21 Jul 2012

How deaf is the FT817 at 136, 472 and 500kHz?

You may have read that the FT817 is deaf below 160m. This matters if you want to use the rig "as is" without preamps as a receiver for 136, 472 or 500kHz. So I decided to measure the performance using a signal generator. I measured the MDS on CW (the level at which I could just still hear a  CW tone without additional filtering), the level for S1, S5 and S9 on the FT817's meter. I also checked whether having the IPO switched in or out made a difference

These were my results:

136kHz (best results with IPO on)  DEAF!
MDS -103dBm
S1 -72dBm
S5 -68dBm
S9 -48dBm

472kHz (best results with IPO off)    SLIGHTLY DEAF
MDS  -120dBm
S1  -84dBm
S5 -81dBm
S9 -60dBm

500kHz (best results with IPO off)    A BIT DEAF

MDS  -124dBm
S1 -85dBm
S5 -82dBm
S9 -60dBm

What conclusions can be drawn? Well, the FT817 is definitely very deaf on 136kHz and needs a preamp to be usefully sensitive. On 472/500kHz, although the MDS is worse than at 1.8MHz, the sensitivity is arguably OK without a preamp. Yes, a small amount of high dynamic range gain with good filtering to stop overload from adjacent broadcast stations may give you a slightly better sensitivity, but the question is whether this matters when external noise may be the limitation. I have used to FT817 on 500kHz for several years and heard most of what was going, including transatlantic stations. At 472kHz it is slightly worse but still useable I think.


g4fre said...

Are these results are with the ssb filter, or are they with the 400Hz cw filter in circuit?

Roger G3XBM said...

Using the standard SSB filter.