Apex 700 DTA Active Antenna

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ka3jjz

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While I don't have any direct experience with it, I do see one big issue - no way to adjust the gain. This means that you get the (claimed) 20db more or less throughout the spectrum - and where the band might be very crowded (such as in urban areas where AM stations are plentiful), overloading can be a real problem. Too, with too much gain, you can also get noise issues.

IMHO (OK maybe not so humble), actives like these are useful only as a last resort, and only when there's a way to adjust the gain for band conditions, or the gain isn't really all that high. Let's hear about what receiver you are planning to use this on, and what your particular environment is like. Can you put something up outdoors? That is the best option....HTH...Mike
 

Graboon

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Re: Apex 700 ADT Active Antenna

I live in a big (and beautiful) urban apartment building, with lots of stone and steel to shield sw and ham signals from receivers inside. I cannot mount any kind of outside antenna. Thus, I listen to shortwave and hams signals by sitting on my fourth floor patio balcony. Might seem odd, and it has its problems, but overall I make it work. My radio is a new Sangean 909x which I purchased from Radiolabs in California. I bought their "modified" version which features improved audio filters. Also, the 909x has a separate RF Gain control and a working squelch. With the radio's own whip, I pull in many signals. Hope to find a way to improve on that. Also hope to find an antenna that is portable, which the 707 ADT active antenna is. A decent antenna is the key to shortwave listening, and I am always looking to improve my situation. Thanks for your questions.
 

Graboon

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Mike: did you get my reply? If not, let me know and I will respond again. I am trying to find my way around this forum. Graboon
 

ka3jjz

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Patience, Graboon - people have to work and sleep y'know...

As I suspected - a portable like the 909X would only get horribly overloaded by something like the 700DTA. Another issue is that you cannot separate the receiving element (the whip) from the amplifier, so you'd have to have both the radio and antenna out on the balcony. That would tend to get a little unwieldly I would think.

If you have a 4th floor patio balcony, one thing I would try would be to sneak some very thin clear speaker wire around the perimeter of that balcony a few times - making it both thin and clear would make it darn near invisible, particularly since you're up 4 floors.

Another possibility is another active antenna, but this one has much lower gain, and not as likely to cause overloading - the North Country Active Antenna...

Active Antenna 10kHz - 30 MHz

The advantage here is that the antenna and amp element can be remotely placed - preferably on your patio, perhaps on a wooden dowel - and you can get it somewhat away from the building. You would need, of course, to solder up a jumper to go from the antenna to the 909x, but that shouldn't be all that hard.

Those are just 2 suggestions I can think of at the moment. I'm sure other folks would have some ideas, but like you said, the construction of your building really makes it tough. The little wire antenna that radio comes with lets you know that it won't take all that much to wake it up...HTH Mike
 

nanZor

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Graboon - I just picked up a stock 909X a few days ago, and a semi-review with my observations is awaiting approval.

But the short of it is, when operating the 909X solely from batteries and the stock whip, HF signals will be down a bit because it is missing a ground - not uncommon with portables, but definitely noticeable with the 909X.

Can you use the ac-adapter? It is a VERY quiet unit rf-wise, and will provide the missing ground. If the ac line itself isn't too noisy, this might be the quickest improvement, although Mike's suggestions are spot on too.

Can you string out the included ANT-60 wind-up antenna to the external antenna jack somewhere?
 

woebbers

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What i did was use the ground side of the AM antenna jack. Ground that to a sufficent ground source and use the whip or the long wire as normal...You need a 1/8 jack and a piece of wire...give it a try.
 

nanZor

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Three years later and a mini-review ....

I just picked up the Apex 700DTA and am very happy with it. I apparently got the earlier production model with light-colored knobs and not the latest black knobs.

However, I am only using it with higher-end receivers like a Commradio CR1a, and for now a Kenwood TS590s transceiver (rx only of course!)

At first I was hesitant about the lack of a gain control, but the Apex seems very well under control. The 20db of amplification to the supplied 2-foot whip is about as efficient as my 18-foot non-resonant vertical fed with a 4:1 unun. Note that the top bnc connector is designed to attach to a small whip, and NOT a low-impedance piece of coax. Yes, one could change the size of the whip, but at some point, you are building something very different from a small amplified antenna.

So - no overload issues. Basically the unit is acting similarly to about 15-20 feet of tuned wire. Outside of course. Inside near a window, there is a bit of attenuation inside the house, but not as bad as I thought it would be. 20 feet of wire to a portable *may* be a bit too much, but I cannot really comment on that since I have given up on most portables.

The construction is superb and there are some thoughtful touches. The case is gasketed with a dedicated channel. Screws to allow access for the 9v battery don't fall out into the grass or carpet. It comes with about 10 feet of what appears to be quality RG-174 coax and bnc connectors. Portable ops are very nice, but of course this unit is NOT rated to be outdoors in rain or moisture.

One of my major concerns was making sure that the coax itself isn't the antenna. I notice no difference in reception when handling the coax, nor any change when I put some heavy ferrite choking on it. Touching the metallic power switch did not change things at all. Good!

