Authored by VE3EFJ
18.1 THE TR7
(someone with MUCH more experience than I have)
I have read with interest the three versions of your drakemod.txt file and appreciate the time and effort you have obviously put into it. I have no knowledge or experience of the Drake 4-line, and that makes up much of your document. However I can offer some comments and amplification on the portion of your work that deals with the 7-line and its commercial derivatives (more about that later).
First, let me introduce myself and detail my association with Drake equipment. I am very active in HF digital work and have run an APLink/WinLink MBO system for many years. My first piece of Drake gear was a TR7A that I bought new in the mid-80s. I feel the same way as you do about the quality of construction and performance of this gear. The R7 and derivatives have just about the best receiver I have ever seen, and that is saying a bit. My daytime job is with a commercial maritime service provider (HF) and we have evaluated many expensive receivers with names like Harris, WJ and Racal. I always bring them home and compare them with my Drake R4245 (an R7 inside, see below). The Drake stands up to all of them. Yes, they are fancier, computer controllable, DSP based and all of that, but in basic receive performance the best that they can do is equal the Drake.
My radio shack consists of several 'systems', separated by functionality. In the descriptions below I have ommitted the details of the digital hardware software and concentrated on the radios.
Twenty Meter MBO system - a TR7A (w/PS7) slaved to an R7A, both driven by the same RV75. I have modified the RV75 to scan eight channels on the 14 MHz. band.
The transmit antenna is a Butternut vertical on the carport, and a dipole serves as a separate receive antenna ....
Thirty Meter MBO system - a TR7 (w/PS7) driven by another RV75 with similar mod, scans ....
HF Intercept system - a Drake R4245, an Icom R71A and various digital modems and decoders. This system ....
In addition I also have a complete marine test 'ship' setup with with Raytheon and Furuno radios where I do software and hardware testing for the day job.
Drake also sold a commercial version of the 7-line. The transceiver was called a TR4310 and the receiver a R4245. I have little knowledge of the TR4310 except a description in a four page brochure. (I would be happly to fax you a copy.) However, I do own an R4245 and can describe it briefly for you. It is in a rack mount cabinet. Upon removing the top and bottom covers, one finds an R7 mother board and card cage. The major change is that the PTO is gone, as is the DR7. In place of the DR7 is a board that contains circuitry similar in function to the outboard RV75. This makes it fully synthesized, very stable radio! Other changes include different style knobs (but everything is in the same place as on an R7) and a light beige paint job on the front panel. The default frequency ranges when you switch bands are not the ham bands, but the maritime bands. The radio will run from 12VDC, 24VDC or 110VAC. I obtained the unit, new, during last months of operation of the old Harvey Radio store on 45th Street in Manhattan. I passed up a TR4310 at the same time and have been kicking myself ever since!
Your comments on the TR7's capability for digital operation need a bit of detail added. First, you are correct that the internal PTO is not adequate (stability-wise), that is why I use the RV75s. However, these radios turn around very quickly and are ideal for AmTOR use. I TR7 is a bit slower for some reason, but still under 10 ms. Yes, there is a bit of noise from the clacking relay.
In fact, I had several years ago purchased two replacement relays, anticipating failure, but both transceivers are using their original relays, believe it or not.
Several articles have been published with improvements for the 7 line over the years. My library is not organised at the moment, so I will mention what I can from memory. Given some time, I can dig out either a reference or a copy for you, if you are interested.
There was an article from an author in Switzerland detailing a stabilization mod for the PTO in the TR7. It consisted of a board, mounted under the mother board, that sensed a change in the least significant digit of the counter on the DR7 board and 'bumped' the PTO back on frequency if it drifted far enough for that digit to change. It 'bumped' in 10 Hertz steps, as I recall, which I thought might be too much for digital work, so I never tried it. Also, I had acquired the RV75s by that time.
There have been many mods published over the years to allow full frequency transmit with the TR7. Most simply leave the transmit enable line high at all times by cutting a trace. Because internal signals like PLL unlock can drive this line low, I developed a mod that left this important protection in place. I have not looked at the mod you got from Drake to see if it also does this, but I will.
One author claimed that he had seen low level spurs on both transmit and receive caused by the 23 kHz. oscillator in the +24 volt supply getting back into the +10 volt line. He suggested adding additional filtering to supress it. I have never seen this problem, but do have the parts on hand if I want to make this mod in the future. Similar circuits are used for this supply in the TR7, R7 and R4245.
Another article included several unrelated TR7 mods. The ones I recall were a temperature sensing fan driver and replacement of the TR relay with PIN diode switches. Circuit boards were available.
Your comments on fans are interesting. I have an FA7, or homemade equivalent, installed on both TR7s and on both PS7s, but using the Drake approach, blowing out in all cases. Also, on the subject of heat and fans, I run both the R7 and the R4245 from external 12VDC, which reduces the internal heat somewhat. In spite of that, the regulator on the rear panel runs quite warm, so I have arranged a fan to move air in that area also.
I could go on and on, about such things as changes to the Drake transceive cable kit, a mod to remotely switch between 10 MHz. and 14 MHz. operation. however, I suspect that this is enough for you to chew on for the moment.
73, Craig (writer detail omitted)
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