Alden Corporation147 New Hyde Park RoadFranklin Square NY 11010

Telephone: (516) 328-7501Fax(516) 328-7506

Orders (800)643-7655Price Class: $389

Number 5 on your Feedback card

by Steve Katz. WB2WIKl673 Review

The Azden PCS·75 0 0 H6 Meter FM Transceiver50 watts on 6 in an attractive, low-cost mobile.

AZden Corporation is the only manufactur­er of monoband mobile FM transceivers

for all the popular bands from 28 through 440MHz and really has a corner on the markelfor 6 and 10 meier FM rigs. When given theopportunity to review th e new PCS·7500H6 meter FM rig, I was happy to jump right onit, since the 50 MHz band is lull of FM Sim­plex and repeater activity here in Southerncalifornia.

Six meters is a unique band that combinesthe propagation advantages of both VHF andHF. For line.ol·sight (direct wave) work, 6 isnot much different from 2 meters or 135 em(222 MHz). although the longer wavelengthproduces le ss rapid signal strength flutter.Because a quarter-wavelength at 6 meters isabout 4'9" long, peaks and nulls in signalsare produced by consid erably more move­ment than, say, at2 meters, where a quarter­wave is only about 19' . Tropospherically- en­hanced propagation, especia lly 'trope duct­ing; occurs less on 6 than on 2 or the higherfr equency bands, making th ose occasionalOX contacts a b it more rare; however, the 50MHz band does afford its users much morefrequen t sporadic- E (~E-sk i p") propagation,especially from May through July, and againin December, and 1,200-mile a s o s on 6 me­ters are not rare. Plus, 6 meters enjoys occa­sional F-Iaye r propagation, producin g con­tacts to several thousancl miles wi th relativelylow power during solar-cycle peaks , If youhaven't tried 6 yet, it is surely an inlerestingband that has its share of die-hard users.

Overview

The first thing anyone notices about thePCS-7500H (or any of the new Azden PCS·7000 series) is how incredibly beautiful it is tolook at. It is a fine-looking radiO, with everysingle panel button illuminated with a dark or­ange glow for easy viewing. The LCD displaysc reen is sim ila rly baCklighted and has awarm , inviting glow. Eve n the push-buttonson the DTM F rtcucn-tone') microphone areall Illuminated; a nice touch. The rig comes

eq u ip pe d with a convenient a n d stu rd ymounting bracket, a PTT/DTMF m icrophone,a long DC power cable with the positive sidefused , a connector disconnect point abouteight inches from the rear of the radio, and allmounti ng hardware. It also comes with aCTCSS ("PL-) encoder bu il t in. The PCS-

22 73 Amateur Radio Today- Augusl1994

7500H is rated to produce 50 watts AF outputpower (with a 10 watt "low power" mode front­panel se lectab le), programmable frequencysteps, and other features normally found onmodern FM transceive rs,

The PCS-7500H has good and bad points,and I'll try to discuss both fai rly. I like thought­ful touches, w ith which the Azden is loaded.For example, they used a flat-blade automo­tive-style fuse in the DC power cable. Smallpoint. but these have real advantages overthe old-fashioned 3AG, AGC, MOL (e tc. )glass cartr idge luses used in most otherequ ipment: They can really handle a lot ofcurrent without thermal meltdown, are readilyavailable at gas stations, and are very inex­pensive. I also like the connectorized powercable, whid1 uses an automotive-style mold­ed connector set that has also proven its reli­ability in years 01 service. Its coaxial antennacable receptacle, a stanclard "UHF" 50-239,is lirmly mounted to the rear panel 01 the ra­d io, not hanging on a short coax extensioncab le as in many modern mobile rigs . It shand-held PIT microphone has a solid leeland produces excellent transmit audio, (Moreon this ta ter.] Its receiver audio is full, louda nd uootsto r t eo . a nd so unds b etter th anmany mobile rigs. And the rig is beautifu l, es­pecially at night when one can enjoy all thewarmly lit controls. The Azden can accommo­date any frequency -split~ between transmitand receive , since each channel can be sep­a rately p ro gram med (I nto memory) withTX/RX frequencies, and its 20 memories areadequate for 6 meters. As with all modem FM

rigs, each memory will store frequency ~split"

and PL tone (if requi red).I al so like the built-in heat-sink fan in the

PCS-7500H , It activates after a few minutesof continuous transmission at normal roomtemperature and helps m aintain a "coot-to­tne-toucn" heat sink, undoubtedly pro longingthe operating lite of the final amplifier stage.

