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Helix - was Microwave oven test


G8TZJ
 

Thanks for all the advice on plastics for the helix. Attached should hopefully be a picture of the finished Helix with a LNB. I configured it above the LNB, because if the helix is in front of the LNB, there is a 2dB loss of signal into the LNB from QO-100. The SWR (I don’t have a VNA) was 1.15:1 without the LNB present. With the LNB it increased to 1.25:1 and when sprayed with water (to simulate rain) it was 1.2:1. Interesting that the SWR improved with water.

 However when it was mounted on my dish (a 1m offset) it returned a signal 2-3 dB worse through QO-100 than my BaMaTech patch feed. Removing the LNB so I could drop the Helix nearer to the dish’s focal point, improved things so it was now equal to my BaMaTech patch feed. Had I been able to drop it fully into the focal point, it may have been better. I then tried a POTY feed in place of my BaMaTech patch feed and it was 2-3 dB better than the BaMaTech. In fact Leila jumped on my test signal. Same power used throughout.

 So I’m not going to use a Helix. I may eventually use a POTY but that needs a few more changes to accommodate it.

73 Andrew G8TZJ



Colin Ranson
 

Hi Andrew,

 

Just as an aside I use a separate uplink antenna in the form of a 16 turn helix RHCP (VAS Super Canon) with an impedance match modification. It sits next to the main 80cm RX dish and is so small it sits on a tiny mount and at only 15 inches long it can hardly be seen.

 

Best regards,

 

Colin de G8LBS.

 

Sent from Mail for Windows 10

 

From: G8TZJ via groups.io
Sent: 15 October 2020 18:35
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Helix - was Microwave oven test

 

Thanks for all the advice on plastics for the helix. Attached should hopefully be a picture of the finished Helix with a LNB. I configured it above the LNB, because if the helix is in front of the LNB, there is a 2dB loss of signal into the LNB from QO-100. The SWR (I don’t have a VNA) was 1.15:1 without the LNB present. With the LNB it increased to 1.25:1 and when sprayed with water (to simulate rain) it was 1.2:1. Interesting that the SWR improved with water.

 However when it was mounted on my dish (a 1m offset) it returned a signal 2-3 dB worse through QO-100 than my BaMaTech patch feed. Removing the LNB so I could drop the Helix nearer to the dish’s focal point, improved things so it was now equal to my BaMaTech patch feed. Had I been able to drop it fully into the focal point, it may have been better. I then tried a POTY feed in place of my BaMaTech patch feed and it was 2-3 dB better than the BaMaTech. In fact Leila jumped on my test signal. Same power used throughout.

 So I’m not going to use a Helix. I may eventually use a POTY but that needs a few more changes to accommodate it.

73 Andrew G8TZJ