Comet CF-4160 Duplexer SWR results

[dosw]

I have a Comet CF-4160J Duplexer that accepts either two inputs (one in the 1.3MHz-170MHz range, one in the 350-540MHz range) to output to a single antenna, or that accepts one input to output to two antennas -- it works in either direction. The duplexer: Comet CF-4160J

 

I have been testing it on a Comet CA2X4SR antenna. The antenna: Comet CA-2X4SR-NMO. With this antenna, no duplexer, in the MURS range, I get an SWR of  <1.1:1. In the GMRS mains I get an SWR of <1.4:1. In the GMRS repeater inputs & interstitials, I get an SWR of <1.1:1. So pretty darn good results.

 

Now add the duplexer. Antenna plugged into the duplexer. The radio plugged into one of the two frequency-ranged inputs. So plug the radio into the VHF side and test MURS: I get <1.2:1 SWR. Now plug the radio into the UHF side of the duplexer. In the main 467 frequencies, I get an SWR <2.3:1. In the repeater/interstitial frequencies, I get <1.1:1.

 

My Surecom SR-102 is located inline between the radio and the duplexer. Here are the results in a more tabular format.

SWR Meter between Radio and Antenna (NO DUPLEXER):

MURS: <1.1:1

GMRS 462: <1.4:1

GMRS 467: <1.1:1

 

SWR Meter between Radio and Duplexer:

MURS: Duplexer: <1.2:1.

GMRS 462: Duplexer: <2.4:1

GMRS 467: Duplexer: <1.1:1.

 

2.4:1 is survivable. But it's strange that the duplexer seems to have very little effect on SWR at MURS frequencies, and at the 467s, but at the 462s it is markedly worse performing. 

Now if I move the Surecom to be inline between the duplexer and the antenna, instead of between the radio and the duplexer, I get the following results:

 

SWR Meter between Duplexer and Antenna:

MURS: <1.1:1

GMRS 462: <1.4:1

GMRS 467: <1.1:1

So the outlier is the GMRS mains in the 462 range, between the radio and the duplexer.

 

Do I have a defective duplexer, or is this a pretty typical experience; that there may be rough spots at random places in the spectrum when using the duplexer?

 

 

 

 

[SteveShannon]

I would put an analyzer on the input of the duplexer, a dummy load on the output, and look at the response as frequency rises. Sweep it from 462 to 470 MHz.

[Socalgmrs]

Do you have a good ground plane under  the antenna?   It doesn’t have arials since it’s designed to go on a roof/truck ect.  

[dosw]

19 minutes ago, WRXP381 said:

Do you have a good ground plane under  the antenna?   It doesn’t have arials since it’s designed to go on a roof/truck ect.  

No change to the ground plane when swapping in the duplexer. I do think that having an SWR <1.1 for both MURS and GMRS 467, and <1.4:1 for GMRS 462 without the duplexer is an indication that the setup is pretty well configured until I add in the duplexer.

[dosw]

I'm just following up in this thread to report back on my tests with the CF-4160J Diplexer (or Duplexer... which is what it's labeled as).

 

The setup:

UV5G -> Surecom SW-102 -> CF4160J -> XRDS-RF 50W Dummy Load.

 

I put the dummy load on the "single" end of the diplexer, and connected the transmitter, through the SWR meter, to the 350-540MHz end of the diplexer.

 

• 462.xxxx: 1.01:1 SWR, and about 3.4W power output.
• 467.xxxx: 1.01:1 SWR, and about 3.1W power output.

 

Next, I attached the transmitter, through the SWR meter, to 1.3-170MHz side of the diplexer and set to MURS frequencies:

• 151.9400: 1.01:1 SWR, and about 2W power output.

 

Next I switched over to Marine VHF 16:

 

• Marine VHF 16 (156.8000): 1.0:1 SWR and 4.97W power output.

 

Because I like to live dangerously, and don't care that much about a $25 radio, I keyed up on a GMRS frequency for a moment, with the transmitter feeding the 1.3-170MHz side of the diplexer. The SWR was around 11.5:1 or 12:1. The radio seemed to survive the experience, so I switched over so that the input feed was on the 350-540MHz side, and keyed up in a MURS frequency. Again, a nearly 12:1 SWR.

 

Next I moved the SWR meter to between the diplexer and the dummy load. This will test how much power the diplexer robs from the antenna feed.

 

At GMRS frequencies feeding into the UHF side of the diplexer, I saw no appreciable drop in power (in watts) when the SWR meter came AFTER the diplexer, feeding to the dummy load. And SWR measurements were nearly identical.

 

• At Marine VHF frequencies, I saw about a 0.25w drop in power.
• At MURS frequencies I saw about a 0.2w drop in power.

 

Again, living dangerously, I keyed up on the VHF side of the diplexer at a GMRS frequency. The SWR meter, that was inline between the diplexer and the dummy load registered nothing at all. Similarly, keying up at VHF frequencies when the feed line was plugged into the UHF side, the SWR meter that came after the diplexer registered nothing at all.

 

For another test I reversed the diplexer so that I was transmitting into the single-feed side, and had the dummy load on the UHF side. At GMRS frequencies, I saw pretty much exactly what I measured in the opposite direction; same power, same SWR. And at VHF, the results also lined up with my previous VHF tests.

 

And as a final test, I fed from the transmitter into the diplexer, into the SWR meter on the VHF side, into the dummy load. No power registered on the SWR/power meter when I keyed up at GMRS frequencies. And swapping over so the SWR and dummy were on the UHF side, while keying up at MURS and Marine frequencies, again nothing registered on the SWR meter.

 

Conclusion: The CF-4160J doesn't significantly alter SWR into a well matched dummy load. It also only drops transmitted power by between 1% and 10% depending on the frequency. None of those values should matter much at all, in isolation. For example, dropping from 5w to 4.75w is not going to make an appreciable difference in range or signal quality except in some ideal situation.

The CF-4160J also does a good job of isolating the UHF and VHF bands; the SWR/Power meter never registered any power on the output side, if the input was going into the wrong frequency branch. And likewise with the diplexer turned around, sending input to the common branch produced no measurable output on the wrong frequency branch.

 

In an earlier post in this thread I mentioned that at GMRS simplex 462.xxxx frequencies I was seeing a higher SWR when I ran through the diplexer feeding a Comet CA-2X4SR antenna, than when I took the diplexer out of the equation. Given the results testing the diplexer in isolation, dummy load instead of antenna, and none of the magnetic mount's RG-too-thin cable between, it seems like the diplexer isn't the source of reflected power.

 

In a situation where someone needs to use a common feed line to one VHF and one UHF antenna, or a common antenna for one VHF and one UHF radio, I think I can say that the CF-4160J is a really good option. In fact, I read a thread elsewhere in this forum where someone was using two of these; one connected two radios to a single feed line, and the other connected the feed line to two antennas. It looked like their results were pretty good.

 

The only down-side I see with this unit is the fact that it's not weatherproof, so if it's going on an outdoor installation it will need to be in an enclosure.