Racal Drivers unite

[WA1GFZ]

you never have enough coax jumpers for playing under the hood. 3080s are high frequency pins if I recall Trr 100 us. Download the data sheets I just got them at home. I think the 3079 or 3379 is the low frequency one. The Racal DF ised a pin that is Trr= 2.5 uS . Trr should be greater than 1/F for it to work right.
I need to get into this filter module. I suspect the design was cheaped out until it effected the spec. A stock radio easily passes spec with the present configuration.
Imagine holding the first mixer performance through the radio....that is my goal.
The special second mixer appears to degrade system to IP3 of 26 dBM so not too shabby inside the bandpass of the first IF.
 

[Glenn NY4NC]

Hey Frank;

Is this the DSP receiver you mentioned you recently got?

http://cgi.ebay.com/Rare-Quailty-TCI-BR-8172-1-5-30MHz-HF-DSP-Receiver-NR_W0QQitemZ5841122807QQcategoryZ4673QQrdZ1QQcmdZViewItem

John,
I hope to do some dynamic range checks tonight. The trade off will be the filter dynamic range VS phase noise. I'm thinking of a voltage amplifier ahead of the filter module with plus and minus 15 volts across tha amplifier. A 50 ohm resistor to ground at the input. 2N3375 stud mounted bipolar running at 100 ma should do it.1 Kohm collector resistor should be a good source for the filter input. I guess I should put some sort of a limiter ahead of the filters to protect them. It seems the dynamic range of the mixers is no longer an issue. I hope the ability to measure dynamic range will become an issue soon. There is always the H mode mixer to explore if I get lucky IP3 plus 44 dBM.  fc

[WA1GFZ]

Yes, I bought the 8174. Let me know if you buy one. I have TCI remote control program and most of the manual. Too bad they don't have the second DSP installed for the spectrum display. It works pretty well. I need to put a better machine in my shack so I can use it. It has a calibrated S meter in dBM. It will be a good tool for antenna and pecker matching tests.  I need a set of schematics and a TCI contact. A number of us have bought the radio. They have been selling for $500 to 600 except one that went for $305 Thanksgiving week.

[VE7 Kilohertz]

Yes, I bought the 8174. Let me know if you buy one. I have TCI remote control program and most of the manual. Too bad they don't have the second DSP installed for the spectrum display. It works pretty well. I need to put a better machine in my shack so I can use it. It has a calibrated S meter in dBM. It will be a good tool for antenna and pecker matching tests.  I need a set of schematics and a TCI contact. A number of us have bought the radio. They have been selling for $500 to 600 except one that went for $305 Thanksgiving week.

Hi Frank,

Cool! I want one. Tell me a bit more about it. i.e. What advantage would it have over say a Collins 2050 or RA6790 etc? What can be controlled by the control software? Bandwidth, tuning, mode etc? What is the RF performance compared to the Racals?
 
Wonder where they came from? Sounds like he has lots.

Cheers

Paul

[WA1GFZ]

Martha told me Adam worked for a company that used them and he got the pile when they went out of business. It has a 15 KHz IF at 40.455 second IF 455 and third of 5 KHz into the DSP. It has 8 or so filters 300 hz to 6 khz. Not a bad radio.
There is option for a second dsp that did the spectrum display but not installed in these radios. go to ebay ham radio TCI there is a pair on there now. The 8172 requires an external reference. Sounds ok cool s meter function. I have not played with my radio much yet. I had to run a 50 foor rs232 cable to the shack to use it.
Having the same ifs as the racal looks interesting for interatial marriage.
I don't care for the 2050 not enough bandwidths. Calibrated s meter is the coolest thing. DSP does a pretty good job. 20 KHz sample of 5 khz IF. DSP running at 40 MHz.
I have not been under the hood yet. I have most of the manual pdf and sent them a copy also have the tci interface software.

[Glenn NY4NC]

Oh man!!!! I want one of these to go along with my 6790

http://cgi.ebay.com/RACAL-MA-1723-HF-DRIVE-UNIT-EXCITER_W0QQitemZ5841756222QQcategoryZ4674QQrdZ1QQcmdZViewItem

[WA1GFZ]

Glen,
I configured one of my 6830s to bring all the oscillators out so a drive unit could be built. I was thinking of taking a 6830 chassis and building a TX unit. Still it would be cool to have the real thing!

[WA1GFZ]

Testing with the DF 3 filter module yielded the best performance I have ever measured. MDS -130 due to built in amp and 1 stage of external amp ahead of the filters.  Dynamic range 103 dB at 10 KHz. and 113 dB at 40 KHz spacing. I still have 20 KHz filters in the first IF so can't measure in close I'm sure I will run into the phase noise floor with this performance. That will be later.
Next I installed the stock 5 filter module with 1 filter installed. MDS -120 with about 100 dB dynamic range 10, 20 and 40 KHz spacing. This confirms I need a low noise amp at the output. Only gained 2 dB of mds removing 4 filters so that isn't the issue.
I will try shorting the switching diodes to see if there is any loss.
Converting the emitter follower to a gain stage after the filters should help all Racals 6790, 1792 and 6830 by shifting the gain distribution after the second mixer and should help close in dynamic range. Stock spec was 80 dB so hitting 100 would be a big gain. I usually measure almost 90 dB in a stock radio.

[WA1GFZ]

Well, I tried changing the switching diodes around a filter and no change in performance.
I did a lot of reading and found there shouldn't be any difference in that circuit.
I also bypassed the emitter follower and that hurt the mds.
Bottom line is I need to improve the mds of the second IF to improve performance.
I went back to the radio input and find the first and second mixers will process a
1 volt RMS signal but the second mixer post amp saturates. I have to drop back to 1/2 volt to take it out of saturation. A single resistor change dropping the gain a bit
would bring it out of saturation but it would cost some gain.  Imagine a radio that would work clean from -130 dBM to plus 10 dBM. The only way to approach this performance is to reduce the gain ahead of the filters and mixers.
The trade offs Racal choose start making sense and it is very interesting to see harris did almost the same thing in the 590 with similar parts.