40 - $180 depending totally on the seller. Before making a purchase, inspect the antenna closely as they had a few minor failings that if combined with owner neglect or stupidity might yield an impressive looking piece of junk.
As noted, the Band
Spanners have a very long & hollow load coil made from
fiberglass. This when combined with a stainless steel resonator
(with an unusually large diameter), resulted in an extremely stiff
antenna. If the antenna had been used mobile without a spring, or
with a spring that was too stiff, they could be easily broken (as
many of them are). Also, as this load coil is hollow it could fill
with water, and if left on the vehicle in the winter, it would
surely freeze & bust (without exception). So before
purchasing a Webster, closely inspect it for signs of
cracks. As the coil is imbedded in the fiberglass even the
slightest of hair line cracks could render it useless. Though a
very good performer when used as outlined above, the Band Spanners
are a very poor choice for any kind of
permanent installation. So be careful, they are too good to tear up!
This antenna was intended for use with a low power radio. I would not be comfortable trying to use it with any radio capable of more than 20 watts. While it will work very well as a vehicular antenna, just as with the Webster it will not take physical abuse or constant exposure to the elements. So use it with some common sense, then take it down & put it away for the next time.
You will not be able to precisely adjust the AS-1887 for a specific frequency like you can the Hygain/Hustler or Webster. So either a simple/small tuner will be needed, or a radio that has this feature built in.
The length of non-resonant type antennas, usually 'are' resonant at the upper extreme of the radio's frequency range. This is done so as to allow a tuning device (either internal or external) to load this same antenna/length at frequencies 'lower' than the actual resonant frequency of the antenna.The short tape antenna of the PRC-25 & -77 are nearly resonant at the upper end of their frequency range. At lower frequencies the radio provides internal base loading. The same is true of the PRC-8 (20-27mc) and the AT-271. [Note, the PRC-8 is of the PRC-10 family radios which were the first to use the AT-271 antenna with this designation number].
And why the AT-271 antenna & 9 feet you ask? In the early days of portable communications, & radios with tube type design, internal space, and physical size & weight were of major concern. It was easier to couple the high impedance of a vacuum tube to a likewise high impedance thus reducing parts count, size & weight. A 1/2 wave end fed antenna has a very high impedance (several K ohms). Hence it was nearly possible to connect the whip antenna directly to the plate of the radio's output tube. This is indeed what was done on such radios as the BC-222 & BC-322 (our very first "Walkie Talkies"). The AT-271 family antennas presented an approximate 1/2 wave at the frequencies the BC-1000 worked at. Ever wonder why such a tiny radio as the BC-222 needed an antenna nearly 18 ft long when operating around 27mc ? Now you know.
What makes this antenna unique among low band duckies is that it's field tunable. A field strength meter and a standard plastic tuning wand (supplied) are all that's needed to make this antenna operable on any radio, or frequency you wish. This is accomplished by simply removing the plastic cap at the top of the antenna, inserting the tuning wand, and adjusting a slug. It works great. At about 10" long, the antenna outwardly seems identical to those made for the CB market about 10 years ago (supplied with many HT, & emergency type CB's). I have been using these antennas for years, and have found absolutely nothing that even approaches their quality & performance.
As the catalog I have seems to have the pictures & descriptions inverted I'll not give you the model number of the antenna. And as it's available with every conceivable connector style it wouldn't do much good anyway. I believe that what your after is the Style 'L' < note this link is NOT to the field tunable version, working on it, Brooke> field tunable 30-50 MHz. Neoprene shrink sleeve. Do not get the injection molded version as it is base loaded/tuned, not as efficient, looks like a miniature Saturn Rocket, is more expensive, and is only slightly more flexible than a broom handle.
If you are a user of a PRC-68 family radio, you know that it is capable of using a 6" duckie (not worth a shit!), long rubber helical (pretty good), and tape antenna similar to, or even the same as that of the PRC-25/77. You may not know that it can also be used with a standard 50 ohm load. The problem is, that to swap between any of these options the radio must be taken apart & retuned. With the Centurion Rubber Duckie you can align the 68 for use with a 50 ohm load, and swap between it & the Duckie (once properly adjusted) at will without the need of retuning the radio. The performance of the Duckie will be far better than the original 6 incher, and on a par with, if not better than the 1.5 foot rubber helical.
Centurion is also the company that makes the distinctive antenna used on the PRC-127 & I've been using them for years (even before the PRC-127 existed). This is listed as their Style "H" broad band. If you need a new antenna for your PRC-127 (or any other high band VHF or 2 meter radio) here you go. You can buy them direct from the OEM for less than they go for on Ebay! They will make a 2 watt VHF radio think it's a 5 watter (if it's using a standard 6" duckie)!
If you have a low band HT that was intended to use a high band telescoping antenna, wish to use a rubber duckie, and do not want to mess with removing radio's internal load coil, this is the one for you (I use it on my RCA/Comco/Repco clones)!
P.O. Box 82846
Lincoln Nebraska 68501
USA & Canada
You might check to see if they yet have a web site, or e-mail capabilities. If they do, let me know.
If there is a lot of interest we may investigate a quantity purchase as a group. Again, let me know.
Dennis Starks; Collector/Historian
Midwest Military Communications Museum
Box 95, Cross Timbers Mo. 65634 USA
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Page created 10 June 2001.