On the other hand , the Azde n Is full ofqUir1<s, some of which I found a bit annoying.First, the PCS-7000 series all seem to sbareone instructio n manua l, written arouncl thePCS-7000(H) 2 meter rig. The PCS-7500Hmanual contains an ~adderxlum· sheet (one

page) whictI modifies the PCS-7000 manualto suit the 6 meter rig. but this means reter­ring back and forth between two sets of infor­mation. And the original PCS-7000 manualcontains mistakes and typographical errors .Most aren't meaningful, but I started 10 prool­read the manual in sea rc h o f errors andstopped when I found a dozen by the fourthpage. This reminded me 01 how badly writtenthe older Japanese equipment manuals usedto be, befo re the manufacturers em ployedEnglish-speaking technical writers to maketh em better,

Next, there Is no easy way to use the rigwith tone-activated (CTCSS) repeaters whenin the "VFO· or "Direcr mode. PL-tones areeasily programmed in to memo ry, ancl onceth is Is performed, tone-activated repeatersa re easy to use ; but if YOU're -scannin garound~ looking for activity in an unknown re­giOn and stumble across a tone-activaled re­peater not al ready in merTlOfy, there's no easy

Passbandmonitoring

tion on the task. But the Azden inst ructionmanual makes the job sound more difficultthan it is, with 12 paragraphs assigned to thedescription. The Azden is unique in that it on­ly stores the memory data when you turn therig off, and then back on. To quote from themanual, "Note: Be sure to turn off the powerwhen you have completed programming. Thisprocedure is required to get each setting pre­grammed in and then to get out of the pro­gramming mode." Weird, but It works.

With all these quirks to write about, youmay get the idea that I really don't like the Az­den. This Isn't true. I do like the rig, but it tookmore getting used to than it should have. Interms of performance, the Azden is an im­pressive package.

The Technical Side

One thing I like a lot is that Azden provides"lull-sized" schematic diagrams for thei r rigs.They are clear and easy to read without amagnifying glass, and wlll be of value tothose who like to perform modifications or dotheir own service work. The schematic for thePCS-7500H reveals the transmitter final pow­er amplifier to be discrete (2SC2097), ratherthan a molded hybrid ~b rick· (modular) ampli­fier as used by most other manufacturers. Ilike the discrete approach better because it ismore user-serviceable for reasonable cost.Should the PA "final" ever go out, it will bemuch cheaper to replace a $10 transistorthan a $90 module. Not that I would expectthe final to fail; the people at Azden assuredme they've never seen one fail yet.

The PA circuit board also contains a dis­crete driver stage (2SC1972), the thermaldetector which switches on a cooling fan ifthe heat-sink temperature gets too hot, theVSWR protection detector c ircuit (whichshuts the transmitter down if a gross antennamismatch occurs) , and a bandpass filterci rcuit which is in line with the antenna toboth the receiver and the transmitter. PAstage tuning is accomplished by a three-sec­tion low-pass matching network. One draw­back to the discrete PA stage is Its cr iticaltuning: The PCS-7500H does deliver 50 wattsas rated into a perfect 50 ohm resistive load,but power output falls off rapidly when thetransmitter is faced with any mismatch at all.The antenna I used for most of my testing, avertical with a measured VSWR of 1.5:1, onlyallowed the transmitter 10 deliver between 28and 42 watts, depending on the operating fre­quency and exact nature of the mismatch.Some of the "brick" stages, while COStly to re­place, are more forgiving of mismatches.

