For my main activity on 2m FM I use a pure 2m FM transceiver, no dual- or multi-band TRX there.
My antenna is the Diamond V-2000 capable of operating on 6m, 2m and 70cm.Until recently I used a cable running into my attic space, then extended down to the living room.
Having two extra junctions in the cable is bound to increase losses in the system, so I decided to lead the cable directly into the ground floor, eliminating the extra junctions. Just a single length of about 25m type 400 cable with a PL connector at the antenna, and N-connector in the living room.
Add a triplexer and 2m, 70cm and 6m can be connected to 3 different transceivers :
6m : My old IC-575 6/10m TRX for 6m. Only 10 W, but I do have a 100-150W PA lying around.
2m : A 70W 2m FM TRX.
70cm : My FT-8900 running on 2 frequencies on 70cm.
The results are encouraging . The RX, as well as TX performance of the system has improved audibly on 2m and 70cm. 6m was not tested. I estimate an improvement of 2-3 dB on he 2m part, and probably a bit more on the 70cm part.
Now I think of possible improvements.
Power capability :
The limit on power capabilities are with the antenna itself. The spec in the table at from Wimo's website says max 150W. The triplexer is somewhat better, specified for 800W PEP on 6m and 2m, and 500W on 70cm. I estimate from this that the FM capability for the triplexer is around 250/250/200W, so the limit is at the antenna.
Receiver sensitivity :
On 6m there is no problem at all. The antenna noise is clearly audible on the IC-575.
On 2m the loss in the cable/triplexer is probably low enough to be acceptable.
On 70cm, however, the cable/triplexer loss is probably around 3dB, reducing the RX sensitivity of the total system considerably. In any case more than 3dB, probably a deterioration of about 5dB when compared to an "ideal" system.
Conclusion :
There is room for improvement all around. on all 3 bands, though mostly on 70cm. This would mean moving the triplexer up into the mast, near the antenna. Oops, then we need more cables, but that is acceptable to me. The preamp(s) can then be mounted near the antenna, improving the system sensitivity (noise figure), especially on 70cm.Now, the antenna is located near my (big) shed, so it should be possible to mount linear amplifier(s) near the antenna, again with 70cm being the best improvement. For 6 and 2 the linears would probably be fine mounted in the shack.
I do have a set of German preamplifiers for 2m and 70cm, and even one for 6m, with noise figures around 0.6 - 1dB. This I consider sufficient for use with FM, for mostly local, or, as I call it, "local tropo" (distances within 250km from me). I know, with the right conditions this could be much more.
This is my idea for an optimized use of my antenna/linear/TRX combinations.
Further, I have a low placed antenna for 2m/70cm with a dual band TRX, for monitoring a local cross band repeater.
Additional :
I love to monitor several frequencies simultaneously, so, in addition to this, I would like to extend the receive side of the bands to include more receivers.
I see two options, either, a separate receive antenna with a preamp, and separate cable with power splitters going to different receivers, or, making switch boxes on each of the transceivers, each with a receive preamp and a power splitter for the receive signals.
For now, I monitor one frequency on 6m, 2 on 2m, and 3 on 70cm with the antenna system just described. Of course, when transmitting on one band, all other reception on that band is out of the question .... or is it? That is a story for another time.
All in all, receiving on 6 frequencies on 3 bands, and with TX capability on 3 bands, is not too bad for two antennas.
I have yet to improve the RX/TX capabilities as described, but that is a story (or more stories) for later. For now I am happy with the current improvement.
You may ask, why this is of interest . Well, I enjoy a local (or not so local) FM chat as much as many people, so there you have it.
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