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Author Topic: IC-761 vs. IC-765  (Read 8785 times)
KQ6UP
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Posts: 136




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« on: June 01, 2007, 11:26:06 PM »

I am the proud owner of a IC-761.  I love this radio.  However, I see that it's close relative the IC-765 has better receiver specs according to:

www.sherweng.com/table.html

As a matter of fact, the IC-765 is Icom's best radio ever.  Has anyone done any A/B comparisons with these rigs? I do a little contesting, and plan on a big antenna upgrade.  I am wondering if the stronger front end of the 765 be noticeable in a pile up during a contest.  The 761 is no slouch when it comes to receiver performance.  Would I even notice these performance differences? Should I just stick with my 761 or hunt down a 765?  I think the Pro III's are slick, but I can live without a band scope, and I love these big ol' beauties.

Thanks,
Chris KQ6UP
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K8AC
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Posts: 1465




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« Reply #1 on: June 03, 2007, 04:34:51 AM »

Never owned a 761, but have had a 765 for several years.  Don't forget that Inrad has a roofing filter for the 765 - haven't seen a test on one that had the roofing filter however.  The 765 has held up well over time, with very few common failures to worry about.  I wouldn't want to be without a spectrum scope and that's why my 781 is still the main rig here.  Not of much use on the lower bands during a contest, but very useful on the higher bands in spotting activity that might otherwise escape your notice.
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KQ6UP
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Posts: 136




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« Reply #2 on: June 03, 2007, 06:23:54 AM »

I have a local ham here who does six meters.  He actually preferred his old IC-761 over the ProIII, but he could not live without the scope too.  He works a lot on 6m.  Change I change filters on the 761 to get similar specs on the 761 as the 765 does.  The 2KHZ dynamic range (rejection or whatever the heck it is) is supreme on the 765.  It even beats the IC-7800 for the strength of its front end.

Chris KQ6UP
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N9DG
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Posts: 308




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« Reply #3 on: June 03, 2007, 07:44:03 PM »

Keep in mind that the IC-765 numbers on the currently posted Sherwood chart are for a "modified" IC-765 as noted by footnote "m". Unfortunately he did not also keep the original listing of the unmodifed 765 in the chart that is posted. This is a bit puzzling given that the FT-1000 MK V Field is listed both with, and without, the Inrad roofing filter mod. Would have thought that 765 entry would have been treated the same way.

BTW the original test results showed the 765 to have a 73dB close spaced DR. That would put it about on par with the 781 entry on the current web posted chart. So not significantly better than a 761 in that regard.
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KQ6UP
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Posts: 136




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« Reply #4 on: June 03, 2007, 08:09:26 PM »

Is there a good article describing a practical interpretation (meaning) of these test results.  I would suspect that The 2K spaced Dynamic range is an indication of the receiver's ability to reject close and strong stations.

If the 761 were modified with these filters, would they have similarly good specs?

Chris KQ6UP
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K9KJM
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Posts: 2416




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« Reply #5 on: June 04, 2007, 01:20:16 AM »

I have owned an Icom 761 for over 15 years now. GREAT old radio!   But the 761 and 765 do NOT have 6 meters in them..........  At least none of the models I have seen........  160 thru 10 meters plus all band receiver.  I heard that the 761 had some kind of patent infringement problem.......   Thats why it was kind of  a short lived radio, And Icom came out with the different receiver in the otherwise very similar 765.
I agree with the other post, Once you have used a radio with a good bandscope, You will not go back to a rig without one.  My favorite "bang for the buck" HF radio right now is my IC 756PRO.
I now have three HF rigs in my shack, A Kenwood TS-2000 (Love it's cross band repeat and "Jack of all trades" ability, But it does not compare to either the good old 761 OR the 756PRO.
I find myself using the 756PRO for most HF use. Just cannot bring myself to get rid of the good old faithful 761!!
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N9DG
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Posts: 308




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« Reply #6 on: June 04, 2007, 07:57:46 AM »

For a discussion about the receiver performance parameters you will want to look at these:

http://www.sherweng.com/images/MeasurementAccuracy&SampleVariation.pdf

http://www.sherweng.com/presentation.html

http://www.w8ji.com/receivers.htm

Here's a link that has some details about the differences between a 761 and a 765.
http://www.ab4oj.com/dl/765_108.pdf

You may also want to look at the AGC mod by N6BV. Try doing a Google search with "Icom 765 AGC", it gets a number of hits related to the issue and the mods. It improves the in band audio IMD performance of the 765. I did the mod to mine with modest improvement to the audio fidelity. Don't know if the 761 has a similar AGC issue or not.

I also agree with those who say that once you've used a good panadapter with a radio you really won't want another radio without it. The best pandapter for my tastes is the one built into Flex Radios PowerSDR program. Winrad is also very good. The "in radio" panadapters that I looked at Dayton this year were *all* rather slow, and not the greatest for resolution.
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K8AC
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Posts: 1465




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« Reply #7 on: June 05, 2007, 06:01:38 AM »

KQ6UP asked:
"If the 761 were modified with these filters, would they have similarly good specs?"

