Antenna Tuning?

[SoCalRally]

Now lets throw in a Zinger! Your antenna was tuned for Smith's Team @ 151.xxx and now you are chasing for Joneses Team @ 159.xxx and your antenna is no longer properly tuned. A good radio not seeing a good antenna match is going to attenuate it's power to save the final transistors, (that make all the power), from too much heat so they don't smoke! What I am saying here is that a 110 watt radio with a properly tuned antenna will put out 110 watts, (the smith example). Now change frequencies to chase for the Joneses and your radio maybe putting out 60 watts! So what is the answer? Multiple antennae? Broad band antenna that would accept the different frequencies but no gain? Speaking for myself, I use three different antennas tuned optimally for the three radios I employ doing the Weatherman Relay. Antenna #1 does the low frequencies from 150.xxx ti 153.xxx. Antenna #2 does the high frequencies from153.xxx to 159.xxx and antenna #3 stays on the P C I Customer Channel, (for P C I Customers only). These antennas have been previously tuned for maximum preformance on all the frequencies being used and are re checked upon erecting them on the Weatherman Relay Site.
In summary, I would talk to P C I Scott, I think some of me rubbed off on him. I personally like the idea of two radios in every race and chase vehicle and two antennas, (properly tuned and identified of course as to which radio they belong to). If you can't employ two radios, I would certainly employ two antennas if you are using substantially diferrent frequencies.

It's a cost vs benefit issue. There are some complex techniques that broadly fall under antenna diversity that can be applied e.g. frequency diversity, MIMO antenna arrays, adaptive antenna arrays etc., combined with switching, selecting, combining & dynamic control etc. However, the cost & complexity is not practical for most race teams, and the added weight would not be desirable for a race car.

A reasonable solution, which is cost effective as it saves the cost of a 2nd radio, but is obviously not as flexible as 2 separate radios, is to use a single radio connected to an antenna switch, which is connected to 2 antennas each tuned to optimal frequencies.

For example, the typical race or chase truck scenario is as follows:

Weatherman frequency (151.625, let's call that 'WXMAN') - all teams generally want to monitor that for general race info, to take advantage of Weatherman's HAAT to reach teams that are not line of sight etc.

Race team frequency (individual, different for each team, let's call that 'RACE'). If a team's race frequency, is more than 3-6 MHz (typical bandwidth for the VHF antennas in use) away from WXMAN frequency, then a 2nd antenna specifically tuned to RACE will provide better response when trying to communicate on RACE, but at the expense of signal quality with WXMAN.

So one solution is to connect 2 antennas, one tuned to WXMAN, and the other tuned to RACE to an antenna switch, and then connect the output of the antenna switch to the radio antenna connector. Then, with the flick of the antenna switch, one could switch to whichever antenna is optimized for the desired frequency.

A potential enhancement to that would perhaps be to also run a splitter/combiner with a feed from WXMAN & RACE, and a 3-way antenna switch, so you could have 1. WXMAN only, 2. RACE only, 3. WXMAN + RACE. The advantage of position 3 i.e. WXMAN + RACE is that one could potentially listen to 2 different frequencies at once with a single radio. The disadvantage would be some signal loss on both, and if there was voice activity on both frequencies at the same time, it might sound garbled and/or difficult to distinguish between the two. However, in that case, you could just switch the antenna selector to RACE only or WXMAN only to listen to the desired frequency. A further disadvantage would be that it would probably be difficult to tune the combined feed for a low TX SWR, but I guess it would be unlikely that one would want to have the same conversation with both your RACE team & WXMAN at the same time on different frequencies. (and for this specialized case, Bob could dial to your RACE channel on one of his extra radios).

Anyway, it seems a cost effective & simple practical solution for most race teams & chase trucks would be to run a single radio to an antenna switch, which is connected to 2 antennas, one tuned to RACE, and the other tuned to WXMAN & then switch back & forth as desired. One would just have to make sure one was connected to the desired antenna e.g. not leave it on WXMAN by mistake, and then wonder why you haven't had contact with your RACE team for the last 30 mins!!

Another option for chase trucks would be to run the simple 2 antenna solution as above, and then use a handheld programmed to those same 2 frequencies, possibly connected to an external antenna, for receive only. That way you could leave your antenna switch for your main mobile radio connected to your RACE frequency for communications, and your handheld dialed to the WXMAN frequency just for monitoring. Then, if you needed to talk to WXMAN, you could use the antenna switch to click your main mobile radio over to WXMAN, make your transmission, and then click the antenna switch back to RACE, and resume communicating with RACE on the main mobile radio & monitoring WXMAN on the handheld.

Obviously, as Bob pointed out, the most flexible solution is to have 2 (or, more, in his case) completely separate setups each optimized for its intended frequency use, but that might be too cost prohibitive for most teams.

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[wrightracing.net]

Years ago I started running an antenna tuner in line. I would cut the antenna for 151MHz but when you get to frequencies up to 158HMz the swr would be off the charts and power output would be cut in half. The antenna tuner I use for out pit is mounted right net to the radio in our pit box with a 110watt Kenwood it helps getting out to the team.