[TMC] R5007/FRR-502 Tuning Unit Info

[w3jn]

----- Original Message ----- 
From: "Tom Brent" <tgb at telus.net>
To: <tmc at mailman.qth.net>
Sent: Saturday, February 05, 2005 1:26 AM
Subject: [TMC] R5007/FRR-502 Tuning Unit Info



>The other big problem is the tuning rate. Remember, these receivers were 
>not
> designed for band scanning, they were set up on one frequency and locked
> there for days or weeks. For our use however, the tuning is "touchy", to 
> say
> the least. There are a number of ways to get around this. A small DC power
> supply (perhaps tapping off the filament power) could be used to control 
> the
> reactance tube for its intended purpose of remote frequency control. At
> least one of our group has added varactor tuning. Perhaps the easiest 
> method
> however, involves a modification to the crystal tuning control on the 
> front
> panel. If you do not use crystal control for the HFO, this 50 pf. variable
> can be connected in parallel with the main tuning capacitor to provide 
> fine
> tuning. On the 2 - 4 MHz. tuning unit for example, disconnect the lead 
> from
> the ungrounded side of C532 (crystal tuning). Solder 1 lead of a 5 pf.
> capacitor to C532. Solder the other lead to the ungrounded side of C527. 
> Set
> C532 to mid-range and do a realignment.
>

THanks for the info, Tom.  Although I'm a staunch TMC fan I never really 
liked these radios too much, mainly because of the funky tuning.  ALthough 
the GPR series tunes smooth as silk, the tuning mechanism in the FRRs feels 
like trying to shift a 3-on-the-tree on a '59 Rambler - loose, full of 
backlash, yet full of uneven tension.  They could also benefit from a 
strapping pair of 6L6 audio output toobs, or at least something better than 
that wambly little single-ended 6AQ5.

I've used a synthesized signal generator on these and other radios (such as 
a SP-600) for a nice stable and clean LO.  Just set the sig gen for (receive 
frequency)+(receiver IF frequency), run the output of the sig gen into the 
xtal socket.  Depending upon your sig gen (some have tuning knobs) you can 
easily tune around, but you have to make sure you tune the radio as well so 
as to keep the front end in sync with the oscillator frequency, and you have 
to mentally subtract the IF freq from the display on the sig gen.

One of those little DDS cards, programmed already to take into account the 
offset, might be just the ticket.  Be prepared for a higher noise level, 
considering the crap coming from these little cheapo cards.

73 John