eHam Forums => Misc => Topic started by: W0XX on December 21, 2012, 01:22:49 PM

Title: ICOM IC-781 Impressions
Post by: W0XX on December 21, 2012, 01:22:49 PM
I have heard that even at this point in time, many still consider the 781 a very good radio (albeit the 2 khz close adjacent QRM ability is a bit lacking).
Any inputs or thoughts on this radio?  Just curios.

Title: RE: ICOM IC-781 Impressions
Post by: W0XX on December 21, 2012, 01:28:11 PM
And, for that matter, can one run the SDR software to get the bandscope external to the 781 (using its IF).

Title: RE: ICOM IC-781 Impressions
Post by: W0XX on December 21, 2012, 08:03:42 PM
As good as the FT-1000MPMK5?  WHich would one consider better?

Title: RE: ICOM IC-781 Impressions
Post by: K8AC on December 23, 2012, 06:18:53 AM
Having owned both the 781 and Mark V, I'll give you my opinions.  I don't understand the comment regarding the "2 khz close adjacent QRM ability".  If you're talking about the ultimate filter attenuation, the 781 and the Yaesu FTDX-5000 measured out exactly the same at 90 dB.  While the narrow spaced dynamic range (see Sherwood charts) is below the bogey of 80 dB, I never experienced a problem with IMD when operating many CW contests on bands full of strong signals.  I did experience IMD problems on my Icom Pro III, which had a slightly better narrow spaced dynamic range measurement.  In any case, roofing filters are available from Inrad for the 781 and that should eliminate any concerns there.

The problem with running SDR software for an external bandscope is the high first IF frequency of the 781 (just like all other more modern Icom rigs and most others).  I understand that there are some new SDRs that can handle the VHF range and it's possible that one of those would handle the 781 IF signal OK.  You would want to use one of the Clifton Laboratories buffer preamps at the IF tap point.  The other problem would be having the SDR that supports the SDR receiver you use also support the 781 from a CAT standpoint.  A panadaptor whose frequency is not synced or calibrated to the transceiver frequency isn't very useful.  Getting all this to work in a stable reliable manner is not a trivial matter and in exploring panadaptor solutions with other transceivers, I found that things rarely worked as well as some folks claim.

The FT-1000MP Mark V was one of my favorite radios for CW, RTTY and SSB.  I'd have to rate the 781 above the Mark V from a CW standpoint because of the terrible key click problem with the stock Mark V, although that can be pretty much resolved using either the W8JI or Inrad modifications.   The 781 suffered from an ALC problem that caused a leading edge power overshoot, but that one could be resolved by restoring the ALC circuitry to what the schematic showed (this is well documented).  The 781 also had problems with the switching regulator and that's something that just about all of them have sooner or later.  The repair of that problem is not easy.   Some Mark Vs had a problem with the high voltage power supply that powered the display, resulting in a rather dim display.  Again, there are fixes available for that. 

Either rig would be a nice addition to the shack if the common problems are corrected.  You can expect both of them to be problematic over time as things age.  In retrospect, I wish I had kept both of them!

73, Floyd - K8AC

Title: RE: ICOM IC-781 Impressions
Post by: N2RRA on December 23, 2012, 07:16:45 PM
I agree with Floyd!

My choice owning both would be the IC-781 for numerous reasons, but if I'm understanding your question about the 2khz splatter from adjacent stations I'll tell you this.

My IC-781 did very well and as good as any radio in filtering stations that close to my QSO. "No" radio in the market other than maybe an SDR radio like a Flex 5000 will do the job in eliminating that close of a station.

Hope this helped and 73.

Title: RE: ICOM IC-781 Impressions
Post by: G3RZP on December 24, 2012, 03:13:21 AM
In many cases, it doesn't matter how good the rx is on close in rejection of signals, the interfering tx is the problem because of its intermodulation products and phase noise.

Title: RE: ICOM IC-781 Impressions
Post by: W0XX on December 24, 2012, 03:17:03 PM
Here is the reason I am asking.  I have the Mark 5 with the key click mod, NB mod, stuffed with filters and works great.  A friend of mine is offering a possible trade of his 781 for Mark 5.  I never used the 781.  I know it is like 15-18 years old, mine 7 years old. I think the performance is about on par with each other, at least from the numbers ARRL and Sherwood put out.  The 2 khz adjacent (near field) ability to reject QRM is lacking in both a bit, as both have dynamic ranges in the low to upper 70s.

The Mark 5 has two receivers, you can run SDR IF Stage from it's IF (if you are into that), has VRF where you can vary the front end signal (not sure if the 781 can do that), and has of course, NR where the 781 doesn't.  I don't use the NR function as the radio handles noise very well with it's two NBs.  I can't speak to the 781's.

I am concerned, even though I know some 781s bring around 1800 used, mine brings 1500-1700 used, again, about the same.

So, would the 781 be better in performance, weak signal work, etc. say on 160....

And would I be well advised to just keep my radio and not swap...hard for me to tell....

Title: RE: ICOM IC-781 Impressions
Post by: KA5IPF on December 24, 2012, 03:49:46 PM
781 produced 1987-1993

Title: RE: ICOM IC-781 Impressions
Post by: W0XX on December 24, 2012, 05:06:11 PM

Title: RE: ICOM IC-781 Impressions
Post by: G3RZP on December 25, 2012, 03:50:20 AM
I'd say stick with what you have. What is the spares situation like on the 781 - that's something else to consider?

Title: RE: ICOM IC-781 Impressions
Post by: W0XX on December 25, 2012, 01:29:32 PM
Probably the best choice, but as to spares, the CRTs are readily available, other parts, don't know and that goes for any of the big three...after the end a production run, they won't support their product...I don't know many that have had repair issues on the 781 other then the power supply mod which is still being done....other than that..hard to say...

Title: RE: ICOM IC-781 Impressions
Post by: W0XX on December 31, 2012, 06:07:39 PM
Still never got any real feedback on the 781.  Those that have them generally have hung on to them...the only repairs I have ever heard of, is the power supply which should be readily repairable and the CRT which I haven't heard of any issues.  There are spare CRTs available out there on Ebay.  Other than the age thing, power supply cooling mod, I know nothing of the performance, etc.  Wish I had one to play with for a few days.

Title: RE: ICOM IC-781 Impressions
Post by: W0XX on January 01, 2013, 12:33:14 PM
Still, never received a direct answer to my question.  Is the 781 as good as or worse than the Mark 5 1000?  Putting aside age, NR.  ? ???

Title: RE: ICOM IC-781 Impressions
Post by: WN2C on January 01, 2013, 02:47:42 PM
If your friend is that good of a friend, then why don't you two agree to trade radios for say two weeks with the proviso that if either of you does not want to do the trade you get your radio back.  This way both of you get to try another radio that you haven't used before.

Rick  wn2c

Title: RE: ICOM IC-781 Impressions
Post by: W0XX on January 01, 2013, 04:34:31 PM
I have asked that, he is a bit worried I suppose something happening...doesn't do "try it out" scenarios...likely, I will pass then...

Title: RE: ICOM IC-781 Impressions
Post by: NO9E on January 03, 2013, 08:35:33 AM
These radios are good until the next repair. Then costs are piling up unless one has lots of time and equipment for a fix in house.

Mark V Field has a pretty good reputation for reliability but it needs many filters. It used to be my choice for good looks, built-in PS, nice sounding SSB, all under less competitive work. K3 with one factory filter does pretty well and may be a better value if resale price is considered.