I’m having trouble with the performance of the Yaesu FTM-150Rasp radio I just bought on the 70CM band. I have 3 different antennas and 3 radios. I always run SWR tests with a new radio and the antennas before using the new radio. With all three radios, the SWR
test results on the 2M band are good. The graph of the results shows a nice
curve. It looks sort of like a shallow bowl. The SWR test results for the
70CM band are not good. The graph of the results looks like an upside-down
V or mountain peak. This occurs whether I run at 5w or 50w. The 50w
readings are a bit higher than the 5w readings. I think that is to be expected. Very similar results occur on all 3 antennas. I’ve also tried swapping antenna cables, and the
results are similar. Regardless of the combinations of radios/cables/antennas I have tried, the graph of the SWR readings for the 70CM band looks something like a mountain peak or up-side-down V. The other two radios I have produce a normal shallow bowl looking graph of SWR readings on 70CM with the same antennas. I’m wondering if the FTM-150Rasp has a bad electronic component that is causing this problem. Is there something else I can test? Please advise. Thanks for the help!
73,
Dave W.
KC6DTW
@David_Webb
2m and 70cm don’t generally have swr issues, due to the small size of the antenna. You didn’t mention what type of antennas you have…I am assuming magnetic mount. You also didn’t mention if the antennas have any type of length adjustment. And of course, if there is anything around the antennas, or if they are inside or outside. 70 cm repeaters are 440 - 450 and the simplex calling frequency is 446. Not sure what frequency your “peak” in your swr is and what the swr reading is. However, I do not believe it is your radio that is the issue, but rather the location or grounding of the antenna.
@David_Webb I think Harry is on the right track. Hard to mess up a v/u antenna unless you are operating out of band. I agree with Harry. Sounds like a lack of proper ground to the mount. Have not had any problems reported on the 150 Rasps at all. Please try better grounding to the frame of the vehicle and take new measurements again. Keep us posted and thanks for shopping Gigaparts!!
Douglas:
I put together a detailed reply post to Harry’s questions and explained the situation ans SWR readings with several graphs. When I tried to post, I got this response.
Can you fix this so I can post the real message? Or can I email it to you for you to post? Thanks for your help!
Best regards,
-Dave
@David_Webb there isn’t a way to fix it. If you have 3 graphs, or other pics, etc. you will need to separate into 3 responses that include the graphs or other imbedded media items. Sorry for the inconvenience.
Thanks for the guidance Sue.
Harry: Thanks for your kind reply. You raise some good questions I hope to answer and elaborate on.
Douglas: Thank you also for adding your insight.
So here’s the situation:
Radios used for testing: Yaesu FTM-150Rasp and Yaesu FT-60 (5w handheld).
Antennas used for testing: Diamond X200A 5/8s wavelength 2m Dual Band antenna with 3 radial ground plane, and Diamond NR770HNMO Dual Band Mobile antenna on top of the cab.
When I set up the Diamond X200A in the attic (outside antennas not allowed in our neighborhood), I wondered if it would work at all. The ceiling of the attic (inside base of the roof) is lined with a reflective foil for heat reflection. I tried the FT-60 connected to the Diamond X200A in the attic and was surprised to connect to the local repeater and ARES net. The SWR readings were fair, not great, but I decided to buy the FTM-150Rasp for more power and flexibility in the home shack and mobile in the F-150 pickup (aluminum body).
Here is a graph of the SWR readings for the Diamond X200A in the attic and the two radios. The curve is inverted with the worst readings in the middle of the band.
The 70cm band readings were not as bad as the 2m reading, but they were still odd. They started high at 448 MHz and trended down across the band, and were lowest at 440 MHz. Neither SWR readings graph looks “normal” to me, nor does it look like the SWR readings graphs from Diamond for that antenna. I guessed the foil lining in the attic might be causing some of the problem.
So, I decided to test the FTM-150Rasp on a different antenna (one I had used successfully before, and put the dual band mobile antenna Diamond NR770SHNMO on the roof of the truck cab and got the SWR readings results below. I added a Baofang 5w cheapy handheld just for further comparison. My next post will show that info.
(I would post the graph but the website won’t allow more than 1 graphic per post).
