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www.southgatearc.org
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The Icom 7800 on Data
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The Icom 7800 -
front view showing the TFT display
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The TFT display on the 7800 is superb. At first sight, it was difficult
to take my eyes off the analogue meter on the display. This is so realistic!
It is not a transceiver to go straight on the air out of the box, but
of course I did! I got some awful audio reports so I decided to do the
sensible thing and read the book.
To say it is menu driven is an understatement. It really is a computer
with some excellent RF circuitry attached. The audio had to be set up,
and there are several adjustments to be made, after finding your way within
the menu. Once done, they can be stored, either in memory or on Compact
Flash disk. Thus, if used in contest or expedition situations, each operator
can store his own parameters, thus saving a lot of setting-up time.
I spent some time playing, and finding my way round the various menus, having some contacts on CW and SSB. I found it to be a very enjoyable transceiver to use, and was very impressed with the performance. It would take a lot more space to describe the parameters and other information displayed on the TFT screen and to discuss the two completely independent receivers, but my mandate is to try it on data so I will leave the rest to somebody else. One small thing I must just comment on however. Working split when trying to contact a rare DX station can sometimes result in calling, by mistake when pressing the wrong button, on the DX station's frequency. Working split with the 7800 is so obvious. There is a very bright white LED in the middle of the top that you just cannot miss, a nice thought.
Data Operation.
In order to operate data modes, a USB keyboard has to be plugged into
the rear panel.
I did not have one, so decided to ask a friend who works within the computer
industry.
He did not have one, so I asked around locally. Nobody had one, so I decided
to visit PC World and buy one. They did not have one. This was becoming
a problem! A friend suggested Maplins, and perhaps a USB to PS2 adaptor
would cure the problem. Success, I managed to buy an adaptor. Asking at
Maplins about a USB keyboard, they said that it would become the norm
eventually, but at present there are not many around. Arriving back home
I connected my PS2 keyboard with adaptor. Still no success. A phone call
to Icom confirmed that the driver in the 7800 is for a USB keyboard and
despite the adaptor, the PS2 keyboard would not work. Icom posted their
USB keyboard to me.
CW.
This being the basic data mode, I decided to try this first. I had several QSO's and operating the transceiver with it's internal keyer is a real pleasure. Tuning around the bands can be quite fast by selecting the appropriate tuning speed. The frequency can be changed in kHz steps from 0.1 to 25kHz. For fine tuning, the ¼ tuning function can be selected. This reduces the dial rotation to ¼ of normal. Then for extra fine-tuning if needed, a 1Hz step can be selected. There is also a tuning step function, which is similar to the shuttle-jog tuning on the FT1000MP. The speed can be set in the menu to high, low or off. I found leaving it on high to be the most useful.
[Operation]
The transceiver features DSP controlled CW keying waveform shaping. The keying sidetone is pleasant to listen to, and can be adjusted to suit the operator with a pitch control from 300 to 900Hz without affecting the transmit frequency. Full break-in is available if required, or semi-break-in, or off. Personally I don't like full break-in. A neat feature is the ability to listen to the tone of the transmit signal whilst receiving. This enables a zero-beat net without actually transmitting. I was particularly interested in the keying characteristics and arranged a sked with a local, Dave, G3MPN, whose opinion I respect. Having an FT1000MP with key clicks (haven't they all?) I wanted to find out what this was like. In the tests, we adjusted relative signal strengths from S-2 to about S-9 plus 20. No clicks were detected, and the ability to adjust the keying waveform rise-time resulted in the conclusion that the default of 4ms was the best position.
There are four positions to chose from and 4ms produced the best sounding
keying. We also tried it close in to a strong signal. The IC-7800 has
two types of AGC loops. One of the loops detects the AGC voltage at the
BPF input in the DSP unit and feeds back to the 1st IF amplifier. This
AGC loop prevents saturation of the 1st IF amplifier from strong signals
out of the BPF bandwidth, and improves the dynamic range against adjacent
signals. The other AGC loop detects the AGC voltage at the digital IF
filter output which has only passed the intended signal and draws the
full potential from the digital IF filter. Looking at the shape factor
on the TFT screen, the selectivity is really text-book and coupled with
the band-pass filtering, I would think this would be difficult to beat.
An audio peak filter is also available to boost a weak signal. Selectivity
is superb and under crowded band conditions, the 150Hz position with APF
as well, really pays off. There are four memory locations that can be
edited and each location has a maximum of 70 characters. Barred characters
can also be entered, such as AR, SK and so on. For the casual contest
operator, there is an incrementing serial number, with cut numbers if
required. Dot/dash ratio can be adjusted too.
