Hello OMs,

I’m going to share some measurements made on my UHF Diplexer that will be installed on my MMDVM equipment for the upgrade from simple hotspot to a repeater, using a Diamond X-510 antenna.

I bought this very cheap Diplexer from the Chinese e-shop “409Shop”, at only 97$: http://www.409shop.com/409shop_product.php?id=104460

SGQ-450D-N

caratteristiche

It’s a 6 cavity Diplexer (2 notch + 1 bandpass for each path), so I expected a very good out-of-band attenuation, which is a very interesting feature in installation sites with strong RF signals coming from other transmitters.

I choose the 50W version, because the price difference between the 35W and 50W was only 14$.

For the payment, I used paypal, without any problem. As suggested on the site, I specified the Low and High Frequency of my repeater in the order notes.

The Diplexer arrived very quickly. The order dates are the following:

  • Order and Payment: 14 November 2017
  • Order Confirmation: 15 Novemver 2017
  • Shipment confirmation and Tracking Number: 18 November 2017
  • Arrival: 01 December 2017

Before the installation, I took some measurement with a Vector Network Analyzer, at ambient temperature and at cold and hot temperatures, in a climatic chamber, in order to verify the tuning made by the seller, and the temperature drifts, which affects the low-cost Diplexers.

I choose +55°C and -25°C as worst case temperature, although my region has a very mild climate.

Note: during every measurement, the third port (not connected to the VNA) is connected to a 50ohm dummy load.

The frequency of my repeater are:

  • Low (TX): 430.325 MHz
  • High (RX): 435.325 MHz

The more interesting measurements are:

  • Attenuation from Antenna port to RX port;
  • Attenuation from TX port to Antenna port;
  • Matching at RX, TX, and Antenna ports;
  • Isolation between TX and RX ports;

Here below, the ambient temperature measurements are reported:

P1antP2high_3

P1lowP2ant_3

MATCHING_TX

MATCHING_RX

MATCHING ANTENNA

P1lowP2high_3

Considerations about performances at ambient temperature

  • The isolation between RX and TX ports is >70db, as declared on the datasheet
  • The loss from ANT to RX port and from TX port to ANT is <1dB
  • The resonance at RX and TX ports are slightly different from the desired frequencies, but the matching is very good anyway (>20dB)
  • The matching at antenna port is good (>20dB)

 

Here below, the temperature drifts of the main measurements are reported:

P1antP2high_hot_cold_1

Note: the attenuation @435.325MHz is 1.2dB at +55°C and 1.1dB at -25°C

P1lowP2ant_hot_cold_1

Note: the attenuation @435.325MHz is 1.1dB at both +55°C and -25°C

P1lowP2high_2_HOT_COLD

Considerations about performances at cold and hot temperatures

  • In all the cases, the responses moves up in frequency when the temperature increases.
  • The isolation is still >=70dB also at hot and cold temperatures.
  • The attenuation from ANT to RX port and from TX to ANT increases slightly (1.2dB),but is still very good, even if the curves move in frequency.

Conclusions

Here below, I judged and assigned a score for every aspect of Diplexer, from 0 (min) to 5 (max):valutazioni

Considering the cost, this Diplexer is a good compromise between cost and performances, and I suggest this product for hamradio applications.

The out-of-band rejection is good as well as the temperature stability, so it can be used also in mountain sites or in RF polluted sites.

 

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