The Transmit Exciter Board; Page 7. The Digital Board; The AUX-7 Accessory Board; The Digital Display Board; The Power Supply Board; Page 8. The Power Amplifier; The High Pass Filter boards; The Low Pass Filter Boards; The ALC Board; Page 9 Making Basic Adjustments To The TR-7; The Power Meter Calibration; The RIT Centering Adjustment.
Hs anyone compared the receivers in these two radios side by side - Iam interested in hearing all comments from hams and swl' operators. Ifthe TR-7 is basically the same receiver as the R-7 - i would opt forthe TR-7 so i can transmit as well. Is the TR-7 as sensitive andselective and does it have the same continuous coverage as the R-7??also how are these radios on LW and MW BCB - very interested inhearing - thanks so much in advance to all on this great sitejohn - ki4ucwPete KE9OA14.11.07 0:08. I've got both the R7 and the TR7. Both of them receiver fairly well, andboth of them use the same 1st mixer. The differences?
The TR7 is a dualconversion unit while the R7 is a triple conversion unit, the differencethat the R7 has a 50kHz final I.F. The TR7 uses an envelope detector for AMwhile the R7 uses what they call a Synchro Phase detector. Actually, this isa Quasi-Synchronous detector of the same type that is used in the Racal 6790receiver. What is done in this approach is that the I.F. Signal is brokeninto two paths. One path feeds the RF input of a product detector while theother path is squared up through a limiting stage and applied to the LO portof the product detector.
Demodulated audio is extracted from the I.F. Portof the product detector. If you are getting the impression that a productdetector is actually a mixer, your impression is correct!Anyway, further on.the R7 has a switchable 10dB RF preamp whilethe TR7 has none; the R7 has RF bandpass filters for every range, downthrough the VLF band while the TR7 only has filters down to the 1.5MHzrange. In order to have LW/MW coverage on the TR7, you must use an antennaconnection that bypasses the RF preselector (input bandpass filters).Both of the units are ok out of the box, but I have improved the performanceof both of my units by replacing theVari-L CM-1 1st mixer with a Mini-Circuits SRA-3MH.
This is a Level 13 mixerthat has only 4.77dB of midband conversion loss vs the 6.5dB conversion lossthat the CM-1 has. The CM-1 is rated down to 500kHz (or is it 1MHz?)while the SRA-3MH is rated down to 40kHz.Drake got around this problem by interchanging the RF and I.F.
Ports, sincethe I.F. Port on this mixer is rated down to DC. Still, the replacementmixer has lower conversion loss, so you can improve the noise figure of theunit by 1.73dB. And that is without having to use an RF stage ahead of themixer.
The result is better performance, since any RF amplification ahead ofthe mixer would degrade its IP3 performance by the amount of gain that thisRF stage is providing. As an example, if your IP3 is +20dBm, if you place10dB of amplification ahead of the mixer your IP3 will degrade to +10dBm.Another improvement that I did with my units was to replace the 1N4148diodes that Drake uses in the 2nd mixer with a matched quad set of 1N5711hot carrier diodes.
This will improve the IMD performance of this stageAfter all of these mods, the MDS improves from 0.15uV to 0.07uV. Not bad fora few hours work!For all out DXing, I would purchase the R7.if you also want totransmit, get the TR7.
Both of the units are respectable for LW/MWreception.The R7 is going to run you around 1000 dollars, while the TR7s run between400 and 700 dollars, depending upon what is included in the deal.If the seller pulled out the extra filters (which many sellers seem to do),expect to pay another 100 dollars to purchase anAM filter from INRAD.Expect the fact that you might have to do alignment of the BFO injectionoscillators. My TR7 needed a bit more than that. I purchased one on eBayfrom a fellow in Ohio that was selling it because 'it was excess to hisneeds'. Whenever I would try to transmit, the circuit breaker on my DrakePS7 power supply would trip. Somebody defeated the ALC in order to get alittle bit more power on 10 Meters. The unit would put out 250 watts on 80Meters, but the power would droop as you went higher in frequency.
When Inoticed that the BFO injection level was low, I traced the problem to a coldsolder joint on the exciter board. When I e-mailed the seller about thissituation, he said 'oh, I was wondering why I had to turn up the mic gain sohigh on this rig'.The point of what I am saying is that you really need to be careful whenpurchasing one of these things. Come to think of it, almost every radio thatI ever bought over the web needed some kind of repair, except a Sony 6800Wthat I bought from Mike Magakian and a Lowe HF-250 that I bought from DaveZantow (N9EWO).Good luck on your search.no, I am not selling either of mine. Youwill understand why, when you get ahold of one!Pete'john' wrote in [email protected].