The receiver's front end, a 3$K101 dual­gate MOSFET, is protected against transientsby 'back-to-beck" signal diodes and featuresbandpass tuning of both its input and outputto help reduce interference and intermodula­non from adjacent services. The first RF mix­er, another 3$K1 01 with an output of 14 MHz,is followed by a four-pole crystal filter whoseoutput drives the IF SYSTEM integrated cir­cuit, an MC3361D. The receiver's second IFat 455 kHz is filtered by a 15 kHz bandwidthceramic filter, type KBF455R15A. The recelv-

way to access it without programming therequired frequency, offset and tone data intomemory fi rst. Azdan did provide me withan updated sheet entitled, "Error in AzdenPCS-7000H Instruction Manual" which doesdescribe how to use a Pl tone in the "Direct"mode, but the procedure is so complicatedit couldn't possibly be performed while driv­ing.

The rig's 20 memory channels are storedIn two banks of 10, called AO-9 and BO-9. Nobig deal, although simply calling them 0-19 or1-20 might have been nicer. But the rig al­ways "powers up" on memory AO, regardlessof where you used it last. This is frustrating,especially si nce all my other modern FMtransceivers "remember" where they werelast used and "power up" on the last-usedchannel .

Also, there's no VFO/memory knob of anykind on the Azden, nor may frequencies ormemory channel numbers be entered directlywith keypad strokes. The only way to go from.say, memory A3 to memory B5, is by usingthe 'uo" or "down" buttons (either on the frontpanel or on the PTT microphone) to gothrough all the memories in between. And ifyou depress the "up" or "down" button morethan momentarily, the rig begins scann ingthrough the memory channels very quickly,much too fast to stop on the channel of yourchoice. With the technology and chip setsavailable today, there's no reason for anychannelized radio to not have "direct frequen­cy entry" with keypad strokes. (That is. if youwish to 'dial up" 52.525 MHz, you'd just de­press 2-5-2-5 on the keypad , and the rigwould go th ere instantly.) This used to betricky in the old days, but can now be donewith one $2 chip. In Azden's defense, howev­er. I must admit that many modern FM mobilerigs still don't contain this feature. Darned if Iknow why not.

Another minor annoyance is that a user ofthe PCS-7500H must refer to a "Tone CodeTable" when programming Pl tone frequen­cies. That is, the CTCSS frequencies, ofwhich there are 38 in common use, are notactually displayed by the Azden during the Plselection process. Instead, tones are select­ed and displayed by two-digit codes whichmight only be memorized by The AmazingKreskin. Since I'm not so amazing, I had 10constantly refer to a chart on page 14 of theinstruction manual to determine which two­digit code corresponded to each Pl tone fre­quency. For example. Code ~19" correspondsto a CTCSS frequency of 127.3 Hz. Sid Wolinat Azden in New York did advise that thenewer-generation PCS-7000 series (unavail ­able at this writing) would incorporate a newmicroprocessor which allowed direct Pl fre­quency address and readout, as on theirhandle-talkies.

Programming the PCS-7500H takes somegetting used to if you are more familiar withone of the other brands of equipment. It's notdifficult, but might be too complex for use "enthe fly" while driving. Again. to be fair, most ofthe mobile rigs I've used are too complicatedto program without focusing complete etten -

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on six anyway, but if you really wanted to, youcould home-brew a PIN diode modificationfairly easily.

A listing of manufactu rer's ra tings vs.bench measu rements made on the PCS·7500H is contained in the sidebar.

Summary

It took me a while to get used to the Az·den . It does have quirks, as described earlier,that make it more troublesome to use than I'dlike. But for an affordable, single-band 6 me­ter FM rig, it's almost the only game in town.Same goes for 10 meters, with the PCS­7800H. I understand the Southern CaliforniaSix Meter Club, which actively promotes theuse of this band, has ordered a great numberof these radios for their members and theyare well accepted. In speaking with local 6meter repealer owners, ! found they were allvery aware of the Azden and were either us­ing one personally or had at least had theirhands on one. It does disturb me a bit thatth e transmitter po wer output fa lls off sosharply when connected to other than a per­lect load, but since the FM subband on 6 me­ters is a narrow window of our spectrum (3MHz), I suppose anyone with a lick of sensecould tune his antenna to provide a goodmatch if he had to.