The unit is very high-q. That is, aside from choosing the proper preselector band, the tuning control is VERY touchy. It is manageable, and if a portable WAS getting overloaded, you could detune it slightly to act like an rf attenuator I suppose. Once you tune it, you can go across a band without having to tweak it again, unless you are very low in frequency, like below 4 mhz where you'll want to touch up when making large frequency excursions. But, having to tune it may be an inconvenience if you have this on the window-sill, and your operating position is 10 feet away. :)

I have not noticed any weird squeals or other bad noises when placed close to, or even on top of the receivers.

While I have not finished full evaluation of it, so far so good. I need to take it into a contest to see how it handles massive rf exposure. At the end of the day though, one has to figure out if using the equivalent of about 20 feet of wire with a 2 foot whip is worth it. Under certain circumstances, the small footprint of the 700DTA may be more convenient than stringing 20 feet indoors - and much easier to find a noise-free "hotspot" with.

So if one was expecting the equivalent of 120 feet of tuned wire antenna - this is not it. And thankfully so.

Note that this unit is NOT something to transmit into, yet after about a minute of playing around, I accidentally hit an auto-tune function on the Kenwood transceiver and thought that even at 5 watts, I just kissed $180 down the toilet. Don't ask me how, but it survived! This is not a recommended procedure of course! :)

I like the 700DTA so far - it is exactly what it is and built very well it seems. Could you do the same with 20 feet of wire, a tuner, supports, and making sure that the wire doesn't cross through some noise zones indoors? Sure. But the Apex's small footprint makes it easier. Choices .....
 
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nanZor

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700DTA with Commradio CR1a notes

With a bit more time, I noted that the combination of the Apex and the 700DTA can produce a *low-level* feedback when touching the CR1a knobs or doing something dumb like touching the oled display.

It appears to be a desense along with very light growling, and once you take your hand away, it returns to normal. This can hamper weak-signal tuning. This is not unlike the early Uniden BC125at's which changed the clock freq in later firmware updates.

Common-mode happens, and with two battery-operated, ungrounded and unbalanced high gain amplifiers, separated by 10 feet of coax, I can understand.

Without laying fault to either unit, I figured it is best to fix the problem and not the blame.

Wrapping about 4-5 turns of the RG-174 coax through an MFJ snap-on RFI choke right at the Commradio antenna input bnc fixed the issue. Fortunately the coax still does not seem to be part of the antenna, but this combo may have brought out an issue that most may not ordinarily see.
 

nanZor

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Further update on the CR1a ...

After listening to a quiet band, the interaction even after the choke was applied was still there to some extent. Good, but not good enough.

A total solution was to use an rf isolation transformer, in this case a Radiowavz ISOX transformer. Breaking the physical connection in the transmission line between the cr1a and the dt700 cured this small problem for good!
 

nanZor

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More user notes ...

The knife-edge tuning is kind of driving me crazy. This thing could sure use a vernier tuning dial. Pencil markings help repeatability when retuning....

While removing the whip from the unit essentially makes it go dead, it does seem to rely on the 10-foot coax as a radial. This is especially so when I use the isolation transformer / galvanic isolator at the end just before the rig. It seems to actually work better that way. Outdoors of course works better than indoors, but I consider this a window-sill antenna, and not really a desktop antenna buried deep within the building. :)

Whip notes - I already broke the included whip, so I used a Diamond RH-789 telescopic as a replacement.

Note that I also tried using a 54-inch 6-meter telescopic (MFJ "walkabout") and when fully extended, you lose the ability to peak the high bands. At 7 mhz, the gain becomes too high providing about an S5 noise floor on the '590. Fully extended, the MFJ 6-meter whip works good on 80/160m. Well, as good as any window-sill indoor 160/80m antenna can work! :)

I suppose hard-core windowsill users might want to choke the feedline at the unit, and run some opposing small radials clamped to the shell of the bnc connector...

Operationally, I turn off the preamps on the Kenwood 590, and basically adjust the whip and antenna telescopic tuning so that band noise just barely moves the s-meter - perhaps S1 or S2.

Fun, and I think I'll keep it for very special purposes since it does actually work ok. However, I can run outdoor antennas and and don't really have a windowsill limitation, but these notes might come in handy for those that do.
 
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nanZor

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Works well with Icom R20 and Kenwood TH-F6 handhelds on hf too ...

Tested the Apex 700dta (along with an MFJ 1020c) and it plays well with them. Both of the handhelds run with NO attenuation and full gain internally.

I noticed a minor amount of too much signal near 7mhz with the Kenwood - and while the Apex doesn't have a gain control, all it took was a very *slight* off-tune to accomplish it.
 

pjxii

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Great information on the 700DTA. I was wondering about using a longer whip, I'm glad you tried it.

I just got an older AOR LA320 to use with my loopsticks and it also has a very fidgety tuning knob just like the Palomar LA1, actually even more difficult really. It works well when you hit it just right but very frustrating to find that spot, so easy to pass it a dozen times! The Palstar LA30 is so much more enjoyable to use in this regard.

These small proximate antennas fascinate me especially since I'm in a condo. Hope to find a 700DTA sometime to play with, too bad they're discontinued.
 
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