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$: http://www.409shop.com/409shop_product.php?id=104460
It’s a 6 cavity Diplexer (2 notch + 1 bandpass for each path), so I expected a very good out-of-band attenuation, which is a very interesting feature in installation sites with strong RF signals coming from other transmitters.
I choose the 50W version, because the price difference between the 35W and 50W was only 14$.
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:
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:
Note: the attenuation @435.325MHz is 1.2dB at +55°C and 1.1dB at -25°C
Note: the attenuation @435.325MHz is 1.1dB at both +55°C and -25°C
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.
Here below, I judged and assigned a score for every aspect of Diplexer, from 0 (min) to 5 (max):
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.