SM7LCB - 0.9m Dish

Last updated 10 August 2010

For more then 10 year ago I got a 0.93 meter dish from Mats/SM6EAN. This dish have been lying in Stockholm and also here on Öland without any action. During 2003 I did some measurements on the dish and found that the dish have a f/D of about 0.38. I at that time have some ideers to us it on 3 bands 13/6/3cm I calculated the performance of the dish to be as table below. It is compared with my current 60 cm dish which I use on 3 cm (not used on 6 cm).

Band [MHz] Gain [dBi] (50%) 3 dB beam width   Current 60 cm [dBi]
2320 24.1 --
5760 32.0 ?(28.2)
10368 37.1 ?33.3

During summer 2009 after I build and setup my 1.9 meter dish for 23/13/9 cm I start looking on my 0.9 meter dish again and this time only to use it on 6 and 3 cm. During the winter 2009/2010 I ordered a dual band ring feed from RF HAMDESIGN for 6/3cm.

Measurement setup

To test the antenna and also to see were to set the feeder I build a small antenna measurement setup.
To build this measurement setup I borrow following equipment from Niklas/SM7UFW,
  • Network analyzer Anritsu MS2036A (up to 6 GHz)
  • Transmit antenna, VP250/54 (5470-5875 MHz, 12 dBi).
  • Coaxial cable, Bedea # 2261 HFX 50 1336 - PVC.

View from transmit antenna to the 0.9 m dish.

The measurement of focus distance with sliding ring feeder.

Feeder position

Because the network analyzer only worked on the 6 cm band I only could do all measurements on this band and hope that the performance on 3cm will follow. But I realized during the work that it would have been very nice with measurement on 3cm.

To find the focus position I first measure the received power at the ring feeder with different distant between it and the dish. I did this three times with some adjustments between each measurement to see that antenna alignment was correct etc. These three measurements was plotted into a diagram and is showed below. All the measurements gave the same result with a peak at about 35.5 cm. The calculated focus distance was 35.6 cm so it seems that I'm at the correct place with the ring feed. 

Focus distance is measured from bottom of the dish
to front of the ring feeders housing.

Antenna Gain Measurement

During the measurement for best focus distance I also measured the gain of the antenna with the best focus distance for that measurement. These measurement gave that the gain on 5.7 GHz is in the correct order.
Band Measured value [dBi] Calculated value [dBi]
5760 MHz, M1 31.0 32.0 (50%)
5760 MHz, M2 31.2 32.0 (50%)
5760 MHz, M3 31.7 32.0 (50%)

The last measurement (M3) was don't when the focus was fixed to 36.0 cm.

Mounting pictures of ring feeder and feed holder,

Antenna Beam Width Measurement

I did one attempt to measure the beam width of the antenna. Not easy with this setup!

This measurement gave the following result.

Band Measured value Calculated value
3 dB 10 dB 3 dB 10 dB
5760 MHz 5.1 8.9 - -

Antenna Return Loss Measurement

Measurement of return loss on 5760 MHz was measured to be -17 dB.

Antenna Installation

In the evening (4 August) I installed the antenna and then replaced the current 60 cm dish with this 93 cm dish. The installation went very smooth and easy.

Antenna and 3 cm transverter.

All antennas and Columba oenas (I think).
- 6 element Vårgårda (2 m).
- 93 cm dish for 6/3 cm (today only 3 cm).
- 1.9 m dish for 23/13/9 cm.

Real Test of the Antenna

That evening (4 August) I only heard the SK1SHH in JO97CJ. Not far away but that beacon have 60 cm dish pointing towards SM0 (Stockholm) and it's not common the hear the beacon from my QTH. But this don't say anything how will the antenna is working. Did a test with Håkan/SM7GEP but NIL from him but that normal because I have a lot of trees in his direction. We can maybe work during winter time when all leaves is gone from them. Else conds seems bad this evening but hope get better possibility soon to test the antenna.

Worked Torben/OZ3ZW easy on three bands and with nice signals on 3cm so also when I worked SP2MKO in JP93CB. JP93 is a new # on 3cm. You can listen on the signals of this page.

Hopfully more will come... (soon).

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