Azden_PCS-7500H_review_1994

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Azden_PCS-7500H_review_1994 | Manualzz
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Alden Corporation
by Steve Katz. WB2WIKl6
147 New Hyde Park Road
Franklin Square NY 11010
Telephone: (516) 328-7501
73 Review
Fax (516) 328-7506
The Azden PCS·75 0 0 H
6 Meter FM Transceiver
Orders (800)643-7655
Price Class: $389
50 watts on 6 in an attractive, low-cost mobile.
A
Zd en Corporation is the only manufactur-
er of mon oband mobile FM tran sceivers
for all the popular bands from 28 through 440
MHz and really has a corner on the ma rkel
for 6 and 10 meier FM rigs. When given the
opportunity to review th e n ew PCS·7500H
6 meter FM rig, I was happy to jump right on
it, since the 50 MHz band is lull of FM Simpl ex and repeater activity here in Southern
california.
Six meters is a unique band that combines
the propagation advantages of both VHF and
HF. For line.ol·sight (direct wave) work, 6 is
not much different from 2 meters or 135 em
(222 MHz). although the longer wavelength
p roduc e s le ss rapid signal strength flutter.
Because a quarter-wavelength at 6 meters is
about 4'9" long, p eaks and nulls in signals
are produced by c o nsid e rably more movement than, say, at2 meters, whe re a quarterwave is only about 19' . Troposphe ric ally- enhanced propagation , es pec ia lly 'trope d ucting; occurs le ss on 6 than o n 2 o r the higher
fr equency band s, making th o se occasio nal
OX contacts a b it more rare ; however, th e 50
MHz band do es afford its users much more
freq uen t spora dic- E (~ E- sk i p") propaga tion,
especially from May thro ugh July, and a gai n
in December, and 1,200-mile a s o s on 6 meters are not rare. Plus, 6 meters enjoys occas ional F-Iaye r propaga tion, produc in g contacts to s everal thousancl miles wi th relatively
low power d u ring solar-cycle peaks , If you
haven't tried 6 yet, it is surely an inleresting
band that has its share of die-hard users.
Overview
The first thing anyone notices about the
PCS-7500H (or any of the new Azden PCS·
7000 series ) is how incredibly bea utiful it is to
look at. It is a fine -looking radiO, w ith every
single panel button ill uminated w ith a dark o ra nge glow for easy viewing. The LCD d isplay
sc re e n is s im il a rly b a Ckli ghted a nd h as a
warm , inviting glow. Eve n the push-button s
on the DTM F rtcuc n-tone') mi crop hone a re
all Illuminated ; a nice touch. The ri g comes
eq u ip pe d with a convenien t a n d s t u r d y
mounting bracket, a PTT/DTMF m icrophone,
a long DC power cable with the positive side
f used , a c onnector disconnect poin t a bout
eight inches from the rear of the ra dio, and all
mounti ng h ard w are. It also comes with a
CTCS S ("PL-) e ncoder bu il t in. T he PC S22 73 Amateur Radio Today- Augusl1994
7500H is rated to pro duce 50 watts AF output
power (w ith a 10 watt "low power" mode frontpanel se lectab le), programmable frequency
steps, and other features normally found o n
modern FM transce ive rs,
The PCS-7500H has good and bad points,
and I'll try to discuss both fai rly. I like thou ghtful touches, w ith which the Azden is load ed.