No.  The problem lies with the effects from signals lying outside the passband of the filters.  Mixer design, gain distribution, etc. different among the various receivers.  Haven't looked at the 761 filter lineup, but many of the Icom models shared the same filter lineup but the receiver performance could be quite different.  See the W8JI discussion of receiver performance for more info.
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NR9R
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Posts: 147




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« Reply #8 on: June 27, 2007, 11:57:23 AM »

From what I understand, the IC-761 and the IC-751A, are basically the same radio.  The IC-761 was offered as a bigger box, with a built in power supply and narrow filters as standard.  If you search in the ICOM service bulletins you will find that the IC-751A and IC-761 are cross referenced.  The IC-765 is a totally different transceiver, however.    
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SANBORN_EX_AD9DX
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Posts: 5




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« Reply #9 on: September 08, 2007, 03:45:54 PM »


 I have owned an IC-761 and wish I would not have let a friend talk me into selling it to him.

 In talking with Scott at MTS I understand the 765 does not have the factory TCXO nor the preferable filters found in the 761.

 He also mentioned two other interesting details, he owned a 761 NOT a 765 by preference, and he mentioned the synthesizer in the 761 provided less phase noise in comparison to the 765.

 I have not yet had an opportunity to operate a 765, but considering the factory differences alone I believe the 761 may be the better value, however, I also wonder why better test results from the 765 were attained.

 73,
 KC6Ocean
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KI4Z
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Posts: 37




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« Reply #10 on: October 06, 2010, 06:16:09 PM »

IC-761 to IC-765 Receiver Front End Comparison thru 455 Khz IF Stage.

I both both the ‘761 and ‘765 service manuals and did a cursory comparison of the receiver front ends of each at the block diagram level.  They appear identical with the following exceptions:

1) First IF Frequencies are Different:  ‘761 is 70.4515 Mhz      ‘’765 is 69.0115 Mhz  Filtering after the first IF appears to be identical implementing a monolithic crystal filter (MCF) followed by a dual gate mosfet IF amplifier. It would appear that the INRAD roofing filter replaces this MCF.

2) ‘765 includes an additional 9 Mhz  monolithic filter right after the 9 Mhz second mixer, but before the Noise Blanker.  FL-23 is called a Monolithic filter in the parts list, and has a 9.0115 Mhz  Center Freq. with a bandwidth of 15 Khz.  This FL-23 filter is used elsewhere in both the ‘765 and ‘761.

The receiver front end schematics appear to be similar, but were redrawn, making direct comparison a bit complicated.  I will attempt to make detailed schematic comparisons over the next few weeks.

’73  mark   KI4Z
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N1YE
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Posts: 38




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« Reply #11 on: October 07, 2010, 04:19:59 PM »

I have both, a 761 and a 765, side by side in an SO2R station. Both are connected to same type of antennas and both are computer controlled through the CI/V network.  Both are loaded out with all of their filters. They perform equally well. The receiver boards are different. The 761 is similar to the receiver board in the 751A, but has more slots for filters than the 751A. (I have one of these also).  The control layout is very similar between the 761 and the 765, but there are some differences as well.  If I had to choose one, I would probably choose the 761, but that is only because I have had it longer and thought of it as "my favorite" long before I ever had the 765. If I just happen to be on the 765 when I snag the next "rare one" or bust a pileup, the 765 could become my new favorite. Either radio, one can't go wrong.

 73
Gene
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AA4PB
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Posts: 12667




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« Reply #12 on: October 07, 2010, 04:31:04 PM »

As I recall, they came out with the 765 primarily to eliminate the pass band tuning function of the 761. They were sued by another company over the 761's pass band tuning implementation.

I don't think there were any other significant differences between the stock 761 and the stock 765.

I had a 761 and never did get the 765. I went from the 761 to a 756PRO.
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KI4Z
Member

Posts: 37




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« Reply #13 on: October 07, 2010, 07:39:58 PM »

N1YE is right, life is too short to do an indepth difference comparison between the two radios, they're both good.  Except for the additional FL-21 9MHz filter after the first mixer in the '765, the relevant receiver front end schematics look identical, same active components, same filters etc.  There are likely gain/frequency tweek differences which would affect overall receiver performance specs.  I'm sure the '765 has improvements in PCB layout etc since it is a later design, but the '761 includes better filters, PBT, and the high stability oscillator stock.  The surperb Sherwood specs for the '765 are more likely a result of a  precision alignment, and more modern/capable test equipment rather than specific circuit differences.  Either rig remains near the top of the analog rig game.  I just bought my second loaded mint '761 for $500 and plan on some diversity/stereo RCVR experimentation.  Might install the "experimental" '761 INRAD 70 Mhz roofing filter in both for fun. 

Over an Out on this subject.

'73  mark
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KI4Z
Member

Posts: 37




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« Reply #14 on: May 28, 2011, 02:11:43 PM »

Bought two Inrad 70.415 Mhz roofing filters for the IC761 plus adapter boards.  Looks fairly easy to install.  This plus a Norton Preamp, quad fet PE4140 first mixer with +25 dBm LO drive, and a few product detector/audio fixes should make this a rig at the top of the game.  I will be able to do A/B comparisons with two 761's. 

mark 
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