ICOM R75 radio review

 

ICOM R75 radio review

Comparisons  between ICOM R-75 and LOWE HF150

A very thorough refiew of ICOM R75 in two times arond 2001 and later (2005?) 

Here  you will see my impressions on my NEW R- 75 and how it was to oprerate this receiver. I have spent a lot of time ( more than 20 hours) to provide such  information Together  with it  I will state soem comparisons  with my previous HF150 of LOWE

updates  are made with bue colour (see at the end of this file)

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1. Impression on operation

Ergonomics and button operation: At first contrary to what I read in a web page , many buttons use more than one operation. For example by pressing SSB you can have either LSB or USB . Using other buttons such as filter , this information can be retained still after changing the operation mode . If you press AM and then SSB , it can show at first last active operation ( say LSB together with its bandwidth say wide LSB)

The tuning knob was very easy to use , somehow softer than the HF150 which recently has been stiffened too much that I can only use it with a screwdriver ààThere is also a adjustment knob for more stiffer usage

It also has the same facility with LOWE by having fast tuning together with its slow tuning. The tuning steps can be set from 0.1 to 50kHz steps but still there is a nice facility to tune it down to 1 hz ! Adjustments can be set either to MHz or to kHz but easily û by pressing the step knob for 2 secs the adjustment can come down to 1 Hz with full feq readout !

The most interesting button is the RF/SQL button. It can be set either as RF/ SQL( squelch) or only SQL . Its left part works for RF and in its right part works as Squelch. When adjusting to SQL the S meter indicator shows the squelch level for half a second  or keeps  clipping level

The second interesting button is the PBT with its twin passband . It works best in the narrow filters as I have not seen any differences while in normal or wide filters . In contrast to what I read , only the one knob ( the 2^nd IF) is required to offset the frequency ( RIT) by 1.25 kHz  only when the naroewest filter is selected ( 2.4)

Settings

: All modes and operations are easily set via the [SET/ ANT] button . When you push at once the set button rolls a menu with more than 20 settings starting from SQL/RF , to S indicator , LCD lighting ( with 1% steps tough on the screen 10% steps are only shown) and setting for the optional units as voice synth and also BFO settings for CW andRTTY It was somehow tricky however to adjust freqs for my MFJ reader 462 in order to properly tune in the range ( it required the lower setting of 1200 Hz forRTTY and abt 600 hz for CW. In some cases CW requires also external filter )

For filter setting there is another button, at same bank with mode buttons It is saved with the mode.In genaral  by pressing any settings , it shows the last used operation

Modes: MOdes  are set directly  from the coresponding  button right  side from the LCD display There are  some variants made  by pressing the button   for 2 secs (esp on CW an RTTY). Here are the modes i found  with it

AM ........CW...........LSB...... RTTY.....FM
AMS.....CWN........USB......RTTYN....DSB*

CWN( Inverse) and RTTYN( Inverse) are made with the consistent pressing of  the mode for more than 2 secs
DSB  is made with a filter technique  shown later . (see filtes)
Each mode (duringVFO) keeps  the last selected filter and AGC

 

Noise  blanker: I saw that Noise blanker  can work relativel well under the SSB mode. However  in many cases  the MB can still work on AM  but not always . Durign soem observations the AM NB mode can work when:
-AM is used on narrow band only
-you can use it  in relatively low signal band ( as 9-9.2 MHz ) and only when a standard level of preampliication is given

 

AFC:

AFC operation is saved with the mode . Did not see any difference between normal and fast AFC on AM(/S) though in SSB  worked properly  . AFC-off does not show any signal in the S-unit and audio comes disturbed during normal AM

Bandwidth:

The receiver has normally 3 bandwidths 2.4 , 6 and 15 kHz and you can join them from the two IF stages and set them via a set menu . The 2+2 kHz filters are capable to off tune during  NB AM operation  soemtiems it ahppens also to 6kHz
During AM mode the 15 kHz surely can pass QRM from nearby stations but there is nearly no significant difference in audio fidelity when using headphones. This fidelity  can be heard  a little  from the built in  speaker

Filters :

There are many intereting points  regarding to the filter selection.  from the filter set mode. Each mode keeps  diferent filter settings for  the normal , wide and narrow band, however LSB and USB still keep the same filtering ( you cannot have dieferent seting for LSB Wide and USB wide) . same can happen to CW  with CW inv, and RTTY  with RTTY inv

Each filter mode ins mostly a combination of the 1st and 2nd IF filters or no combuination at all. The combinations are between 2.7, 6, 15 kHz or setting the 9 MHZ filter off ( then using only the 455kHz filter) . I could like to see however the receiver having a 4th combination when  the optional  filter is used.

