JumboSpot on VHF

MMDVM_HS Hat hardware
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Posts: 8
Joined: Thu Jan 17, 2019 2:06 am

JumboSpot on VHF

Post by KC9DK »

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.
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Joined: Sun Apr 29, 2018 12:12 pm

Re: JumboSpot on VHF

Post by n9mxq »

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.
Gene in Belvidere IL
Please don't email me with questions.
That's what these forums are for.
There's much more brainpower collected here
than I have alone.
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Joined: Wed Jan 09, 2019 4:07 am

Re: JumboSpot on VHF

Post by K9EQ »

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.

Chris, K9EQ
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Joined: Thu Aug 30, 2018 8:13 pm

Re: JumboSpot on VHF

Post by CA6JAU »

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).

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Joined: Thu Jun 18, 2020 5:03 am

Re: JumboSpot on VHF

Post by N5HUM »

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
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