So, I put the dual band mobile antenna Diamond NR770SHNMO on the roof of the truck cab and got the SWR readings results below. I added a Baofang 5w cheapy handheld just for further comparison.
The 2m band results look normal and pretty good. All the SWR readings are below 1.5:1. But then, the 70cm band results show the FT-60 handheld and the cheapy Baofang handheld look good, but the FTM-150Rasp has a problem. See the graph below. What do you think?
I’m not sure what to deduce from all this. Ultimately, my goal is the best antenna performance possible in the attic with the Diamond X200A.
SIDEBAR FOOTNOTE for Mobile in the F-150
Since the body of the truck is aluminum, mag mount does not work. For testing I put a steel wire rack on top of the cab with ground plane wires coming off it. For permanent, I installed a bracket where the windshield meets the engine hood and side fender and the “A pillar” for the cab. That location works fine for the 2m band, but is terrible for the 70cm band (SWR readings between 4:1 – 5:1). I am guessing the aluminum “A Pillar” is reflecting the signal back on to the antenna in sync with the wavelength. Incidentally, it is even worse for the 10m band CB frequencies. The SWR readings are over 10:1. I wonder if this is unique to my installation on the truck, or endemic on all aluminum body vehicles. Anyone got thoughts on this one??
Ultimately, I’d like to get the Diamond X200A performing as best possible in the attic. And, I don’t know what if anything can be done on the aluminum body truck. I would appreciate any ideas and suggestions.
Thanks for all your thoughts and ideas on these issues.
73,
-Dave
@David_Webb
Dave,
Well I am not too concerned that your X200a has a 1.7 swr in your attic…and that your attic has the reflective foil. So your antenna is near or possibly touching the roof…and there is a foil shield in proximity to your antenna…so with that in mind you are getting a good swr. The real key, to me, is not the SWR (you will never reach 1:1) but whether the antenna hits the repeater and is performing as you want. Remember, even dipoles, when measured for swr are generally measured “in free space”. Clearly the height of your X200a is a plus but the foil, shingles, rafters, etc. are detractors. Diamond’s specs on that antenna show swr 1.5:1 or less…and that is not in an enclosed/foil covered space. You could adjust the radials slightly, but not necessary. See what Diamond says:
“All X-Series antennas are completely adjustment free. If VSWR of an anten-
na is extraordinarily high, see if each connecting part is well contacted. It is
most likely due to bad contact in the coaxial cable and/or connector connec-
tion, or soldering problem. Be sure to use 50ohm coaxial cable to feed the
antenna.” (so, re-check your coax)
Clearly your indoor installation will be different from outdoor.
I believe the difference between your FT-60 (with a rubber duck) and your FT-150 is that the FT-60 the body of the HT is the ground plane for the antenna (see TigerTail) while the FT-150 does not have that setup, even though the SO-230 is still part of the radio.
I believe the same holds true for your NR770H. You may try a lip mount, on the driver’s side of the hood, for a better ground and clearer path for your NR770H. The set screw on the antenna could be used to adjust the length of the antenna slightly, but these antennas are designed to operate “out of the box”.
In short, I believe your X200a is working as well as can be from the attic and the gain in altitude is worth it. Your NR770 should not be beside that “pillar”.
And the final issue, is whether your SWR meter is calibrated correctly.
Harry: Thanks again for your response and thoughts on all this. You have confirmed what I thought (had hoped for better) on the X200A in the attic. Though I may try hanging the antenna at different lengths from the top of the attic to see if that improves anything.
The FTM-150 vs. the FT-60 handheld; I put an antenna cable adapter on the FT-60 so it was driving the same antennas (X200A and the NR770HNMO) as the FTM-150. That is why my concern for the FTM-150 when it was driving the NR770HNMO when compared to the FT-60 and the Baofang 5-R handhelds.
The SWR readings curve for the FTM, driving the same antenna in the same place as the two handhelds, is concerning. These SWR readings for the FTM just don’t make any sense at all. Because of the temporary antenna placement for this test, maybe I should just ignore these results, even though I cannot explain them and understand why they occurred.
Well, thanks again for your help and insight.
73,
-Dave
