Conversión de Kenwood/Trio TK 701S

Kenwood/Trio TK 701S Conversion

Conversion to amateur band.

This radio was given to me or I picked it up at some swap meet, and it sat in a corner until now; I decided to put it into operation for an APRS digipeater/iGate.

The radio was originally for the 150-174 MHz land mobile terrestrial band. It’s channelized (6 channels) and is programmed through a pair of unknown ICs that encode the PLL counters from a front key/encoder. The PLL is N-fractional type, based on an MC145152 and uses a dual-modulus prescaler (%64-65) UPB571C (apparently good up to 500 MHz); with the LO at 10.240 MHz the channel step is 5 kHz.

What I needed to do was see if I could bring it down to 144-148 MHz first, and second, determine how. My preferred search engine (because it doesn’t track me) DuckDuckGo immediately produced a couple of articles by G8UYZ published in the ’80s that explain the readjustment and give some conversion tables for setting the PLL dividers. I had to wait the two days that the friends (…) at mods.dk demand to download two PDF files… but well.

Colleague Dave G8UYZ either had a model with a different PLL, or something was poorly edited in the article because the tables he published for the dividers are not appropriate for this radio. Therefore I did the homework and prepared this spreadsheet to facilitate the work.

The rest of the info in the 701 article is relevant for adjusting the radio in reception and transmission; much of the necessary/interesting info is in the 801 article which is the UHF version of the same radio.

Since I currently have no need to change frequency, I didn’t worry much and simply soldered the necessary pins on a couple of sockets and put them where U22 and U23 go. But it’s possible and relatively easy to make a controller with a PIC that allows frequency changes, memories, repeater offset, etc. and a display. Maybe another day.

The radio works nicely, at 145 MHz it reaches about 45W but I left it at approximately 22W. According to the referenced article, these radios are specified for only 20% duty cycle (typical of this type of radio). The receiver is nothing special but sounds good and doesn’t seem insensitive.