The radio as reviewed is good. With theimprovements Azden has planned, such aseliminating the twO-digit Pl tone codes, it willbe even better. II they also rewrote the in­struction manual, and had one specificallydedicated to the PCS-7500H, it would be bel·ter still. [Factory Note: New and improvedmanuals are in the works.] On a scale of oneto 10, with a "10" being perfect, I'd rate thePCS-7500H a strong 8: a good rig for themoney and, as I said earlier, maybe the onlygame in town for a modestly-priced 6 meterFM rig. iii

Manufacturer's Specifications vs. Bench MeasurementsVariable Specification MeasuredTX output power 50 walls (high) 47·52W (H)RX sensitivity <0.35!.iV/20 dB NQ 0.30!!V/20 dB NQ*Squelch sensitivity <0.12f.iV threshold O.10flV threSholdSelectivity 15 kHz/-60 dB 15 kHZ/·57 dBRX audio output 2W,10"lo THO 2,2W, 10"1" THOPower consumption O.SA RX 0,5A RXFrequency coverage 50.0-53.995 MHz 50.0-53.995 MHz

' Receiver Sensitivity is usually measured in j.lV/12 dB SINAD. For comparison purposes. the 0.35 ).lV/20dB Noise Quieting would be a lower number if measured using SINAD. At 50 MHz, the difference in lhisspecification for anything less man 1 flV is not critical.

Items unspecified by manufacturer, but noted:

Display window bar graph, number of bars illuminated for 50W TX output: 10. For 10W TX output: ato10, varies With frequency and VSWR.

Display-window bargraph used as RX S-meter, number of bars illuminated ve. received signal level:1bar = 0.9).lV (-108 dBm)2 bars = 1.2).lV (-106 dBm)3 bars = l.4f1V (-104dBm)4 bars = 1.8 uv (-102 dBm)5 bars = 2.0 uv (-101 dBm)6 bars = 22 flV (-100 dBm)7 bars = 3.0 uv {-97.5 dBm)8 bars = 4.0 uv (-95 dBm)9+10 bars = 5.5).lV (·92dBm)

Note: The 9th and 10th "bar" in the bar graph display illuminate together. Signal level change from"51 " (1 bar) to "S9-+" (a ll 10 bars) is 16 dB. This makes the resolution extremely good for weak signalbeam peaking. but results in "full-scale" readings for any reasonably strong signal. Not uncommon forFM receivers.

er isn't razor-sharp, but suffices nicely withthe 20 kHz channel spacing commonly usedon 6 meters . One might think that a VHF rigwith a lirst IF at 14 MHz could be easily inter­fered with by strong 20 meter signals, but Ididn't find this to be a problem.

The transmitter uses what Azden proudlydescribes as "true FM~ for modulation, and Iguess it is, with the microphone ampli fierstage directly driving the veo variable-ca­pacitance tuning diodes. However, I've neverbeen able to tell the difference between "t rueFM" and "phase modulation," since, mathe­matically speaking, one is the reciprocal ofthe othe r and a phase -modulated signal,when integrated, becomes "FM.~

I did have a problem with the unit as re­ceived, in that the transmitted modulation wastinny and distorted. Azden was surprised tohear this, and immediately shipped a new mi­crophone, thinking that was likely to be theproblem. It was, and the new microphoneproduced clear, crisp modulation that re­ceived compliments on the air. (I must say,Azden's service in this instance was remark­able. They must have shipped the new mikethe day I called them on the telephone, be­cause I received it the next day, 3,000 milesaway!)

One thing I think is a bit "clunky" about theAzden is that it uses an old-fashioned relayfor transmit-receive RF switch ing. Relayswork fine, and Azden claims they've neverhad one fail, even in prolonged packet radioservice, but their switching "turnaround"speed is rather slow compared with solid­state switches, and if the radio is used forpacket, the user may have to re-set switchingparameters in his TNC program. I was usedto using 30 milliseconds (mS) or less in pack­et switching, but this is too fast for a relay. I'drecommend more like 300 mS for a relay-op­erated rig. There 's not a lot of packet activity