Topics

6cm Advice/experience please?


Anthony Coldman
 

I am looking for advice on 6cm.

 

I have a Kuhne 5.7GHz G2 transverter, this is mounted on the mast and connects using 2m of LDF450 to the RFHamdesign TRI BAND ring dish feed for 23,13,6cm on a 1.9m mesh dish, the IF is 432Mhz which is feed to the shack into another Kuhne transverter and then into my Icom 7300 on 28Mhz.

 

My question are to do with RX capability, I have been using this system in the UKAC for a few months now and always seems that people seem to be able to hear me better than I can hear them, I am running 7w which might account for some of this but I have also been monitoring the beacons and the only one I can occasionally just about hear is GN3FNM. (this can always be heard on 13cm and 5 points higher, similar system TVTR on mast and same dish).

 

Does anyone else use a mast mounted system and do you have an extra LNA? 

 

Can anyone that can hear the GB3FNM beacons confirm if they RX it a lot stronger on 13cm then 6cm? even though the ERP is higher on 6cm?

 

Am I expecting too much on this frequency?  Any pointers or experience gratefully received.

 

Anthony


Mark GM4ISM
 

Anthony

You say a 1.9m Mesh dish.

Is the surface  accurate for 6cm, and  what is the mesh size(needs to be about 6mm or smaller)

 Importantly  is the feed  perfectly aligned in the middle of the dish, any droop may cause the  beam to go off axis and this would be most pronounced at 6cm  you may not notice at the lower bands

Mark GM4ISM

On 12/09/2020 18:21, Anthony Coldman via groups.io wrote:

I am looking for advice on 6cm.

 

I have a Kuhne 5.7GHz G2 transverter, this is mounted on the mast and connects using 2m of LDF450 to the RFHamdesign TRI BAND ring dish feed for 23,13,6cm on a 1.9m mesh dish, the IF is 432Mhz which is feed to the shack into another Kuhne transverter and then into my Icom 7300 on 28Mhz.

 

My question are to do with RX capability, I have been using this system in the UKAC for a few months now and always seems that people seem to be able to hear me better than I can hear them, I am running 7w which might account for some of this but I have also been monitoring the beacons and the only one I can occasionally just about hear is GN3FNM. (this can always be heard on 13cm and 5 points higher, similar system TVTR on mast and same dish).

 

Does anyone else use a mast mounted system and do you have an extra LNA? 

 

Can anyone that can hear the GB3FNM beacons confirm if they RX it a lot stronger on 13cm then 6cm? even though the ERP is higher on 6cm?

 

Am I expecting too much on this frequency?  Any pointers or experience gratefully received.

 

Anthony




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John Lemay
 

Anthony

 

I have no experience with 6cms, but I’m not going to let that stop me giving some advice !

 

I purchased a RF HamDesign dish for 3cms (1m diameter) and after a few months of somewhat lacklustre performance I took a close look at the profile. I decided that the ribs were suitably accurate, but there was not nearly enough support between the ribs to give the mesh a decent profile. I stripped the dish and added quite a lot more metal.

 

So I agree with Marks point that you need to check the profile accuracy.

 

Secondly, of the three bands that you are equipped for, locating the phase centre of the feed at the dish focus is much more critical on 6cms. Get it right for 6cms and you will be sufficiently close for the lower bands. When measuring your dish, don’t forget that the central hub has a nominal thickness, and it’s flat which means that the parabola apex is a few mm behind the surface. Also, in the triband ring feed the phase centre is between the ring and the reflector. It’s a sealed unit and you can’t see inside, but the loop will be about 8mm from the inside face of the feed. I’ve mentioned “a few mm” several times, and these start to add up.

 

Finally, the dish is a significant weight, all on one side of your mast. Make sure that you are still pointing at the horizon, and not “drooping” a little.

 

I’m afraid that none of this helps about your question regarding RX capability !

 

Regards

 

John G4ZTR

 

From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of Mark GM4ISM via groups.io
Sent: 12 September 2020 18:34
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 6cm Advice/experience please?

 

Anthony

You say a 1.9m Mesh dish.

Is the surface  accurate for 6cm, and  what is the mesh size(needs to be about 6mm or smaller)

 Importantly  is the feed  perfectly aligned in the middle of the dish, any droop may cause the  beam to go off axis and this would be most pronounced at 6cm  you may not notice at the lower bands

Mark GM4ISM

On 12/09/2020 18:21, Anthony Coldman via groups.io wrote:

I am looking for advice on 6cm.

 

I have a Kuhne 5.7GHz G2 transverter, this is mounted on the mast and connects using 2m of LDF450 to the RFHamdesign TRI BAND ring dish feed for 23,13,6cm on a 1.9m mesh dish, the IF is 432Mhz which is feed to the shack into another Kuhne transverter and then into my Icom 7300 on 28Mhz.