Using the expanded filter mode you  can expand the bandwidth of SSB  towards a DSB  operation  for 6 and 15 kHz  bandwidths thus having   higher fidelity audio.
When you are on USB expanded  operation  by changing the mode to LSB is like  to listen to the same signal .....
IN the case of listening to AM  stations ,carrier is not totally deleted neither  blanker efectively works
Expanded  filter effects  to all the modes.

CW /RTTY settings

: By pressing CW for more than 2 secs the CW operation is inverted , same happens toRTTY by choosing reverse mode ( and tuning again )

Sensitivity

: when using A/B testing with parallel listening theR-75 shown a slightly better sensitivity with preamp off. And LOWE was with ATT on ( and usage of two mini ear headphones)

Stability : The R-75 seems to be very stable also  after hours of using. HF150 seems not so much as R-75

Display:( bad poits)

LCD display does not have any protective glass  , so touching it the  displayed information  becomes nearly dull . Toching  it also can produce some little noise eap in the lower bands ( LW- MW)

Preamplifier

: The preamp seems to work properly with good amplification in most cases also when using the loop with inductive coupling. See also on overloads

Memories:

There are only  99 memories plus 2  for  scanning purposes. As i m not so keen on memorizing stations  i thik these are OK  for me. When  you recall a memory  and then tune, go to VFO and  back to memory  the previously tuned signal  is lost.
All memories contain the following : freq, mode, AGC , amplifier, attenuator and antenna selection . Storing memories is very easy .R-75 offers also facility to skip unused memories. Mode retains the last used AGC 

Signal indicator: It is a good facility and my best in my signal measurements .Stations  can be still readable  even the indicator canot  show anything.However with signals higher than S9 the S meter seems not to correspond corectly in signal fluctuations and required from me to use the attenuator and the preamplifier  in order to see the fading levels

Audio

:R-75 shown good audio from its internal speaker , sharper than LOWEÆs and comes only from the fidelity of the built in speaker . In the contrary using headphones the LOWE had better and higher fidelity sounds (good for HIFI reproduction while on AMS )
Audio is always clear and no background hiss is heard during no signal

Reception  coments:

Am reception:

it is something I did not like so much. Most of the signals on AM mode can show some instability lower or greater depending on the fading level and speed On co-channel QRMed stations it can be a BIG problem , The Lowe does it much better without any instabilities.

AMS

: synchro mode shown no enhancement from normal AM ,. When the wide filter is used ( 15 kHz) and QRM is inside the determined bandwidth , signal is distorted . LOWE was much better by giving good signals without any distortion at any case even when there is some QRM inside the bandwidth The  range the AMS with the 6 kHz filter  can 'lock' (?) is  +/-  3.3 kHZ  then the BFO signal is heard !

SSB

: this is my most important point on this receiver. When reception on AM is not good , the SSB works excellent. The use of PBT ( and also with the usage of DSP noise canceller ) can provide very good results even in very low AM signals ( for less than SO11) so sometimes you can identify at least the language. I think that the SSB operation is better than the LOWEÆs also from the audio reproduction . As in result my MFJ audio filter is now useless in this point !Only the PBT of the narrow filter is mopstly required. In some cases the LSB mode took part from the carrier showing part of it though the USB showed the modulation  of the signal (?) or must to tune off the passband

CW andRTTY

: It seems there is a audio filter fitted in the receiver though it is not very narrow ( esp for the CW operation)MY reader 462 in CW operation seem still to require the MFJ filter in order to read the poorer signals . As onRTTY after the trick by lowering the BFO the reader can recognize well the signals

FM mode: Unfortunately  there are NO stations in our area  using FM  so i cannot give any opinions.