Dave, G3MPN and Malcolm, G3PDH, both visited and I asked them to try the
transceiver on CW. Both agreed it was a very agreeable transceiver to
use, plus they both agreed with me that QSK was not for them. Malcolm
tried it on 14.025 and being an FOC member, he had a pile-up that took
him about 45 minutes to quell!
RTTY
Having received the USB keyboard from ICOM, I plugged it in and set
the transceiver for RTTY receive. I was beaming to the Far East at the
time and the first station I decoded was DU7/G4DUM, Vic, and he came back
first call. We had a chat and then I found BX4AN. After a QSO with him,
I then had a contact with Claude, XU7ABM. Not bad for the first three
RTTY contacts!
The displayed RTTY screen is very similar to my MMTTY and Writelog combination.
The screen is split, with the receive screen above the transmitted text.
The tuning indicator is the usual two vertical lines, one at 2125Hz Mark
frequency and the other at 2295 Space frequency, giving the required 170Hz
shift. Again in the RTTY mode, selectivity is superb. The digital IF filter
has superior filtering performance and a distinguished shaping factor
that demonstrates the power of 32-bit floating point DSP. The digital
filter is completely free from deterioration due to deviations in band
characteristics, temperature change, or mechanical vibration. The digital
IF filter also provides excellent ripple characteristics and the filter
shape is selectable from soft and sharp, depending on the purpose.
Bandpass filtering is also available, as well as a notch. The DSP-based
manual notch provides stable performance and completely shuts off undesired
beat signals without affecting AGC gain. I normally use bandpass tuning
in MMTTY with the notch set in the middle of the passband. Operating this
way, with very tight filtering, it is possible to squeeze stations really
close together. The 7800 also has a twin peak filter, which boosts both
mark and space frequencies. This is fine and works well on weak signals,
but only when the station is tuned in. I found that tuning around with
this function enabled was difficult due to the increase in noise level.
A few stations send in reverse mode, and to compensate for this, there
is also a RTTY-R or reverse mode. The threshold level can be adjusted
too; this helps to prevent too many stray characters being displayed on
the screen. As the receive screen has no scroll back, a hold function
has been provided so that the contents of the screen can be frozen for
a while. However, there is a facility for saving data to the CF memory
card. The sequence for achieving this is somewhat convoluted and would
require some practice, but once committed to memory ( the human kind!
) I don't think there would be any problem.
The newly designed push-pull power MOS-FET amplifiers work with 48V DC
and provide 200W of output power at full duty cycle with low IMD in all
bands. However, regardless of statements like this, I always err on the
side of safety and reduce the power for RTTY transmissions, being a 100%
duty cycle mode. Another factor to consider for RTTY is stability. No
problem here! The IC-7800 has a standard stability of 0.05ppm. This is
why there is no optional extra of a high stability oscillator unit!
Other bells and whistles in the RTTY mode include Unshift on Space function,
selectable on and off, a diddle condition ( boy how I hate those diddlers!
), auto CR/LF capability and a time stamp facility which gives date/time
and frequency depending on how it is set up. There are eight memories
all of which can be pre-programmed but, like the CW memories, each has
a maximum capacity of 70 characters. Editing these can be accomplished
in two ways, one from the key selection on the transceiver and rotation
of the dial, or directly from the keyboard. The second method is far superior
for obvious reasons. Font colours can be changed to suit individual tastes,
and saved data on the CF disk is compatible with a PC and can be transferred
to the computer if desired. There is NO incremental serial number in the
RTTY mode.
I set up my FT1000MP with my PC together with MMTTY and Writelog, and carried out some tests with Dave, G3MPN, comparing both systems. In order to obtain a weak signal, we used 21MHz and side-on beams, with pre-amps off. Over a period of several minutes, using the same text, the IC7800 was better at producing more legible copy. The keying was very clean with no distortion or IMD products, as indeed we expected as FSK is used. The signal was barely perceptible over the noise and was probably of the level that would be ignored.
PSK
It was interesting to note that when changing modes from RTTY to PSK,
the tuning display did not alter. I had to press EXIT/SET and then DECODE
once again in order to display the PSK tuning. The main dial has to be
tuned to the desired signal and has to coincide with the waterfall display.
There is also a vector tuning display that can be used for accurate tuning.