 

My question are to do with RX capability, I have been using this system in the UKAC for a few months now and always seems that people seem to be able to hear me better than I can hear them, I am running 7w which might account for some of this but I have also been monitoring the beacons and the only one I can occasionally just about hear is GN3FNM. (this can always be heard on 13cm and 5 points higher, similar system TVTR on mast and same dish).

 

Does anyone else use a mast mounted system and do you have an extra LNA? 

 

Can anyone that can hear the GB3FNM beacons confirm if they RX it a lot stronger on 13cm then 6cm? even though the ERP is higher on 6cm?

 

Am I expecting too much on this frequency?  Any pointers or experience gratefully received.

 

Anthony

 


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Neil Smith G4DBN
 

It is a bit weird though. If your dish was wonky or pointing at Alpha Centauri, or the feed was out of focus, then you'd have problems being heard as well.  I'm assuming you don't have elevation on the dish, but can you see the horizon anywhere at sunrise or sunset so you can use sun noise to check if your rx is up to snuff?  You can use the VK3UM calculator to see how much sun noise to expect. Are there any trees or buildings you can beam at and see if you can hear/see their thermal noise?

To get a bit more of an objective measurement of performance if you can't look for sun noise, can you find someone within a line of sight path and do some tests while the other station gradually beams further away from you, and see if your rx signal drops off faster than theirs does.  If you and the other station can use WSJT-X and send a single tone using the TUNE facility or @1000 or something and then use the power slider, you should be able to compare notes on signal level versus TX power.

First stop for me is always the sun, using my SDR software on a 192 kHz slice, or continuum mode on Spectran or the analysis modes on Spectrum Lab.  A quick check to see if I can see the warm wall of the neighbouring house with the dish down is also a good sanity check.

If you have an isolation relay on the 5.7 GHz input with a 50 ohm load, you can try flipping between that and horizon noise to see if the ratio makes sense (with AGC off).

If you haven't got an isolation relay and you've used other bands while the 6cm system is connected to the ring feed, you might have degraded your front end FET.  Do all of the systems on the feed go into TX mode before any power is applied to any of the rings?

Neil G4DBN

On 12/09/2020 19:59, John Lemay wrote:

Anthony

 

I have no experience with 6cms, but I’m not going to let that stop me giving some advice !

 

I purchased a RF HamDesign dish for 3cms (1m diameter) and after a few months of somewhat lacklustre performance I took a close look at the profile. I decided that the ribs were suitably accurate, but there was not nearly enough support between the ribs to give the mesh a decent profile. I stripped the dish and added quite a lot more metal.

 

So I agree with Marks point that you need to check the profile accuracy.

 

Secondly, of the three bands that you are equipped for, locating the phase centre of the feed at the dish focus is much more critical on 6cms. Get it right for 6cms and you will be sufficiently close for the lower bands. When measuring your dish, don’t forget that the central hub has a nominal thickness, and it’s flat which means that the parabola apex is a few mm behind the surface. Also, in the triband ring feed the phase centre is between the ring and the reflector. It’s a sealed unit and you can’t see inside, but the loop will be about 8mm from the inside face of the feed. I’ve mentioned “a few mm” several times, and these start to add up.

 

Finally, the dish is a significant weight, all on one side of your mast. Make sure that you are still pointing at the horizon, and not “drooping” a little.

 

I’m afraid that none of this helps about your question regarding RX capability !

 

Regards

 

John G4ZTR

 

From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of Mark GM4ISM via groups.io
Sent: 12 September 2020 18:34
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 6cm Advice/experience please?

 

Anthony

You say a 1.9m Mesh dish.

Is the surface  accurate for 6cm, and  what is the mesh size(needs to be about 6mm or smaller)

 Importantly  is the feed  perfectly aligned in the middle of the dish, any droop may cause the  beam to go off axis and this would be most pronounced at 6cm  you may not notice at the lower bands

Mark GM4ISM

On 12/09/2020 18:21, Anthony Coldman via groups.io wrote:

I am looking for advice on 6cm.

 

I have a Kuhne 5.7GHz G2 transverter, this is mounted on the mast and connects using 2m of LDF450 to the RFHamdesign TRI BAND ring dish feed for 23,13,6cm on a 1.9m mesh dish, the IF is 432Mhz which is feed to the shack into another Kuhne transverter and then into my Icom 7300 on 28Mhz.

 

My question are to do with RX capability, I have been using this system in the UKAC for a few months now and always seems that people seem to be able to hear me better than I can hear them, I am running 7w which might account for some of this but I have also been monitoring the beacons and the only one I can occasionally just about hear is GN3FNM. (this can always be heard on 13cm and 5 points higher, similar system TVTR on mast and same dish).

 

Does anyone else use a mast mounted system and do you have an extra LNA? 

 

Can anyone that can hear the GB3FNM beacons confirm if they RX it a lot stronger on 13cm then 6cm? even though the ERP is higher on 6cm?

 

Am I expecting too much on this frequency?  Any pointers or experience gratefully received.

