forum.pistar.uk

Has anyone had any luck using the 2018 version of JumboSpot on VHF? I know the description says it's compatible but I'm not having any luck finding the correct offsets. The board came with a TX offset of -475 and RX offset of -475. I set both of these offsets in the expert menu. The TX appears to be pretty close, I have no issue hearing the RF from the JumboSpot. However, it does not detect my transmission from my radio into the board. I've tried offsets from -700 to 0 with no luck. Just looking to see if anyone has ran into this issue. I did flip over to UHF and both suggested offsets worked perfectly. Unfortunately my mobile rig is VHF only, and I'm hoping to be able to go that direction.

Work both ways + and - with your offsets. I've seen some really outrageous numbers out there on Jumbos, 4000+. Yea, they can work on VHF, but they do so at a severely diminished state.

To use the AD7021 transceiver on VHF it is necessary to use the external inductor VCO. (The internal inductor VCO is only good for 420 MHz and higher.) This requires the board to actually have this inductor which should be between pins 44 and 46. In addition the firmware must actually select the use of the external inductor VCO. It sounds like a feature of this board is that it includes this inductor. (It also needs a change to the filter beteween the chip and the antenna.)

The best that I can tell looking at the firmware is that it does change register 1 between VHF and UHF but it does not enable the external inductor VCO. At best using the wrong VCO would cause dramatic errors in frequency and perhaps instability.

So it looks like your board might be able to do it. It's just that the firmware doesn't.

73,
Chris, K9EQ

Hi Chris,

MMDVM_HS firmware has support for VHF from the first version (Jan, 2017) and works correctly, I enable the external VCO when is needed according to ADF7021 datasheet (bit 25, reg 1). Personally, I use VHF regularly because is the popular band in my country.
Reasons if VHF doesn't work: frequency offsets, hardware doesn't support (no external inductor at least) or bad hardware (TCXO issue).

Regards,
Andy CA6JAU

Can someone explain how to enable the external VCO please. Or go further into how to get one of these boards to "hear" VHF...

Thanks and 73,
Scott N5HUM