Ok, that makes sense..............on 13.5V, the Icom runs great. I still
have to do the audio mods to mine one of these days. It is a super
performer, RF wise.
Right now, I am revamping a McKay Dymek DR-33C. I just measured the LO
injection from the synthesizer. At +17dBm, I would expect much better IM
performance. LW is laden with multiple MW signals.
I am going to replace that whole kludge of a 1st mixer with a Mini-Circuits
TAK-3H. This device has an IP3 of +29dBm.
The 2nd mixer is getting a Siliconix E431..............this device has an
IP3 of +30dBm.
It should be a very good receiver when I get through with it. I used the
TAK-3H when I upgraded my KWM-380. With a wide open front end on MW / LW, no
IMD products were noted.
These mods should improve the MDS of the DR-33C. I will post my results.

Pete

"Guy Atkins" wrote in message
...
Hi Pete,

I was the one who mentioned the cool-running R-75. I should have also
mentioned I *only* power it by a 13.5vdc Astron supply. I've never used
the ICOM power brick.

Guy


"Pete KE9OA" wrote in message
...

"mike maghakian" wrote in message
...
Pete G on this group raves about how great it is.

however it does not mean it is fun to use. commercial receivers are not
always fun to use.

I have a Drake maritime 5000 dollar receiver, I find it no fun at all to
use compared to the satellit 800 or a modded DX-394 or similar fun to
use receiver.


The 6790 is a good receiver........if you want all of the "creature
comforts", this isn't the receiver to use. It is my favorite as far as
performance, but it is so DEEEEEEEEEEEEEEEEEEEEEEPPPPPPPPPPPPPPPP! We are
talking about over 20 inches of depth.
The gain of the I.F. system is higher than any of my other receivers. The
MDS measures less than .1uV over the whole tuning range, which is in line
with just about every other receiver being sold today.
My favorite receiver? My Lowe HF-150.
I also have the HF-225, but it doesn't compare with the 150 for MW
reception, because of the lossy duplexer that it uses on the MW range
(why they don't use a bandpass filter for this range, I don't know).
My 2nd favorite is my NRD-515, followed by the Palstar R30, Yaesu
FRG-100, Icom R75, AOR7030, SW-8, and all of the others (I lost count).
Many folks are concerned about getting ahold of parts for the 6790, but
the same could be said about the Cubic, WJ, Collins, and all of the other
premium receivers. The main advantage of the super high end receivers is
that most of them can be used for shipboard operation, where they will be
co-located with high power transmitters.
An example is the Collins HF-2054 or the 851S-1 receiver............these
receivers can handle 100V of RF at the antenna input without damage to
the receiver, whether it is powered on or turned off.
Is this kind of robustness needed for the home receiver. Probably not.
The ESD protection that these receivers afford would be helpful, as
evidenced by the number of Lowe receivers that I have replaced the 1st
mixer in recently.
Somebody made a comment about how cool the Icom R-75 runs..........I bet
that you haven't attempted to touch that internal 5V regulator.
There have been some failures with this regulator recently. The failure
mechanism is caused by the fact that Icom chose to use an 18V supply to
power the radio. Dave Zantos has modified his power supply by adding a
pre-regulator that brings the voltage down to 13.5V before it enters the
radio.
My advice? Either modify that Icom power brick or replace it with a
regulated 13.5V power supply.
Looking inside of that supply, you will find spots on the circuit board
for adding bypass caps across each rectifier diode.
Add .01uF caps in these places and it will prevent the diodes from
rectifying RF. Another good mod for this power supply is to add a 1uF NP
cap from each leg of the SECONDARY of the power transformer to ground.
This snubs the switching noise from the rectifier diodes.
I have heard mention on this NG that purchasing a good regulated supply
gets rid of these emissions........this is not really the case. Any power
supply can be made quiet by using the aforementioned techniques.
The AOR7030s power supply can also benefit from these mods.

Pete