DSP operation

: despite whatÆs refered that DSP does not work on AM , I have seen good results as noise canceller and auto notch
The references ( and the book guide) shown that autonotch  does not kill carriers. It is not true During my MW research on 11-2 the filter indeed,in auto notch mode  can cancel-out any carriers at good levels if not completely It can also cancel out completely the BFO generated during offtune of an AM station when using SSB.
The DSP  worked best   with white noise but other noises  ( such as  from fluorescent lampsor other locally generated noises ) are ot completely cancelled, only  from 10% to 40%
Levels  up to 7  are working OK without masking  except of cases of overmodulated audio signals or badly modulated   signals ( such as  poor modulation index or bad carriers found in greek pirates as example) with signal  masked or truncated
Moreover , DSP in no operation produces clicks  when you make freq adjustements from the freq nob

Overloads etc.

BDX reception:

Though I m living relatively close ( abt 15 km far) from the local MW stations all signals on MW band ( and even on the SW band ) did not exceed the S9 +40 db , neither the receiver shown any overload with preamp on . IN contrast to what is stated , I had good reception in the MW bands with the sloped 8 m antenna  

As  for example, 1044  , the local ERA  station transmits with a 50 kW signal  making a S9+30 dB . During nights  the signals on the nearby  freqs ( 1035+ 1053  at nearly S9 level ) are still heard without any signaificant problem except  some little splatter when ERA plays  music

SW reception

: There was no overload on any bands at any case. Many strong broadcast band stations do not exceed the S9+20 db limit . IN some cases the HF150 did overload or received some splatter from nearby strong signals butR-75 not.With the replacement of  the 8 m antennas however to the 16 m antenna  , there is some real overload especially in the SW band

Seflf generated carriers ( new) :

 Using the  technique  of connecting a very short wire betwen the  500 ohm  input and ground  and  full preamplification  i hae found the follwing cariers
Stronger 456 kHz and 39982
Lower: 7995.....9997...11995...15990...19660...19990...21987...23003...27982...30000...31981...35977...39320...44236...
45971...47970...49150...51967...54065...55690...58980
There are still  lower carrier  but are too many to mention
Still  under   connection with the extenal antenna  ther are soeme products generated  found on 9370 and other s still not treid to  see

VHF harmonics

R75
As usually  he receiver generates some harmonics by its own,. I found  that the armonic generates is exactly the 2nd harnmonic of local VFO plus  the frequency used ie (VFO+ QRG) * 2 checked with the MVT7100 For erxample for 3500 becomes 145020 Also the change of the mode varies the harmonic according to the  VFO used
As in  result  considering  that with AM mode being  x khz the frequencies found are as follws:
LSB........0.2
USB......6.4
FM.......3.3
CW......1.5
TTY.....1.2  kHz  above the AM mode
Signal is ound to be S9 on the MVt7100 , attenuator on , with full antenna located on the left edgeof the  receiver

HF150
Nearly the same happens  with the Lowe HF150 according to the fiormula of (70MHz +QRG)* 2. In contrast to what is happened with R75  varrying smoothly with the frequency , the HF150 changes by the kHz  freq so making a skip.
Signal  S6 on the left edge of the receiver

Front panel harmonics

By sudden  try the R75's  front panel seems  to generate  soem mysterious harmonics esp on the 108-165 mHz band when the MVT was too close to it even with the R75  being off ( but not when plugged off the mains) . Do not know  if this  is an efect on the MVT's internal circuits or if it comes really  fromthe  R75 front panel  but i have found that all this band was full of  carriers  with strongers  bein on the follwing  freqs ( signals  were of S4 to >S10 being zero at a distance of 1-1.5 m  )

115.5...117.96...120.42...122.88...132.7...137.62...140.08...142.54...150.98...153.6...154.82...157.28...162.2...

These carriers  are also heard inthe R75's reecption on upper LW band

 

Overall

: Despite of the main problems ofR-75 with its synchro detector and its instability with co-QRMed stations om AM mode it is worth a buy . In general I like the receiver too much , much better than my previous LOWE HF150 especially for the very poor signals I live most. The nicer operation for me is the twin PBT that can enhance too much a DX reception and the slightly better sensitivity !Also the excellet S meter and frequency readout down to 1 Hz !