Similar conditions apply to PSK as I have already mentioned regarding
RTTY and the bandwidth can be narrowed even further of course.
BPSK ( Binary Phase Shift Keying ) is the more common mode used on the
bands, but QPSK ( Quadrature Phase Shift Keying ) is also covered with
the 7800. This requires more accurate tuning and is not used very much.
Threshold level can be adjusted in the same way as RTTY, and the memory
functions are also the same, with eight pre-programmable memories to choose
from. Time-stamping is also the same as is the selections of font colours.
Data can be saved to a PC if required.
I did similar tests again with G3MPN, and again found the 7800 to be extremely sensitive, with legible print on an almost inaudible signal. The RTTY/PSK modems are really first class and produce very pleasing results.
Other facilities.
There are many more aspects to discuss in this transceiver, but I was
primarily concerned with the data modes. Along with these abundant functions,
a large 7-inch wide color TFT LCD display that displays settings and operating
conditions, forms the main focal point of the transceiver. Looking at
the two photographs, one with RTTY
and the other with PSK displayed, you can see that everything you need
to know about the operation is displayed here. The readability is surprisingly
good, even for an old G3 like me, who now has to wear reading glasses.
The main aspects of any transceiver in data modes are selectivity and
stability. The 7800 has both and the performance proves that.
The IC-7800 uses highly reliable and durable mechanical relays for BPF
switching instead of non-linear semi-conductors, which cause distortion.
The mechanical relay prevents 2nd order distortion at the primary stage
of signal processing. The IC-7800 has two roofing filters before the 1st
IF amplifier stage. One is 15kHz filter for FM mode and the other is 6kHz
filter for SSB, CW, AM and data modes. The IC-7800 switches between these
two roofing filters depending on operating mode. The use of roofing filters
dramatically improves adjacent strong signal blocking characteristics.
One feature that I have not seen on a transceiver before is a timer. If,
like me, you forget times of skeds, then this can be programmed into the
transceiver so that it comes on at the correct time, frequency and mode.
It is much like a timer on a video recorder, with time, date, period,
and modes, together with a sleep function.
To buy or not to buy.
Apologies to Bill for that quote, but this is a serious question. I
suppose that with a price tag of £6,500, a G3 would have to think
long and hard about it. The problem here is that having attained the bus
pass numerical equivalent; I equate prices of today with what I could
have bought some years ago. For example, the price of this transceiver
is three times more than I gave for my first 3 bedroom, 3 reception detached
bungalow in half an acre of ground! I am told I should not do this, but
it really is difficult. Put another way, the cost of the transceiver is
more than my yearly pension. Hmmmm, I really must get a life!
Looked at from another perspective, if I have more years after me than
I have before me, and have some money set aside for a rainy day, then
I could say "Here's that rainy day". Nice tune by the way. Whatever,
I would say that purchasers there will be for this transceiver, whether
it's the big boy's toy syndrome, the latest technology, or the thought
that if I spend that money I will always be first in the pile-up. I would
come into the second category. If you are in the third one, just remember
that whatever transceiver you have, your signal is only as good as your
antenna.
For a general-purpose transceiver covering two data modes as well, to
work dx-peditions on RTTY and PSK as well as SSB, CW etc, then this is
ideal. With my FT1000MP, to work 3B9C on RTTY, I had to link up the PC,
initiate the software and interface. The 7800 does the same job far more
elegantly. Flipping from mode to mode is so easy, making DX-ing a doddle.
However, if you were an avid contester on RTTY for example, then my FT1000MP
with the PC running Writelog and MMTTY would beat it hands down. But,
if you wished to do this with the 7800, it is possible to hook up the
PC and do just that, plus you can also have that lovely display transferred
to the PC screen as well! So, the bottom line is that if you want it and
can afford it without going short on food or heat, then go for it; I know
I would!
The only criticism I have is the fact that the user has to supply the
USB keyboard. I would have thought that this price range would have included
that. However, I also note that no microphone is supplied either. It is
also an "option".
I am grateful to Icom UK for supplying the transceiver - twice - for review,
and also for sending me a keyboard, but am disappointed that I have to
return it
73 de Roger G3LDI
News views and pictures to Roger, G3LDI @ GB7LDI Tel:
01508 570278
E-mail
rcooke@g3ldi.freeserve.co.uk
g3ldi@amsat.org
g3ldi@qsl.net
Post: The Old Nursery, The Drift, Swardeston, Norwich, Norfolk, NR14 8LQ
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