For example, they used a flat-blade automotive-style fuse in the DC power cable . Small
point. but th ese have re al a dvantages over
th e old - fashioned 3AG , AGC, MOL ( e tc. )
glass c ar tridge luses used in most o ther
equ ip ment: They can really handle a lot of
c urrent without thermal meltdown, are readily
available at gas stations, and a re very inexpensive. I also like the connectorized power
cable, whid1 uses a n automotive-style molded connector set that has also proven its reliability in years 01 service. Its coaxial antenna
cable receptacle, a stanclard "UHF" 50-239,
is lirmly mounted to the rear panel 01 the rad io, not hanging o n a short coax extension
c a b le as in many modern mobile rig s . It s
ha nd -held PIT microphone has a solid leel
and produces excellent transmit a ud io, (More
o n this ta te r.] Its receive r a udio is full, loud
a nd uo otsto r t eo . a nd so u nds b ett er th an
many mobil e rigs. And the rig is beautifu l, especially at nig ht when one can enjoy all the
warmly lit controls. The Az den can accommodate a ny fr eq uency -split~ between tra nsmit
and receive , since each channel can be sepa rately p r o g r a m med (I nto memory) w ith
TX/RX frequencies, and its 20 memories are
adequate for 6 meters. As with all modem FM
rig s, 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 a ctivates after a few minutes
of continuous transmission at norma l ro om
temperature a nd helps m aintain a "coot-totne-toucn" heat sink, undoubtedly pro longing
the operating lite of the final amplifier stage.
On the o ther hand , th e Azd e n Is full of
qUir1<s, some of which I found a bit annoying.
First, the PCS-7000 seri es all seem to sbare
one in structio n manua l, w ritten a rouncl the
PCS-7000(H) 2 mete r rig. T h e PCS-7500 H
manual contains an ~adderxl um· sheet (one
page) whictI modifies the PCS-7000 manual
to suit the 6 meter rig. but this means reterring back and forth between two sets of information. And the ori ginal PCS -7 000 manual
contains mistakes and typographical errors .
Most aren't meaningful, but I started 10 proolr ea d the man ual in sea rc h o f erro r s a n d
stopped w hen I found a d ozen by the fourth
page. This reminded me 01 how badly written
the older Japanese equipment manuals used
to be , b efo re the manufacturers e m p loy ed
English-speaking technical writ er s to make
th em better,
Next, there Is no easy way to use the rig
w ith tone-activated (CT CSS) repeaters when
in the "V FO· or "Direcr mode. PL-tones are
easily programmed in to memo ry, ancl o nce
th is Is p erformed, tone-acti vated repeaters
a re easy to use ; but if YOU' r e -scannin g
around~ looking for activity in an unknown regiOn and stumble across a tone-activaled repeate r not al ready in merTlOfy, there's no easy
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Multiple open windows
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over FFT size, sampling rale, scaling, gain, and
averaging. Requires 386 or better, Windows 3,1
and any Windows compatible 8 or 16 bit soundcard,
~-A strob of brilliance...a groundbreak;ng and
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CIRCLE 311 ON READER SERVICE CARD
24 73 Amateur Radio Today. August. 1994
way to access it without programming the
required frequency, offset and tone data into
memory fi rst. Azdan did provide me with
an updated sheet entitled, " Error in Azden
PCS-7000H Instruction Manual" which does
describe how to use a Pl tone in the "Direct"
mode, but the procedure is so complicated
it couldn't possibly be performed while driving.
The rig's 20 memory channels are stored
In two banks of 10, called AO-9 and BO-9. No
big deal, although simply calling them 0-19 or
1-20 might have been nicer. But the rig always "powers up" on memory AO, regardless
of where you used it last. This is frustrating,
especially si nce all my other modern FM
transceivers "remember" where they were
last used and "power up" on the last-used
channel .
Also, there's no VFO/memory knob of any
kind on the Azden, nor may frequencies or
memory channel numbers be entered directly
with keypad strokes. The only way to go from.
say, memory A3 to memory B5, is by using
the 'uo" or "down" buttons (either on the front
panel or on the PTT microphone) to go
through all the memories in between. And if
you depress the "up" or "down" button more
than momentarily, the rig begins scann ing
through the memory channels very quickly,
much too fast to stop on the channel of your
choice. With the technology and chip sets
available today, there's no reason for any
channelized radio to not have "direct frequency entry" with keypad strokes. (That is. if you
wish to 'dial up" 52.525 MHz, you'd just depress 2-5-2-5 on the keypad , and the rig
would go th ere instantly.) This used to be
tricky in the old days, but can now be done
with one $2 chip. In Azden's defense, however. I must admit that many modern FM mobile
rigs still don't contain this feature. Darned if I
know why not.
