YAESU ... m  o  d  i  f  i  e  d
Before ...
... After
Oldies but Goodies. Well, sort of. Yaesu put a decent effort into developing these accessory devices for their FRG-7700 (The FROG) receiver back in the late 1980s. The hardware quality is typical of the period for high-end receivers and the components are all first rate. The choke coils in their active antenna and tuner are good high Q devices and the gear driven air variable capacitors are excellent ... but their circuit design, of that period, needed some help in being brought up-to-date with current technology and current development knowledge. The finished units are very, very effective. I can knock out a 5 KW station 2 miles across the river only 10 KHz away from my target station, WLW in Cincinatti, - and I'm several hundred miles away in Southern Connecticut!
I have been aware, for some time, that these two Yaesu products are nicely built products with good quality components. However, I was never really happy with the circuitry as designed. Above is the  FRT-7700 receive-only tuner. I really didn't change much inside this unit: I added SO-239 connectors on the back for input and output and rewired the "ANT" switch so that the "Out" position grounds the antenna terminal. Also, the "OUT" switch now either enables or inhibits the Attenuator. These mods only added some user convenience and flexability.
Very Sharp tuning - thanks to the high Q coils provided.
Above is the FRA-7700 which was originally Yaesu's attempt at an active antenna. Inside is a "parallel" resonant preselector (not very effective with a very low "Q") but a nice quiet transistor preamplifier. This little bugger took all afternoon to modify. As above, I added two SO-239s on the rear apron. The "PREAMP" switch turns on the 9-volt feed and switches the preamp in and out of the RF path. The "OUT" switch now switches the preselector in and out of the RF path (it was always "in-circuit" in the old configuration). I cut new lands into the printed circuit board and reconfigured the preselector from parallel to series resonant. WOW, real sharp filtering now !
Here's some shots of the completed listening post in the family room. Everything has to be very neat and orderly to pass the "wife test." Note the sexy blue LED pilot light in the preselector (left photo).
Page 2, Schematics
Page 3, Antenna Mods
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