The AM Forum

Has anyone ever tried setting these two units (sx115 and HT32a) up to operate transceive?  One vfo controlling both transmit and receive. The VFOs in both output at 5-5.5MHz.  Shouldn't that work or am I way off base thinking this?

Hi all,

I'm going out on a limb here, so be gentle. I think, realistically, the answer is no.

The HT-32 transmitter has an IF of 9.0 MHz. For 80 and 20, this is mixed directly with the VFO. That means that on 80 meters, the 5.5 MHz vfo = 3.5Mhz and 5.0 vfo = 4.0 MHz (IF - VFO). On 20 Meters, the frequency is IF + VFO. That means that 5.0 VFO = 14.0 MHz and 5.5 vfo = 14.5 MHz. These two bands therefor, tune in the reverse direction. For the other bands, the Heterodyne oscillator comes into play, but again, it appears, that some bands tune opposite others.

The SX-115 receiver mixing scheme is different with the 1st mixer = Heterodyne oscillator minus the desired signal freq for a 1st IF of 6.5 (low end of the band) to 6.0 (high end of the band). The VFO is subtracted from the 1st IF to yield a 2nd IF of 1.005 KHz (6.5 - 5.5 = 1.0 and 6.0 - 5.0 = 1.0). This is then mixed down to the 3rd IF at 50 Khz.

Putting these two things together and using 20 meters as an example in the HT-32, a VFO frequency of 5.0 = 14.0 MHz, in the SX-115, a VFO frequency of 5.0 MHz yields a receive frequency of 14.5 MHz.

So, while the VFO frequency range is the same, due to the mixing schemes used it doesn't seem that transceive operation is feasible.

note to all: please feel free to correct my math - it will not hurt my feelings...

Bob  K7DYB

Hi again,

Just a follow up to my earlier post.

I think this highlights why Hallicrafters never came out with separates that could transceive. The HT-32 reflects the earlier use of the phasing method of SSB generation at 9 MHz which determined the ultimate mixing scheme.

The SX-115 reflects the earlier double conversion schemes with a first IF near the broadcast band and a second IF at 50 KHz to provide selectivity.

The SR-2000, SR-400, SR-150 transceivers addressed the transceive function in a single unit, but as far as I know this never made it into separates (like the Collins 75-s / 32-s or Heathkit SB-300/400 products).

Bob

SX-117 and HT-44  Twins

(https://www.qsl.net/ka9s/Twins/images/SX-117_HT-44_shack-1.jpg)

SX-146 and HT-46

(https://www.qsl.net/ka9s/Twins/images/SX-146_HT-46-100X.gif)

HT-32 uses a crystal filter.  The HT-37 uses the phasing method.  The HT-30 uses L/C filters at a low IF as I recall.