Date
1 - 20 of 28
I'm I likely to hear anything off the moon? Newbie question
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Am I kidding myself or am I likely to hear anyone off the moon on 23cm's ?
Dual Antennas 70 ele SG-Labs LNA, quoted as 0.8dB IC-9700 I have just measured the sun noise at around 2 to 2.5 dB compared to the cold sky, the SFU is l think low today at 67. I need to do some more reading and use the VK3UM software, but this is sort of all done portable so one step at a time. Thanks Nick |
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SAM JEWELL
Nick,
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Point at the moon when the elevation of the moon is above 10 degrees (actually in Belgium, but therefore close for the UK). You should be able to detect the ON0EME beacon on 1296.000MHz. Remember, due to doppler, it will be up to 2kHz above that on moonrise, although the beacon won’t yet be on at that elevation!) and 2kHz low at moonset (it will have set in Belgium and therefore have been off for around an hour). The beacon will be weak on that setup you describe, but you should hear it and certainly see it on Spectran or similar. Run WSJT (not X) on JT65C and you will get a measure of the beacon level. I expect you will see around -20 —22dBJT, even though it is not running JT modes. 73 de Sam, G4DDK On Wednesday, June 19, 2019, 12:25 pm, Nick Gregory via Groups.Io <nickg0hik@...> wrote:
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Thanks Sam,
That is encouraging, trying for ON0EME was one of my next steps. I was thinking I would not hear it as see the station is not particularly large. I'll get the software loaded up and give that a try. Does 2 to 2.5dB sun noise sound about right ? Nick G0HIK |
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SAM JEWELL
Nick,
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Yes, a little low, but not unacceptable with the yagis, that LNA noise figure and the current SFI. A VERY useful test is to switch the LNA on and off. AGC should be disabled (easy on the 9700). The level of noise should go up by at least 10dB when the LNA is on. It should be terminated in 50R for this test. A noise rise of around 15dB would be better. The noise figure of the IC9700, on 23cm, is around 4.8dB measured on mine (internal preamp on). Use AppCad to determine what noise increase you should get. Also, be aware, when the LNA is off it may have a significantly different impedance to when on and this may affect the IC9700 noise output, so a few dB difference from what Appcad says is not unrealistic. Let us know what numbers you get. 73 de Sam, G4DDK On Wednesday, June 19, 2019, 12:50 pm, Nick Gregory via Groups.Io <nickg0hik@...> wrote:
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Thanks again Sam,
I'll do some more tests then, when I can get the kit setup up again and will report back. Nick G0HIK |
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SAM JEWELL
Thanks Andy,
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I did think just a synth harmonic and simple BPSK modulator. Maybe GVA123 amplifier..... I don’t think that the RSP2 has anywhere enough bandwidth to lock to the 10486.800MHz beacon and tune at 618MHz. Anyway, you would be beaming at vastly different headings for terrestrial monitors of beacons etc, I never thought to try checking lock to a carrier only. The pseudo beacon looks easy enough. Sam On Wednesday, June 19, 2019, 1:17 pm, Nick Gregory via Groups.Io <nickg0hik@...> wrote:
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It's a little bit strange.
With the AGC off, the 9700 Pre-amp on and the LNA terminated into 50R, I am getting a ON/OFF change of 7dB. Any ideas why it is so low. Measured using a A.C. millivoltmeter. Nick G0HIK |
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SAM JEWELL
LNA gain too low? Cable loss too high? IC9700 noise figure a bit higher? What does Appcad say for the parameters you have?
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This should be easy to determine. My guess is low LNA gain, but what cable and length do you have between the LNA and 9700? Sam On Wednesday, June 19, 2019, 8:37 pm, Nick Gregory via Groups.Io <nickg0hik@...> wrote:
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The cable is 2mtrs of RG223, about 1dB loss including connectors.
LMR400 would improve this to around 0.5dB including connectors, I dont know if SMA's are available for LMR400, if not having an adapter is going to bring the loss up to 1dB again I would think. I've never used Appcad, I'll have to load it up and learn it when I get time. Nick |
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SAM JEWELL
Not cable loss.
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What is the gain of the LNA? Is the LNA really close to the yagi feedpoint? How much cable and type? Sam On Wednesday, June 19, 2019, 10:11 pm, Nick Gregory via Groups.Io <nickg0hik@...> wrote:
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SAM JEWELL
Yes, SMAs are available for LMR 400. I just bought some from Superbat on line (Chinese company, of course).
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Sam On Wednesday, June 19, 2019, 10:11 pm, Nick Gregory via Groups.Io <nickg0hik@...> wrote:
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Sorry I've just reread you message, I've got approx 8 mtrs of RG223 after the pre-amp, which is around 4db, I thought that loss after the pre-amp was not as important as before.
The reason for the 5mm cable is the whole station can be made carryable to fell tops, but I can easily change to something better, for which SMA's are available for. Nick |
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Right thanks. I'll look into that.
Nick |
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SAM JEWELL
The cable loss is a second stage contribution. Depending on the gain of the LNA it can be significant.
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My VLNA23 has 38dB gain. Sometimes that is not enough if you have a bias tee and, maybe, extra bandpass filter, ahead of the radio. Sam On Wednesday, June 19, 2019, 10:16 pm, Nick Gregory via Groups.Io <nickg0hik@...> wrote:
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Martin Phillips G4CIO
If it's the SG-Labs preamp / 25 W PA,
the claimed spec is 0.8 dB NF and 10 dB gain. 4 dB cable loss
downstream is quite significant. Can't find my spreadsheet ATM but
someone will do the calcs...
Martin/
On 19/6/19 10:16 PM, Nick Gregory via
Groups.Io wrote:
Sorry I've just reread you message, I've got approx 8 mtrs of RG223 after the pre-amp, which is around 4db, I thought that loss after the pre-amp was not as important as before.
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Yes that is the SG-Pre-amp/PA I have, I was not aware it only had 10dB of gain though.
I've just done the ON/OFF test with a short run of LMR400 and the change has now gone from 7dB to 10dB, I presume that says my coax between the pre-amp and the 9700 is 3db better ? Thanks for all the help chaps, this is really stimulating. I'm looking forward to having a go a plugging the numbers into the computer though later Nick G0HIK |
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Martin Phillips G4CIO
I've got one of the SG-Labs PA/ preamps
waiting to go up on the mast when time and weather permit. I did
all the sums and one really does still need some good cable on the
output to avoid degrading the NF.
On 20/6/19 11:09 AM, Nick Gregory via
Groups.Io wrote:
Yes that is the SG-Pre-amp/PA I have, I was not aware it only had 10dB of gain though.
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SAM JEWELL
Yes, 10dB is just acceptable. It really does help to do this check. Simple, but often overlooked.
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Sam On Thursday, June 20, 2019, 11:19 am, Martin Phillips G4CIO <martin@...> wrote:
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I've spent the last two mornings, chasing the moon and watching on Spectan, with no sign of ON0EME, which according to the status page is running.
I've noted the doppler, I've also mounted the SG-Labs LNA at the aerial with around 30cm's patch lead. Getting a bit disheartened. Should I wait till the weekend of 6/7 July and hope there will be some larger signal on? Nick G0HIK |
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SAM JEWELL
Can you attach the LNA direct to the antenna feedpoint?
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What coax are you using between the LNA and feedpoint? You may have said already. Where are you located? 73 de Sam, G4DDK On Friday, June 28, 2019, 1:29 pm, Nick Gregory via Groups.Io <nickg0hik@...> wrote:
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