Another minor annoyance is that a user of
the PCS-7500H must refer to a "Tone Code
Table" when programming Pl tone frequencies. That is, the CTCSS frequencies, of
which there are 38 in common use, are not
actually displayed by the Azden during the Pl
selection process. Instead, tones are selected and displayed by two -digit codes which
might only be memorized by The Amazing
Kreskin. Since I'm not so amazing, I had 10
constantly refer to a chart on page 14 of the
instruction manual to determine which twodigit code corresponded to each Pl tone frequency. For example. Code ~19" corresponds
to a CTCSS frequency of 127.3 Hz. Sid Wolin
at Azden in New York did advise that the
newer-generation PCS-7000 series (unavailable at this writing) would incorporate a new
microprocessor which allowed direct Pl frequency address and readout, as on their
handle-talkies.
Programming the PCS-7500H takes some
getting used to if you are more familiar with
one of the other brands of equipment. It's not
difficult, but might be too complex for use "en
the fly" while driving. Again. to be fair, most of
the mobile rigs I've used are too complicated
to program without focusing complete etten -
tion on the task. But the Azden inst ruction
manual makes the job sound more difficult
than it is, with 12 paragraphs assigned to the
description. The Azden is unique in that it only stores the memory data when you turn the
rig off, and then back on. To quote from the
manual, "Note: Be sure to turn off the power
when you have completed programming. This
procedure 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, you
may get the idea that I really don't like the Azden. This Isn't true. I do like the rig, but it took
more getting used to than it should have. In
terms 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 a
magnifying glass, and wlll be of value to
those who like to perform modifications or do
their own service work. The schematic for the
PCS-7500H reveals the transmitter final power amplifier to be discrete (2SC2097), rather
than a molded hybrid ~b rick· (modular) amplifier as used by most other manufacturers. I
like the discrete approach better because it is
more user-serviceable for reasonable cost.
Should the PA "final" ever go out, it will be
much cheaper to replace a $10 transistor
than a $90 module. Not that I would expect
the final to fail; the people at Azden assured
me they've never seen one fail yet.
The PA circuit board also contains a discrete driver stage (2SC1972), the t herm al
detector which switches on a cooling fan if
the heat-sink temperature gets too hot, the
VSWR protection detector c ircuit (which
shuts the transmitter down if a gross antenna
mismatch occurs) , and a bandpass filter
ci rcuit which is in line with the antenna to
both the receiv er and the transmitter. PA
stage tuning is accomplished by a three-section low-pass matching network. One drawback to the discrete PA stage is Its cr itical
tun ing: The PCS-7500H does de liver 50 watts
as rated into a perfect 50 ohm resistive load,
but power output falls off rapidly when the
transmitter is faced with any mismatch at all.
The antenna I used for most of my testing, a
vertical with a measured VSWR of 1.5:1 , only
allowed the transmitter 10 deliver between 28
and 42 watts, depending on the operating fre quency and exact nature of the mismatch.
Some of the "brick" stages, while COStly to replace, are more forgiving of mismatches.
The receiver's front end, a 3$K101 dualgate MOSFET, is protected against transients
by 'back-to-beck" signal diodes and features
bandpass tuning of both its input and output
to 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 whose
output drives the IF SYSTEM integrated circuit, an MC3361D. The receiver's second IF
at 455 kHz is filtered by a 15 kHz bandwidth
ceramic filter, type KBF455R15A. The recelv-
er isn't razor-sharp, but suffices nicely with
the 20 kHz channel spacing common ly used
on 6 meters . One might think that a VHF rig
with a lirst IF at 14 MHz could be easily interfered with by strong 20 meter signals, but I
didn't find this to be a problem.
