GPSDO
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Jim Lill
Whether Bodnar or other, it seems like this is only needed for FST4W "slow" modes, am I correct?
Besides the added cost, I wonder if there is any penalty with the required hook-up adding common-mode or any other form of noise? -Jim WA2ZKD |
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WA2TP - Tom
Jim
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I did not notice any additional noise on the kiwi. Without antenna waterfall/spectrum were both clean. I was powering the bodnar via usb so that was a pleasant surprise. I have not seen any significant depreciation in performance yet. It’s only been a few days. On Aug 5, 2022, at 2:03 PM, Jim Lill <jim@...> wrote: |
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Since there doesn’t seem to be degradation, is there any noticeable improvement?
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Is the phase noise with the Bodner so much better than the stock GPS locked oscillator? I am still trying to justify an external device that costs more than half of the cost of the whole receiver. The transmitter is more likely the place where a hi stability standard is needed. With long transmit times heating probably cause more frequency instability than at the receiver. Steve KD2OM On Aug 5, 2022, at 14:22, WA2TP - Tom <myis300@...> wrote: |
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Glenn Elmore
Yes, there can be improvement. It's too soon to give an exhaustive report, there is a lot of data, but rig stability on either tx or rx ends can definitely exceed ionospheric spread much of the time on some band/mode combinations and compromise or completely prevent spots. Compromise happens when the short term frequency variation cause one symbol to smear into another's spectrum - effectively reducing the SNR. How to distill what we are finding into practical guidance is a challenge that we are still working on. The tx/rx frequency accuracy/stability requirements for longer
FST4W modes have a good deal in parallel with what we found on
WSPR at VHF/UHF. Extra effort is required to gain the benefit of
narrow digital modes but some very interesting things are found
when one does. See the 2m+ WSPR group
to get an appreciation of what's involved in getting commercial HW
up to the task. So-called "high stability" and TCXO radios simply
weren't good enough and we had to build our own HW. Do understand that a 'native' Kiwi is not phase locked to GPS -
it's only a periodic SW frequency correction and while it has
good long term accuracy, short term it isn't so good. It's
pretty clear that this translates to fewer spots under some FST4W
band/mode circumstances. I don't think there's need yet to
upgrade all the Kiwi's involved but perhaps it will be worthwhile
in some situations and will provide additional depth of spot SNR,
more DX and more total spots. We are already seeing better systems
getting well into the -30's on 20m. Stock Kiwis seem to miss
these. I think a single GPSDO can likely serve a multitude of
Kiwis if one is careful with fan-out and common mode ground loops. In a related area, I've started looking at the QRP Labs QDX performance and it's already clear that there is a great difference between operating receive-only and rx/tx creates thermal cycling, greatly increases the delta-T and spreading for both tx and rx. Injecting a GPSDO 25 MHz in place of the TCXO greatly improves receive performance. I'm trying to understand some transmit issues now. Much more to examine on this...
Glenn n6gn
On 8/5/22 15:28, KD2OM wrote:
[Edited Message Follows] Since there doesn’t seem to be degradation, is there any noticeable improvement? Is the phase noise with the Bodner so much better than the stock GPS locked oscillator? I am still trying to justify an external device that costs more than half of the cost of the whole receiver. The transmitter is more likely the place where a hi stability standard is needed. With long transmit times heating probably cause more frequency instability than at the receiver. Steve KD2OMOn Aug 5, 2022, at 14:22, WA2TP - Tom <myis300@...> wrote: Jim I did not notice any additional noise on the kiwi. Without antenna waterfall/spectrum were both clean. I was powering the bodnar via usb so that was a pleasant surprise. I have not seen any significant depreciation in performance yet. It’s only been a few days.On Aug 5, 2022, at 2:03 PM, Jim Lill <jim@...> wrote: Whether Bodnar or other, it seems like this is only needed for FST4W "slow" modes, am I correct? Besides the added cost, I wonder if there is any penalty with the required hook-up adding common-mode or any other form of noise? -Jim WA2ZKD |
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Edward (W3ENR / K3WRG)
On 8/5/22 5:28 PM, KD2OM wrote:
I am still trying to justify an external device that costs more than half of the cost of the whole receiver.I don't know how many Kiwis you have, but I'll experiment more with getting one Bodnar mini to feed two Kiwis early next week. If successful, that would bring the cost substantially down if you have multiples. Since there doesn’t seem to be degradation, is there any noticeable improvement?I've actually had a decline in spots, but this is probably because I mucked something up when moving stuff around so much to get the Bodnars up and running. One of the BNC connectors on my W6LVP is a little wonky and might be to blame. A second loop will be here in a few days, so I'm not going to mess with it for the time being, since everything will get jostled around again when I install it. Edward |
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Jim Lill
if you're trying to run several kiwis. I'd consider a distribution amp. Something like a channel master CM3414 might work nicely.
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On 8/5/22 18:15, Edward (W3ENR / K3WRG) wrote:
On 8/5/22 5:28 PM, KD2OM wrote:I am still trying to justify an external device that costs more than half of the cost of the whole receiver.I don't know how many Kiwis you have, but I'll experiment more with getting one Bodnar mini to feed two Kiwis early next week. If successful, that would bring the cost substantially down if you have multiples.Since there doesn’t seem to be degradation, is there any noticeable improvement?I've actually had a decline in spots, but this is probably because I mucked something up when moving stuff around so much to get the Bodnars up and running. One of the BNC connectors on my W6LVP is a little wonky and might be to blame. A second loop will be here in a few days, so I'm not going to mess with it for the time being, since everything will get jostled around again when I install it. |
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I have 3 kiwis running. I am already running a Rhode and Schwarz frequency standard that is much better than the Bodner but is 10 MHz, I would sure like to use that.
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Steve KD2OM Sent from my iPhone. On Aug 5, 2022, at 18:15, Edward (W3ENR / K3WRG) <manager@...> wrote: |
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WA2TP - Tom
So far, I have seen that kiwi7 (on bodnar)
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Has decoded more 4w spots than kiwi1 at times. I have also seen kiwi1 decode spots that 7 does not and vice versa. Although the number is minimal ( 1 or 2 per 2 minutes cycle) it is there and noticeable. I have no explanation for this at this time. The conditions for those two kiwi sharing the same antenna are under controlled conditions. I have even take the time to sweep the sma jumpers used to connect to the elad 52 splitter, as well as injecting a signal into the elad and measuring the output levels to verify that they are at least close with my limited measuring equipment. On Aug 5, 2022, at 6:36 PM, KD2OM <steve@...> wrote: |
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