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Author Topic: ICOM IC7700 Roofing Filter Mod?  (Read 10056 times)
KT0DD
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Posts: 451




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« on: November 13, 2014, 02:03:30 AM »

 I just noticed on Rob Sherwood's site that the 7700 is down a ways from the other $6K rigs in 2K DR performance.

Does anyone make a mod for the narrow roofing filter in the IC-7700?

I might be able to purchase a 7700 for a good price but I'd like to know if a filter upgrade option is available.

Thanks.

Todd
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ZENKI
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Posts: 1636




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« Reply #1 on: December 05, 2014, 11:32:30 PM »

Dont waste  your time. Even if you could improve the IMD dynamic range  @ close in signal spacings there is nothing you can do about the other operators bad SSB IMD performance. Your excellent receiver will be blocked by SSB crud and keyclicks.

For the current standards of transmitters and on air TX signal performance, the IC7700 has enough RX performance. Anything more  and you will never be able to exploit the improvements you make because your receiver is being jammed by SSB crud and keyclicks. Just enjoy your radio and put   the effort into a 150ft high tower!

If you want more RX performance buy a new SDR radio like SunSDR or Flexradio 6300. You  will get much better receiver performance than  the IC7700 and  also get a superb bandscope  with the SDR radio.  The same comments apply to the SDR receivers. They have receiver performance  that is way better than needed because transmitters are  still so filthy.  Even if you bough the new Icom 7850 with  technically excellent receiver performance you would still be wasting your money because of the TX crud factor which blocks your receiver performance.

Transceiver  ultimate performance is about achieving a good balance between RX and TX performance. Currently in transceiver design we  have anal obsession with receiver performance while   transmitter design performance is just cheap and nasty. We will one day will be able to use all this receiver performance when every ham cleans up their crap radios. While we have  hams  that think that  spending thousands of dollars on radios with  transmitters that are no better than a $10 CB radio we will never be able to realize ultimate receiver performance in the  long run. A good example of  this dumbness will be the new Icom IC7850  design, it will have glowing RX performance with a less than impressive transmitter. 

Even if every ham used a IC7850, the excellent receiver performance could never be used in the real world because the IC7850 transmitter will have Icoms standards of transmitter IMD performance that has ALC  compression splatter and generally a lot of garbage being emitted.  For the price that they going to charge for this IC7850 I would have expected a super clean transmitter and a calibrated S-meter. Ham transceivers today remind me lot of those fake Ferraris and Porsches  you used to see  the 80's made of fiberglass, all looks and no performance. Gold color knobs  is more important than actual real world transmitter performance. Just plain stooopid window dressing like putting lipstick on a pig of a radio! They put all the engineering into receiver performance that can never be used and basically ignored the transmitter design performance.  Design dumbness at its best from Icom! The initial previews of the IC7850 have glowing  reports of the receiver performance but everybody is ashamed about talking about the transmitter performance, they complicit in covering up the issue with technical review dumbness.

The other point about  is the phase noise performance of the IC7700 at very close signal spacings. The synthesizer design phase noise design at close signal spacings is not really good enough for spending effort  on things like roofing filters. The other point is that its hard build  roofing filters for up conversion radios that have good performance. AC0C tried designing better roofing filters for the FT2000 which is a up conversion design. The results were marginal at best.

Really directly sampling SDR radios make better receivers than up or down conversion analogue radios of yesteryear. The receivers sound so much better without the distortion and group delay from  crystal and  other filters. SDR synthesizer performance is getting close too perfection and the phase noise performance  and low inband RX distortion just blows the pants off any analogue designed radio. Buy a SDR radio for better performance!
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KD8MJR
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« Reply #2 on: December 06, 2014, 12:01:32 AM »

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“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
PA1ZP
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Posts: 688




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« Reply #3 on: December 07, 2014, 01:17:20 AM »

Hi to you all

Zenki is blunt as always, very blunt.
But he is 100% right though.

A reasonable SDR rig will have far better RX performance.
Though I have seen measurements that some SDR radios have the worst transmitter of all radios ever measured.

Even a much cheaper TS590S will have better RX performance as the IC7700.
And they will not blow the finals as easy the IC7700 or even the IC7800 do.

But if you want a poor performing RX with all the bells and whistles you will never need, with the weight of an HF amp the price sky-high and a user manual as thick as a phonebook, you will be at the right adres with the IC7700 and IC7800.

For about the IC7850 I think it will be more expencive as the Hilberling, so go for a Hilberling PT8000 instead of the IC7850, better performance and much more high-class and rare it is the Rolls-Roice or Maybach of hamradio these days.

It will not help a bit in improving bad TX performance of stations that you are recieving with it though

73 Jos
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