The transm itter uses what Azden proudly
describes as "true FM~ for modulation, and I
guess it is, with the microphone amplifier
stage directly driving t he veo variable-capacitance tuning diodes. However, I've never
been able to tell the differen ce between "t rue
FM" and "phase modulation," since, mathematically speaking, one is the reciprocal of
the othe r a nd a phase -modulated signal,
when integrated, becomes " FM .~
I did have a problem with the unit as received, in that the transmitted modulation was
tinny and distorted. Azden was surprised to
hear this, and immediately shipped a new microphone, thinking that was likely to be the
problem. It was, and t he new microphone
produced 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 mike
the day I called them on the telephone, because I received it the next day, 3,000 miles
away!)
One thing I think is a bit "clunky" about the
Azden is that it uses an old-fashioned relay
for transmi t-receive RF switch ing. Relays
work fine, and Azden claims they've never
had one fail, even in prolonged packet radio
service, but their switching "turnaround"
speed is rather slow compared with solidstate switches, and if the radio is used for
packet, the user may have to re-set switching
parameters in his TNC program. I was used
to using 30 milliseconds (mS) or less in packet switching, but this is too fast for a relay. I'd
recommend more like 300 mS for a relay-operated rig. There 's not a lot of packet activity
on six anyway, but if you really wanted to, you
could ho me-brew a PIN diode modification
fairly easily.
A listing of manufactu rer's ra tings vs.
bench measu rements made on th e 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'd
like. 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 California
Six Meter Club, which actively promotes the
use of this band , has ordered a great numbe r
of these radios for their members and they
are well accepted. In speaking with local 6
meter repealer owners, ! found they were all
very aware of the Azden and were either using one personally or had at least had their
hands on one. It does disturb me a bit that
th e t ran sm itter po we r output fa lls off so
sharply when connected to other than a perlect load, but since the FM subband on 6 mete rs is a narrow window of our spectrum (3
MHz), I suppose anyone with a lick of sense
could tune his antenna to provide a good
match if he had to.
The radio as reviewed is good. With the
improvements Azden has planned, such as
eliminating the twO-digit Pl tone codes, it will
be even better. II they also rewrote the instruction manual, and had one specifically
dedicated to the PCS-7500H, it would be bel·
ter still. [Factory Note: Ne w and improved
manuals are in the works.] On a scale of one
to 10, with a "10" being perfect, I'd rate the
PCS-7500H a strong 8: a good rig for the
money and, as I said earlier, maybe the only
game in town for a modestly-priced 6 meter
FM rig.
iii
Manufactu rer's Specifications vs. Bench Measurements
Variable
TX output power
RX sensitivity
Squelch sensitivity
Selectivity
RX audio output
Power consumption
Frequency coverage
Specification
50 walls (high)
<0.35!.iV/20 dB NQ
<0. 12f.iV threshol d
15 kHz/-60 dB
2W,10"lo THO
O.SA RX
50.0-53.995 MHz
Measured
47·52W (H)
0.30!!V/20 dB NQ*
O. 10flV threShold
15 kHZ/·57 dB
2,2W, 10"1" THO
0,5A RX
50.0-53.995 MHz
' Receiver Sensitivity is usually measured in j.lV/12 dB SINAD. For comparison purposes. the 0.35 ).lV/20
dB Noise Quieting would be a lower number if measured using SINAD. At 50 MHz, the difference in lhis
specification 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: ato
10, varies With frequency and VSWR.
Display-window bargraph used as RX S-meter, number of bars illuminated ve. received signal level:
= 0.9).lV (-108 dBm)
1 bar
2 bars
= 1.2).lV (-106 dBm)
3 bars
= l.4f1V (-104dBm)
= 1.8 uv (-102 dBm)
4 bars
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-+" (all 10 bars) is 16 dB. This makes the resolution extremely good for weak signal
beam peaking. but results in "full-scale" readings for any reasonably strong signal. Not uncommon for
FM receivers.
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CIRCLE 194 ON READER SERVICE CARD
73 Amateur Radio Today · August, 1994 25

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