 

Anthony

 


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Neil
http://g4dbn.uk


Neil Smith G4DBN
 

The other issue on 6cm is the plethora of wifi and PTP/PMP unlicenced domestic broadband services, which are a major nightmare and raise the noise floor here by 15dB or more in some directions. Rural broadband delivery is the culprit here, there are still a dozen or more transmitters with 30cm dishes pointing at the master node which is right in the middle of my target area for the parts of IO91 which are not behind trees.

Neil

On 12/09/2020 20:31, Neil Smith G4DBN wrote:

It is a bit weird though. If your dish was wonky or pointing at Alpha Centauri, or the feed was out of focus, then you'd have problems being heard as well.  I'm assuming you don't have elevation on the dish, but can you see the horizon anywhere at sunrise or sunset so you can use sun noise to check if your rx is up to snuff?  You can use the VK3UM calculator to see how much sun noise to expect. Are there any trees or buildings you can beam at and see if you can hear/see their thermal noise?

To get a bit more of an objective measurement of performance if you can't look for sun noise, can you find someone within a line of sight path and do some tests while the other station gradually beams further away from you, and see if your rx signal drops off faster than theirs does.  If you and the other station can use WSJT-X and send a single tone using the TUNE facility or @1000 or something and then use the power slider, you should be able to compare notes on signal level versus TX power.

First stop for me is always the sun, using my SDR software on a 192 kHz slice, or continuum mode on Spectran or the analysis modes on Spectrum Lab.  A quick check to see if I can see the warm wall of the neighbouring house with the dish down is also a good sanity check.

If you have an isolation relay on the 5.7 GHz input with a 50 ohm load, you can try flipping between that and horizon noise to see if the ratio makes sense (with AGC off).

If you haven't got an isolation relay and you've used other bands while the 6cm system is connected to the ring feed, you might have degraded your front end FET.  Do all of the systems on the feed go into TX mode before any power is applied to any of the rings?

Neil G4DBN

On 12/09/2020 19:59, John Lemay wrote:

Anthony

 

I have no experience with 6cms, but I’m not going to let that stop me giving some advice !

 

I purchased a RF HamDesign dish for 3cms (1m diameter) and after a few months of somewhat lacklustre performance I took a close look at the profile. I decided that the ribs were suitably accurate, but there was not nearly enough support between the ribs to give the mesh a decent profile. I stripped the dish and added quite a lot more metal.

 

So I agree with Marks point that you need to check the profile accuracy.

 

Secondly, of the three bands that you are equipped for, locating the phase centre of the feed at the dish focus is much more critical on 6cms. Get it right for 6cms and you will be sufficiently close for the lower bands. When measuring your dish, don’t forget that the central hub has a nominal thickness, and it’s flat which means that the parabola apex is a few mm behind the surface. Also, in the triband ring feed the phase centre is between the ring and the reflector. It’s a sealed unit and you can’t see inside, but the loop will be about 8mm from the inside face of the feed. I’ve mentioned “a few mm” several times, and these start to add up.

 

Finally, the dish is a significant weight, all on one side of your mast. Make sure that you are still pointing at the horizon, and not “drooping” a little.

 

I’m afraid that none of this helps about your question regarding RX capability !

 

Regards

 

John G4ZTR

 

From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of Mark GM4ISM via groups.io
Sent: 12 September 2020 18:34
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 6cm Advice/experience please?

 

Anthony

You say a 1.9m Mesh dish.

Is the surface  accurate for 6cm, and  what is the mesh size(needs to be about 6mm or smaller)

 Importantly  is the feed  perfectly aligned in the middle of the dish, any droop may cause the  beam to go off axis and this would be most pronounced at 6cm  you may not notice at the lower bands

Mark GM4ISM

On 12/09/2020 18:21, Anthony Coldman via groups.io wrote:

I am looking for advice on 6cm.

 

I have a Kuhne 5.7GHz G2 transverter, this is mounted on the mast and connects using 2m of LDF450 to the RFHamdesign TRI BAND ring dish feed for 23,13,6cm on a 1.9m mesh dish, the IF is 432Mhz which is feed to the shack into another Kuhne transverter and then into my Icom 7300 on 28Mhz.

 

My question are to do with RX capability, I have been using this system in the UKAC for a few months now and always seems that people seem to be able to hear me better than I can hear them, I am running 7w which might account for some of this but I have also been monitoring the beacons and the only one I can occasionally just about hear is GN3FNM. (this can always be heard on 13cm and 5 points higher, similar system TVTR on mast and same dish).

 

Does anyone else use a mast mounted system and do you have an extra LNA? 

 

Can anyone that can hear the GB3FNM beacons confirm if they RX it a lot stronger on 13cm then 6cm? even though the ERP is higher on 6cm?

 

Am I expecting too much on this frequency?  Any pointers or experience gratefully received.

 

Anthony

 


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-- 
Neil
http://g4dbn.uk
-- 
Neil
http://g4dbn.uk